The CheyenneTornado
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.

                                                                  
                        
                           

Meteorological Discussion



                                        A strong shortwave trough moved across the northern plains on July 14. This helped push a cold front from
                                        northern Wyoming on the 14th to northern New Mexico on July 15. But with the jet remaining across the northern
                                        plains, the front underwent frontolysis late on July 15 and into July 16. Frontogenesis occurred from far western
                                        Wyoming into Kansas and southern Missouri on July 16. At midday July 16 (19UTC) the front was located 
                                        immediately north of Laramie and Cheyenne. This boundary sagged south through Laramie by 20 UTC, but was
                                        still immediately north of the Cheyenne airport. The southward push of the front was possibly due to thunderstorm                             
                                        outflow as storms developed along the boundary by late morning and early afternoon. 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. The surface based CAPE was around 2800 j/kg at Laramie at 22 UTC. I
                                        made an approximate sounding for Laramie based on 00 UTC 700-200mb charts/soundings and the
                                        22 UTC surface observation at Laramie.  71/56 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.
                                       

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



                                        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.
01 UTC 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




 A jet streak also slowly moved east from 12 UTC July 15 to 00 UTC July17 across the northern plains.
                                        Southeast Wyoming was located in the right rear quadrant of this jet on the afternoon of the 16th.



                                       
               

 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.



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