The Cheyenne Tornado
July 16 1979

Jonathan D. Finch

Historical Tornado Cases for the Boulder Warning Area

Historical Tornado Cases for the Cheyenne Warning Area

Historical Tornado Cases for the United States

April 23  1960 Cheyenne Ridge Tornado

May 7-8  1965 Front Range Tornado

June 14-17  1965 Front Range Superstorm

High plains and front range topo maps



Overview

                                        On July 16, 1979, the most damaging tornado in Wyoming history touched down 3 miles west-northwest of the
                                        Cheyenne airport. This strong tornado moved east or east-southeast across the northern part of Cheyenne,
                                        causing $22 million in damage and 1 fatality.  140 houses and 17 trailers were destroyed. 325 other houses were
                                        damaged.  Four C-130 aircraft and National Guard equipment sustained $12 million damage. Municipal hangars
                                        and buildings suffered another $10 million damage. There were no hail reports with this storm or any other storm
                                        that day in Wyoming. A woman was killed instantly by lightning after climbing to the top of Pingora Peak (11884 ft)
                                        about 28 miles west of Lander.
                                                                                                               
                           

July 14

       
                                        On July 14 a strong shortwave trough and associated jet streak was moving across the northern plains as shown by
                                        the 00 UTC July 15 500mb and 250mb charts. Behind this feature across Wyoming, a cold front was already
                                        beginning to surge down the plains as of 21 UTC. Severe weather actually developed by early afternoon in western
                                        SD and Nebraska and in the evening in Colorado. The warmest part of the 700mb warm plume at 00 UTC July 15
                                        extended from central NM to northern Colorado into southern Utah and eastern NV. Late on July 14th a cold surge
                                        developed primarily in the lee of the Rockies. By the end of July 14th (06 UTC July 15th), the cold front had already
                                        surged into northern Colorado. A front that was enhanced by outflow was located across southern Nebraska into
                                        central Missouri.


July 15

                                        By 12 UTC July 15, the surface to 700mb cold surge was apparent. The cool air was actually spilling over the
                                        Rockies into southwest Wyoming and central CO. The shortwave trough (500mb)  and associated jet streak that
                                        moved across the northern high plains the previous evening was located over Minnesota and Iowa. The front that
                                        was draped across southern Nebraska and Missouri at 00 UTC July 16 was surging into central Kansas by 12UTC.
 
                                        By 18 UTC the front had stalled over western Colorado but was still pushing south into New Mexico. The outflow
                                        boundary that was located over eastern Kansas and Missouri at 12 UTC had raced south into northeast Oklahoma
                                        and northern Arkansas.

                                        By 00 UTC July 16, low level moisture was beginning to surge upslope(to the southwest) from northwest Kansas
                                        into eastern Colorado. The surface front was beginning to stall out across central New Mexico. An outflow boundary
                                        stretched from near Dodge City to near Tulsa. Another clusters of convection in the Texas Panhandle resulted in
                                        rain cooled air at Amarillo. The front in New Mexico was about to undergo frontolysis since it had already moved
                                        to near the mean ridge position at 500mb. The northern plains frontal boundary tightened considerably on July 15     
                                        as the elevated mixed layer hot plume shifted north and the low level cool dome shifted south. 700mb temps on the
                                        15th ranged from about 3 C around Sheridan to around 15-16C at Jackson Hole. With  no upper air data between
                                        Boise and Lander, one may ask how I analyzed +15C 700mb temps across western Wyoming. Well, I was able to
                                        make judicious use of surface data to fill in details where upper air data were lacking. This wedge of warm air analyzed
                                        based on the surface tempertatures at Jackson Hole and Yellowstone. Afternoon surface temperatures at Jackson
                                        Hole and  West Yellowstone  were lifted up to 700mb to yield the 700mb temperatures above these stations.
                                        Sometimes the low levels become superadiabatic, yielding a 700mb temp that is too warm. So the best method is to
                                        use the  mixout temperature, whether this occurs at local noon(in windy conditions) or sometime in the early afternoon
                                       in lighter wind conditions. In most of my high front range tornado cases, surface winds under the mid level hot plume
                                        are breezy to windy and afternoon dewpoint depressions are fairly high. Surface winds on July 16, 1979 were not as
                                        strong. Also notice the 700mb baroclinic zone across the midwest and northern plains. There is upper level support for
                                        a front across this area, but not further south in New Mexico. By the end of July 15 (06 UTC July 16), the front over
                                        New Mexico is about to undergo frontolysis. The surface winds over eatsern Colorado were becoming more 
                                        southeasterly, resulting in strong moisture transport onto the front range. The surface dewpoints at Denver and Akron
                                        were up to 59F and 60F respectively.

