May 18, 2003 Photogenic Palmer Divide Storm

Weak upslope flow of moderately moist low-level air produced an aesthetically-pleasing storm west of Limon, Colorado this evening.

Meteorology:

The degree of heat and moisture (of the lifted parcel) required to get a thunderstorm decreases as the station elevation increases. For this reason, surface temperatures and dewpoints that would ordinarily be far too low for moist convection over the lower plains are more than sufficient over the high plains. Such were the conditions over eastern Colorado yesterday where temperatures were near 70F and dewpoints around 50F. Shear was marginally supportive of updraft rotation. Under such a regime, the thing to do is target specific topographic features that become convective "hotspots" under upslope conditions (i.e., when surface winds are blowing uphill). One such topographically favored region is the Palmer Divide near Kiowa, Colorado. A moist southeasterly flow will almost always initiate thunderstorms here (assuming the ambient thermodynamic stratification is such that that low-level flow possesses non-negligible CAPE) and this occurred this evening.

Chase Summary:

To be given by Roger Hill, Tour Director.

Figures and Pictures:

A "colorific" shelf cloud encircles a menacing precipitation core over the Colorado prairies west of Limon.	Incredible cloud-to-ground lightning bolt.	What colors!	Beneath a striated, tiered shelf, a lowering takes shape on the forward flank.