Oct 182010
 

Wednesday, 20 October 2010: Update

 

It looks like two or three specific days are shaping up to be potential severe storm/chase setups across the southern Plains. I already wrote about the October 22 setup in western Oklahoma/Texas in a recent post.

The European models show two intense shortwaves ejecting into the Plains early next week, presenting even more severe potential across the southern Plains. One shortwave moves into the Dakotas and Nebraska on Monday, developing a deep surface low over southwestern Kansas. Even if the model is anywhere close to verifying, that will be something to keep an eye on for a dryline supercell day anywhere from Oklahoma to Nebraska, especially considering the amount of energy coming from the Pacific.

Then on Tuesday, a secondary shortwave digs into the four corners region and New Mexico, which causes pressure falls over the Texas panhandle. A dryline and warm front may both be present on this day from the Texas panhandle into Oklahoma, potentially initiating severe storms. At any rate, deep, low level moisture will be available for all these setups, so it’s definitely something to watch over the coming days…

- Jim

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Monday, 18 October 2010

An active jet stream across the northern Pacific is expected to bring a series of strong troughs into the western U.S. this week into the weekend. Some of the shortwaves within these troughs will eject into the southern Plains as early as Friday and Saturday, but also into next week. With quality low level moisture already in place across south Texas, only a couple days of solid moisture return could set the stage for severe storms across north Texas, Oklahoma and other areas over the southern Plains with each passing shortwave.

Quality low level moisture (mid 60s dewpoints) are in place in south Texas and the western Gulf of Mexico

Surface dewpoints valid the morning of October 18

Surface dewpoints valid the morning of October 18

The graphic above shows there are already dewpoints in the mid 60s in place across south Texas, with plenty more moisture further south across the western Gulf of Mexico.

 
Brownsville, TX sounding from October 18 showing the depth of the moisture

Brownsville sounding October 18

Brownsville sounding October 18

 
The image above is the sounding profile from Brownsville, TX. It clearly shows that the depth of the quality, low level moisture extends up to 800mb.

All medium range models are forecasting a ridge to be centered over the Southeast this weekend into next week, with a deep trough over the western states. If you look at the individual runs of the GFS or European models, you will see that they show various shortwave troughs ejecting into the Plains. Some of these suggest promising severe storm setups, but each model run will show changes to these setups this far in advance.

The point here isn’t to pick out the day or the area that these models show a chase setup now, because they will likely be wrong this far out. The point is to mention what we know. We know that: 1)moisture will be in place when these troughs eject into the Plains and 2)with how active the Pacific jet stream is right now and the depth of the troughs these models show digging into the western states this weekend into next week, there will be severe storm setups somewhere across the southern Plains in the Oct 22-28 period. With some luck one or two of these setups will be chaseable and have tornado potential. But, we’ll see…it’s early. For now, it’s just nice to have the potential for some good setups with an active weather pattern.

- Jim

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