July 16


                                        By 12 UTC July 16, the front over New Mexico was undergoing frontolysis. A 700mb baroclinic zone was located
                                        across the Iowa. The surface front associated with this baroclinic zone was further south as one would expect in
                                        Illinois and Missouri. A shortwave trough was evident from the 500mb chart over Montana and northwest Wyoming.
                                        The tail end of the upper jet streak was located over eastern Montana. The surface dewpoints at Sidney, Akron, and
                                        Cheyenne were up to 60F, 61F and 56F respectively. Note again that an adjustment of 7F was made to the Sidney
                                        dewpoint. Strong surface pressure rises were occurring at Dodge City and about to occur at Garden City at 12 UTC.
                                        I am not sure why. Accas was reported at Cheyenne on the morning of the 16th after the low clouds burned off. Therefore,
                                        high lapse rates were likely present along the eastern extremity of the warm plume(elevated since low level cooling
                                       occurred at Cheyenne overnight).


                                        From 17 to 20 UTC July 16, an area of thunderstorms moved east-southeast across Nebraska, leaving an outflow
                                        boundary trailing back to the west into southeast Wyoming. Frontogenesis was also occurring across southern Wyoming
                                        and northeast Colorado. By 20 UTC, the leading edge of a strong pressure gradient marked the location of the new
                                        surface frontal boundary. This makes sense based on the position of the upper jet at 12 UTC. I was able to plot the
                                        location of the outflow boundary at around 15 UTC using time series of surface observations from Scottsbluff, Alliance,
                                        Mullen and Ainsworth, NE.   17 UTC   18 UTC   19 UTC  20 UTC.   It is possible that this boundary sagged into
                                        the Cheyenne area around the time of the tornado.
                                       





Time(UTC) VIS/WX/CLDH T/TD Wind ALT
Scottsbluff
 1553
 1023.3
 14010 029
1657 07010 wshft 1655 032
Alliance 1549 20 SM 1020.6 14020
1650 2SM BR OVC007 04012
Mullen 1645 10SM OVC020 69/55 13010 034
1730 1/2SM +TSRA A  OVC005 53/53 04020 040
Ainsworth 1643 67/57 05015 042
1715 -TSRA 34015 045
1745 7 -TSRA 60/59 34015 050


                                  
                                        By the afternoon of  July 16, a well defined frontal boundary extended from east of Yellowstone to east of Jackson
                                        Hole to west of Lander to near Rawlins, to near Laramie to near Cheyenne. Note that Lander was north of the front
                                        all day on July 16 since the winds were light and the dewpoints were high (uper 40s F). The boundary was undoubtedly
                                        situated west of Lander where the woman was struck and killed by lightning. The observations at Rock Springs show
                                       the frontal boundary to the north of them in the afternoon. Then the wind shifted to the  northeast at 00 UTC signafying
                                       a frontal passage.

                                        Between 20 and 21 UTC, the front or outflow boundary sagged south through Laramie, possibly as a result of late
                                       morning and early afternoon thunderstorm activity near the front that was hovering close to Laramie and Cheyenne. The
                                        dewpoint at Lqaramie jumped to 56F at 21 UTC but the temperature was a cool 65F. Local thunderstorms in vicinity
                                        of the front near Laramie was probably the reason for this cool temperature. The frontal positions were estimated by
                                       looking at time series of surface observations for surface stations across the plains. For example, at 19 UTC, it is clear
                                        that the front is north of Rawlins, north and east of Rock Springs and east of  Jackson Hole and West Yellowstone. It
                                        appears that the front is immediately north of Cheyenne and Laramie since thunder was reported at both stations. The
                                       front was very difficult to find across central and eastern Kansas, but the pressure gradient north of the front became
                                        more pronounced during the day.


