The Cheyenne Ridge Tornado
April 23 1960

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

May 7-8  1965 Front Range Tornado

June 14-17  1965 Front Range Superstorm

High plains and front range topo maps



Overview


                                        On April 23, 1960 , a thunderstorm developed near Fort Collins, Colorado. This storm moved north-northwest and
                                        and became severe, producing tornado(es) in western Laramie county in Wyoming.  The tornado touched down
                                        about 23 miles west-southwest of Cheyenne or about 3.5 miles west-southwest of Granite, WY at 7500ft elevation.
                                        The tornado moved northwest or north-northwest into eastern Albany county (elevation 7900ft). 
                           
                           

Meteorological Discussion


                                               
                                        The 00z April 23 1960 500mb chart showed 2 branches of the westerlies, one from Old Mexico into the southern
                                        plains, and another from southern California into western Utah. Moisture was streaming north from the Gulf of
                                        Mexico with dewpoints in the 50sF as far north as Nebraska. Elevated moisture was present north of the surface
                                        front across the nothern plains with 750mb dewpoints/mixing ratios around > 5C / 7.5 g/kg).


02 UTC Elev(ft) Pres.(mb) SLP(mb) T(F) Td(F) MR(g/kg) theta(F) theta-e(K)
Cheyenne 6140 800 998.4 65 46 8.3 99.5
 336.6
Galveston 6 1016.6 1016.1 72 67 14.1 69.6 334.5



18 UTC Elev(ft) Pres.(mb) T(F) Td(F) wind theta(F) 500mb T verif
Lander 5586 813 65 23(?) 18030 96.9
 -19.8
Casper 5300 823 68 11 20025 98.2 -19.0
Rawlins 6813 780 59 14 18025 97.1 -19.5
Laramie 7200 767 58 9 19010 98.7 -18.7
Craig 6193 794 60 7 21023 95.4 -20.6
Leadville 9927 691 45 5 24020 101.0 -17.4
Rifle 5540 814 65 13 20015 96.7 -18.2
Grand
Junction		 4858 839 66 4 20022 93.0 -21.9
Gunnison 7678 760 57 11 19022 98.4 -18.9
Montrose 5759 809 66 21020 98.7 -18.7
Colo. Springs 6100 801 66 19023 100.4 -17.7 * -17.1 -16.0
Denver -18.8 * -17.6
101.3 -17.2 * -16.6
Alamosa 7539 764 59 15 18025 100.4 -17.8  
Albuquerque 831 73 19 19020 101.9 -19.9 *-17.0 -17.0
Grants 794 65 2 22015 100.7 -19.6 *-17.6
Las Vegas 6800 784 64 34(?) 22025 101.7 -19.0 *-17.0
Farmington 824 65 8 21015 94.8
Zuni 6300 797 60 6 24025 94.7





                                        The 00 UTC upper air charts showed the leading edge of the strong 500, 400mb, 300mb and 200mb flow
                                        somewhere between Denver and Grand Junction. To construct approximate soundings for Cheyenne 
                                        and  7700ft elevation to the west of Cheyenne, I used the 00 UTC thermal profiles at Rapid City, Denver and
                                        Glasgow, and 500, 400 and 300mb wind/temperature comparisons at 00 and 12 UTC.  Since the mid  to high                           
                                       level winds increase between 00 UTC and 12 UTC, and since the tornado occurred atter 02 UTC, I interpolated
                                        the winds from the surrounding upper air sites and then adjusted a little based on higher winds progressing east
                                        between 00 and 12 UTC.  I made use of  500, 400 and 300mb wind/temperature/front comparisons as well. One
                                        important thing to note is that the 500, 400, 300mb and 200mb temperatures changed very little by 12 UTC in
                                        southeast Wyoming.  Here are sounding comparisons at Denver, Rapid City and Glasgow which also show
                                        how the 500-300mb temperatrues changed very little after 00 UTC.

                                        The surface front was well west of the surface location at 00 UTC. Given the dry adiabatic profiles (that are
                                        implied from the surface to 500mb in the dry air at Rawlins), 500mb cold advection would have required surface
                                       cooling as well.

                                        As already discussed, 700mb temperatures were known with fairly high accuracy. Of course, surface dewpoint,
                                        surface temperature and surface pressure at Cheyenne were known quantities. I made a few assumptions to find
                                        the T/D at 7700ft out to the west of  Cheyenne. Surface based CAPE values were about 2000-2400 j/kg. 

                                        The surface wind was from 120 deg. at 20 kts.  The 500mb wind (3 km) was from 180 deg. at 35 kts. The 5km
                                        wind (400mb) was from 180 deg. at 50kts. The 7 km wind (300mb) was from the south-southwest at 60kts. Thus,
                                        the vertical wind shear was excellent.