The relief has been palpable.
Richmond, a city known for swamplike mugginess, saw its least humid June in a decade, according to Sean Sublette, chief meteorologist for the Richmond-Times Dispatch. Because dry air sheds heat more quickly than moist air at night, the city also registered its lowest temperatures in June since 2012.
Washington has likewise missed out on its typical share of scorching days and saunalike nights. On Independence Day, the dew point — a measure of humidity — dropped to 49 degrees, a shockingly low value. Average dew points in July are in the upper 60s.
Any dew points under 60 are refreshing in the Mid-Atlantic this time of year. In late June, they even dipped into the 30s in Washington, which is practically unheard of.
The nation’s capital has yet to see a heat wave this summer, defined as three days in a row with 90-degree weather. It has recorded just 12 90-degree days so far, six fewer than normal. The last summer with this few to date was 2009, and it had only two heat waves, the first not occurring until August.
Readers of the Capital Weather Gang have taken notice of the muted heat and are not complaining:
“This has been the mildest summer I can recall in a long time,” tweeted @NattyBDC.
“I’ve been loving this weather! Last summer seemed relentlessly hot and very little rain in July,” tweeted @uwchelsita.
The number of 90-degree days is also down in New York and Boston.
New York has had seven — a near-normal number, but Boston has seen only two, which is three fewer than typical.
“[S]ince mid May it’s been nothing but great almost every day,” tweeted Eric Fisher, chief meteorologist for Boston television station WBZ.
The reprieve from the heat can be traced to the shape of the jet stream, which is the high-altitude wind current that divides hot and cold air and is the superhighway for storms.
While the jet stream has bulged northward over the western and central United States, it has taken a dip in the eastern United States, frequently running through the Mid-Atlantic. That has allowed a somewhat regular stream of dry, cool Canadian air to funnel into the Northeast.
The jet stream has curled around the Pacific Northwest, which has also seen a relatively mild summer — a welcome break after last year’s historic heat wave.
But for areas south of the jet stream — in the central and southern United States — the heat has been punishing and persistent. Texas has been hit particularly hard.
The nice weather in the Northeast has come at a cost, though. Because it has remained north of the storm track, very little precipitation has fallen. Moderate to severe drought has developed from eastern Connecticut through southern Maine.
The Mid-Atlantic, meanwhile, has been in a prime position for heavy rainstorms — situated right along the jet stream’s path. Both Washington and Richmond have been slammed by intense storms in the past several weeks. The Washington region has also seen multiple instances of flooding, as have many locations to its southwest.
While much of the Mid-Atlantic and Northeast have avoided long spells of excessive heat and temperatures have hovered near the recent 30-year average, temperatures have still been elevated compared with historic averages.
The average summer temperatures so far this year in Richmond, Washington, New York and Boston rank among the top 45 highest across the past 125 to 150 years. In other words, this summer’s weather would have been abnormally warm a century ago, even if it’s considered normal now — a testament to the influence of human-caused climate change.
Computer models are signaling a warming trend in the upcoming week.
Richmond and Washington are forecast to see highs in the 90s, while New York and Boston are predicted to be near 90.
Rather than taking a dip over the Northeast, the jet stream is predicted to flatten out and jog slightly northward — shifting enough to allow some heat to swell over the region.
As we head into August, it’s not clear whether the jet stream will shift farther north, causing the Northeast to bake, or whether it will revert to taking a dip.
The National Weather Service leans slightly toward a warmer-than-normal first half of August for much of the eastern United States.
Even if it heats up some, average temperatures begin to very slowly dip in late July in much of the Northeast. Temperature averages start to decline on July 21 in Washington and on July 26 in Boston.