From the ABC 7 Weather team

Tuesday Severe Weather: The latest risk and timing

September 17, 2012 - 04:45 PM
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The combination of a storm and rain moving near us and a strong cold front moving in from the west will generate a combination of rain and likely strong winds and what is called "shear" in the air above us.

10:00PM Update:  No reason to change this.  Risk of severe weather for Tuesday continues.  Damaging winds LATE and will increase risk of small whirlwinds but risk of large tornadoes very low.  The late outlooks from Storm Prediction Center remain the same

Usually when we get into mid-September the chances of severe thunderstorms diminish.  But Tuesday, the combination of a storm and rain moving near us and a strong cold front moving in from the west, will generate a combination of rain and likely strong winds and what is called "shear" in the air above us. 

All likely to combine to bring a high risk of strong and perhaps damaging winds.  Here is how we see the risk of tornadoes, wind, hail and flooding for Tuesday. 

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The National Weather Service Storm Prediction Center has the D.C. area right at the center of a 30 percent probability of severe weather Tuesday.  

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Here is one of the the things that show us the risk of severe weather Tuesday. It's a "model" or simulation of the temperature, moisture and wind profile above us Tuesday afternoon.  

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I've circled the winds near the surface and about 3 miles above us.  You can see the very moist winds from the south at the surface and the indication of winds about 75 mph above us and from the southwest.  

 

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The combination of the change in wind speed with height, and the change in direction is what is wind shear and one of the indications of possible severe weather.  The very latest from some of the ensemble simulations at the Storm Prediction Center also do show a risk of possible small tornadoes because of all the shear or spin in the atmosphere. 

 

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No sign of a big outbreak, but even rotating rain showers can generate a small tornado or whirlwind in our area.  More to come and we will also be live blogging starting Tuesday morning to keep you posted and any severe warnings go out immediately on our @StormWatch7 Twitter account.  We will keep you informed.

 

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