Saturday, October 13, 2012

Complex, Potentially Dangerous Severe Weather Situation This Afternoon and Evening...

A highly complex and equally dangerous scenario is shaping up in the Plains later this afternoon and into this evening.  The potential exists for one or more significant episodes of severe weather on a regional and/or local scale, with large (1-2 inch diameter) to very large (2+ inch diameter) hail, damaging winds (in excess of 70 mph) and tornadoes all possible.  I also continue to believe that one or more strong and/or long track tornadoes are possible.

First, the current situation and outlook for Kansas, Oklahoma, Missouri and Arkansas.  Showers and thunderstorms extend from northwest Missouri across southeast Kansas and into southwest Oklahoma and west-central Texas at this hour:

This activity is non-severe, though it is producing quite a bit of lightning, and is complicating matters insofar as the rain cooled air is preventing the low levels of the atmosphere from becoming more unstable.  Recent visible satellite imagery is indicating numerous breaks and/or thin spots forming in the overcast over central Kansas, western Oklahoma and west-central Texas, as shown by the yellow arrows on the image below:

As cloudiness thins and/or erodes this afternoon, this should allow for additional heating and destabilization of the atmosphere across this region.

The latest run of the high resolution NAM computer model is forecasting thunderstorm activity to break out in central and southcentral Kansas by 4-5pm CDT:

...and in western and central Oklahoma by 5-6pm:

While I would not take to the bank the fact that storms will be in the exact locations shown on the above images at their respective times, I do agree with the idea that thunderstorm activity will break out in these general areas by late afternoon into early evening.  I also agree that, at least initially, some of the storms will be discrete (i.e., isolated) in nature.  It is that type of storm that will be the most capable of producing tornadoes, one or more of which could become strong and/or have a longer than normal track.

This is a potentially dangerous weather situation for the indicated areas.  Please do not be lured into a false sense of security because of the lack of a "moderate" or "high" risk severe weather forecast from the National Weather Service.  If you live in central or eastern Kansas, central or eastern Oklahoma, as well as adjacent portions of Missouri and Arkansas, please pay close attention to the weather this afternoon, evening and early tonight.

Later this evening this activity is forecast to congeal into one more clusters of thunderstorms with an increasing threat of damaging straight line winds, and less of a tornado threat.  The same computer model forecast valid at 10pm this evening indicates an intense squall line extending from near Kansas City to Tulsa to the DFW Metroplex region:

Again, the locations may not be exact as this is only a computer model simulation, but I do agree with the overall idea shown above.

Further South in Northwest and West-Central Texas, thunderstorms are forecast to develop along the cool front and/or dryline in northwest and west central Texas by mid afternoon.  The sun is shining ahead of the frontal boundary in northwest Texas, which is allowing the atmosphere to destabilize rapidly.

Initially, the activity will be isolated to scattered in nature, with large hail, damaging winds and a few tornadoes possible.  

Here again, as indicated by the last computer model image above, the activity will eventually congeal into a more solid line by mid to late evening, with a more pronounced threat of damaging winds developing by that time.

In southcentral Texas, short-range computer models continue to suggest that a few thunderstorms may develop along the I-35 corridor from Austin to San Antonio between 5pm and 9pm this evening.  Any such development would be taking place well ahead of the frontal boundary over West Texas, and appears to be focused on the nose of strong moisture flowing North from the Gulf of Mexico, and beneath a band of increasing winds in the middle and upper atmosphere:

If an isolated or scattered storm were to develop in this region (as noted within the red circled area on the above computer model forecast image valid at 7pm CDT), large hail and damaging wind gusts would be possible, along with torrential rainfall.  While the chance of a storm at any given location in this region is only 30 percent, the chance of severe weather would be close to 100 percent if this development is realized.  This is what we call a "conditional" risk of severe weather.

Regardless of the potential for isolated development in southcentral Texas this evening, by later tonight the activity in Northwest and west-central Texas will continue to develop Southward, with a swath of torrential rain and gusty wind producing thunderstorms likely by dawn across southcentral through east-central Texas.  The computer model forecast below is valid 6am CDT Sunday morning, and supports this idea quite well:

If you live in the severe weather threat areas for today and/or tonight, please pay particular attention to the weather.  Listen to NOAA Weather Radio, local media or another trusted source for the latest information, watches and possible warnings.  

Take the time now to make sure your severe weather safety kit is prepared and/or re-stocked, and be sure to identify your best sheltering options so that you can move there quickly if need be.

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The Planet Pink said...

Our weather people are saying after 6pm for us. Does that sound about right?

Rob White said...

Planet Pink,

Things are coming at you from about 3 different directions. I'd say things will start to heat-up around 5-6pm, but that may be only round 1 of several, depending on how things come together to the West...