Wyoming Tornadoes on
 June 3 1958

A special case study

 Jonathan D. Finch


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

                                        There were only 3 reports of severe weather on June 3, 1958. Two tornadoes were reported in Wyoming and there                    
                                        was 1 report of 3/4" hail in Idaho. Both tornadoes were in open country and did no damage. One tornado occurred 7                   
                                        miles east of Gilette at 530 pm and the other was just west of the Bighorn mountains near Shell at 3 pm. But June 3
                                        1958 featured a classic severe weather pattern for northeast Wyoming. The author believes that a lot more severe
                                        weather occurred than was reported on this day.



The northeast Wyoming severe weather hole

                                       

                                        From January 1955 to December 1973, there was a large area in northeast Wyoming with no large hail reports
                                        greater than or equal to 1". This area is greater than 6000 sq mi and contains the town of Wright and the tiny town
                                        of Bill. During this period, severe weather reports were not sought after. Occasionally someone would report this event
                                        by telephone.  With almost nothing to hit over such a large area, significant tornadoes are very rare in this area. On
                                        rare occasions, a small town takes a direct hit with a strong tornado. This was certainly the case on August 15, 2004
                                        when 2 people were killed in Wright. Undoubtedly, tornadoes of this magnitude or even stronger have occurred and
                                       hit nothing (rated F0).  The town of Bill is pretty  much a ghosttown with a population of only 76.                             

                                        One undocumented hailstorm and tornado that occurred in this severe weather hole occurred in June 15, 1965 about
                                        about 40 miles north of Douglas. This tornado barely missed the farm house but destroyed 2 trailer houses. A man inside
                                        of the trailers suffered 2 broken ribs. Thousands of valuable trees were destroyed by the tornado, some of which were
                                        giant trees that stood for long time. Giant masses of uprooted and broken, giant trees were all that remained. This
                                        event was documented in the Douglas Budget but never made it into the official storm databases. I stumlbed across
                                        it when researching the June 1965 tornadoes.

                                        The event I would like to discuss occurred on June 3 1958. All the ingredients came together for high-end severe weather.             
                                        But officially, not much happened on this day!!



Meteorological Discussion


            12 UTC June 3

                                        At 12 UTC June 3 1958, a strong upper jet was located from southern California into Utah and Wyoming. The
                                        speeds in this jet are unknown since many of the soundings were missing at upper levels. But 80 to 100kt winds were
                                        probably common. A deep 500mb low (about 558 dm) was located over northern CA with southwest flow across
                                        the Rockies. A  500mb ridge was centered over Missouri and eastern Kansas. The 500mb wind was missing at
                                        Grand Junction. However, the 550mb wind was from the southwest at 52kts. So I made an approximation of 55 kts
                                        for the 500mb windspeed (hence the blue star next to the observation). Ahead of a pacific cold front, a mid level
                                        warm plume covered much of eastern Arizona, eastern Utah, New Mexico, Colorado and probably southern
                                        Wyoming as shown on this 700mb chart. Ahead of the 700mb baroclinic zone in the warm sector, 500mb temperatures
                                        were chilly by early June standards with -13C at Grand Junction. 850mb dewpoints were quite high at North Platte
                                        and Omaha. There was an 850mb front between North Platte and Rapid City, with 850mb dewpoints quite high
                                        across the central plains and up to the front range. Note that I did not analyze for the 500mb observations at Rapid
                                        City and Huron, SD since the upper parts of these soundings were contaminated by convection.


            21 UTC June 3


                                        The 21 UTC surface chart showed a pacific cold front charging into western Wyoming. The progression of this front
                                        was pinpointed using surface observations from Provo, Salt Lake City and Evanston. A warm front was located north
                                        of  Riverton, Casper, Cheyenne, North Platte and Norfolk, but south of Sidney and Douglas. A dryline was buldging
                                        east of Imperial in southwest Nebraska, and a front extended from northern Wyoming into North Dakota. The warm
                                        front stopped advancing after 21 UTC and remained just southwest of Douglas. North of the front in the Nebraska
                                        panhandle, moisture was surging to the west-west-northwest into eastern Wyoming as shown in the surface observations
                                       at Chadron and Scottsbluff.
                     

                                        The surface observation at Casper at 21 UTC shows completely mixed out conditions with T/TD of  85F/13F and wind
                                        of 21025kt. They just recently mixed out and winds were howling from the southwest. The low levels were probably not
                                        strongly superadiabatic since the winds are so strong and since they just recently mixed out after the warm frontal passage.
                                        Given a dewpoint depression of 72F, the temperature profile over Casper at 21 UTC was probably dry adiabatic from
                                        the surface to 500mb.                                        
                                     