                                        Southeast Wyoming was located in the right rear quadrant of a jet streak on the afternoon of the 16th.
 


                                       
700mb temperature approximation


                                        The mid level warm plume shifted east from July 15 to July 16, with 700mb temps warming to +18-19C across parts
                                        of southwest and south central Wyoming and adjacent northern Colorado. A strong sfc-700mb baroclinic frontal zone
                                        was apparent across Wyoming. The 00 UTC 17th Denver sounding showed +14C 700mb. However, this sounding
                                        was contaminated by convection. Since Denver mixed out completely by 20 UTC with a surface temperature of 93F,
                                        the 700mb temperature was surely 17C just before the cool outflow arrived. The 700mb temperature at Grand
                                        Junction at 00 UTC July 17 was 17C. The maximum temperature was 97F. If you lift a parcel dry adiabatically from the                                                         surface(856mb) to 700mb you get 18C. Therefore it is typically better to subtract 3F from the high temperature before
                                        lifting to 700mb when determining 700mb temperatures, especially in light wind situations. In strong wind and very dry
                                        situations at elevations above 6000ft, the local noon temperature would give a closer approximation. In this case I used
                                        the maximum temperature or maximum temerature (F) -3 depending on the station to augment the 700mb chart.  700mb
                                        temps in the hot plume on the morning(12 UTC) of the 15th and 16th were about 2 to 3C cooler than at 00 UTC. This
                                        is because the diurnal cooled layer extends up beyong 700mb at stations above 5000ft. This is obviously not the case
                                        at high plains stations such as Amarillo and Dodge City. At these locations, the hot plume sometimes actually moves east
                                        away from the rockies between 00 and 12 UTC, yielding very warm 12 UTC 700mb temps.




The mid level warm plume shifted east from July 15 to July 16, with 700mb temps warming to +18-19C
                                        across parts of southwest and south central Wyoming and adjacent northern Colorado. A strong sfc-700mb
                                        baroclinic frontal zone was apparent across Wyoming. The 00 UTC 17th Denver sounding showed +14C
                                        700mb. However, this sounding was contaminated by convection. Since Denver mixed out completely by 20
                                        UTC with a surface temperature of 93F, the 700mb temperature was surely 17C just before the cool outflow
                                        arrived. The 700mb temperature at Grand Junction at 00 UTC July 17 was 17C. The maximum temperature
                                        was 97F. If you lift a parcel dry adiabatically from the surface(856mb) to 700mb you get 18C. This is why
                                        it is typically better to subtract 3F from the high temperature before lifting to 700mb (when determining 700mb
                                        temperatures). This is especially true in light wind situations. In strong wind and very dry situations, the
                                        maximum temperature would give a closer approximation. I used the maximum temperatures at several stations
                                        to augment the 700mb chart.

Elev(ft) Pres.(mb) MaxT(F) MaxT(F) -3 700mb T
Rock Springs
 6760 800 88 85 18
Rawlins 6813 799 88 85 18
Jackson Hole 6560 805 87 84 16.5
Yellowstone 6640 803 83 80 15
Eagle 6540 809 91 88 18
Rifle 5540 835 93 90 17
Denver 5300 841 93 90 16.5
Grand Junction 4858 856 97 94 17
Vernal 5280 841 92 * 93 16.5


                                        The maximum temperature at Jackson Hole was 87F. Lifting 87F at 805mb up to 700mb yields a 700mb temperature
                                        of 18.5C. However, you can see that Jackson Hole had not "mixed out" by local noon since they were stuck in a fairly
                                        fairly light wind regime. Therefore, I decided to use MaxT (F) -3 = 84F as the mixed out temperature. This yields a                                                                 700mb temperature of 16.5C. The same procedure was used for Yellowstone.  Vernal, UT as well as much of northern                
                                        UT is lower in elevation. I used the maximum temperature there to find the 700mb temperature.                            
                                        

