Monday, August 13, 2012

Isolated Severe Weather Tuesday 8/14/12

Another chance for isolated severe weather tomorrow with a cold front that'll swing through the area. 
  As of 8:30pm, this front has already produced severe weather(mainly wind reports, a few hail) across portions of the upper Mississippi Valley.
This front will continue to near the area overnight.  A few showers may break out across portions of the area during the early morning hours of Tuesday.  This is important because it will likely effect how widespread we see strong storms when line associated with the actual cold front moves through.  Below is the 18z NAM for Tuesday morning 6am from WeatherBell (great site for models by the way).  Lift out ahead of the front should form a few light rain showers, especially across northwestern areas of the state. 
Of course with showers occurring early in the morning, and leftover cloud debris associated with them, instability won't be maximized since this will not only steal some of the energy in the atmosphere to begin with, but also take away from the sun's ability to get out and charge everything up.  A big part of the uncertainty is how long early morning convection and clouds hangs around.  Below is 18z NAM for 8am Tuesday morning.  As you can see, showers are out of a good portion of the area.  If the sun can break out for a sufficient amount of time, the chances for severe weather later in the afternoon will go up.
18z NAM cape values for Tuesday evening are a bit more impressive than earlier runs, mainly due to more clearing after the first batch of showers moves through.Cape Values 2000+ across parts of the northern half of the state with an advancing cold front would definitely spell at least isolated severe weather.
The 18z NAM shows convection firing late tomorrow afternoon and evening after this clearing has taken place.  Here's Tuesday 7pm:
Overall, a lot depends on the amount of clearing that can take place in the mid morning/early afternoon.  Right now, based on latest model runs..this is where I think the best chance for strong and severe storms will be.  Biggest threat will be winds...but small hail cannot be ruled out.

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