May 22 2008
Tornado Outbreak
Under construction(last updated July 24 2008 0147
UTC)
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Related items of
interest
Historical Tornado Cases
for the Cheyenne Warning Area
Detailed
Tornado Cases for the Cheyenne Warning Area
Historical Tornado Cases
for the Boulder Warning Area
Historical Tornado Cases for
the United States
Elevated Mixed
Layer
Elevated
Heating
Overview of Events
On May 22-23, 2008, a favorable pattern for
severe thunderstorms developed for the high plains, front range and
eastern slopes of the Rockies. Slow moving meridional troughs
have historically provided some of the more notable severe
weather outbreaks for this region. Examples include
April 23
1960 and
June
14-17 1965.
Several tornadic storms occurred on
May 22,
and a few of these produced large, long-lived tornadoes. This severe weather episode was well
forecasted by the ECMWF model. This model indicated that a deep,
slow moving, meridional trough would approach the high plains on May
22-23. It also predicted a deep trough over New England, with an associated
surface front behind this system through the lower midwest into northeast
Kansas, southwest Nebraska and eastern Wyoming. The ECMWF did an excellent
job with these features well in advance. The 144 hr ECMWF showed a
stationary front through northern Kansas and southern Nebraska, with strong
upslope flow across western Nebraska and eastern Wyoming. On May 17, I
expressed my
thoughts
about the
severe
weather pattern.
A tornado
watch was
issued by the
Storm Prediction Center at 1725 UTC (1125 am MDT) for much of
northeast Colorado and part of southeast Wyoming.
Towering cumulus clouds developed southeast
of Denver International Airport around 16 UTC on May 22. By 1635 UTC, 45
dbz echoes were noted at 23,000 ft about 3 miles northeast of the airport.
By 1657 UTC, a 61 dbz echo was located 14 miles north of Denver at
21,000ft. The first 50 dbz on the lowest slice occurred at 1648 UTC. The first
60 dbz echo on the lowest slice was noted 5 miles west-southwest of Hudson at
1652 UTC. By 1701 UTC there was a 62 dbz echo up to 26,000ft and 47
dbz echo up to 32,000ft. The storm was severe at this point. At 1705 UTC, the
storm had 63-66 dbz echoes northwest and west of Hudson at the lowest
slice.
It is well known that thunderstorms tend to
develop along the front range earlier than on the low plains. This is because
capping tends to be weaker due to elevated heating, and lower moisture content
of the air allows for a rapid warmup to the convective temperature by
local noon. Also, the front range of Colorado is above the traditional capping level. But
convection began even before local noon on this day. The first tornado
report was east of Platteville at 1726 UTC. The tornado was already doing
damage by 1726 UTC and was reported to be 1/2 mile wide at 1727 UTC. This
tornado was
very
large (published by the
Denver Post) and
damaging and
continued for 37 miles to northwest of Wellington at 1825 UTC.
I am currently trying to determine
whether tornado damage reported by CoCoRaHS observers 4.2 miles
northwest of Wellington and 4 miles west-northwest of Wellington were
caused by the primary tornadic storm or a later storm after 2040 UTC. The most damaging part of the tornado path ended northwest of Windsor. Very large hail up to baseball size occurred along and
west of the tornado path. The tornado moved generally to the
north-northwest at 35 to 40 mph. The elapsed time between the first 50
dbz echo on the .5 deg slice from the Denver radar and initial tornado
damage was 37 minutes!!
The storm weakened a little as it moved
northwest of Wellington, CO, but then strengthened and accelerated as it passed
east of Virginia Dale. This storm produced a 2nd tornado from 1857 UTC
to 1935 UTC. There may have been a break in the damage northwest of
Overlook Rd after 1922 UTC. This tornado was accompanied by quarter to
golfball sized hail(and apparently
larger at the
Mitros residence). These pictures were taken by Jeff Mitros. I received this
picture from the Laramie Fire Department/EMA that was supposedly the Laramie tornado. They
said that this picture was taken at the Walmart, but they had no
details and couldn't vouch for its authenticity. It is unclear whether
the
tornado
that hit Laramie was a 3rd tornado from the same supercell or whether
the 2nd tornado continued into Laramie. It is more probable that the tornado shrunk in size just before
entering the eastern edge of Laramie. The tornadic storm continued
well northwest of Laramie. Radar indicated another possible tornado
7 miles north of Harper, WY at 2017 UTC.
Since I have a strong interest in high
elevation severe weather, and since this was a particularly rare and exceptional
tornado event on the high terrain, I decided to document the
Wyoming part of the tornado outbreak. This was accomplished using the internet
white
pages along with
live maps. But when I first started this
task, I had no names to work with. So I ordered a phone book for Cheyenne,
WY called the "Country Cowboy". I started with the H's, and after about 5
minutes I found the name Paul Hanselmann on Ramshorn Road. Ramshorn Road
was close to the tornado path. So I called Paul Hanselmann. This
immediately paid off as his house was unfortunately hit by the
tornado. He gave me 2 other names and then those people referred me to
others. So information piled up quickly. I want to thank all
those who
took the time to share information over the phone.
The 1st and strongest Albany county
tornado touched down about 0.4 miles east of the intersection of
Albany, Larimer and Laramie counties, or about 3/4 mile west of
Harriman road along the state line(elevation 7500 ft) at 1858 UTC (1258
pm MDT). I used radar to determine the exact times as this is usually
the most accurate method. Prior to the tornado, dense fog shrouded
the eastern slopes of the Laramie mountains, with
visibilities almost zero at the residence of Wylie D. Walno II Lt. Col. near the
tri-county border. Wylie Walno arrived home just
before the storm hit the area. He said that the visibility
suddenly jumped from near zero to unlimited as
the storm passed to his north. He could see low-hanging
clouds pass by. Golfball sized hail also occurred at the Walno
residence. The first signs of tornado damage occurred at the residence
of Richard Miller. Two trees on his property were downed and his garage
door was bent. Half dollar sized hail also occurred there. Immediately
to the northwest, 20 ponderosa pine trees were downed on the Claire
Hoover farm as the tornado passed between the house and a
barn. Then the tornado toppled 4 more trees on Belinda Scott's
property. A few trees were downed on Wylie Walno's property.
Storm relative
velocity loop (1845 to 1934 UTC)
Reflectivity loop (1845 to 1930
UTC)
Keep in mind that beam blockage was likely occurring with the .5° slice from the Cheyenne radar. As the storm moved from 7500ft to 8500 ft, the lowest slice of the Cheyenne radar
was partially beneath the ground, resulting in lower
reflectivity(50-55 dbz) values from southeast of Vedauwoo to Laramie. The actual
reflectivity values were probably 60-65 dbz. The 1.5° slice supports
this notion.
