A Soaking...
We really have just scratched the surface as far as rain goes with the heaviest batch still on the way for later tonight and tomorrow morning. To this point, the greatest amounts have occurred in SE Mass, for example, New Bedford has received 1.9" while Boston has only about a quarter of an inch and towns to the north and west even less than that. While the results will be similar with this next wave of rain, everybody is in for a solid soaking.
A surface coldfront lies just to our west in the Hudson River Valley it is expected to slide through late tonight and stall in our coastal waters. At the same time a new area of low pressure is developing in North Carolina, induced by a shortwave rounding the base of the longer wave trough responsible for all this unsettled weather. Out ahead of the developing low, deep southerly flow is pooling moisture in Southern New England...ready for the tapping. In fact, dewpoints are an early summer-like 60 degrees throughout the area. That, coupled with great lift and dynamics from the right rear quadrant of the 300mb jet, the shortwave and the intensifying surface low, leads to a healthy rainfall early tomorrow morning. We are looking at around an inch in Boston, half inch to the NW and 1-2 inches to the SE.
The rain will taper by mid-morning and NW winds in the wake of the low will aid in creating some sunny breaks. Even though the air will be drying out in that flow, there will still be a thunderstorm threat in the afternoon and evening as another mid-level vort max will provide a trigger.
Friday, a large pool of colder air will exist thousands of feet in the air and with daytime heating from the sun, clouds will bubble up. It also appears that enough instability will be present for those clouds to grow isolated showers...maybe even a rumble.
That airmass and colder pool of air will shift east of the region for the weekend and more zonal or even some slight ridging will lead to ample sunshine and temps about 10 degrees above normal...in the mid 70s. By the end of Mother's Day, the next trough is moving in ready to replace the weekend ridge. With the slight temp drop aloft there may be enough instability for a late Sunday shower or thunderstorm...but most of the day looks great!
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