Moist Flow Sweeping Out Record Arctic Blast over the Northeast

By: Bob Henson , 10:00PM,GMT on February 15,2016



 

A winter’s worth of cold seemed to be stuffed into this President’s Day weekend across the eastern United States. The most frigid air in years--in some places, in decades--swept across much of the Northeast from Friday into Sunday. Borne on strong northwest winds, the Arctic air had little chance to modify, which allowed subzero readings to penetrate virtually all of New England, including Nantucket Island and Provincetown, MA--a rare occurrence even in this chilly corner of the United States. Crisp sunshine allowed a feeble recovery on Sunday, but the bigger shift began on Monday with the gradual organization of a major inland storm. A precipitation shield extending from the mid-Atlantic to New England began as snow but will transition to freezing rain in many areas and eventually to heavy rain by Tuesday, as the freezing line whips northward (it was already through the D.C. area by late Monday). Further south, multiple tornadoes were reported on Monday afternoon along the central Gulf Coast as several supercell thunderstorms spun up within a larger region of severe weather.

The area most at risk of prolonged, serious icing, according to NOAA’s Weather Prediction Center, is a strip from central PA to central NY. West of the surface low, this event should deliver mostly light to moderate snow from the mid-Appalachians across western PA and NY (heaviest over western NY, where more than a foot is possible). As of late Monday, winter storm watches and warnings were plastered from northeast Georgia to Maine.

Meanwhile, Westerners are asking “What winter?”, as springlike conditions work their way eastward from California. Beneath a stout upper-level ridge, southern California is pleasantly warm but unnervingly dry, while forecasters in Phoenix, AZ, are projecting that Wednesday could be the city’s earliest 90°F day on record by a full week.


Figure 1. This striking visible satellite image from Sunday, Feb. 14, 2016, shows cloud streamers forming offshore--the result of instability produced by cold air flowing off the northeast U.S. coast onto warm Atlantic waters. The most prominent streamers are downstream of bays that allow more moisture to be concentrated into the developing bands. Image credit: NASA Worldview, courtesy Tom Niziol, The Weather Channel.

Saturday night in the deep freeze
When a cold air mass invades a region, record-low daytime highs can occur when cloud cover keeps the sun out by day, and clear skies can allow temperatures to plummet to record lows at night once a cold air mass is entrenched. This weekend, the cold air was anything but entrenched: it ripped through the region, which made the arrival and departure of the air mass more important than any local warming and cooling. The depth of the cold air was especially evident at higher elevations (see Figure 1). The radiosonde launched at Albany, NY, at 7:00 pm EST Saturday night observed a temperature at the 850-mb level (about a mile above sea level) of -30.8°C (-23.4°F). This was among the lowest readings observed at this height for any Albany radiosonde since routine upper-air observations began in 1948.


Figure 2. Temperature, dew point, and wind chill at the summit weather station operated by the Mount Washington [NH] Observatory on Saturday, Feb. 13, 2016. Readings bottomed out on Saturday evening at -40°F before a steady warm-up began that continued through Sunday and into Monday. (The -40°F reading is not apparent on this trace but was tweeted by MWO.) The last time Mt. Washington was any colder than -40°F was on Jan. 15, 2004, when the site dipped to -45°F. Wind chills on Saturday evening approached -80°F. Image credit: Mount Washington Observatory.


New York City’s major observational sites all set record daily lows on Sunday morning. Central Park made it down to -1°F, while LaGuardia and JFK airports got down to 1°F and Newark hit 0°F. Islip, on central Long Island, made it down to 0°F, the coldest Islip has been outside of January since records began there in 1984. Bridgeport, CT, set a new monthly record low with -6°F; records there began in 1948. Most stations with century-long datasets saw their monthly records unchallenged.

Boston (Logan International Airport) dipped to -9°F on Sunday morning and clawed its way back up to 12°F by evening. As noted by Phil Klotzbach (CSU), those were the coldest daily minimum and maximum temperatures observed so late in the year in Boston since Feb. 15, 1943. The last time Boston and Worcester got as cold as they did on Sunday was in 1957.

We’ll have our next post by midday Tuesday. WU contributor Steve Gregory has a new Monday post that looks in depth at the factors that will bring springlike weather later this week, but with plenty of uncertainty beyond that.

Bob Henson


Figure 3. Low temperatures across southern New England on Sun., Feb. 14, 2016 (degrees °F). Image credit: NWS/Taunton, MA.


Figure 4. From Highland, MI, Jeff Masters reports: “We had our coldest night of the winter Sunday morning, bottoming out at -13°F. The plot from my PWS on Sunday looked remarkably like a step function.”