Friday, July 19, 2013

Elaborating On Tomorrow PM's Storms


Tomorrow's storms present a risk for some gusty winds and perhaps some isolated damage.  The slight risk that we were under has been nudged back a bit to the northwest according to the Storm Prediction Center.  I'm not sure I buy how much of a nudge back they put into it and I would not be surprised if we see the slight risk nudged closer to Philadelphia as we work into tomorrow.  That said, the highest risk for severe storms tomorrow will be to the city's north and northwest.

Instability is quite high -- it usually is when you  have a 90+ airmass out there and a decent amount of atmospheric moisture. Dew points should come down a bit tomorrow but it will still remain pretty high overall (70ish) in the afternoon.  That said, timing may be such where thunderstorms work into the region during the early evening hours and off of "peak heat" time.


The above graphic shows the NAM computer model for 5 PM, showing the storms working through Northeast and Central Pennsylvania. Storms will push southeast during the afternoon and evening hours and probably reach into the Philadelphia region after 7 PM.  These storms may weaken or be on the cusp of weakening as they approach Philadelphia...and probably weaken out a bit more as they work through South Jersey and Delaware...so the risk for severe storms will be lower than it will be over the northern and western burbs.

Some earlier modeling had played up a chance for storms in the afternoon prior to the line moving in but it does appear those odds are dwindling as we approach tomorrow. It looks like we get through most of the day with a mostly sunny or a variable mix of clouds and sun during the day, although the heat index values probably won't be as high as they were the past couple of days.