Fairly extensive tree damage occurred just
northwest of the initial touchdown location as the tornado widened.
Peter Hansen reported to me that the tornado downed trees for several
miles on his property. Tim Warfield told me that there was extensive tree
damage on his land. By 1904 UTC the tornado was over 1/4 mile wide and was
climbing up the Laramie Ridge to 8000ft. Very old pine trees 3 to 4 ft. in
diameter were mowed down by the tornado. Tom Nowak, Jim Price and
another person were putting fish into Imson Pond in the dense fog
with visibilities near 100ft. Quarter to ping-pong ball sized hail chased
them to their trucks. This is a good thing since they were then hit by the
tornado around 1908 UTC. They described a frightening experience. The
tornado buffeted their vehicles. One truck contained a 1000 lb fish
tank. This truck rocked back and forth by the tornado and most of the
windows were smashed out. Another truck was actually lifted off the ground and
set back down, with windows knocked out as well. A camper shell was broken
off one of the trucks and flung 1/2 mile to the south. Debris was
flying everywhere during the tornado including picnic tables. Large
trees were downed on both sides of the road near the
pond.
After leaving the pond, the tornado
hit on Ramshorn Rd. Ted Lewis measured 153 mph winds on his Davis Monitor
2. His house faired fairly well even though huge pines were blown
down. A 12 ft. aluminum boat was blown 500 yds. The tornado then hit the Paul
Hanselmann house also on Ramshorn Rd. The front half of his roof was blown off,
with pieces of it found over 2 miles away. The back part of the roof
was heavily damaged. The Hanselmann house was well constructed
with concrete-filed styrofoam and was reinforced with steel rebar anchored
to the foundation.
After leaving the Hanselmann house,
the tornado moved over very rural territory for several miles. But
there was a continuous damage path all the way northwest to
Overlook Rd, with trees and fences downed all along the .6 to .9 mile
wide path according to Bob Adams who documented the tornado path. Along
this path the tornado climbed in elevation to 8500ft. Major damage
occurred on West Vedauwoo road at 8400ft. The Gayle Wilson house was destroyed by
the tornado. 2X4's from her roof were embedded in the ground several feet. She told
me this was quite an accomplishment since the ground is so
hard(gravel-like) that it is difficult to even dig a shovel into it.
She also reported that nails from her roof were embedded the wrong
way into fence posts 500 yds away at another residence. A woman in the
Vedauwoo area was injured by flying glass as one of the windows in her
house was blown out. All the south facing windows were either knocked
out or punched through by hail at the Jeff Mitros residence. Mitros
also reported numerous hail dents in vehicles. These dents were mainly
on the sides of the vehicles. Many of the wooden logs of his log cabin
were damaged by hail. Ping-pong to golfball sized hail occurred on
Overlook Rd and Howe Lane. A grove of pines was downed by the tornado
on Overlook Rd. The Harriman-Laramie tornado path was
continuous for 18 miles from west of Harriman to north of Overlook
Rd, and possibly for 31 miles to north of Laramie. There is a hilly area between Overlook Rd and Laramie where no people live.
Bob Adams told me that the continuous path seems to have
ended beyond Overlook Rd. I am not sure if it will ever be
determined whether the tornado continued all the way to Laramie
continuously.
Here are some pictures taken by Jeff
Mitros who lives on Vedauwoo Rd. Mitros reported that dense fog with
visibilities around 100ft prevailed all day. These show the extensive
damage to the windows of his house
caused by very large hail. His Datsun Z-280 was dented by very large hail. Some of the holes in his house windows were the size of baseballs and even softballs. The elevation of the Mitro residence is 8400 ft. Mitros
also took some pictures of the tornado damage.
All the pictures below were taken by Jeff Mitros and Jack Riske:
Pic1
Pic2
Pic3
Pic4
Pic5
Pic6
Pic7
Pic8
A Datsun was dented and passenger window shattered at the Mitros residence.
Holes in "object" and dent in fence behind the hole in purple "object" at Jeff Mitros residence
A tree was snapped off and other uprooted near the Jeff Mitros residence.
Tree damage Tree Damage Tree Damage
Another house received holes in south facing windows from large hail. This house is 1 miles west-northwest of the Mitros residence.
A small trailer located southeast of the Mitro residence was thrown up to 500 yds.
Jack Riske took these pictures of the Gayle Wilson house.
Fence located southeast of the Wilson residence was scattered.
A 15 gallon galvanized steel wash tub was wrapped around a fence.
A house 1/2 mile north of the Gayle Wilson house was damaged on the periphery of the tornado.
This trailer on Monument road (not far from I-80) exit 329 was flipped (Occurred on the northeastern extremity of the tornado).
This is tree damage northwest of Harriman in far southeast Albany county.
Beam blockage was occurring with the .5° slice from the Cheyenne radar.
As the storm moved from 7500ft to 8500 ft, the lowest slice of the 88d
was partially beneath the ground. This resulted in lower
reflectivity(50-55 dbz) values from Vedauwoo to Laramie when the actual
reflectivity values were probably 60-65 dbz. The 1.5°
slice supports this notion.
A CoCoRaHS observer 1.3 miles
southeast of Laramie reported that 1.5" hail caused car dents.
According to Dave Claypool, a master technician at the College of
Agriculture's Plant Science Center, "It got very noisy from the hail
and wind. There was a lot of pea sized hail, but there were many big
ones mixed in. "We picked up one hailstone that was 1.5" across."
A
tornado moved across I-80 southeast of Laramie around 1928 UTC, and
then across the far eastern and northeastern part of
Laramie between 1930 and 1935 UTC. F1 damage was done to
many structures. I did not document the Laramie segment of
the tornado. A quick internet search revealed the following damage:
A truck driver suffered a broken ankle when his truck was overturned on I-80
Numerous homes damaged
Church damaged
Dance hall
damaged
College of Agriculture greenhouse facilities damaged (5 of 18
greenhouses damaged and the hoophouse greenhouse destroyed)
Storage shed and
wooden pole barn were destroyed near the greenhouses. Huge pieces of the barn
were carried 250 yds.
10 large spruce trees were either uprooted of snapped
in half at the greenhouse facilities
Many trees were snapped in half or
uprooted at the Jacoby golf course
The tornadic storm continued to
the north-northwest through central and northern Albany county. No tornado
damage occurred, but this area is very rural. Given the fog, it
is possible that tornadoes went unreported.
