High Plains Drifter


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and do not necessarily represent those of official National Weather Service forecast products,
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March 7, 2011

Southwest Kansas Winter Storm 8 March 2011 [1]

Filed under: 2011 Mar 08 — Mike U @ 7:09 pm

Significant, much needed precipitation event headed for southwest Kansas! For the better part of the last week or so, it appeared a major winter storm would affect the western Plains.  Mid to late last week, all of the global spectral model solutions (and to a large degree their associated ensemble members) were focusing on western/central Nebraska…into southern South Dakota for this storm.  By Friday and Saturday (March 4-5), the models were beginning to suggest a more southern track to the storm.  It then became apparent that northwest Kansas into south-central South Dakota would see the brunt of the storm.  Now that the storm is now within striking distance, all models are locked in on a solution with the mid level PV anomaly and evolution, and it really does favor Southwest Kansas for substantial precipitation.  While the placement in the models was always in question, what was a near-constant was precipitation potential with the storm.  36-hr storm total precipitation from the GFS as well as the Canadian GEM consistently showed potential for 1.0 to 1.5″ of storm total precipitation within the “sweet spot”.  Late last night and early this morning’s model runs showed this 1.0 to 1.5″ storm total QPF shifting south to generally a Lakin-Dighton-Wakeeney line… continuing northeast to north-central Kansas and southeast Nebraska.  18z runs of both the GFS and the NAM have continued this southward shift of the 1.0 to 1.5″ axis even further… to roughly a Ulysses to Garden City to Jetmore corridor.  Both the 07/18z NAM and the GFS show 1.0″+ storm total QPF for Dodge City.  It stands to reason now that Dodge City will be included, if not VERY close, to the sweet spot of the storm.

Now precipitation type.  Today, a shallow arctic cold wedge was moving south and was more aggressive in its movement south than any of the models from last night were suggesting.  This isn’t a surprise (early last week’s arctic cold wedge event in southwest Kansas is a classic example).  As I type, the temperature in Dodge City 33 degrees (See Figure 1), and advection on north winds 15-20 mph will continue to lower the temperature through the evening into the upper 20s.

Precipitation in Dodge City will likely commence as some light freezing drizzle later on this evening with more widespread precipitation in the form of freezing rain/sleet sometime around midnight or thereafter.  Huge questions regarding how shallow the cold wedge will be in Dodge City and whether it will be deep enough for the warm layer aloft to be pinched off enough to support all snow (entire sounding below zero Celsius).  I think we will see several hours of accumulating sleet overnight with a change over to snow probably 4-7am or so tomorrow morning.  I took a look at the 12-hour QPF from the 18z run of the GFS ending 09/00z and it showed about a half inch of QPF during this time frame… this would suggest as much as 4-6″ snowfall after the sleet/freezing rain.  Below are some figures I put together

Figure 1:
20110307-3

Figure set 2 (18z NAM model depiction of 700mb RH/Omega, 850mb Temperature):

Figure set 3 (18z NAM model depiction of 400mb Potential Vorticity/Wind Speed, 500mb Heights):

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