💧 Thunderstorms could leave an inch of rain Friday and again Sunday

💧 The heaviest of the rain will be in southwest New Hampshire

💧 Saturday will be the best day of the weekend

Periods of heavy rain are headed to the Seacoast Friday and again Sunday, but the worst of it should be in areas of western New England that are already saturated.

A series of systems traveling along a stalled cold front will bring a threat for showers and thunderstorms Friday and Sunday with locally heavy rainfall, gusty winds, and an increased threat for flooding all weekend, according to meteorologist Jon Palmer at the National Weather Service in Gray, Maine.

The first round of storms on Friday could have an inch of rainfall on the Seacoast, but won't have the same potential impact as in southwestern New Hampshire.

"It has been drier in the Seacoast than in other parts of New Hampshire, so I would say maybe some isolated flooding is possible," Palmer told Seacoast Current.

Saturday will be the best day of the weekend with cloudy skies and high in the low 80's with only a slight chance of showers and thunderstorms in the morning. The humidity will remain high.

As a cold front approaches the area, Sunday thunderstorms could be more widespread and expected further east with heavier rain. Western New Hampshire will have the most total rainfall.

Expected rainfall totals through Friday night
Expected rainfall totals through Friday night (NWS Gray)

What has been the source of our damp spring and summer? Palmer blames the negative phase North Atlantic Oscillation.

"It generally makes the jet stream more dynamic. In a positive phase NAO, the jet stream is pretty flat and kind of moves east to west across the country. When you have a negative NAO, there's a lot more broad waves. The jet stream is kind of moving up and down a lot more and becomes wavier," Palmer said.

The wavier jet stream allows for more interaction between warm moist air and colder, drier air to the north in Canada, allowing for more storm development. It's also contributing to ridging in the western United States, which has brought record-high temperatures in the past several weeks.

Contact reporter Dan Alexander at Dan.Alexander@townsquaremedia.com or via Twitter @DanAlexanderNH

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