The Harriman-Laramie tornado moved to the north-northwest at an average
speed of 47 to 50 mph. The heading of the tornado was 320 degrees
at the beginning of the path and 330 degrees toward the end. This was
an exceptionally fast moving tornado by Wyoming standards.
Typically the mid level (600-300mb) flow over
southeast Wyoming is fairly weak in tornadic situations, hence
strong right-movement and slow storm motion (10 to 30 mph). The fast
storm motion on May 22 is more typical of the southeastern United
States in winter or early spring. The storm accelerated as
it climbed closer to the strong mid level flow. Basically, the
storm was closer to the strong mid level winds after it climbed to
7500ft. As previously mentioned, the tornadoes on this day moved to the
northwest and north-northwest. This is unusual, but certainly not
unprecedented. The Wyoming tornado on April 23, 1960 moved to the
north-northwest.
A small tornado apparently touched
down 3 miles south of I-80 on Harriman Road a little later in the
afternoon from another storm. This tornado moved to the
north-northwest and downed trees in several locations. Several trees
were downed 3 miles south of I80 on Harriman Rd on the William Prince
property with this storm. They estimated winds up to 80 mph. An old log
cabin was extensively damaged on Crystal Lake Road, with the
roof blown across the road. This tornado continued north-northwest. A
few trees were downed and shingles were torn off of a house. A heavy
camper was turned upside down. This damage occurred about 4 miles
east-northeast of Buford. Residents described this event as a
mini-tornado. The tornado most likely started between 2115 and
2125 UTC (325 pm MDT) and ended before 2140 UTC. These times were
obtained by matching the radar imagery to the locations that received
damage. However, the radar signatures were not nearly as clear cut with
this storm since the tornado was so small. This storm was not as strong
as the Harriman-Laramie storm, but still contained dime sized hail
that was blowing horizontally at the William Prince residence. The
southern end of the storm was centered just east of Wellington, CO
at 2038 UTC, 6 miles east of Harriman at 2108 UTC, 3 miles
west of Granite at 2129 UTC and 4 miles west-northwest of
Granite at 2137 UTC. The area southeast of Granite is completely
devoid of people. It is possible that
tornadoes occurred earlier with this storm.
I
am currently trying to determine whether tornado damage reported by
CoCoRaHS observers 4.2 miles northwest of Wellington and 4 miles
west-northwest of Wellington were caused by the primary tornadic storm
or this later storm. The path of this tornado was very close
to the path of the
April
23, 1960 tornado. It appears that the 1960 tornado path was about 1 to 2
miles west of this tornado, and about 4 to 7 miles east of the
Harriman-Laramie tornado. I
drew the path of the 1960 tornado in 2000 with the
help of Walter Ferguson whose family has resided in the local area
for several generations.
According to Wylie Walno II Lt. Col.,
another tornado apparently destroyed a barn 4 miles west of the
tri-county border. Hail accumulated to a foot deep
in this area and took 3 days to melt. I am still trying
to confirm this tornado, but the area is very sparsely populated. The
same storm produced large amounts of hail west of Virginia Dale.
This center of the storm was located 5 miles southeast of Virginia
Dale at 2012 UTC, from Virginia Dale to 4 miles northwest of
Virginia Dale at 2025 UTC, 4.5 miles northwest of Virginia
Dale at 2029 UTC (6 to 8 miles west of Harriman) and 1.5 miles
east of Tie Siding at 2038 UTC.
A storm developed about 40 miles
west-southwest of DIA at 1630 UTC. Radar indicates that this storm may
have produced large hail several miles northwest or west-northwest of
Golden, CO. This storm was right on the edge of the Rockies about 9000
ft.
Another storm developed near Broomfield, CO at 1752 UTC and produced a
tornado southwest and west of Dacona between 1823 and 1832 UTC. 2" hail
and 1.5" hail were reported via CoCoRaHS 3 miles east and 2.5 miles
northeast of Longmont respectively. This storm temporarily weakened
after moving past Longmont. The storm intensified near Masonville and produced
golfball sized hail 1 mile east of Buckhorn Mountain. Golfball sized
hail dented cars in Poudre Park.
A severe storm developed north of Hardin, CO in Weld county at 2055
UTC. Large hail probably occurred with this storm southeast of
Barnesville. This severe storm continued to 3 miles northeast of
Purcell at 2135 UTC.
A very brief tornado apparently occurred just west of Interstate 25 (time ??) in southeast Wyoming and caused no damage.
A storm moved into Wyoming from Colorado after 02 UTC and produced a
tornado about 13 miles east of Cheyenne at 0233 UTC. A pole barn was
destroyed. The Laramie Fire Department and EMA provided me with this picture of
the
tornado
(supposedly from the Hillsdale area). However, they told me that this
could also be the Laramie tornado. They didn't have high confidence
about where this tornado occurred. This tornado is not
shown on the smaller scale maps, but is shown on this larger scale
terrain map.
A large map with 2 of the 3 Wyoming tornadoes can be found
here. This map shows the possible break in damage between Overlook Road and I-80. Another
map
shows the hail swath and tornado paths. The largest hail was likely
southwest of the tornado path as the storm moved from west of Harriman
to Ames Monument. However, this area is unpopulated so reports were
unavailable. I plotted a
damage path on a satellite image using
http://maps.live.com with
both Wyoming tornadoes. I also
plotted the
Windsor, Harriman-Laramie and other tornado paths on a terrain map off
of AWIPS. This image is less detailed, but shows the topographic
features well. The possible
tornado that occurred several miles west of Harriman is not plotted
here. Wylie Walno reported to me that there may have been another
tornado that destroyed a barn about 4 miles west of his house(or about
5 miles west of Harriman). Interestingly, a severe storm did move along
US-287 from west of Virginia Dale to 5-8 miles west of Harriman to
just east of Tie Siding. But there is just not enough information thus
far about this event to plot a damage path.
Although I plotted the primary Wyoming tornado as a continuous
path on the satellite image, I have no evidence of tornado damage on
the rugged terrain between Overlook Road and the southeast outskirts of
Laramie along I-80 (about 3-4 mile stretch). This area is uninhabited
and a storm survey on foot would probably be required. Perhaps high
resolution satellite data would also help determine if the tornado was
continuous to Laramie or whether the Laramie tornado was a
different tornado.
An updated map showing the path of the primary Colorado tornado is
here.
Apparently, several tornadoes caused damage near the end of the path to
the west and northwest of Wellington. Actually a waterspout was seen
over Douglas Lake and this tornado caused significant damage along
county road 17. This information is still being compiled.
