Forecast discussion: For Boston, it felt more like a day in late March than the end of April. Between the cloudy skies, the showers, and the easterly winds off the ocean, the high at Logan Airport for the day was only 45 degrees. The normal for this year is about 63. Unfortunately, we will not see normal temperatures until the weekend. For now, we still have to get through another night of showers.
An upper level low has created a second surface low, which is over western Vermont at the moment. The low will bring showers and even a thunderstorm through eastern Massachusetts during the overnight. The low will move offshore by Sunday morning, ending our scattered showers. However, any sunshine during the afternoon may help the atmosphere create isolated showers. We will finally see some starlit skies by Sunday evening.
A high pressure ridge coming down from eastern Canada will give us mostly sunny skies on Monday, with temperatures in the middle 50’s. But, a new low pressure system that will bring some severe weather to the Central U.S. and Ohio River Valley into Monday will become blocked by the ridge. The low will eventually weaken the ridge, allowing the low to move east. We will begin to see the first rain drops by the middle of Tuesday afternoon.
As we go through the week, this low will become quasi-stationary. An upper level high over Greenland will actually block any more systems from moving east. So, the low’s center will rotate back into the Great Lakes. However, the cold front will remain over the east coast. New low pressure centers will form along the front and move into New England Wednesday and Thursday. The computer models are predicting we will see the heaviest rainfall on Wednesday, with embedded thunderstorms giving us an inch and a half of rain on Wednesday alone.
Due to the blocking of the upper level systems, it is still tough to predict if the models are correct after Friday. Right now, the models agree that the blocking pattern will end, allowing the cold front to move offshore. This will give us partly sunny skies by Friday afternoon. Also, if we will see sunshine, we could see high temperatures near 70 degrees for Saturday. However, an upper level low to our west will bring the threat of more showers by next Saturday afternoon. Because the models have a hard time knowing when blocking patterns will end, my confidence in the forecast after Thursday night remains low.
72 hour forecast:
Tonight: Overcast with scattered showers, a possible thunderstorm, and patchy fog. We will see a low of 40.
Sunday: Isolated showers end by 11 a.m. with partly sunny skies by the mid-afternoon. We will see a high of 51 with north-northeast winds at 8-11 mph.
Sunday night: Partly cloudy with a low of 43. Winds will come from the north-northwest at 7-10 mph.
Monday: Mostly sunny with a high of 56.
Monday night: Partly cloudy before midnight, with mostly cloudy skies afterward. We will see a low of 43.
Tuesday: Overcast skies with showers developing by the mid-afternoon. We will have a high of 50.
Tuesday night: Showers/light rain with a low of 42.
Wednesday: Showers/light rain. Highs 47-50, lows 42-45.
Thursday: Moderate to heavy rain by the early morning, with possible thunderstorms by the late morning. Highs 55-58, lows 47-50.
Friday: Showers/light rain ending by mid-morning with partly sunny skies during the afternoon. Highs 64-67, lows 46-49.
Saturday: Partly sunny with the threat of showers by the early afternoon. Highs 63-66, lows 48-51.