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June outlook: When will 90-degree weather return to the northeastern US?

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The unofficial start to summer has come and gone along with steamy weather in many areas. When will the 90 F weather return?

June is likely to be a month of atmospheric mood swings and highly variable weather conditions.

While the very chilly weather from April into early May is a thing of the past, there will be multiple bouts of cool air and unsettled conditions into the middle of the month.

"Several more southward dips in the jet stream are likely to plunge into the Northeast through the first half of June," according to AccuWeather Lead Long-Range Meteorologist Paul Pastelok. "More waves of cool air will result."

The waves of cool air will last several days each.

Since the sun is intense during June, when and where the sky is clear for a few hours on a given day, temperatures will generally bounce back to near seasonable levels.

Average highs for the middle of June range from the lower 70s in Caribou, Maine, to the middle 70s in Boston, near 80 in New York City and Pittsburgh and the middle 80s in Washington, D.C.

In between the waves of cool air will be brief spikes of warmth, where temperatures can climb a few degrees above average. The strong sun will provide occasional comfort for summertime activities, including swimming.

A pattern such as the one forecast through the middle of the month has the potential to bring nearly daily rounds of showers and thunderstorms.

With this setup, the sun will warm the ground early in the day, then the downpours will erupt during the afternoon hours, cooling the air.

It can get cool enough to require a jacket and long sleeves at times, especially in the mountains.

"We expect the pattern to change during the last third of the month or so," Pastelok said.

Later in the month, the jet stream may bulge northward enough to turn off the cool air episodes and frequent showers.

"It is possible the jet stream may bulge so far to north not only to bring very warm conditions on a more consistent basis, but perhaps also to deliver more 90-degree days in the mid-Atlantic and New England during the last third of the month," Pastelok said. "This change could occur a bit sooner farther west across the Midwest."

Even though not all locations in the Northeast may reach 90 during the latter part of the month, it will feel like summertime around the official start of summer: June 20 at 6:34 a.m. EDT.

The general pattern during the last 10 days or so of the month will favor AccuWeather RealFeel® Temperatures often reaching well into the 80s and 90s in many locations.

"Cool spells aside, when June is all said and done, temperatures for the month as a whole will average slightly above normal east of the Appalachians and solidly above normal west of the Appalachians," Pastelok said.