Meteorological
Discussion
A deep upper trough was digging into the
intermountain west at
00 UTC
May 22, 2008. 500mb winds of 100 kts on the back side of this trough were
indicative of a deepening system. The 500mb height in the center of the upper
low was 550 dm over central UT. The
surface
chart at 00 UTC showed a surface front stretching from central LA into north
TX and then into northeast NM and eastern Colorado. Only marginal moisture
was in place across western Kansas with surface dewpoints in the 50-55F range.
However, rich moisture in the Red River Valley of southern Oklahoma and north
Texas was poised to make a fast return.
The
03,
06, 09 and
12
UTC surface charts show a strong surge of moisture through western Oklahoma,
western Kansas and eventually eastern Colorado. By 03 UTC, 60-65F dewpoints
were surging through northwest Oklahoma and into the eastern Oklahoma
panhandle. In fact by
06
UTC, 55-60F surface dewpoints were already surging into eastern Colorado. By
09 UTC, the dewpoint at Limon, CO was up to 58F, with 53-55F dewpoints
along the front range of northern Colorado. Limon reported overcast skies
at 1800ft, which indicates the low level moisture was at least 1800 ft deep.
By
12
UTC the moist axis was located from southwest Kansas into eastern and
northern Colorado and had shifted a little to the northeast since 09 UTC. The 12
UTC 500mb chart indicated strong cooling since 00 UTC. The
500mb
temperature was down to -14C at Denver. The pacific cold front had already
progressed through Albuquerque as seen on the
700mb
chart. The 700 mb temperature was down to -1C at Albuquerque. Mid level cooling
had obviously occurred even ahead of the front across the plains and at Denver.
By
15 UTC,
the warm front had progressed into central CO and western Kansas. Rich moisture
was in place across the front range of northern CO with 54 and 55F dewpoints at
Greeley and Akron respectively. The surface theta-e axis extended from central
Kansas into northwest Kansas to Woodrow and Greeley, CO. Strong upslope flow was
occurring and rich moisture was being transported into the Laramie Ridge and up
the Laramie mountains. A surface dryline was beginning to take shape from the
western Panhandles to extreme eastern Colorado.
By
16
UTC,
55-56F dewpoints were noted as far west as Kersey and Boulder, CO, or
just south and southwest of Greeley. Initial radar
echoes began to develop just south of the Denver International
Airport by 16 UTC. This area of development was along or just west of a
N-S boundary that was probably forced by the terrain. A surface front
stretched from Platteville to Hoyt to Woodrow. This front actually
pushed southward on the western end between
1600 and
1630 UTC, stalling in southern Weld county. The dewpoints in this initiation area were only in the 40s to near 50F.
But higher dewpoints were located just to the north and west. By
1635 UTC, 45 dbz echoes were noted at 23,000 ft about 3 miles
northeast of the airport. The
front
at 1635 UTC stretched across southern Weld county. A terrain
related feature (at least that is our current thinking) extended from
Parker to east of DIA to near Fort Lupton. As earlier noted, 50 dbz
echoes were
present on the lowest radar slice from Denver by 1648 UTC. The storm
was severe by
1700 UTC just west of Hudson, CO.
The
17 UTC
surface chart showed a T/TD of 70F/55F at Greeley, CO.
Modifying
the 18 UTC Denver sounding with these values yields 2800 j/kg surface
based CAPE. This represents the upper limit for surface based,
pre-storm CAPE that was available. The moist axis extended all the way
northwest to Red Feather Lakes and Crystal Lake, where the T/TD were
43F/43F at both stations. Interestingly, the theta-e values were the
same at these stations as Haigler, NE and Concordia, KS. T/TD values of
43F/43F at Crystal Lake and 47F/47F at Harriman at 17 UTC have almost
the same theta-e as T/TD values of 72F/61F at Emporia, KS and
74F/61F at Chanute, KS.
At
1701
UTC the storm north of Denver and southwest of Hudson was rapidly
becoming severe after encountering dewpoints between 50 and 54F. The
storm was 25 minutes away from producing a strong
tornado. The storm was about to encounter a surface
boundary that
stretched ese to wsw from Woodrow to Wiggins and then ene to wsw
from Wiggins to north of Brighton. There was a very narrow corridor of
higher theta-e surface air immediately north of the front.
Sunshine was warming the low levels north of the boundary on the front's western end (east of Greeley to Wiggins to east of Platteville).
This elevated heating, along with dewpoints from 54 to 56F, and
reasonably cool 500-300mb temperatures, was allowing for moderate
surface based CAPE ahead of the storm(particularly in the inflow of the
storm). Another surface boundary was oriented generally south to
north from Parker to east of DIA to near Hudson, and was likely forced
by terrain. The storm initially developed along this N-S boundary. Thus
far, the
storm was located in marginal instability immediately to the west of
the N-S
boundary, but south of the warm front that stretched from generally
west
to east. Surface based CAPE values in this region near DIA were about
1500 j/kg. Dry
air was actually located east of the storm (south of the boundary) from
just east of Hudson to Prospect Valley to Hoyt and southward to
the Front Range Airport. The T/TD were 72F/29F at the Front Range
Airport (FTG) while the T/TD at DIA were 65F/50F.
The wsr-88d is located at FTG.
Backed winds and relatively high theta-e low level air existed
northwest and north of the storm over southern Weld county. In fact the
storm was about to move into a very
favorable area for tornadoes. Fairly high dewpoints actually existed
north of DIA but south of the boundary. So the storm became severe by
17 UTC even before reaching the warm front. By
1727
UTC when the storm became tornadic, the storm was located along the surface
boundary. From 1727 to 1745 UTC, the surface
boundary
surged
to the north and northwest immediately behind the storm so that the
storm stayed in an ideal location, with high theta-e air and strong
east winds immediately on the cool side of the boundary. Here is the
1740
UTC radar image with the boundaries drawn in. At this time the storm
was immediately north of the boundary, with relatively high theta-e
inflow into the storm from the east.
This dry surge actually kept
surging
northwest and was through Peckham, CO through 1745 UTC. But by
18 UTCthe
boundary that had been surging northwest was stalling just
northwest of Peckham and the storm was beginning to move further away
from the boundary. At 18 UTC the storm was
obviously still ingesting high theta-e air from the east. Therefore,
the storm managed to stay in a favorable location for
tornadoes through 1810 UTC. After 1810 UTC the storm
passed south and west of Wellington where
surface temperatures were cooler. By 1820 UTC, a tornado was still
occurring west of Wellington. The T/TD at Wellington were 55F/54F at 18
UTC and 58F/56F at 19 UTC. Thus, as the storm moved west of Wellington,
surface based CAPE was down to roughly 1500 j/kg. There may have been a
small inversion near the ground as the storm suddenly moved into cooler
air. The storm temporarily weakened.
