Thursday, April 4, 2013

Significant Threat of Severe Storms, Tornadoes Next Week...

While Texas has been pummeled with several severe hail events over the past week, overall, the spring severe weather season has been off to a slow start so far.  That's about to change...

Last week I posted about trends favoring a wet and stormy April, and such a scenario continues to appear likely.  Toward the end of the same post I also mentioned that with an active April would unfortunately come an increased threat of severe weather, and that is indeed what appears to be taking shape for as early as next week.

A threat of severe weather may develop as early as Monday afternoon and evening across portions of the High Plains of western Kansas and northwestern Oklahoma, as suggested by the latest severe weather outlook for Monday from the SPC in Norman, OK:

Very large hail, damaging winds and tornadoes would all be a threat with severe storms that form in the above region on Monday afternoon and evening.  A threat for isolated severe storms will also likely extend Southward into at least western Oklahoma and perhaps parts of northwest Texas.

Of greater concern is the pattern developing into Tuesday and Wednesday of next week, which will carry a threat of significant severe weather in portions of the Plains and Mississippi Valley regions.

Below is the latest composite forecast output from the European Model (top half of image) and the U.S. based GFS model (bottom half of image) valid Tuesday afternoon (click to enlarge):

As you can see, both models forecast a strong trough of low pressure in the middle amtmosphere (black backround images).  The European model shows a cold front/warm front/dryline intersection across northwest Kansas, with the dryline trailing Southward into West Texas.  The GFS model is faster in moving the cold front, depicting it already Southeastward into Oklahoma and northwest Texas by late Tuesday afternoon.

Since the threat of severe weather Tuesday afternoon and evening will exist ahead of the cold front and dryline, to the South of the warm front, if we assume a compromise between the two models we would have a pronounced threat extending from southern Kansas across much of Oklahoma and northwest through northcentral Texas, as shown on the image below:

(FYI, I apologize, but when you overlay the red on the green and yellow and make it semi-transparent, it turns orange.  The orange shaded area should be regarded as "Isolated/Scattered Significant Severe" as indicated by the red block on the map's legend).

Keep in mind that if the faster GFS model forecast solution should prevail, then the severe threat would shift toward the central and southern two-thirds of the outlined area, as well as further Southeast across Arkansas and Texas.  At the moment I tend to agree more with the European and/or European/GFS compromise solution as far as the timing goes, which would be in close proximity to the severe weather outlook map above.

Model differences in the exact geographic location of the threat aside, the potential exists for significant severe weather Tuesday afternoon and evening.  This would include very large hail (i.e., greater than 2 inches diameter), damaging winds and tornadoes, some of which could be strong and/or long tracked.

By Wednesday, both models forecast the threat of severe weather spreading East/Southeast into the Lower Mississippi Valley region as well as the Deep South, though again the GFS model is faster with the progression of the cold front as you can see on the image below (identical to the model composite image shown earlier, but valid at 7pm CDT on Wednesday this time):

The threat on Wednesday could potentially be significant, as is expected on Tuesday, with large hail, damaging winds and tornadoes a distinct threat along and ahead of the cold front across the South.  

If you live in or near the areas described above or have travel plans into these areas for the first half of next week, please remain on alert.  Take the time now to review your severe weather safety and preparedness tips, identify your best sheltering option, and make sure that you will have a way to receive weather warnings.

We'll continue to monitor this situation with additional updates forthcoming as details become more clear...

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