Theta-e Comparison



                                        The first indication of a tornado was 3.5 miles west-northwest of the Cheyenne airport at 335 pm MDT(2135 UTC). The
                                        22 UTC surface chart shows the front just south of Laramie. The T/TD were 71F/56F. At this time the tornado was
                                        probably just finishing its rampage across  northern Cheyenne.  By mid-summer standards in the central or eastern USA
                                        this would be a very cool temperature and a low dewpoint such as would be found behind a strong cold front. However,
                                        the elevation of Laramie is 7270ft. The author of this page believes that the theta-e was similar near Cheyenne and Laramie
                                        on the immediate cool side of the boundary. Despite the T/TD being 12F/16F lower at Laramie than Topeka, the theta-e
                                        was actually slightly higher at Laramie than at Topeka.

01 UTC Elev(ft) Pres.(mb) SLP(mb) T(F) Td(F) MR(g/kg) theta(F) theta-e(K)
Laramie
 7270
 788 1023.3
 71 56 8.3 98.3
 354.3
Topeka 881 991 1020.6 83 72 11.2 80.8 353.6



CAPE Approximation


                                        Since the storm was near the boundary, CAPE estimations were made on both sides of the boundary. To estimate the
                                        CAPE on the cool side of the boundary I used the 22 UTC surface observation at Laramie. This was the only high
                                        elevation location in the most air immediately north of the boundary at 22 UTC. The T/TD were 71F/56F with a
                                        surface pressure of 788mb. I used this information along with nearby soundings from North Platte, Lander and Rapid
                                        City, Dodge City and Denver to create an approximate sounding for the "cool" side of the front. The surface based
                                        CAPE was around 2800 j/kg at 22 UTC. A T/Td of 71F/56F at Laramie would give the same theta-e as 77/57 near
                                        Cheyenne. At Cheyenne it was 81F in the early afternoon. But immedialtely north of Cheyenne it was surely cooler,
                                        with much higher dewpoints. In fact, the dewpoint jumped to 56F at Cheyenne by 22 UTC, but the temperature was
                                        cooler due to nearby thunderstorms.  Just south of the outflow boundary or front, surface based CAPE values were
                                        lower.

                                        The T/TD at Cheyenne at 20-21 UTC were 80/50 and 81F/49F. Using the same thermal profile aloft(500-200mb), the
                                        surface based CAPE at Cheyenne was 1500 j/kg.

                 
Cloud bases        
       

                                        I do not have enough information to determine if the storm was realizing the higher CAPE just north of the boundary,
                                        or if the storm was mainly ingesting air from the warm side. If the former is the case then the storm would have been
                                        lower based and the vertical wind shear would have been stronger given the easterly winds and higher dewpoints in the
                                        cooler air. I cannot reliably compute the shear profile or storm relative helicity. On the front range and mountain region,
                                        it is very difficult to approximate the 1 to 2 km AGL wind profile. While the surface wind and winds at and above 500mb
                                        (~4 km) might be known in this case, wind speed and direction approximations from just above the surface to 3 km
                                        are not very accurate.                                    
                                    

Upper air charts:

7-15-79  00 UTC    700    500    250

7-15-79  12 UTC    700    500    250

7-16-79  00 UTC    850    700    500    400    300    250    200

7-16-79  12 UTC    850    700    500    400    300    250    200

7-17-79  00 UTC    850    700    500    400    300    250    200


Surface charts   21 UTC 14    06 UTC 15    09 UTC 15    12 UTC 15    15 UTC 15    18 UTC 15    21 UTC 15    00 UTC 16
                        03 UTC 16    06 UTC 16    09 UTC 16    12 UTC 16    16 UTC 16    17 UTC 16    18 UTC 16    19 UTC 16                   
                        20 UTC 16    21 UTC 16    22 UTC 16