Tuesday, July 09, 2013

Slight Risk For Severe Storms Nearby Tomorrow PM

With an approaching cool front and our humid airmass overhead, the risk of thunderstorms tomorrow afternoon and evening exists.  Some of those storms may be severe, especially across Pennsylvania, where a slight risk is out generally above Route 222 across the Lehigh Valley and Central Pennsylvania, for tomorrow.

Thunderstorms are expected to fire up in the midday and afternoon hours tomorrow around the region. Modeling varies in terms of placement and timing, but some guidance like the NAM and GFS have suggested a higher risk of thunderstorm initiation closer to Philadelphia as opposed to the west and northwest of the city, as the SPC is suggesting.  Regardless of where storms fire up, I do think some storms around here run the risk of reaching or exceeding severe criteria from a wind standpoint.

I also think any storm that fires up tomorrow afternoon, at minimum, could produce heavy rainfall. PWAT's (our moisture indicator for the whole of the atmosphere) will exceed two inches tomorrow afternoon through the region. With dew point values around 70 or higher across much of the Delaware Valley, there's a lot of low level juice but also moisture in the mid levels to support soaking rainfalls in thunderstorms.

With summertime thunder, it often comes down to small features to determine where thunderstorms fire up initially. I do expect a scattered nature to thunderstorms, at least initially.  Some spots could pick up another one to two inches of rain out of this -- but on a localized basis as not everyone is in line for that amount of rainfall.

The thunder threat extends into Thursday with better parameters for severe storms from an instability standpoint than what we're projected to get tomorrow. The question comes down to how much sunshine filters through what should be a decent deck of clouds around the region. Thunderstorms do appear likely on Thursday but the level of severeness to those storms comes down to how much sun (or even filtered sun) we can get.  More on that as we approach Thursday.