Showers/Thunderstorms Possible Ahead of Cold Front Friday, April 22nd, 2016

Our next weather maker looks to occur on Friday as a shortwave trough and associated piece of shortwave energy drives a cold front east through the region.  As the cold front approaches from the west, there are some indications the front could be accompanied by some showers and perhaps even some thunderstorms.  

When dealing with the potential for thunderstorms, the biggest question we will face is how much instability develops ahead of the approaching cold front.  With some cloud cover and increasing clouds, temperatures are only expected to reach the lower to perhaps mid-60's (cooler along the coast and higher elevations) and dewpoints are expected to climb into the lower to mid-50's.  This combination of temperatures/dewpoints isn't favorable for the development of high amounts of instability, however, with the approaching shortwave and shortwave trough, an area of steeper mid-level lapse rates is expected to move overhead thanks in part to cold air advection in the mid-levels of the atmosphere.  This will work to yield some modest instability values ahead of the cold front.  The GFS computer forecast model is projecting a plume of 700-500mb lapse rates exceeding 6.5 C/KM to 7 C/KM moving overhead early to mid Friday afternoon:

The GFS computer model at this time is forecasting surface-based cape values on the order of 500 J/KG with most-unstable cape values between 500-1000 J/KG.  These values are indicative of some very modest instability and while they aren't overly impressive, when combined with some wind shear aloft, these values may be sufficient enough to not only produce thunderstorms but perhaps a few stronger to marginally severe thunderstorms:

With the approaching shortwave trough, we will also see an increase in the winds aloft.  While the winds aloft aren't expected to be overly impressive, they should be sufficient enough to further enhance the degree of lift across the region, thus increasing the potential for showers and thunderstorms to develop ahead of the cold front.  While the upper-level jet around 200-300mb isn't forecasted to be overly strong, there will be some enhanced support from the mid-level jet at 500mb.  In fact, parts of southern New England, particularly south of the MA Pike will briefly enter the left-front quadrant of a 50-60 knots mid-level jet streak passing just to the south of CT.  This is a favorable quadrant for enhanced lift.  Bulk shear values from the surface to 700mb are forecasted to be around 25-35 knots with bulk shear values from the surface to 500mb forecasted to be 30-40 knots.  These values are sufficient enough to yield the possibility for organized thunderstorms if any develop:

What can we potentially expect on Friday?  For Friday we can expect winds to increase from the southwest as the morning progresses and the front approaches.  We'll see a mixture of sun and clouds as well with clouds increasing heading into the afternoon.  Expect showers to develop as well during the early afternoon hours.  If enough instability materializes, we could see a line of heavier downpours and thunderstorms develop ahead of the cold front.  Given the potential for fairly steep mid-level lapse rates and adequate shear aloft, some of the thunderstorms could become strong to marginally severe and pose a threat for hail and strong winds.  This potential though is highly dependent on the degree of instability that materializes.  Showers/thunderstorms should clear by early evening and temperatures at night will drop into the 30's with afternoon temperatures on Saturday and Sunday right at seasonal levels.