Much of the country is already sweltering under high summer temperatures, and drought conditions are spreading south and east from the Dakotas. That’s the latest from the U.S. Drought Monitor.

But most of the Northeast and Michigan may escape prolonged heat waves from now into mid-August, predicts Paul Pastelok, AccuWeather’s lead long-range meteorologist. Waves of cool air will continue dropping down from Canada and will keep prolonged heat waves at bay across the Northeast. Southwest Pennsylvania, Maryland and Delaware, however, are on the southern cusp of that cool-air breeze.

This southward jet stream dip is likely to be a semipermanent feature over the Great Lakes and Northeast through at least midsummer. It will allow bouts of cool air to routinely sweep through — with “some brief switches back to heat,” he adds.

Those spikes in temperature will be the longest-lasting over the lower Ohio Valley and coastal Mid-Atlantic. When and where the sun is out, the strong midsummer sunshine can negate the cooling effects to a great extent.

Nighttime cooling impact
Nighttime temperatures are expected to fall to noticeably cool levels for this time of the year, according to this meteorologist. The greatest swings in temperature and humidity levels will be across the upper Great Lakes, upstate New York and northern New England. Temperatures in these areas may fluctuate by 10 to 20 degrees F or more from one day to the next.

Temperatures in parts of the northern tier and the central Appalachians will occasionally dip into the lower 60s and even the 50s in some cases at night in the coming weeks. Farther south, day-to-day changes in temperature, and especially humidity levels, are likely to be less extreme.

Each cool-air wave will crash into moisture coming up from the Gulf of Mexico. Those collisions will likely bring showers and midsummer thunderstorms that can be locally heavy and gusty. That setup can lead to greater flash flooding and severe weather incidents.

"It’s possible that toward the end of July and at the start of August, an even more pronounced and longer-lasting dip in the jet stream occurs in the Northeastern states," says Pastelok. Such a pattern could result in greater cooling and possibly even stormier and wetter conditions for some areas than what’s anticipated through most of July.

Bottom line: Keep your haying equipment ready to roll and your tractors fueled in anticipation of those breaks of good haying weather.

Source: AccuWeather