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Boston Weather: 30.0°F | Partly Cloudy

Weather: Making Split Decisions

Greg Lawson
STAFF METEOROLOGIST -- April thus far has proven to be anomalously wet. It’s already rained more than an inch in excess of what we typically expect for the entire month. It is clear that the dominant weather patterns have changed lately, accounting for the recent spell of grey, dreary weather. Explaining the change is more difficult than just noting it. For some reason we’ve entered a split-jet regime where the jet stream has split into two weakened jets flowing past an upper-level di-pole, that is a low and a high in very close proximity. The di-pole blocks the typical flow as it effectually tries to “swim upstream.” This slows the upper-level steering winds which usually blow surface storms out to sea rather quickly, leaving us with slowly propagating, albeit weak, disturbances which are free to dump rain on us. However, the other consequence of a split jet is that storms are less likely to be steered up the east coast. A large storm over the Mid-Atlantic states which would usually certainly deliver us rain, is just going to toe the line with New England over the next couple days. It is likely that we won’t be strongly threatened, but one cannot rule out chances for showers. Expect a 30 to 40 percent chance of showers over the next several days with temperatures remaining close to what they have been: highs in upper 40’s and lows in the upper 30’s

Today: Partly cloudy and cool. Northerly winds of moderate strength.

High of 49°F (9°C).

Tonight: Cloudy and chilly. Northeasterly breeze. Low of 38°F (3°C)

Wednesday: Overcast and cool. Chances of showers. Northeasterly

winds increasing in speed. High on only 43°F (6°C). Low of

40°F (4°C).

Thursday: Partly cloudy. Breezy. Chances of showers continue. High

in low 50’s (10 to 12°C). Low in the mid 40’s (6 to 8°C).