Blame the jet stream, the west-to-east river of wind, for forecasts that Friday might be the first sunny day with no rain this week.

High above the atmosphere, this current of air has pushed a bit further south than typical, creating the “kind of cooler weather conditions” that have prevailed this season, said Jay Engle, a National Weather Service meteorologist based in Upton.

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“It seems like every third day or so we run into cloudy or unsettled weather; we’ve kind of had this pattern through most of the summer.”

On Wednesday, there is an 80 percent chance of showers, and perhaps a thunderstorm, according to the weather service. The high will be 76 degrees.

The risk of riptides remains high through Wednesday, thanks to an arriving cold front and a southerly wind, Engle said.

Wednesday night also could see showers. On Thursday, the likelihood of rain falls to 50 percent, mostly before noon, according to the weather service.

“Late Thursday afternoon, we may get some sun; the next real full sunny day will be Friday,” Engle said. The thermometer that day should climb to about 73 degrees.