Pueblo, CO

Weather Forecast Office

Alamosa County tornado 8/16/08

Overview

Mid-afternoon on August 16th a strong supercell thunderstorm, which had already caused extensive crop damage in southern Saguache County, spawned a tornado northeast of Alamosa. The tornado was witnessed by many, and occurred around 8 miles east-southeast of Mosca (2 1/2 miles south of San Luis Lake), in a rural area. The tornado only lasted a few minutes, but, remarkably targeted and destroyed a structure...an unoccupied mobile home. This was an unusually strong supercell for the San Luis Valley. Crop damage in southern Saguache County totalled at least $42 million.

Zoomed-Out Location of Tornado

Zoomed-In Location of Tornado

Photos & Video:


Large Wall Cloud and Tornado	Image of the Tornado	Wall Cloud Forming	Base of the Supercell


Damage of an Unoccupied Mobile Home; Image Courtesy of Willard Williams	Damage of an Unoccupied Mobile Home; Image Courtesy of Willard Williams	Damage of an Unoccupied Mobile Home; Image Courtesy of Willard Williams	Large Hail in Respect to the Dollar Bill

Environment

The Alamosa tornadic event was a pretty rare event, since tornadoes generally do not form in the San Luis Valley. In this case, the environment was just right to produce a mesocyclone based tornado. The SPC's Convective Outlook maps did not hint at a threat for tornadic weather, but did include the state of Colorado under a "See Text" contour. The text described that there was a chance for thunderstorm development, but again, did not hint at a tornadic environment. There were a few hints, though. Looking at the 6:00 AM MDT upper-air sounding from KABQ indicated that just south of the San Luis Valley, the helicity values were at 289 m^2/s^2, which indicates that the environment was sheared enough to produce a rotating storms. Illustrated in the 6:00 AM MDT absolute vorticity plot from Plymouth State University, there is indeed a region of high vorticity located to the west of tornadogenesis. The differential absolute vorticity advection is one of the main lifting mechanisms, the other source of lift, which can be analyzed from the SPC upper-air maps, is the ageostrophic circulation of a jet streak just to the west of where tornadogenesis occurred. The location of tornadogenesis is located in the poleward exit region of the linear jet-streak, implying upper-level divergence. The only variable missing from this tornadic equation, is the instability. There were no good signs of surface warming during the day, or upper-level cooling, therefore, it is implied that there were small values of CAPE, since a supercell was produced. The combination wind shear, implied low CAPE, and the vorticity maximum/jet streak location was enough spawn a mesocyclone based tornado in the San Luis Valley.

6AM MDT SPC Outlook

6:00 AM MDT SPC Upper-Air Maps


Surface Analysis	850-hPa Analysis	700-hPa Analysis


500-hPa Analysis	300-hPa Analysis

6:00 PM MDT SPC Upper-Air Maps


Surface Analysis	850-hPa Analysis	700-hPa Analysis


500-hPa Analysis	300-hPa Analysis

6:00 AM MDT Skew-T Soundings (From Plymouth State University)


KABQ Sounding	KDDC Sounding	KDNR Sounding

6:00 PM MDT Skew-T Soundings (From Plymouth State University)


KABQ Sounding	KDDC Sounding	KDNR Sounding

Absolute Vorticity Analysis at 6:00 AM MDT (From Plymouth State University)

Absolute Vorticity Plot over the U.S. Southwest

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