                                        Let's lift a parcel at Casper(830mb) at 21 UTC to 700mb and then 500mb at 21 UTC to estimate the 700mb and
                                        500mb temperatures. This gives 700mb and 500mb temperatures of 15C and -11.3C respectively.  The 21 UTC
                                        temperature of 85F at Casper also corresponds to MaxT-3 since the maximum temperature was 88F. But when Casper
                                        initially mixed mixed out at 20 UTC the surface temperature was 83F. Lifting 83F up the dry adiabat yields 14C and
                                        -12.3C. To corroborate this finding, let's look immediately upstream at Rawlins(788mb) and use the same procedure.
                                        The 19 UTC (local noon) temperature at Rawlins had leveled off at 75F. In fact the temperature was 75F at both 18
                                        and 19 UTC. The temperature then  increased to 77F at 20 UTC and then 79F by 21 UTC. The winds during this period
                                        were gusting from the southwest at 35 to 40kts. Using the mixout temperture of 75F and taking this up the dry adiabat
                                        yields 700mb and 500mb temperatures of 14C and -12.3C. Using Max-T -3 = 77F yields 15.1C and -11.2C.  The
                                        bottom line from this exercise is that the 700mb and 500mb temperature at Casper and Rawlins during the afternoon
                                        was 14C - 15C and -11.2C -12.3C respectively. Using an average of these values gives 14.5C at 700mb and -11.8C                  
                                        at 500mb.

                                        Using upper level data from surrounding raobs sites, the most probably thermal profile at Casper from the surface to
                                        500mb at 21 UTC looks something like this.

                                        Lets attempt to construct a sounding from the surface to 500mb and compute the lifted index at Douglas, WY and
                                        northeast of  Casper at 21 UTC. The surface pressure at Douglas was 844mb at 21 UTC. This was calculated by
                                        looking at the 21 UTC station pressure for Douglas(24.95) and multiplying by 33.86. Since the surface T/TD at Douglas
                                        were 79/58 at 21 UTC, the mixing depth in the boundary layer was probably about 4000ft. The approximate sounding
                                        for the area around Douglas from the surface to 500mb yields a lifted index around -10. Given the strong southeast
                                        winds at Douglas, the temperature and dewpoint at Douglas were similar similar to the T/TD values to the northeast
                                        (downstream) of Casper.        

                                        This skewt diagram demonstrates how the dry air over Casper is located over Douglas in elevated fashion. Notice the
                                        Casper sounding is bone dry at low levels but becomes "moist" above 500mb. But the mixing ratios are similar. The
                                        reason why it is moist at mid levels is because this is the top of the boundary layer and it is closer to saturation. The
                                        area above 500mb is where very high based cumulus develop over the higher terrain. When this area of moist air is
                                        advected over the plains, accas often results. The dry air to the southwest of the front at Casper advects northeast
                                        over the moist low level air. So the sounding above 700mb at or just northwest of Douglas is the same as the sounding
                                        in the dry air over Casper above 700mb. The only difference in soundings is the moist low level air northeast of the 
                                        front. Surface theta-e is obviously much higher on the cool side of the boundary owing to the much higher mixing
                                        ratios. The potential temperature is cooler on the cool side of the boundary. The moist layer at Douglas is probably
                                        about 4000ft thick since the dewpoint depression at the surface was about 20F. At the top of this moist layer, dry and
                                        potentially warmer air serves as a cap. The mountians immediately southwest of Douglas and the surface boundary that
                                        was in this same location both served to initiate storms.                          
                              
                                        Using the above technique with several stations in the dry air, I was able to augment the 00 UTC 700mb chart. Notice
                                        that there is a huge gap on the 700mb chart between Denver and Grand Junction to the south and Lander and Rapid
                                        City to the north. I was able to extend the +15C line into southern Wyoming and the +12C line into central Utah. This
                                        enabled me to analyze a sharper 700mb front.

                                        Let us compare moisture and temperature parameters at Douglas on the front range with several stations on the low
                                        plains. The following table shows altimeter, station pressure, temperature, dewpoint temperature, mixing ratio, potential
                                        temperature and theta-e for these locations:

                   

21 UTC Elev(ft) Alt. Pres.(mb) SLP(mb) T(F) Td(F) MR(g/kg) theta(F) theta-e(K)
Douglas 4900 24.95 844 1005.1 79 58 12.4 105.7
 352.7
Wichita 1333 28.52 965.7 1012.6 95 61 12 100.6 348.4
Topeka 881
 29.03 983 1014.9 88 70 16.3 90.7 354.7
OKC 1295 28.61 968.7 1014.2 88 67 14.8 92.7 351.8


                                        Notice from the above table that the theta-e was higher at Douglas than at Wichita despite the temperature being 16F
                                        cooler. The mixing ratio was about the same at these two stations owing to the 1F/1000ft dewpoint lapse rate. In other
                                        words, a 58F dewpoint at Douglas actually has slightly more moisture than a 61F dewpoint at Wichita. The potential
                                        temperature was actually higher at Douglas (106F) than at Wichita (101F). Even though the mixing ratio was 31%
                                        higher at Topeka than Douglas, the potential temperature was 15F higher at Douglas. So the higher potential temperature
                                        made up for the lower mixing ratio. Even though the T/Td were both 9F lower at Douglas than at Oklahoma City, the
                                        the theta-e was slightly higher at Douglas.

