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
High plains and front range topo maps
Overview
On April 12, 1967 , a thunderstorm developed west of Cheyenne, WY and moved NE over mostly wide open
country. The first tornado was seen 4 miles south west of Veteran, WY. This tornado moved NE and then north,
passing 4 miles west of Torrngton. No large
hail was reported. Its is possible that the core of this storm on
the northern and northwest side of the storm hit no
populated areas. Also, phone calls were not made to collect
hail reports in the 1960s. Hail was only documented
if someone actually called the report in to the office. Hail as
large as golfballs did occur in the Nebraska
panhandle near Chadron.
Meteorological Discussion
Morning Upper Air Charts
At 12 UTC April 12 1967, a very deep 500mb trough was located over southern California. A 700mb
warm plume covered the plains with 700mb temps up to
7C. A high level speed max was located over the
northern plains but another jet streak was entering
southeast Arizona. 500mb temps were fairly cold (17-19C)
from Albuquerque to Denver to Rapid City. Even though the 700mb
temperature was cooler at Albuquerque
at 12 UTC (-1C), the 700mb cold front had not
passed yet. Elevated
heating and then the rapid transport of
this warm
plume downstream was leading to warmer 700mb
temperatures to the
east of Albuquerque(ABQ).
Surface features
By 18 UTC, a warm front stretched from central
Colorado into northern Kansas and Missouri. Low level upslope
flow was apparent across northeast Colorado, western
Nebraska and southeast Wyoming. This in conjunction with
elevated heating was leading to rapid
destabilization across the central high plains and front range. A
surface cold
front stretched from western CO to near ABQ.
The cold front passed ABQ shortly after 18 UTC as shown
by the surface observation sheet. Another cold front stretched from North Dakota into eastern Wyoming. A well
defined outflow boundary existed across the
southern plains.
A surface dryline was located from west Texas to just
east of Goodland. I pinpointed the
location of the
dryline using the surface observation sheets from Goodland and
Garden City. I pinpointed the warm front using surface observations from various sites including Akron, Denver
and Goodland. The warm front was a little harder to
find across western Kansas.
By 20 UTC, the warm front stretched from just south
of Denver to just south of Akron to near North Platte. The
pacific cold front was about to pass Las Vegas, NM.
The dryline had pushed east of Garden City. The dryline
was well east of Goodland, KS but had not yet passed
east of Imperial, NE. The T/TD at Cheyenne were up to
59F/39F with upslope winds.
What Happened?
A thunderstorm developed west of Cheyenne around 3
pm MST (22 UTC) and moved generally northeast. At 5 pm
MST (00 UTC) this storm produced a tornado
southwest of Veteran, WY. This tornado
moved northeast then north
over mostly rural areas, destroying 10 buildings.
The tornado passed 4 miles west of Torrington. Severe
weather probably
occurred between Cheyenne and Veteran, but
this is a sparsely populated area.
Elevated Heating
The surface T/Td at Cheyenne and Fort Collins at 18
UTC were 53F/39F and 61F/41F respectively. The surface
dewpoint at Muskogee was 62F/60F. However, the
theta-e was actually higher at Fort Collins and about the same at
Cheyenne. This is despite the dewpoint being much
lower on the front range. But why? The key is that elevated heating
compensated for the lack of moisture on the front
range. In this case, the potential temperature was 32F higher in
Cheyenne than Muskogee even though it was 9F cooler
at Cheyenne. So even though the mixing ratio was 78% lower
at Cheyenne than Muskogeee, the potential
temperature was 22.6F higher in Cheyenne, resulting in similar theta-e
values. Since the 500mb temperature was much
cooler at Cheyenne and Fort Collins, the lifted index was
much lower
there. See the table immediately below for details.
| 18 UTC |
Elev(ft) |
Pres.(mb) |
SLP(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
H5 T |
LI |
| Cheyenne |
6140 |
795.4 |
991.0 |
53 |
39 |
6.4 |
87.6 |
323.5 |
-18 |
-3.5 |
| Fort Collins |
5000 |
828 |
990.6 |
61 |
41 |
6.6 |
89.8 |
325.6 |
-18 |
-4 |
| Muskogee |
607 |
980.2 |
1005
|
62 |
60 |
11.4 |
65 |
323.9 |
-11 |
+3 |
The surface T/Td at Cheyenne at 20 UTC was 59F/39F.
The surface T/Td at Topeka and Emporia were 67F/60F
and 70F/57F respectively. However, the theta-e was
actually about the same at all 3 locations. Again, the
key is
elevated heating. Since the 500mb temperature was
much cooler at Cheyenne, the lifted index was much lower
at Cheyenne. See the table immediately below for details.
| 20 UTC |
Elev(ft) |
Pres.(mb) |
SLP(mb) |
T(F) |
Td(F) |
MR(g/kg) |
theta(F) |
theta-e(K) |
H5 T |
LI |
| Cheyenne |
6140 |
793 |
990.6 |
59 |
39 |
6.4 |
94.5 |
327.7 |
-19 |
-6 |
| Topeka |
881 |
971 |
1003.6 |
67 |
60 |
11.5 |
71.3 |
328.2 |
-11 |
+2 |
| Emporia |
1207 |
960.6 |
1003.3
|
70 |
57 |
10 |
69.5 |
328.2 |
-11 |
+2 |
CAPE and vertical wind profile
An approximate sounding for Cheyenne at 20 UTC shows
about 1800 j/kg surface based CAPE. I used the 00
UTC Rapid City wind profile at and above 500mb. The
winds veered between the surface and 500mb, but the
speeds and directions in this layer are not known.
The 700mb wind field on the high plains, front range and
intermountain west can be very difficult to resolve
since 700mb is in the boundary layer. Sometimes 700mb is in
the moist layer and sometimes not. The only way to
know the low level wind profile on the front range is to have a
dense sounding or profiler network. However, there
was greater than 50kts of shear between the surface and 400mb
or in the lowest 6 km. This is very respectable.
I also created an approximate sounding for
Scottsbluff, NE which is east of where the tornado occurred. The surface
based CAPE was about 1300 j/kg.