A satellite loop from 14 UTC to 2030 UTC can be found
here.
Now let's turn our attention to Wyoming. As already discussed, the
primary Colorado storm weakened a little in northern Larimer county and
then intensified before entering Wyoming. By 17 and 18 UTC the surface
temperature was 47F at Harriman, WY. Also, since dense fog was
occurring, the dewpoint was equal to the temperature. Assuming
saturation, what T/TD would be required at sea level to achieve the
same theta-e as Harriman, WY? Since the T/TD were 47F/47F at
Harriman, a T/TD of 66F/66F would be required at 1000 mb to yield the
same theta-e. Why is this? To understand this, let's look at the
potential temperature and mixing ratio's for both locations. For
Harriman, the potential temperature and mixing ratio were 89F and 9.2
g/kg. At 1000mb, a location with T/TD of 66F/66F would have a potential
temperature of 66F and mixing ratio of 13.8 g/kg. Thus, the
mixing ratio would be 50% lower at Harriman than at the sea level
location. However, the potential temperature would be 23F higher at
Harriman. Thus the notion that it was too cool on the Laramie Ridge on
May 22, 2008 for severe storms is obviously misguided. In fact, it was
warm enough so that the level of free convection was near
the ground. This is despite dense fog and actual temperatures from
44 to 48F. Thus, before drawing conclusions about the severe weather
environment, one should modify soundings using actual surface
observations. Sometimes this requires the use of mesonet data since
surface observations are sparse.
Let's compare (Table 1) the theta-e values on the elevated
terrain and lower terrain by displaying temperature, dewpoint, mixing ratio,
potential temperature and equivalent potential temperatures at 17 UTC. Note that
only temperature data were available for Harriman, Lynch, Virginia Dale 7 ENE
and Emkay. Dewpoint data actually were available at the remainder of the
stations including Estes Park, Crystal Lakes and Red Feather Lakes. However,
since dense fog was present at these 4 Wyoming stations through 19 UTC, we will
assume that the dewpoints were equal to the temperatures.
| Table 1 |
|
|
|
|
|
|
|
|
| 17
UTC |
Elev(ft) |
Pres.(mb) |
SLP(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
| Crystal Lake |
8620 |
724 |
986 |
43 |
43 |
8.2 |
92 |
331.6 |
| Estes Park |
7700 |
745 |
983 |
53 |
46 |
8.9 |
98 |
337.5 |
| Harriman,WY |
7450 |
756 |
987 |
47 |
47 |
9.2 |
89 |
332.5 |
| Lynch,WY |
7200 |
762 |
987 |
46 |
46 |
8.7 |
86.7 |
329.9 |
Virginia Dale 7
ENE
|
7000 |
767 |
988 |
47 |
47 |
9 |
86.9 |
330.8 |
| Emkay,WY |
6720 |
774 |
989 |
49 |
49 |
9.6 |
87.6 |
333.1 |
| Cheyenne |
6140 |
789 |
987.7 |
48 |
47 |
8.8 |
83.5 |
328 |
Nunn
|
5650 |
804 |
986 |
51 |
51 |
10 |
83.8 |
331.8 |
| Wellington |
5300 |
813 |
985 |
55 |
54 |
11.1 |
86.3 |
336.5 |
| Briggsdale S |
4838 |
833 |
991 |
55 |
54 |
10.8 |
82.6 |
333.3 |
| Greeley |
4700 |
835 |
984 |
64 |
55 |
11.2 |
91.7 |
340.2 |
| Akron |
4700 |
841 |
990 |
56 |
56 |
11.5 |
82.1 |
335.1 |
| Goodland |
3700 |
870 |
990.7 |
69 |
60 |
12.9 |
90.4 |
344.5 |
| Saint Francis |
3350 |
881 |
|
68 |
55 |
10.6 |
87.4 |
335.8 |
| Hill City |
2600 |
918 |
995.5 |
65 |
58 |
11.3 |
78 |
332 |
| Concordia |
1500 |
948 |
1000.5 |
65 |
59 |
11.4 |
73.1 |
329
|
| OKC |
1230 |
951 |
997 |
81 |
66 |
14.6 |
88.8 |
348.5 |
| Chanute |
1000 |
967 |
1001.6 |
74 |
61 |
12 |
79.1 |
334.6 |
| Salina |
1280 |
957 |
999.1 |
67 |
59 |
11.3 |
73.6 |
329 |
| Emporia |
1170 |
960 |
1001.5 |
72 |
61 |
12.1 |
78.2 |
334.3 |
Notice that Lynch, WY
actually has the same theta-e as Salina, KS even though the
temperature/dewpoint are 21F/13F higher at Salina. The mixing ratio is 30%
higher at Salina, so the potential temperature must compensate to yield similar
theta-e values. Indeed, the potential temperature was 86.7F at Lynch and only
73.6F at Salina.
Surface theta-e continued to increase from 17
to
18
to
19
UTC.
Tables 2 and 3 show temperature, dewpoint, mixing
ratio, potential temperature and equivalent potential temperature values for
various sites over the plains. Again, this is done to demonstrate that T/Td
values cannot be used without elevation to assess how "juiced up" the surface
layer is. In Table 5 the theta-e values between 330K and 335K are
highlighted in red. The
theta-e
values from 330 to 335K are shown in a partially analyzed surface chart for 19
UTC. This terrain map with surface observations for
19 UTC overlain is only partially completed.
Let's compare(Table 2) the theta-e values on the elevated
terrain and lower terrain by displaying temperature, dewpoint, mixing ratio,
potential temperature and equivalent potential temperatures at 18 UTC.
