Dr. Jeff Masters ·

Above: A man reads a book as people walk along the Hudson River Greenway on an unseasonably warm afternoon, February 21, 2018 in New York City. New York City recorded their warmest February day on record: 78°. (Photo by Drew Angerer/Getty Images).

Astonishing summer-like heat cooked the Eastern U.S. on Wednesday, smashing all-time records for February warmth in cities in at least ten states, from Georgia to Maine. At least 24 cities recorded their hottest February temperature on record on Wednesday, including New York City (78°), Hartford, CT (74°) and Concord, NH (74°). According to Weather Underground weather historian Christopher C. Burt, February 20 - 21 marked the most extraordinary heat event to ever affect the Northeastern quadrant of the U.S. during the month of February, since official records began in the late 1800s. He catalogued the following eight states that tied or beat all-time February state heat records over the past two days, noting that in the case of Maine and Vermont, “It is simply amazing to beat a state temperature record by some 8°F!”:



Pennsylvania: 83° at Capitol City (ties old record for the state)

New York: 79° at La Guardia Airport (old state record 78°)

Vermont: 77° at Bennington (old state record 68°)

New Hampshire: 77° at Manchester and Danbury (old state record 72°)

Maine: 77° at Wells (old state record 69°)

New Jersey: 83° at Teterboro (old state record 80°)

Massachusetts: 80° at Fitchburg (old state record 73°)

Ohio: 80° at Cincinnati Lunken Airport (ties old record for the state)

Some states that did not make the cut:

Maryland 82° vs. February state record of 88°

Delaware 78° vs. February state record of 86°

West Virginia 82° vs. February state record of 85°

Virginia 82° vs. February state record of 87°

Rhode Island: 64° vs. February state record of 72° (cool ocean air covered the state)

Figure 1. The NWS Eastern Region tweeted this graphic on Wednesday, February 21, noting: “If yesterday's list of record highs across the Eastern US was impressive, today’s listing is just incredible. 24 of these locations broke or tied their record high for the entire month of February.” Image credit: NWS.

Though it was overshadowed by Wednesday, Tuesday was no slouch when it came to heat records. All-time monthly highs set on Tuesday, as tweeted by NWS Eastern Region, included:

Pittsburgh, PA: 78°F (old record 77°F on Feb. 8, 1900; POR back to 1875)

Indianapolis, IN: 77°F (old record 76°F on Feb. 25, 2000; POR back to 1871)

Charleston, WV: 81°F (old record 80°F on Feb. 24, 2017 & previous; POR back to 1892)

Cincinnati CVG Airport: 79°F (old record 76°F on Feb. 10, 1932; POR back to 1872, though not always at the airport location)

Tuesday also brought a number of cities their warmest daily low ever recorded on any date in February. Here are just a few:

Rochester, NY: 54°F (old record 50°F on Feb. 19, 1981; POR back to 1872)

Erie, PA: 62°F (old record 54°F on Feb. 15, 1954; POR back to 1874)

Cleveland, OH: 63°F (old record 57°F on Feb. 21, 1997; POR back to 1871)

Columbus, OH: 60°F (old record 59°F on Feb. 24, 2017; POR back to 1878)

Dayton, OH: 61°F (old record 56°F on Feb. 26, 2000, and previous; POR back to 1893)

Lexington, KY: 62°F (old record 60°F on Feb. 15, 2018 (!); POR back to 1872)

Louisville, KY: 66°F (old record 62°F on Feb. 10, 1932; POR back to 1872)

Wheeling, WV: 62°F (old record 58°F on Feb. 26, 2000; POR back to 1899)

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

A ridge to remember

The record February heat was caused by an unusually pronounced kink in the jet stream that brought a big trough of low pressure over the Western U.S. (accompanied by very cold temperatures) and a record-strength ridge of high pressure that locked in over the eastern half of the U.S. This ridge brought exceptional warmth miles above the eastern U.S. and northwest Atlantic. All else being equal, warmer air is less dense than cooler air, so a deep, warm air mass raises the heights of various benchmark heights such as 500 mb (roughly the midpoint of the atmosphere’s density, almost four miles up). As shown in Figure 2 below, the 500-mb map at 12Z Wednesday (7 am EST) was simply mind-blowing for mid-February.

Figure 2. The spectacularly strong upper-level high centered just off the southeast U.S. coast at 12Z (7 am EST) Wednesday, February 21, 2018. Colors show the departure in decameters (tens of meters) from the average height of the 500-millibar pressure surface at this time of year. Image credit: tropicaltidbits.com.

To verify just how unusual this ridge was, Lance Bosart (University at Albany, State University of New York) dug through the radiosonde climatology compiled by the NOAA/NWS Storm Prediction Center. The dataset goes back to the start of routine radiosonde launches in the late 1940s. At nearly every site along the U.S. East Coast, the weather balloons launched at 12Z Wednesday found a 500-mb surface higher than anything on record for January or February—and in some cases across even longer seasonal spans, as shown below.

GYX (Gray/Portland, ME): 581 decameters (prev. Feb record 578 dm; record for late Nov > late Mar)

CHH (Chatham, MA): 586 dm (prev. Feb record 580 dm; record for late Nov > mid Apr)

OKH (Brookhaven, NY): 588 dm (prev. Feb record 581 dm; record for late Nov > late Apr)

IAD (Sterling, VA): 588 dm (prev. Feb record 581 dm; record for late Nov > mid Apr)

WAL (Wallops Island, VA): 590 dm (prev. Feb record 586 dm; record for early Dec > late Apr)

MHX (Morehead City, NC): 595 dm (prev. Feb record 591 dm; record for early Oct > late May)

CHS (Charleston, SC): 594 dm (prev. Feb record 593 dm; record for early Dec > early May)

JAN (Jackson, MS) 594 dm (prev. Feb record 592 dm; record for mid-Nov > early May)

XMR (Cape Canaveral, FL): 595 dm (prev. Feb record 591 dm; record for mid Dec > early Mar)

Figure 3. Locations that recorded an all-time record ridge of high pressure at 12Z (7 am EST) Febraury 21, 2018, according to 500 mb height measurements made by balloon-borne radiosonde instruments. Radiosonde records extend back to the late 1940s.

Pronounced jet stream kink causing extreme weather across the entire U.S.

As is usually the case when the jet stream locks into an extreme configuration for multiple days over the U.S., extreme weather is occurring over most of the country. In the Western U.S., where a sharp trough of low pressure has been anchored to compensate for the intense ridge of high pressure locked in over the Eastern U.S., numerous daily record low temperatures marks have been recorded this week (though no monthly low temperature records have been set, as monthly cold records for February are less likely to be set in the last half of the month and in a warming climate). Record lows for the date were set on Wednesday in Denver, Colorado (-7°) and Olympia, Washington (13°). Daily record lows were set Tuesday morning in Billings, Montana (-15°); Rapid City, South Dakota (-9°); Sacramento, California (26°); Oxnard, California (35°, tied); San Francisco (36°) and Oakland, California (31°).

Between the record warm areas in the Eastern U.S. and the record cold regions of the Western U.S. lies a battleground where the warm air meets the cold, extending from Texas to Michigan. Serious flooding is occurring in multiple states in this region, thanks to an intense flow of moist air from the Gulf of Mexico and Eastern Pacific riding up along the jet stream axis. At least three drowning deaths are being blamed on this week’s floods, and full details of the flood situation can be found at weather.com.

Bob Henson co-wrote this post.