More Muggy Air...
A solid summer day out there with a good deal of sun and even though temps climbed above normal, into the mid 80s, it wasn't oppressive due to the low humidity. Kiss the good stuff away...humidity will be steadily increasing tonight and tomorrow and so will the shower and thunderstorm activity.
The first surge of moisture, elevated dewpoints, arrives during the pre-dawn hours and may kick off a cluster of showers with embedded thunder. The greatest chance for getting wet will be in SE Mass. Following its passage, we may see the clouds thin out for some sunshine during the morning hours. As we roll through the day, the shower and storm threat will be rising, and depending on how much sun we see it may get pretty active during the mid afternoon. Any storm that develops will be very slow moving due to the lack of upper level winds so the primary concern is for more street and drainage flooding. But if we get enough heating some of the storms could approach severe limits and damaging wind gusts will be possible.
The mid level trough guiding this whole system into the Northeast will actually sharpen and go a bit negative as it passes over us...this will slow everything down and a wave of low pressure will develop along the front in our coastal waters. In the process, more showers and downpours will occur overnight Wednesday into Thursday morning. Some of the downpours will be heavy ones and soaking rain will possibly plague the morning commute. The trough will lift out beginning in the afternoon promoting drying and some sunny breaks.
That trend will continue into Friday with it likely being the last completely dry day until next Monday. SW flow will provide and a hot wind direction and temps will flirt with 90 for many north and west of Boston.
I still don't like the looks of the weekend right now...a large longwave trough and its continental polar airmass from Canada will expand through the Northern Plains, Great Lakes and Ohio Valley. That cooler air will migrate into New England...the leading edge a coldfront. The problem is with downstream blocking and a strengthening Atlantic ridge, the front will stall over New England and provide a conduit for deep moisture to work up from the south leading to more heavy downpours over the weekend. I hope this doesn't materialize but right now odds favor it.
