The unexpected development of a coastal storm off the Atlantic seaboard has dashed and dampened earlier outlooks for a sunny Memorial Day weekend.

The arrival of cooler air over the Berkshires by early Friday following a potential outbreak of storms and heavy showers sets the stage for a dismal, soggy start to the weekend, with possible gradual improvement on Sunday and especially on Monday, according to National Weather Service meteorologist Warren Snyder.

"Needless to say this is going to feel more like a late October weekend in the Northeast," he stated in an online post from the government forecasters' Albany, N.Y., office.

Whether severe storms hit western New England late Thursday depends on breaks in the cloud cover, allowing the strong late-May sun to drive temperatures up toward 80. The prospects for that remained uncertain as of midday.

A steady, chilly rainfall should spread over the Berkshires before dawn on Friday as the storm develops and gathers strength along the Northeast coast off Long Island. AccuWeather.com is predicting nearly 2 1/2 inches of rain over Western Massachusetts during the next three days, similar to totals currently forecast by the National Weather Service.

The coastal storm will move slowly, not reaching the Gulf of Maine until Sunday, prolonging the rainfall over the Northeast region. North winds up to 20 mph will add to the raw, rainy conditions expected on Friday and Saturday. As temperatures slide on Friday, nighttime lows in the 40s are predicted.

According to AccuWeather senior meteorologist Alex Sosnowski, "Friday night into Saturday could be a flat-out nasty way to start the summer season from a driving wind, rain and temperatures in the 50s and lower 60s in many locations."

"It is not entirely out of the question that it gets cold enough for the highest elevations of the Northeast, especially the Adirondacks, Green and White mountains to have wet snowflakes mixing in during the first part of the weekend," AccuWeather's Henry Margusity added.

So far this month, Pittsfield Municipal Airport has recorded 3 inches of rain, and with the expected heavy downpours this weekend, May should rank as the wettest month in the Berkshires since last September, when more than 6 inches fell. Precipitation has been substantially below normal every month from November through April.