On the afternoon of 4 March 1998, upslope flow along the Colorado Front Range resulted in the development of weak convective cells along the foothills. These long-lived cells slowly drifted northwards along the foothills while developing substantial anvil-like, mid-level blow-off which moved northeastward over the High Plains. Very pronounced virga was associated with snow showers falling from the expanding mid- level stratiform region. Very much like during classic mid-summer High Plains dry microbursts, strong gusty winds were present at the surface beneath these evaporating snow showers.
A CCD weather surveillance video camera system is permanently mounted atop the Yucca Ridge Field Station (YRFS). Remote controls of the azimuth elevation and zoom allows imaging cloud targets over a region of more than 250 km in diameter. During the 4 March snow squall microbursts, the camera was trained, in time-lapse mode, on a region about 20 km north of YRFS when it observed the rapid spin-up of a surface-based vortex. It raised considerable amounts of dust from the surface, We estimate the vortex tube grew to a height of about one kilometer. It did not visually connect with the cloud base. The circulation in the vortex, as well as in the overlying cloud system, was clearly cyclonic. The vortex tube persisted for about four minutes.
We theorize this tornado-like vortex was analogous to a summer time gustnado. In this case the falling precipitation appears to have remained frozen until reaching the surface layer. We would suggest the vortex spin-up occurred during the intersection of two of the numerous snow shower-induced microburst gust fronts. Precipitation activity intensified and became more widespread in the next several hours with 4-8 inches of snow falling over the High Plains by morning.