Forecast discussion: During Sunday, Boston was under cloudy skies with isolated showers passing to the north and south of the capital city. The passing showers were due to a frontal boundary staying right over the northern part of the state. At the moment, there are just isolated showers and embedded thunderstorms over southern Vermont.
As we move through the overnight, we will begin to see more scattered showers and thunderstorms, as the humidity levels remain high. A combination of cold fronts and low pressure systems will move towards New England. So, we will see the chance for some heavy rainfall in isolated areas, especially during the morning hours. As the day wears on, the cold front will slowly make its way into eastern Massachusetts. However, the cold front will not move offshore until early Tuesday morning, as a strong high pressure offshore stalls the front.
Drier air behind the front will move over the area by the start of the morning commute on Tuesday. Thanks to an upper level low staying over eastern Canada, we will continue to see cooler than normal temperatures for the end of July. Also, with northerly winds, the humidity will stay low. The good weather will remain into Wednesday afternoon, although the computer models begin to disagree on how to handle the end of the week.
Over the last couple of days, the American model continues to keep a surface low pressure system over eastern Canada. The moisture from the low rotates out of western New York, and will provide us with isolated showers on Thursday. The activity would eventually dissipate by early Friday morning.
However, a weak disturbance off the coast of South Carolina continues to move northward, giving us the risk of more scattered showers and rain from Friday night through Saturday evening. The European model does not see any precipitation at all for either Thursday or Friday. Then, the American model clears out and brings high pressure into Saturday and part of Sunday.
So, in a nutshell, the models are completely out of phase, and not agreeing at all on where to place the systems. For now, I will try to blend the models together. I am going to stick with continuity within the American model, and give us showers for Thursday into early Friday morning. The disturbances will provide us with some scattered showers by Friday afternoon, and continue into early Saturday morning, before ending. We will see partial clearing Saturday, with the risk of showers arriving from a weak cold front from the west. The showers will end by Sunday morning, giving way to partial sunshine Sunday afternoon. However, my overall confidence in the forecast after Wednesday night is very low. Because there is not any defined weather systems along the eastern U.S. after Wednesday night, the models may be using climatology to create its forecasts.
72 hour forecast:
Tonight: Isolated showers/thunderstorms become scattered after 3 a.m. Patchy fog is possible. We will see a low of 69. Some thunderstorms could bring heavy rain.
Monday: Scattered showers/thunderstorms with the highest rainfall amounts during the morning hours. We will see a high of 81 with increasing south-southwest winds to 18-23 mph.
Fenway Park Forecast (7:10 p.m. vs. Toronto): Cloudy, showers or thunderstorm possible, 77.
Monday night: Scattered showers/thunderstorms end by midnight. Clearing skies expected into dawn. We will see a low of 62 with west-southwest winds of 13-16 mph.
Tuesday: Mostly sunny and less humid with a high of 77.
Tuesday night: Partly cloudy with a low of 62.
Wednesday: Mostly sunny with a high of 79.
Wednesday night: Mostly cloudy with a low of 62.
Thursday: Mostly cloudy with isolated showers by the late morning. Highs 79-82, lows 62-65.
Friday: Partly sunny with a widely isolated shower in the morning, with scattered showers by the evening commute. Highs 79-82, lows 63-66.
Saturday: Partly sunny with possible showers by the early evening. Highs 75-78, lows 64-67.
Sunday: Showers end by the early morning, and becoming partly sunny. Highs 79-82, lows 62-65.