The East Coast feels more like May on Wednesday than February, with temperatures of at least 30 degrees Fahrenheit above average for this time of year. All-time record high temperatures are being set from Florida to the northern tip of Maine, as a southwest flow of air transports mild, moisture-laden air from the Gulf of Mexico and Atlantic Ocean.
These records will add to the milestones already achieved on Tuesday, when cities like Boston and Washington, D.C. broke records. Mirroring the state of our politics, the U.S. is split in two, with record cold across the West, heat in the East, and flooding rains and even thundersleet (yes, thundersleet) in between.
Washington is going for its earliest-ever 80-degree day on Wednesday. On Wednesday morning, a weather balloon launched from the National Weather Service forecast office that serves Portland, Maine, found that the temperature was 66 degrees Fahrenheit at 2,400 feet above the ground, shattering the record high for all of the winter months – December, January, and February.
While the 500mb percentile map shows just how unusual this ridge is, the climatology only goes back to 1979. Washington DC’s sounding record goes back to 1948 – the 588 dam height breaks a 70 year record for Dec-Mar by a decent margin. pic.twitter.com/AhxqxRqs83
— Tomer Burg (@burgwx) February 21, 2018
Mount Washington, New Hampshire, which is typically one of the coldest locations on the East Coast, tied its all-time February high temperature record as of 9:38 a.m. ET on Wednesday when the temperature reached 44 degrees Fahrenheit at the summit. It then set a record for the highest temperature on record for any winter month, at 48 degrees Fahrenheit. Typically, the mountain observatory sees snow through at least June.
Many locations have set both record warm overnight low temperatures as well as record daytime highs. At Dulles Airport in Virginia, for example, the overnight low temperature only fell to 59 degrees Fahrenheit on Wednesday morning, which was tentatively the warmest seen in February.
As of Wednesday afternoon, Newark, New Jersey reached 77 degrees Fahrenheit, breaking that city’s all-time highest temperature on record for February.
The unusual warmth is due to a strong area of high pressure off the Southeast coast. The clockwise circulation of air around this ridge of high pressure is funneling mild and humid air up the East Coast and into eastern Canada. The ridge itself has set records for its intensity.
All-time heat records will also be set Wednesday in Florida, Georgia, and the Carolinas, before a sharp cold front moves in from the west – bringing an end to the May weather and a return to reality.
This might seem counterintuitive, but the unusually warm conditions are, believe it or not, related to a split in the polar vortex that occurred during the past two weeks. One piece of the vortex has been spinning across the West, bringing frigid conditions and heavy snow, while another is spreading cold and snow to Eurasia.
The warm air mass moving up the East Coast is the flip side to the swirl of the polar vortex that is pinwheeling across the West and over parts of Canada. Also, thanks to global warming, which is raising average surface temperatures and increasing the odds of extreme heat events, it’s becoming easier to knock off all-time temperature records during both the winter and summer months. February 2016, for example, also featured a period of record warmth in the East, for example, though it was not as extreme as this one.
What comes next: More extremes
Once the East Coast February heat wave ends, the weather pattern across the Northern Hemisphere is going to undergo a complex evolution that is causing meteorologists to take notice. First, the section of the polar vortex across Eurasia will bring heavy snows to areas from the UK to Siberia, drawing cold air from the east toward the west. Such winds are known to the UK Met Office as “The Beast from the East,” since they’re often associated with the most frigid air of the winter season.
According to our definition of the NAO, models are calling for the all-time strongest -NAO value observed since our archive (beginning in 1980). The record low value since 1980 is from February 2006 (-2.77sigma). We are seeing models call for -3sigma during late February 2018. pic.twitter.com/6AY3SA3ESo
— Michael Ventrice (@MJVentrice) February 21, 2018
In early March, a pattern of atmospheric pressure over the North Atlantic is going to undergo a radical shift, which will in turn trigger an unusually strong atmospheric blocking pattern that will favor cooler and potentially snowier conditions along the East Coast of the U.S., along with continued cold and snow in Europe.
The pressure pattern, known as the North Atlantic Oscillation, is projected to hit record low levels, signaling to meteorologists that the odds of cold and snow will likely rise on both sides of the Atlantic. In fact, some of the cold air from Europe may make it across the Atlantic – from the east to the west – into the U.S., which is the reverse of how the weather normally flows in the Northern Hemisphere.
The ECMWF EPS continue to advertise one of the most impressive retrograding Atlantic high latitude blocking evolutions I have seen in quite some time. The Pacific Jet retraction impacts become more apparent with every ensemble suite as well. pic.twitter.com/EcRmr4xTyG
— John Homenuk (@jhomenuk) February 21, 2018
One reason for this is the projected formation of a powerhouse “atmospheric block,” consisting of a high pressure area aloft over Greenland. This is likely to reroute weather systems like a detour sign around a construction site. Typically, some of the biggest East Coast snowstorms have occurred when such blocking is in place, because it prevents storms from moving quickly away from the U.S.
Because this is a long-range forecast, there is considerable uncertainty over exactly how the weather pattern will play out during the next two weeks, but it’s safe to say this is going to be a time period when there is an elevated chance of extreme outcomes both in the U.S. and Europe.
Meanwhile, with the cold air displaced to the south across North America and Eurasia, the Arctic is likely to continue to see above average temperatures and record low sea ice.
It’s as if someone robbed the cold air bank and is refusing to surrender to authorities.
UPDATE: Feb. 21, 2018, 2:41 p.m. EST This post has been updated to reflect that the temperature record on Mount Washington was tied.