One of the busiest times of the year on Cape Cod — the Fourth of July — is upon us, and the weather looks to cooperate quite nicely through the holiday weekend.
A surface cold front, being propelled southward across New England by a small dip in the jet stream, will pass through the region Thursday afternoon and night (perhaps accompanied by a few showers and thunderstorms) but scoot offshore in time for the Fourth. Behind the boundary, a bubble of cooler air, both at the surface and aloft, will rotate southeastward across New England. This upper-air trough looks to produce some comfortable weather to kick off the forecast period. Dewpoint values, which flirted with the 70° F mark at times through the first half of the week (yielding that muggy feel), will tumble into the 50s and lower 60s Friday and Saturday. That, combined with sunshine and temperatures in the 70s and 80s, should make for some pleasant early summer conditions.
Unfortunately, the pocket of cooler and drier air that slides into the region Friday will slip seaward Saturday night and Sunday as winds come back around to the west and southwest. That wind shift will push the drier air out to sea and signal the arrival of a warmer and much more humid air mass to end the weekend and kick off the first full week of July. The long-range forecast suggests several days of muggy air as dewpoints climb back toward 70°. (Once the dewpoint crosses that 70° threshold, the air becomes uncomfortable for most of us — readings in the lower and middle 70s produce that heavy, tropical feeling.)
The only potential fly in the ointment (at least as of this writing) may come with the passage of that aloft pocket of cold air Friday afternoon. The dip in the jet stream and associated cold air high in the sky will be linked to an upper-level low-pressure system rotating through the region. This time of year, in response to daytime heating, an upper-air low like this can yield midday and afternoon clouds and isolated to scattered showers and thunderstorms. This activity is typically focused beneath and ahead of the heart of the upper-air trough, where the atmosphere is most conducive to rising air. Right now, that feature looks to pass across northern New England, keeping the clouds and shower activity well to our north. Should it venture further southward and pass overhead, Friday would start off sunny and warm with blue skies, but the afternoon or evening would bring bubbling clouds and an isolated thundershower.
Overall, the odds for prolonged inclement weather are quite low, and the holiday weekend should be remembered as a nice one.
