Weather

Here’s David Epstein’s forecast for Fourth of July weekend

We're in for a colder-than-average Independence Day.

fireworks
The Boston Pops Fireworks Spectacular lights up the sky over the Charles River with the Boston skyline in the background, as seen from the MIT Media Lab in Cambridge on Wednesday, July 4, 2012. Yoon S. Byun / The Boston Globe


Logan Airport reached 100 degrees Wednesday for the first time since late July 2011. This marked the 26th time the area has seen a reading of 100 degrees or higher since weather has been reported.

Fourth of July:

Now we take a turn on the other side of the extreme, with colder-than-average conditions arriving late Thursday and continuing through at least the first two-thirds of the weekend.

Indeed, temperatures Saturday afternoon could for a time fall 40 to 45 degrees colder than it was Wednesday afternoon — just an incredible turn of events. If the temperature doesn’t reach 61 degrees Saturday, it would be a new record for the coldest high on July 3 ever. No matter what, it’s about to be one of the coldest July 3rds in decades: In 1987, it reached a meager 62.

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july 3 weather
Near-record cold for July 3 is in place Saturday afternoon. – WeatherBell

Rainfall will be plentiful from Thursday afternoon through the first part of Friday and then more showers for the rest of Friday into Saturday. I think there will be some dry hours Saturday, but it’s going to be so cool and raw, and with the wind coming in off the water, it definitely won’t be very pleasant.

The basic setup for this big change is that a warm front is going to be stuck south throughout New England into Friday morning as an area of low pressure develops and eventually moves into the Gulf of Maine. This is similar to what we would see in the winter. Just like in winter, winds come off the water, but obviously it’s not cold enough for any snow.

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This loop shows accumulating rainfall into Saturday: the heaviest occurs south of the Mass. Pike.

The heaviest rain will be south of the Mass. Pike, but all of us will see appreciable rainfall. There is the chance for some “training” of precipitation during this event. Training can be thought of as experiencing heavy rain over the same area and not moving north or south, much like being stuck on train tracks. When this occurs, it can lead to multiple inches of rainfall and flooding. This is something to watch.

rainfall forecast
The NAM model has a very heavy line of total rainfall forecast. While this might be overdone, it could indicate the potential for some flooding if it occurred. – WeatherBell

I think the showers will continue somewhat on Sunday, but there will be fewer of them. It will be a little bit warmer, too, with temperatures getting well into the 60s to perhaps lower 70s if we can squeeze out enough sunshine in the afternoon. I would not cancel any plans on Sunday.

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There will be great sleeping weather Friday night, Saturday night, and Sunday night.

Monday is the best day of the long weekend, with a return to more abundant sunshine and temperatures getting back into beach territory. Expect highs on Monday in the 75-to-81 degree range. I think many would consider that quite nice for July.

Heat lovers, don’t fret: It turns hot again for Tuesday with more 90-degree weather.

tuesday forecast
By Tuesday, most areas are back into the 90s again. – WeatherBell

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