                       
            00 UTC June 4
                     

                                        A strong shortwave trough and associated jet streak was approaching Wyoming at 00 UTC June 4.  500-300mb
                                        temperatures were fairly cool by early June standards. The Big Horn Basin was in the left exit region of the jet while
                                        northeast and east central Wyoming was underneath the center of the exit region.

                                        Using the 700-500mb thermal profile estimated from the surface data, along with the 00 UTC upper air data we can
                                        come up with surface based CAPE estimate for northeast Wyoming.  I estimated the 500-200mb thermal profile from
                                        the nearby soundings of Glasgow, Denver, Grand Junction, Rapid City and Lander. The full estimated sounding in the dry
                                        air at Casper is shown here. The full sounding at Douglas shows 4300 j/kg surface based CAPE. It is very  likely that
                                        the surface dewpoints to the northeast and north of Douglas were 1 to 2F higher while the potential temperatures were
                                        probably about 1 to 2F lower. Maximum temperatures from cooperative observer locations were 74F just southwest of
                                        Gillette and 75 to the southeast of Gillete. The maximum temperature at Moorcraft(4200ft) was 76F. Areas north of
                                        Douglas probably had dewpoints close to 60F and surface temperatures in the mid 70sF in the afternoon. This would
                                        still result in surface based CAPE values around 4000j/kg.

                                        The vertical wind shear was excellent in the region north of Douglas. The 500mb, 400mb, 300mb and 200mb charts
                                        indicate speeds of 50kts, 60kts, 70kts and 80kts from about 220 degrees. Since the surface winds south of the warm front
                                        at Casper, Rawlins and Laramie were gusting to between 33 and 40kts and sustained at 25kts, the 700mb winds were
                                        probably from the southwest at 35kts. The surface winds were from the southeast to south-southeast at 15 to 20kts.


               
            Big Horn Basin storms


                                        The surface observations at Worland indicate CB W-N at 20 UTC, CB NW at 21 UTC and CB N-E at 22 UTC.
                                        The weather observer at Greybull observed a tornado to the southeast at 2155 UTC. This was probably the same
                                        tornado that occurred near Shell at 2200 UTC. There was apparently no damage with this tornado. It is possible
                                        that this tornado was occurring southwest of Greybull as well. But this is wide open country with very few people.
                                        No hail was reported with this storm. There was a gap in the surface observations between 19 UTC and 2100 UTC.
                                        The surface wind up through 19 UTC was fairly light. Thunderstorm(s) apparently developed west or northwest of
                                        Worland around 20 UTC and then affected the Greybull and Shell areas around 22 UTC. The wind at Worland was
                                        light from the north from 20 to 22 UTC. The vertical wind shear profile was characterized by light winds or light
                                        northerlies at low levels, and fairly strong southwest mid to high level flow. It has been previoulsly documented by
                                        (Evans and Johns, 1996) that northerly low level flow is favorable for getting moisture west of the Big Horns. The
                                        surface based CAPE was estimated using the 21 UTC surface observation from Worland and the 00 UTC sounding
                                        from Lander. The Lander sounding was immediately upstream from the storm location and was probably representative
                                        of the mid and high levels over the storm area. Since the surface pressure was about 862 mb at Worland, I used a recent
                                        sounding from Grand Junction that had a surface pressure of about 862mb since the elevation of Grand Junction and
                                       Worland are similar. The surface based CAPE approximation was 2600 j/kg.



            Storms northeast of Casper


                                        Storms were exploding north of Casper around the same time the storms were developing west of Worland. The
                                        surface remarks on the surface observation sheet from Casper showed "Rapidly Building CB NE" at 20 UTC,
                                        "CB NW-NNW HUGE CB NNE-NE at 21 UTC, CB NNE-NE at 22 UTC, CB NNE at 23 UTC, CB NNE at
                                        00 UTC, CB DSNT NNE at 01 UTC and CB DSNT NNE at 02 UTC.  Its is fairly obvious from a glimpse of the
                                        21 UTC surface chart that areas north of Douglas and N/NE of Casper were in prime locations for severe weather.

                                        Two tornadoes were observed about 7 miles east of Gillete around 530 pm MST (2330 UTC). Storms developing
                                        about 20 miles north of Casper would take about 2.5 hours to move as far northeast as the tornado location by 2330
                                        UTC assuming a storm motion of 30 mph. So the storm that produced the tornado east of Gillete at 2330 UTC probably
                                        developed north of Casper around 230 pm MST (2130 UTC). This makes sense recalling the remarks of HUGE CB
                                        NE-NNE on the Casper surface observation sheet at 21 UTC.                      

                                       

Conclusion


                                        I believe that the storms in northeast Wyoming produced a lot of severe weather between 21 UTC and 01 UTC. Given                
                                        the very favorable environment, very large hail undoubtedly occurred despite the lack of reports. There also may have
                                        been more tornadoes in the wide open areas to the north of Douglas and northeast of Casper.