| Table 2 |
|
|
|
|
|
|
|
|
| 18
UTC |
Elev(ft) |
Pres.(mb) |
SLP(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
| Crystal Lakes |
8620 |
723 |
|
43 |
43 |
8.2 |
91.7 |
331.4 |
| Red Feather |
8214 |
733 |
|
44 |
44 |
8.4 |
90.7 |
331.4 |
| Harriman,WY |
7450 |
755 |
987 |
47 |
47 |
9.2 |
89.3 |
332.7 |
| Lynch,WY |
7200 |
761 |
987 |
46 |
46 |
8.8 |
87 |
330.1 |
Virginia Dale 7
ENE
|
7000 |
766 |
987 |
48 |
48 |
9.4 |
88.1 |
332.7 |
| Emkay,WY |
6720 |
773 |
987 |
48 |
48 |
9.3 |
86.7 |
331.5 |
| Cheyenne |
6140 |
788 |
988.2 |
49 |
49 |
9.5 |
84.8 |
330.8 |
Nunn
|
5650 |
803 |
985 |
52 |
52 |
10.4 |
85.1 |
333.7 |
| Greeley |
4700 |
833 |
983 |
70 |
55 |
11.2 |
98.4 |
344.5 |
| Akron |
4700 |
840 |
989.7 |
57 |
56 |
11.5 |
83.4 |
335.9 |
| Goodland |
3700 |
870 |
990.7 |
64 |
59 |
12.4 |
85.2 |
339.7 |
| MCcook |
2800 |
911 |
996.2 |
61 |
56 |
10.6 |
75 |
328 |
| Hill City |
2600 |
918 |
994.3 |
73 |
62 |
13.1 |
86.2 |
342.4 |
| Concordia |
1500 |
948 |
1000.6 |
67 |
59 |
11.4 |
75.1 |
330.3 |
| Imperial |
3300 |
885 |
995.7 |
56 |
54 |
10.2 |
74.3 |
326.3 |
| OKC |
1230 |
951 |
996.2 |
86 |
67 |
15.1 |
93.9 |
353.4 |
| Chanute |
1000 |
967 |
1001.6 |
76 |
64 |
13.4 |
81.2 |
339.9 |
| Topeka |
890
|
972 |
1004.1 |
66 |
59 |
11.1 |
70.3 |
326.4 |
| Salina |
1280 |
957 |
998.6 |
73 |
61 |
12.1 |
79.7 |
335.4 |
| Emporia |
1170 |
960 |
1001.4 |
76 |
63 |
13.0 |
82.3 |
339.5 |
Notice that Greeley, CO actually has a higher
theta-e than Emporia, KS even though the temperature/dewpoint are 6F/8F higher
at Emporia. The mixing ratio is 16% higher at Emporia, so the potential
temperature must have compensated to yield a higher theta-e at Greeley. Indeed,
the potential temperature was 98.4F at Greeley and only 82.3F at
Emporia.
Notice that Red Feather Lakes, CO actually has a higher theta-e
than Concordia, KS even though the temperature/dewpoint are 23F/15F higher at
Concordia. The mixing ratio is 36% higher at Concordia, so the potential
temperature must compensate to yield a higher theta-e at Red Feather Lakes.
Indeed, the potential temperature was 90.7F at Red Feather Lakes and only 75.1F
at Concordia. Severe storms passed just east of Red Feather Lakes in the early
afternoon.
Let's compare(Table 3) the theta-e values on the elevated
terrain and lower terrain by displaying temperature, dewpoint, mixing ratio,
potential temperature and equivalent potential temperatures at 19
UTC.
| Table 3 |
|
|
|
|
|
|
|
|
| 19
UTC |
Elev(ft) |
Pres.(mb) |
SLP(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
| Harriman,WY |
7450 |
754 |
985 |
47 |
47 |
9.3 |
89.7 |
333.3 |
| Lynch,WY |
7200 |
760 |
985 |
48 |
48 |
9.5 |
89.4 |
333.6 |
Virginia Dale 7
ENE
|
7000 |
765 |
985 |
48.5 |
48.5 |
9.6 |
88.9 |
333.7 |
| Emkay,WY |
6720 |
772 |
986 |
49 |
49 |
9.7 |
88.2 |
333.8 |
| Cheyenne |
6140 |
787 |
987.7 |
50 |
49 |
9.5 |
86 |
331.7 |
Nunn
|
5650 |
803 |
983 |
52.5 |
52.5 |
10.6 |
85.6 |
334.6 |
| Wellington |
5300 |
812 |
983 |
58 |
56 |
11.9 |
87.9 |
341.1 |
| Briggsdale N |
5039 |
826 |
988 |
56 |
54 |
10.0 |
84.9 |
335.1 |
| Iliff |
3900 |
865 |
988 |
55 |
54 |
10.4 |
76.8 |
328.5 |
| Sterling |
3900 |
865 |
|
59 |
56 |
11.2 |
80.9 |
333.4 |
| Briggsdale S |
4838 |
831 |
988 |
58 |
55 |
11.2 |
86.1 |
336.8 |
| Akron |
4700 |
840 |
990 |
56 |
55 |
11.1 |
82.3 |
334.1 |
| Goodland |
3700 |
870 |
990 |
69 |
61 |
13.4 |
90.4 |
345.8 |
| Haigler |
3291 |
883 |
|
60 |
56 |
11 |
78.8 |
331.4 |
| OBerlin |
2736 |
911 |
|
61 |
58 |
11.4 |
75 |
330.4 |
| Saint Francis |
3350 |
881 |
|
68 |
57 |
11.4 |
87.4 |
338.1 |
| Hill City |
2600 |
918 |
994 |
78 |
63 |
13.6 |
91.3 |
347.2 |
| Concordia |
1500 |
948 |
1000 |
71 |
61 |
12.2 |
79.2 |
335.3 |
| OKC |
1230 |
951 |
996 |
87 |
67 |
15.1 |
94.9 |
354.1 |
| Chanute |
1000 |
967 |
1001.5 |
78 |
65 |
13.8 |
83.2 |
342.3 |
| Topeka |
890
|
972 |
1003.7 |
69 |
58 |
10.7 |
73.3 |
327.2 |
| Salina |
1280 |
957 |
998.0 |
74 |
62 |
12.6 |
80.7 |
337.3 |
| Fairbury |
1500 |
950 |
1003.0 |
61 |
59 |
11.4 |
68.9 |
326.1 |
| Scandia |
1450 |
949 |
1001 |
69 |
61 |
12.2 |
77 |
333.9 |
Notice that Harriman, WY actually has almost
the same theta-e as Scandia, KS, even though the temperature/dewpoint are
22F/14F higher at Scandia. The mixing ratio is 31% higher at Scandia, so the
potential temperature must compensate to yield similar theta-e values. Indeed,
the potential temperature was 89.7F at Harriman and only 77F at
Scandia.
At 19 UTC, two mesonet observations and 1
cooperative observer location recorded hourly temperatures. The temperature was
47F at Harriman (756 mb), 48.5F at the cooperative observer site 7 miles
east-northeast of Virginia Dale (767 mb) and 48F at Lynch (762 mb). These 3
observations lie along the same moist adiabat, as one would expect in moist
upslope flow. So I have fairly high confidence in the accuracy of these
measurements. Veta Mitchell, the cooperative observer 7 miles east-northeast of
Virginia Dale provided me with the hourly temperature measurements for her
location. The tornado actually first touched down about 2 miles north-northwest
of her house. So the hourly measurements that she collected are very useful
in determining surface based CAPE.
