Severe Weather Outlook for Tuesday, August 11, 2009...

Overnight Discussion...
A general >10% probability for garden variety thunderstorms will be carried thruout the entire outlook area for now. There is upstream convection over Lower Michigan that will work southeast overnight and reach Western PA/NY later this Morning. With mid-morning update, should be able to tighten the probability gradient as weak cold front advances thru western areas of the outlook area. Onto the severe potential...

First off, no slight risk areas are in effect at this moment with the Overnight Outlook. However, this could change pending on what Morning runs show. Despite that, isolated severe storms will be possible over a fairly wide area Today. The 00z WRF depicts a cluster of storms organizing over western NY by Late Morning and tracking across PA thru early Afternoon hours. It is conceivable this could produce a severe weather report or 2 during it's track, so 5% wind/hail probabilities will start at the Western NY to Central OH line.

In all honesty, the best area I see for severe weather Today is over Eastern New England. Surface heating should yield between 1250-2000 J/KG of instability, and this will be coupled with fairly moderate 0-6 bulk shear of 35-50 knots. SPC does not even have this area tagged in a 5% wind/hail probability, which is beyond me. Nonetheless, this area seems worthy of atleast the minimal 5% wind/hail probability IMO.

As mentioned earlier, low level bulk shear values are lacking across the southern half of the outlook area, which will work against storm organization. But with moderate surface heating and atleast 20-30 knots of shear in the low levels, atleast a marginal severe threat will be present. As mentioned before, Tornado threat is practically zero Today with many factors lacking, led by low-level helicity.

All in all, no 1 area really looks more worthy than a marginal 5/5 probability for severe wind gusts/large hail, so for now, probabilities are capped at 5/5/<2 for damaging winds, large hail, and tornadoes, respectively.

..EGAN.. 08/11/2009