Tuesday, November 1, 2011

Cat Scan of a Wasatch Winter Storm

We have never been able to examine the "guts" of Wasatch winter storms like we can with the Doppler on Wheels radar that is presently here in Salt Lake City.  In particular, we can take a meteorological "cat scan" of winter storms to see their inner workings.

Today we operated the Doppler on Wheels along SR-111 near ~7000 South.  The site affords a view of the entire Salt Lake Valley and central Wasatch Mountains.  While scanning, we took a series of vertical scans across the Salt Lake Valley towards the Wasatch Range.  One of these scans curt across Tin Peaks towards Alta, as shown below.

No storm in the central Wasatch Mountains has ever before been observed in this fashion and the imagery is simply remarkable.

In this loop, our site along SR-111 is on the left and Twin Peaks is the stationary band of high (bright red) radar reflectivity in the center of the image.  There are several precipitation cells or bands that move from left to right and across Twin Peaks, the most dramatic being a convective cell at ~1448-1520 UTC.  If you happened to be on the Twin during this period, you would have observed a burst of heavy snow.

In this case, the impact of the mountains is pretty small.  Most of the precipitation features move relatively unimpeded across Twin Peaks and don't seem to experience much amplification.  In contrast, when the mountains have a large impact, we typically see stationary radar reflectivity maxima sitting stationary over the mountains or the amplification of precipitation features near or over their windward slopes.  In fact,  the precipitation in the Salt Lake Valley (.18-.68 inches depending on location) today was comparable to that observed in the central Wasatch Mountains (.34-.53 inches depending on location).

Meteorologists spend a good deal of time trying to understand why mountains enhance precipitation, but sometimes we should be thinking about why in some storms they don't.

1 comment:

  1. Good post! I think it has to do with direction of the front? I am not sure the direction of this particular storm of the blog post so I shouldn't comment on it.