An important thing to note is that a 47F dewpoint at Harriman actually has
about the same mixing ratio as a 54.5F dewpoint at 1000mb. Of course this
assumes that the sea level pressure at Virginia Dale and 1000 mb are similar. If
the sea level pressure is higher at the lower elevation then the difference
would be greater. Also, even though 47F seems chilly, this temperature
at 7500 ft actually lies along the same dry adiabat as 90F at 1000mb.
Since visibilities were near zero
before the storm, I am assuming that dewpoints were equal to the
temperatures. I constructed approximate soundings for these locations
using the 18 UTC RUC initialization and 18 UTC Denver sounding. Of
course, the boundary layer had to be modified based on the surface
mesonet observations. I modified using the 19 UTC observations since
these are just prior to the tornadic storm. The RUC soundings
were more representative than the NAM/WRF soundings. The nam
soundings were superadiabatic near the surface and dry
adiabatic above the surface layer. This is not reasonable.
The RUC soundings were closer to moist adiabatic from the
surface to above 700mb. The modified 18 UTC RUC soundings
yielded similar CAPE values to the modified 18 UTC Denver sounding. I
have determined that the surface based CAPE was 1000-1300 j/kg near
the beginning of the Harriman-Laramie tornado path where
surface measurements were available. The theta-e values at the
three locations were almost identical. The RUC model, which
typically overestimates surface based CAPE (at least lately), actually
did a reasonably good job with CAPE fields, perhaps for the wrong
reasons. The fact that this model actually forecasted surface based
CAPE values up to 1000 j/kg at 6 to 12 hours could be a result of the
model's usual overestimation. The NAM/WRF dramatically underestimated
surface based CAPE in southeast Wyoming.
The surface temperature at Buford was slightly lower than I expected
(44 F) at 19 and 20 UTC. If this temperature is accurate, then the
surface based
CAPE
was lower at Buford( perhaps 800-900 j/kg). So it is possible that the
surface based CAPE was lower after the storm passed Ames Monument (or
the 2nd half of the tornado path). However, the temperature at Crow
Creek (northwest of Buford at 8600 ft) was 46 F at 19 UTC. Therefore, one
of these surface observations is likely in error. So the CAPE
approximation for the last half of the tornado path is more
problematic. The mixing ratios were lower to the west of the Laramie
Mountains. So the surface based CAPE was surely lower as the storm
moved through the Laramie area. However given the fast storm motion,
the storm didn't have time to weaken much before striking Laramie.
Table 4 and Table 5 show the surface based CAPE
values for Harriman, Virginia Dale and Lynch. Table 4 uses the 18 UTC Denver
sounding while Table 5 uses the 18 UTC RUC initialization. These are modified
using the temperature readings from the 3 stations and assumes saturation (there
was dense fog).
Table 4
|
|
|
|
|
|
|
|
|
| DEN 18 Z/mesonet/profiler modified |
Elev(ft) |
Pres.(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
CAPE(j/kg) |
| Harriman |
7450 |
756 |
47 |
47 |
9.2 |
89 |
332.5 |
1190 |
| Virginia Dale(7ene) |
7000 |
760 |
48.5 |
48.5 |
9.6 |
88.9 |
333.7 |
1217 |
| Lynch |
7200 |
766 |
48 |
48 |
9.5 |
89.4 |
333.6 |
1215 |
Table 5
|
|
|
|
|
|
|
|
|
| RUC 18 Z/NAM/mesonet/profiler modified |
Elev(ft) |
Pres.(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
CAPE(j/kg) |
| Harriman |
7450 |
756 |
47 |
47 |
9.2 |
89 |
332.5 |
1260 |
It is very difficult to achieve low dewpoint
depressions, relatively high theta-e values at low-levels and excellent
vertical wind shear at 7500-8500 ft on the Laramie Ridge/Mountains. As previously
mentioned, the dewpoints were equal to the temperatures along and east of the
summit of the Laramie Ridge. But surface based CAPE values still exceeded 1000
j/kg. In typical low plains severe storm situations, 1000 j/kg CAPE would be
considered very marginal. When CAPE is marginal, tornadic storms can still
occur, especially when LCL and LFC heights are low and considerable surface
based CAPE exists at low levels. This was indeed the case on May 22 on the
Laramie Ridge. In fact, after initially weakening upon moving into cooler air on
higher terrain northwest of Wellington, CO, the storm quickly reintensified
after encountering dense fog east of Virginia Dale. The
LFC (level of free convection) was possibly at the ground as the storm
moved from west of Harriman to Overlook Rd since the approximate
soundings show no CIN above the surface. In preparing the soundings, I
assumed that the vertical temperature profile was moist adiabatic from
the surface through the depth of the moist layer. In this case, the
level of free convection would be near the top of the moist layer.
The vertical wind shear profile featured strong
shear. The surface wind backed to the northeast by midday at the mesonet
locations. However, windspeed is not represented the same way at the mesonet
locations. For some hours the wind speed was the same as the wind gust while for
other hours they were vastly different. Also, some of the winds measurements
were influenced by inflow into the storm. The pre-storm winds were probably
about 25-30 kts from the east-northeast or northeast (060° at 30 kts). Wylie Walno
reported that the winds was about 20-30 kts. For the winds above the surface we
used the Medicine Bow and Platteville profilers as well as the 18 UTC RUC.
The wind just above the moist layer (600mb) was about 140° at 55 kts. So
there was tremendous shear between the surface and 600mb (1.5 to 1.8 km agl).
The 500 mb wind was from 150° at 55 kts while the 400mb wind was from 165 deg
at 75 kts. 400 mb is 4.4 to 4.7 km above the surface, so the shear from the
surface to 4.5 km was about 80 kts. The 0-3 km shear was about 50kts.
The WYDOT stations and 1 cooperative
observer station also helped to assess the shear profile in southeast
Wyoming in Table 6. These stations show a backing in the surface wind around 19
UTC. Windspeeds are in miles per hour. The windspeed at Virginia Dale
is not given since it was much too low and apparently in error. I
currently do not know how these windspeeds and wind gusts were
calculated and exactly what time the measurements represent. For
example, the 1900 UTC observation could be for the period 1800-1900 UTC.
