The last few days of June signal the start of the year’s warmest six weeks in the Berkshires, so right on cue we’ll endure, or enjoy as the case may be, the second three-day hot spell of the month.

An unusually intense heat dome is building offshore from New Jersey and Long Island, but the National Weather Service’s heat advisory on Sunday for New York’s Capital District and mid-Hudson Valley spared our higher-elevation county. The day turned out to be relatively pleasant, with a high of 86 at Pittsfield Municipal Airport and 89 at Harriman & West Airport in North Adams as of 4 p.m.

But the humidity has been rising and after-dark cooling has been minimal, making for difficult sleeping conditions — except for those able to crank up air conditioners overnight.

Monday will be quite steamy, even hotter, and more humid. “The one fly in the ointment is convective potential,” according to forecaster Dan Thompson at the government office in Albany. That’s meteorological-speak for potential but hard-to-predict afternoon and evening thunderstorms, which could develop over New York state and move into western New England. If so, locally heavy rainfall is possible.

Not much change on Tuesday, when widespread severe weather is unlikely, though a few strong storms and locally heavy rainfall are possible wherever thundershowers may develop.

After still more heat and humidity on Wednesday, a cool-down should come, with a greater likelihood of potentially strong thunderstorms toward sunset and after dark. The rest of the work week should be seasonable, ranging from 60 at night to 80 in the afternoon, with mixed clouds and sun, as well as scattered thunderstorms through the extended Independence Day holiday weekend.

Highs Saturday through Monday (July 5) may remain in the mid-70s, with a less-than-even chance of showers each afternoon and evening. Overall, with details to be confirmed closer to the weekend, the extended outlook is reasonably promising for outdoor recreation, theater and musical entertainment, including the Boston Pops July 4 Spectacular next Sunday, with the capacity of 9,000 free tickets at Tanglewood already distributed.

NATIONAL OVERVIEW

The historic, dangerous heat wave continues in the Pacific Northwest. With a sizzling high of 108, Portland, Oregon, broke its all-time heat record on Saturday, as stores sold out of portable air conditioners and fans, hospitals canceled outdoor vaccination clinics, cities opened cooling centers, baseball teams canceled or moved up weekend games, and utilities braced for possible power blackouts. The previous record of 107 in Portland was set in 1965 and 1981.

Seattle reached 101 on Saturday, the hottest June day on record and only the fourth time in recorded history that the city had topped 100 degrees. Fewer than half of the homes in the coastal city have air conditioning. Seattle’s all-time high was 103 in 2009.

The extended “heat dome” over the Pacific Northwest and southwest Canada is a taste of the future as climate change reshapes weather patterns worldwide, according to Kristie Ebi, a University of Washington professor who studies global warming and its effects on public health.

“We know from evidence around the world that climate change is increasing the frequency, intensity and duration of heat waves. We’re going to have to get used to this going forward,” she said. The heat wave over the region is forecast to continue into the 4th of July weekend, becoming somewhat less intense. Little if any rainfall is expected to help ease the excessive heat with growing drought, fire threats and minimal temperature declines overnight increasing the heat stress.

Elsewhere, heavy rain could lead to additional instances of flash flooding over the next few days from the Southern Plains to the Great Lakes, as well as portions of southwest Louisiana and the Texas coast.

Most of Florida will be sunny, with pop-up thundershowers in the afternoons, and highs in the low- to mid-80s, cooler than the Northwest and Northeast regions.

The high-pressure system in the Atlantic west of Bermuda is strengthening, funneling daytime highs 10 to 15 degrees above average, topping 90 degrees from the mid-Atlantic states to southern Maine.

It appears that the East Coast will enter a period of damp/wet weather as we head into the holiday weekend, though some sunshine is expected along the New England coast from Long Island to Maine, as well as in the interior mountains of New Hampshire, Vermont and upstate New York.

Information from the Associated Press was included in this report.

The Outlook is today's look ahead at the week's weather, its impact on the Berkshires and beyond. Clarence Fanto can be reached at cfanto@yahoo.com.