Heat wave to roast Northeast as temps forecast to approach 100 F

The hottest weather of the summer is poised to swelter many areas of the mid-Atlantic, central Appalachians and southwestern and central New England late this weekend to the first part of next week.

A portion of the same weather system, a large area of high pressure, that has been building and broiling the south-central United States much of this week will poke northeastward in the coming days.

Actual temperatures are forecast to rise well into the 90s F from portions of Ohio, Pennsylvania, New York state, Vermont, Connecticut, Rhode Island, New Hampshire, Massachusetts, West Virginia, New Jersey, Maryland, Delaware and Virginia.

A few locations over the mid-Atlantic and Ohio Valley can reach or exceed 100 degrees for a couple of hours in the afternoon on Sunday and Monday.

It will be so hot across the contiguous United States that the average high temperature will be more than 90 F on Saturday, according to Ryan Maue, meteorologist and data scientist at Bamwx.com.

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AccuWeather RealFeel® Temperatures will be several degrees higher than the actual temperature. The RealFeel Temperature not only takes into consideration the temperature and humidity but also sunshine, any breeze and other factors that provide a true representation of how hot the air feels on the human body.

Daily records that have stood since the 1930s and even near the turn of the 20th century will be challenged.

In Washington, D.C., and Cleveland, the records of 102 and 95, respectively, on Sunday were set in 1930. Farther north, in Albany, New York, Sunday's record of 97 was set all the way back in 1904.

In Philadelphia and Baltimore, the records on Monday of 99 and 102, respectively, were also set in 1930.

A heat wave is generally defined as a stretch of 90-degree-Fahrenheit (or higher) temperatures for at least three days in a row over the northern U.S.

The conditions may cause some cities to be dangerously hot around the clock for a several-day stretch. This phenomenon, known as the 'urban heat island effect,' comes into play as the concrete and brick buildings begin to finally cool near daybreak, just as the new day will be getting underway.

People are urged to seek air-conditioned environments where possible and to drink plenty of non-alcoholic and non-caffeinated fluids as alcohol and caffeine can accelerate the dehydration process.

Meteorologists recommend avoiding strenuous physical labor or exercise during the late morning, afternoon and early evening hours when air temperatures climb to the highest levels of the day.

A 20-day streak of temperatures hitting 90 or higher in Washington, D.C., just came to an end on Wednesday -- just one day shy of tying the longest stretch of 90-degrees days on record (set in 1980 and tied in 1988). The high was held to 87 on Thursday due to persistent cloud cover and a breeze off the slightly cooler waters of the Potomac River. The highest temperature at Reagan National Airport during the brutal stretch was 97 on July 3. A new stretch of 90-degree weather will commence on Friday.

So far, this summer's high in New York City was 96 set on July 6. Temperatures on Monday may challenge this mark.

Farther north, the heat wave which spanned June 18-23 may be tough to surpass. Temperatures reached 96 in Burlington, Vermont, but on Sunday, temperatures may not only reach that mark, but they could also challenge the record high of 98 set in 2013.

Even over the mountains in the region, the uniformly hot air mass will allow little relief, except for a cool lake, stream or pool.

How hot the weather will get in eastern New England is a bit more tricky as a sea breeze may step in to mitigate temperatures, including around Boston. Still, temperatures are forecast to approach 90 on Sunday and Monday.

The cooler of the weekend days will be Saturday at most beach locations with an active sea breeze, but on Sunday and Monday, due to a west to southwest breeze from the land, the hot air is likely to be felt on most beaches from New Jersey to Delaware, Maryland and Virginia.

The combination of a slight dip in the jet stream and a weak push of slightly cooler air may be enough to keep high temperatures in the 80s for the middle and latter parts of the week around the eastern Great Lakes, eastern Ohio Valley, central Appalachians and portions of New England.

At least spotty thunderstorm activity is forecast to accompany the slight shift in the jet stream and proximity of surface fronts. Just as a dry landscape functions more like a desert with a rapid rise in temperature during the day, a wet landscape requires more of the sun's energy being used to evaporate moisture, rather than heating the ground and adjacent air. For this reason, it is much easier for temperatures to surge when the ground is dry as opposed to when the ground is wet.

Along the mid-Atlantic coast, even though temperatures may be trimmed a few degrees later next week, highs are still likely to be at or above 90 in most cases. A slight cooling sea breeze may be more active during the middle and latter parts of the week on the beaches, as opposed to the start of the week.

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