Tuesday, April 19, 2011

Storms Trying to Develop Southward in Texas...But How Far???

**Update at 6:20 PM CDT:  The SPC feels that thunderstorms will be able to develop Southward along the dryline in Texas this evening.  A Severe Thundestorm Watch was just issued, valid until 11pm CDT.

Residents of the Austin Metro area, don't feel left out just yet.  If storms are able to form Southward into the Fredericksburg or Kerrville areas, they could still impact the I-35 corridor later this evening...

--------------------------Original post from 5:56 PM is below:

The above radar image, taken just a few moments ago, shows the current Southern (or Southwestward) extent of the thunderstorm line along and ahead of a dryline/coldfront across the region.  The storms across the DFW Metroplex region are severe, and producing large to very large hail.

As you can see on the visible satellite image below, additional thunderstorm development is trying to take place Southwestward along the dryline into west-central Texas (red outlined region depicts towering cumulus clouds forming along the boundary):

The problem at this point (if you want thunderstorms further South along this line) is that the atmosphere is strongly "capped" across this region.  The atmosphere is very unstable along and ahead of the line, with temperatures well into the 90s and dew points well into the 60s, but so far the developing line of towers has failed to break through the cap and form into thunderstorm activity.

We would typically look for some sort of mid or upper level weather disturbance to come along and help the storms form, but today most of that instability is passing well to the North of the region, over Oklahoma and Arkansas.  Therefore, it will be up to the towering cumulus clouds themselves to be persistent enough to break through the cap in one or more spots along the dryline.

We will continue to monitor for this over the next few hours.

Any thunderstorm that does manage to form would become severe rapidly, with very large hail likely (similar to what is taking place in the Dallas area at the present time).

An experimental computer forecast model, called the HRRR (High Resolution Rapid Refresh) is suggesting that at least a broken band of thunderstorms will affect the I-35 corridor between San Antonio and Georgetown between 9 and 10 o'clock this evening (see image below, click to enlarge):  

Keep in mind that this is the computer forecast model's interpretation of what the radar might look like between 9 and 10pm.  Exact locations of storms could be off by tens of miles (or more).  It will interesting to see how accurate the model is.

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