A slow-moving frontal system dropping from northern New England into upstate regions Wednesday brings Long Island a likely stretch of rain and thunderstorms, the National Weather Service said.

The service's Upton office said parts of Long Island could get showers and thunderstorms mostly between 10 p.m. and midnight and then into early Thursday morning, although the heaviest of rain is expected for the lower Hudson Valley and parts of southwestern Connecticut.

The chance of rain Wednesday night is between 60 and 70 percent for most of Long Island, and it dips to 20 to 30 percent all day Thursday.

"We're not expecting much rain during the day Wednesday, maybe a few pockets of drizzle," said David Stark, a meteorologist at the Upton office.

Stark said clouds will hang around Thursday morning, with skies slowly clearing from west to east. There also is a "slight chance" of rain after 11 p.m. Thursday.

Temperatures for Wednesday and Thursday should be in the high 70s with mostly cloudy skies and new rainfall amounts between one-tenth and one-quarter inch.

advertisement | advertise on newsday

Higher amounts could be possible in areas hit by thunderstorms, the service said.

The rain system also brings chances of patchy, nighttime fog and higher humidity, the service said.

The good news is that high pressure builds by Friday, pushing out the rain and delivering a weekend of clear skies and sunshine, Stark said.

Daily highs Saturday and Sunday are expected to be in the low 80s, and dry, sunny weather is likely to linger through early next week, the service said.