Friday, November 2, 2012

Severe Weather Possible Next Weekend

This weekend there will be a chance of thunderstorms across East Texas as a weak cool front moves into the area.  As we transition from summer temperatures to cooler autumn temperatures, the clash of air masses occur more frequently across our area giving us a second severe weather season that typically peaks around the second week in November.  This weekend it appears there is a slight chance one or two of the storms could produce gusty winds and small hail but the overall threat of severe weather looks minimal at this time.

That could change though for next weekend.  Long range forecast models continue to hint at a major trough setting up over the Rockies and sending a very strong jet streak across the Central Plains sometime next weekend.  Now this is still a long way out and the position of the trough and jet streak will probably change but with the models consistently showing this feature it appears likely a major severe weather event could occur somewhere across the central part of the United States next weekend. 

At the writing of this article it appears the greatest threat for severe weather would be form Iowa southwest into North Central Texas.  As the strong jet streak crosses the Rocky Mountains, an area of low pressure will rapidly develop in Eastern Colorado and move northeast towards the Great Lakes by Sunday evening.  Out ahead of this low pressure, strong southeasterly winds will set up all across the Plains bringing in moisture from the Gulf of Mexico.  Above these southeasterly winds, winds will be from the southwest wrapping around the low pressure as it moves across the area.  This will give the atmosphere plenty of spin needed for severe weather.

Now in order to get the severe storms we will need enough instability for thunderstorms to develop.  Right now the models are forecasting just enough instability to get marginal strong to severe storms.  But there are other factors that lead me to believe the storms could be much stronger.  The area across the southern plains is forecast to be under an area if diffluent winds, or winds that spread apart aloft.   We call this upper air divergence and it causes the air to rise from the surface.  This will cause the updraft in a thunderstorm to be stronger than just factoring in the available instability. 

So will this be just a severe thunderstorm event with strong winds and hail or will this be a tornado outbreak?  Well this far out it is too hard to tell.  We need to wait to see how the mesoscale features develop between now and then.  There will be an awful lot of forcing with this system so it appears likely a strong line of storms will develop and sweep across the central parts of the country.  However, the low level shear is forecast right now to be very favorable for tornado development.  So if the line of storms can remain broken there would be an increased threat of tornadoes as it moves through.  But with the amount of forcing that is forecast it seems right now at least the more likely scenario would be an intense squall line with lots of wind damage and a few isolated tornadoes.   Again it is way too far out to even guess at the exact location of severe weather next weekend but it does appear likely there will be a threat somewhere across the central United States from Saturday into Sunday.  More details as we get closer to the event.   

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