Table 6
|
14 UTC |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
supplemental obs. (dddffggg) in mph
|
|
|
|
|
|
|
|
|
|
Virginia Dale(7ene) 4SE of tornado
at 19 UTC |
|
|
ese |
e |
e |
ene |
e |
se |
|
| Lynch 7E of tornado at 19 UTC |
09024g30 |
09023g36 |
03022g37 |
08023g30 |
08039g40 |
06027g51 |
07051g51 |
08027g50 |
09009g22 |
| Buford (7N of tornado at 19 UTC) |
07020g30 |
06027g30 |
05033g37 |
07029g41 |
05038g48 |
03052g52 |
08041g57 |
07052g52 |
07013g26 |
These mesonet observations indicate
that the surface winds near the primary tornadic storm were between 030°
and 060°. It is important to note that the RUC and NAM/WRF showed no
indication of a northerly wind component. But this has important
implications for windshear and storm relative helicity. The low level
storm relative flow was apparently much greater than shown by the
models. This shows that added surface observations can help us assess
the near storm environment. The Cheyenne metar(further east) showed a
slight northerly component at 19 UTC (080°).
Hodographs and a
shear analysis were completed by
Dan Bikos of
CIRA.
He varied the surface wind from 040° to 090°. The surface wind
speed was 25 kts and storm motion vector 150° at 42 kts. The 0-3 km
storm
relative helicity(srh) varied from 200 to 682 m²/s²!!
0-1 km srh ranged from 98 to 314 m²/s² depending on surface
wind direction. 0-6 km shear ranged from 90 to 110 kts depending on
surface wind direction. Storm relative inflow varied from 37 to 56 kts
depending on surface wind direction. These have not been finalized and
future tweaks are likely.
Hodographs for Harriman, WY at 19 UTC using surface wind of:
040 deg
050 deg
060 deg
070 deg
080 deg
090 deg
It is clear that srh values depend strongly on the surface wind direction.
One would think that it would be easier to
get sufficient CAPE and shear on the high terrain(7000+ ft) in June
or July than in April or May. But this is not necessarily the case. Strong
synoptic scale systems in spring can have very strong upslope flow associated
with them, whereas systems in late spring and summer tend to be weaker, with
weaker upslope flow. That said, the upslope flow tends to be cooler in April and
May and oftentimes more stable. Upslope flow tends to be located on the cool
side of a surface front or north of a developing surface low. Again, these
airmasses tend to be too cool in April and much of May. This is why significant
tornadoes are so rare in the immediate lee of the Laramie Mountains. The upslope
flow in the May 22 case was "cooler", but 1000+ j/kg surface based CAPE values
were still achieved. Elevations from 5000-6000 ft do have more severe weather in
June and July compared to April and May. But further west on the very high
terrain, strong upslope flow is generally required to obtain adequate theta-e
values, low dewpoint depressions and high shear that typically accompany
tornadic storms. By mid-June, strong upper systems become less common so that
very strong upslope flow is rare. In the May 22 case, gulf moisture raced
northwestward from north Texas and southern Oklahoma into northern Colorado and
southeast Wyoming in 9 to 12 hours from 00 to 09 UTC. Then during the day of May
22, a very strong upslope flow developed north of a surface front. Very strong
upslope flow is required to keep adequate mixing ratios at the 7000-8000 ft
elevations on the eastern slopes of the Laramie mountains. It is also important
to understand that it is the potential temperature that is important in
achieving higher theta-e values and not the temperature. Even in the presence of
only moderately cool 500-300mb temperatures of -13C, -26C and -40C, surface
temperatures from 7 to 9C were still sufficient to yield moderately high theta-e
values, and hence moderately high CAPE values. When potential temperatures are
high, mixing ratios do not have to be very high to achieve sufficiently high
theta-e values. By later in June and July, surface temperatures become so warm
that cloud bases are typically too high for tornadic storms given the meager
mixing ratios typically found at these elevations.
Additional surface charts will be coming soon.
Since terrain is so crucial to this meteorological discussion, I like to plot
the surface observations on top of the terrain. However, this is a very
labor-intensive process, especially since I need to include the mesonet
observations.
Other Thoughts
Until recently, surface observations
were never taken between Cheyenne and Laramie and southward to
Fort Collins and Akron(except for Sterling, CO for a few years). This
is a shame. Surface observations have always been tied to
aviation in the United States, making one wonder what our observation
network would be like if we never had airflight. Therefore, instead of
surface observations being placed where we need them meteorologically,
we have to settle for widely spaced observations in rural areas and
densely spaced observations around major airports.
The British surface observation network pre-dates aviation and is
superior. A storm in 1859
inspired Robert FitzRoy to establish a surface observation network
composed of 15 land stations that were transmitted via telegraph at
regular intervals. In fact, the British even maintained a nice surface
observation network in south Asia in the 1880s. This surface chart is from
05 UTC April 7, 1888. A storm developed over
northern Bangladesh and moved south-southeast, killing 118 people in
Dacca and 70 people in the district south of Dacca. Of course, this area
now called Bangladesh was part of the British Empire until the
late 1940s.
Meanwhile, there has been a big push for improving tornado warnings
with better lead time. While the WSR-88d improvements help in this
goal, we need more surface observations so we can assess the near-storm
environments. Mesoscale models do not suffice. Real time storm chaser
reports are great too, but we can't wait until there is a tornado
tearing up a neighborhood before issuing a warning. I have chased
storms since 1992 and I admit that much of the time I am confused about
what storms are doing. Sometimes I don't even know exactly where to look
for a tornado. If the tornado is wrapped in rain, storm chasers might
not even see the tornado. Also, some storm chasers might wait 5 minutes
to call in a tornado, perhaps taking video or still shots first. I
can't say I blame them given the high gas prices and the fact that most
of these people are not paid. Legitimate storm chasers are often looked
down upon and not appreciated anyway.
A few AWOS and mesonet stations have
popped up in recent
years. This is a good start. Some of these data are of low
quality, but certainly much better than nothing. Of course, Ken
Crawford established a
statewide "Oklahoma Mesonet" in 1994 with over 100 stations. This is a
fabulous,
high quality network.
The Departments of Transportation in some states have established
roadway surface observations. These observations are oftentimes poorly
placed and not representative of surrounding areas. The data quality is
often not very good. However, when used with caution, these can be very
useful. In fact, WYDOT observations were used in the meteorological
part of this page. Why were these observations so useful? Well, in
this particular case dense fog was occurring, so only the temperatures
were needed to determine theta-e and CAPE values. Also, Lynch
and Buford showed winds backing to the northeast or east-northeast
around 19 UTC. This helped determine the vertical shear profile and
storm-relative helicity. By a stroke of luck, the cooperative observer
location 7 miles east-northeast of Virginia Dale happened to be well
placed and hourly wind direction also showed a backing to the
east-northeast there. Hourly temperatures were also available for this COOP site and these
were very helpful in CAPE calculations(corroborated the sfc theta-e calculation for Harriman and Lynch).
