Wednesday, July 1st, 2015 storm potential

A potent trough and attendant shortwave will slowly be pushing eastward during the day on Wednesday allowing for a cold front to also slowly push east.  Ahead of the trough the surface and low-level flow will be out of the southwest allowing for a warm and moist low-level airmass to set in place.

As the shortwave moves just to our north it will be associated with some pretty cold temperatures in the mid-levels of the atmosphere for this time of year.  The GFS computer forecast model suggests temps at 700mb (~10,000ft ASL) as cold as +4 to +6C with temps at 500mb (~18,000ft ASL) between -10C and -12C and perhaps as cold as -12C to -14C.  This should yield to some fairly steep mid-level lapse rates (change of temperature with height).

With surface temperatures projected to warm into the lower 80's and dewpoints expected to climb into the mid to perhaps upper 60's, the combination of warm temps, high dews, and presence of steep lapse rates should yield to a modestly unstable airmass to develop in the afternoon/evening hours.

There will also be some decent wind shear associated with the trough with winds a few thousand feet up off the ground as strong as 25-35 knots with winds around 10,000ft as strong as 30-40 knots and winds around 18,000ft as strong as 40-45 knots.

What all these ingredients point to is the potential for showers and thunderstorms to develop and perhaps become quite numerous as the afternoon progresses.  While typically we see the threat for showers and t'storms diminish as the sun begins to set, colder air working in the mid-levels of the atmosphere may keep activity going well through the evening hours.  Given the degree of winds aloft and such cold mid-level temperatures leading to low freezing levels, the strongest t'storms will be capable of producing hail and strong winds.  Even coastal areas will have the potential despite a sea-breeze.  Typically in these setups the sea-breeze is a non-factor and if anything can sometimes act as an enhancer.  All t'storms will also produce torrential downpours given degree of low-level moisture.

One thing to watch, however, is the potential for some rising heights across portions of southern New England later in the afternoon into the evening.  The GFS forecast model shows heights rising a bit later in the afternoon.  If this occurs this could diminish activity as the afternoon progresses or prevent further activity developing.