Mid-South, Mid-Atlantic Brace for Heavy Snow, Sleet, and Ice

A record-setting intrusion of Arctic air blasted through the eastern U.S. over the weekend, setting the stage for a bitter week that will remind many of the infamous cold stretch of January 2014. The biggest concern today and Tuesday is an upper-level impulse moving from Oklahoma to the Atlantic that will pull warm, moist low-level air from the Gulf of Mexico atop the surface-based Arctic air. Snow will stretch from southern Missouri to the Washington, D.C., area, with sleet and freezing rain extending from Arkansas to the Carolinas. At 6:21 am CST, law enforcement in Jasper, AR, reported 2 - 3” of sleet accumulation. The surface layer of cold air will generally remain thick enough to favor sleet over freezing rain, but significant freezing rain could occur in some areas; an ice storm warning has been issued for central Tennessee south of Nashville.

Parts of central Kentucky are getting their heaviest snow in years today, with as much as 15” expected. Washington, D.C., could get 6 - 10” or more of snow on Monday night, heaviest toward the south, although there may be large variations across the D.C. area; a small change in the storm track could bump the totals up or down by a big margin. As with the recent nor’easters, much of the snow in this cold storm will be on the fluffy side, with snow-to-liquid ratios of 15:1 to 20:1 adding to the potential accumulations. Tonight’s D.C. storm will be less intense but far better predicted than the unexpected, paralyzing President’s Day storm of 1979.


Figure 1. Ice forms along the shore of the Manhattan side of the East River in New York on Monday, February 16, after a weekend cold front sent temperatures into the single digits. Image credit: AP Photo/Peter Morgan.

The ferocity of the cold front that swept from the Midwest through the Northeast on Saturday was truly remarkable. As temperatures plummeted, winds gusted above 50 mph in at least nine states, taking down trees and knocking out power to hundreds of thousands. Hot Springs, VA, plunged from 30°F at 3 p.m EST to –1°F by midnight, and Washington’s Reagan National Airport tumbled from 44°F at 5 p.m. to 19°F by 11 p.m. Brief snow squalls and near-whiteout conditions were common just behind the front. One mesonet station near Fisherman’s Island, Virginia, reported a gust to 77 mph.

The powerful winds and cold air originated with an upper-level impulse that dove south from Greenland. Occasionally such an impulse will produce a “tropopause fold,” where a pool of air from very high levels gets pulled downward and tucked beneath the jet stream into the circulation of a developing storm. In this case, the fold was so dramatic over the Midwest that it brought the height of the tropopause down to about 8,000 feet from its typical midlatitude level in winter of around 35,000 feet. Such tropopause folds can help momentum from powerful jet-stream winds aloft to descend to the surface.


Figure 1. Winter Storm Neptune, as captured by the Suomi NPP satellite at 1700 GMT on Sunday, 15 February. The most intense precipitation is clustered at the far right of the image, extending north into southeast Canada (not shown). Image credit: Scott Bachmeier, CIMMS/University of Wisconsin.


The New England snow machine strikes again
It didn't take long for a powerhouse nor'easter to develop as the cold front plowed offshore Saturday night. This cyclone developed an intense but unusual structure, with at least three centers of circulation, each with a central pressure of less than 980 mb. The storm’s unusual evolution and its more easterly track produced less snow than expected in some areas: Portland, Maine, only reported 2.4” from Friday night through Sunday, while the far south and far southeast corners of the state each got more than a foot. Some of the storm’s worst impacts were in Canada’s Maritime Provinces: the wind-prone town of Grant Etang, Nova Scotia, recorded a peak gust of 109 mph on Sunday afternoon.



Figure 2. A puppy on a walk braves the epic accumulations in Cambridge, Massachusetts, on Sunday, February 15. Image credit: wunderphotographer salazar28.


Hitting the dubious snow jackpot once more were the eastern Massachusetts coast and parts of the Maine coast. The 16.2” at Boston's Logan Airport on Saturday and Sunday sent February into the record books as the city's snowiest month, with an amazing 58.5” of snow recorded through February 15 and nearly two weeks left to go. The renowned Blue Hill Observatory, just south of downtown, reported 45” on the ground at the summit of Great Blue Hill on Sunday morning—the greatest snow depth in the observatory’s 130-year history, topping the 43” recorded in March 1969. A CoCoRaHS site in Eastport, Maine, reported 78.5” on the ground Monday morning. Snow depth records are especially significant because techniques for measuring snow depth have changed little over the years, whereas the current practice of recording snowfall every six hours could give a slight edge to recent storms over those from long ago, when once-a-day measurements were more common. (Measuring snow at more frequent intervals leads to higher overall totals, since the snow has less chance to compact.)

Wind and cold champion: Mount Washington
New Hampshire’s Mount Washington Observatory, famed for having “The Worst Weather on Earth,” is living up to its slogan on the holiday created to honor its namesake. Just after midnight Sunday night, the temperature atop Mount Washington was –34°F, with sustained winds of 74 mph and an astoundingly low wind chill of –86°F. By 7:57 am EST, sustained winds had increased to 123 mph. It’s no wonder the mountaintop station issued this warning to would-be adventurers in its daily forecast on Sunday: “All [search and rescue] assistance if needed will have to come from below, as summit staff will not be able to assist in any way, shape, or form. A single injury will potentially put several lives at risk not just your own.”

Coldest February on record?
On Monday morning, Erie, PA, tied its all-time record low of –18°F, and Buffalo dipped to –10°F, its coldest temperature since January 6, 1996. Many eastern cities face a uncommonly frigid stretch for late February, especially as a second blast of Arctic air arrives later this week. Dozens of daily records could tumble, and some locations--especially mid-South locations with snow cover--will be in a good position to set records for lowest temperature so late in the winter. The currently predicted lows for Friday of –8°F in Lexington, KY, and –4°F in Nashville, TN, would do the trick. It will be tougher to set monthly lows, given that February is the region’s coldest month of the year. Still, this week could end up as the coldest of the 21st century for millions of people. With no sign of letup in the cold for at least a week, several Northeastern cities and states are within reach of their coldest February in a century or more of recordkeeping. Three examples:



Bob Henson



Figure 3. Thomas Mitchell took this shot in his neighbors’ kitchen in Beverly, Massachusetts on Sunday, February 15: “It's not just stuck to the windows, the snow bank is higher than the windows.” Image credit: wunderphotographer thomashmitchellcom.