Sunday, December 4, 2011

Update on Snow Event #2 for Southern Rockies / Plains...

The latest water vapor satellite image above shows the center of an upper level low pressure system along the Arizona / Mexico border, with disturbances lifting Northeast from the low across the southern Rockies and into the Plains.

The next major disturbance, winter weather wise, that we've been watching for Monday is rounding the base of the trough and still forecast to lift out over the southern Rockies and Plains later tonight and into Monday.  Widespread snow, some heavy, will take place late tonight and into Monday across New Mexico and Colorado into the western portions of the Oklahoma and Texas panhandles, with new snow accumulations by 6pm CST Monday shown on the image below:

Locally heavier amounts of around one foot are possible in the higher elevations of Colorado and New Mexico.

The problem once the system lifts Eastward into Oklahoma, northern Texas, Arkansas and Missouri will be the depth of the cold air, and whether (not to mention when) precipitation will turn to snow.  I have attempted to illustrate the "cold air problem" in a simple manner on the latest surface weather image below:

As you can see (illustrated by the red arrows that I drew on the map), the cold air has sunk Southward at a faster pace on the Western end of the region, rather than on the Eastern end of the region.  This will lead to a slower turn-over to snow across this part of the region on Monday which, as a result, means lower snow accumulation potential.

The image below shows the HPC's rainfall forecast for Monday.  I have drawn, in red, an outline of the area that I expect to see at least a brief change to snow, with accumulation of 1-3 inches possible:

At this time it appears that the potential for accumulating snow will reside to the Southeast of the Tulsa, Joplin and Springfield areas, with the northwest corner of Arkansas, east-central Oklahoma and southcentral Missouri having the best chance.  At this time, I would taper the accumulation potential from 3 inches on the Northeast end of the area, to a dusting on the Southwest end of the area outlined in red.

This is still a "fluid" situation, meaning it could change, but above is the best bet in my book at this moment.  This situation has been particularly complicated due to the fact that the main upper-level system is not lifting out across a given area in one piece at a specific time, but rather ejecting smaller, faster moving pieces of varying strengths from time to time.  This also further complicates the timing issue in relation to how deep the cold air will be at a given place and time when one of those pieces of energy is expected to arrive.

I'll continue to monitor the situation and post any relevant updates as needed...

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