For many towns, it was day #7 of our heat wave yesterday as low to mid 90s were widespread. While the heat was widespread, some coastal towns did stay in the 80s thanks to the seabreeze. Boston’s Logan Airport was one of those locations as the high maxed out at 87, snapping the heat wave at 6 days. There have been 10 other heat waves of 6 days or greater in Boston’s history, so no record there. Today, it’s another hot day with temperatures back into the lower to middle 90s.
What we’re holding onto as a record in Boston is the driest June/July combo as only 1.99″ of rain has fallen in the last two months. That too will likely change tomorrow as a good dose of rain is possible for many of us as we near the close of the month.
I don’t expect much rain today as just an isolated shower or thunderstorm pops up this afternoon across far northern Mass and Southern NH. What we’re waiting for is a cold to our north to slide in late tonight/tomorrow as well as a wave of low pressure to move along that front from our southwest. The combination of the two will allow for a narrow channel of heavy rain to form from the mid-Atlantic to parts of New England on Friday. 
The atmosphere will be loaded with moisture tomorrow with the chart below showing a ton of yellows and reds indicating high precipitable water values (the higher those values, the higher the downpour potential). The key will be, where is the best “lift” of all that moisture? Where we have the upward motion, we have the heaviest rain as it’s possible to get a narrow band of 1-3″ amounts of rain. It’s a bit uncertain if that band settles near the south coast or over more interior parts of southern New England. In that band, localized street flooding is possible too if it rains too hard too fast. North of that band, rain totals drop off substantially and rain is more hit of miss.
Regardless, tomorrow will certainly be cooler as wind turn onshore and temps hold in the 70s.
Weekend: Saturday looks great, while we could have a few scattered showers Sunday afternoon. Highs will be more seasonable, in the 80s.