Forecast discussion: Thanks to a number of factors coming together, Boston and the rest of eastern Massachusetts will have the risk of seeing some heavy rain at times, along with the chance for strong to severe thunderstorms over the next 48 hours. Some strong thunderstorms passed right over Boston a little after 4 p.m. before moving offshore by 6 p.m. Due to the chance of heavy rainfall, the National Weather Service has issued a Flash Flood Watch in effect from 8 p.m. tonight until 2 p.m. Wednesday afternoon.
So, what are the factors? Take the very humid air that is over New England. Dewpoint temperatures are into the lower 70’s, which is very oppressive. Then, take some colder air that only brought high temperatures into the 60’s for Minnesota and Wisconsin. Now, bring that colder air further east, and have it meet with the warmer, more humid air. Finally, add an upper level low moving over the Northeast U.S. and have it be right over a surface low over the state of New York on Tuesday night.
Put all these factors into the equation, and you will have a very unstable atmosphere. This is why we will have the risk of seeing off and on strong to severe thunderstorms, which could create heavy periods of rain. The thunderstorms could have strong, damaging winds associated with it, along with small hail and lightning. There may be times on Tuesday that we go several hours between seeing any precipitation. The best chance for the worst weather will be Tuesday, when the cold front moves closer to New England.
We will continue to see the precipitation until Wednesday, when the cold front finally moves offshore by the late evening. We will still have mostly cloudy skies by early Thursday morning, but high pressure will eventually bring drier, less humid air into the area. We will see good weather and bright sunshine to the end of the work week.
However, as look at the computer models, it appears that the chance for having seven straight weekends without any precipitation will come to an end. The American model shows some light precipitation coming up from the Tennessee River Valley will bring the chance for showers Saturday afternoon. A little high pressure ridge will bring some dry weather on Sunday, but a quick moving low pressure system will bring some showers to moderate rain by Monday morning. The European model brings the low into New England by Sunday, making it rain until early Monday morning. Right now, my confidence in the forecast after Saturday is low at the moment, due to the differences in the models.
72 hour forecast:
Tonight: Scattered showers and thunderstorms, with heavy rain at times and patchy fog. Fog will be dense along the coastline. We will see a low of 72. Some thunderstorms may be strong, with gusty winds, lightning, and small hail.
Tuesday: Showers and thunderstorms expected. Thunderstorms could be strong to severe, accompanied with heavy rain, lightning, gusty winds, and small hail. We will see a high of 81 with south-southwest winds of 13-16 mph.
Tuesday night: Showers/thunderstorms continue with a low of 72. Thunderstorms may continue to be strong. Winds will come from the south at 12-15 mph.
Wednesday: Showers/thunderstorms end by 11 p.m. We will have a high of 78.
Wednesday night: Mostly cloudy with clearing skies by dawn and a low of 67.
Thursday: Mostly sunny with a high of 82.
Thursday night: Partly cloudy with a low of 63.
Friday: Mostly sunny. Highs 82-85, lows 62-65.
Saturday: Increasing clouds by the afternoon with scattered showers by the late afternoon. Highs 80-83, lows 63-66.
Sunday: Partly sunny with showers arriving before midnight. Highs 79-82, lows 65-68.
Monday: Cloudy with rain by the morning. Highs 78-81, lows 64-67.