Northeast Braces for a Frigid, Windy Weekend

A quick but intense shot of blustery cold will sweep across the northeast U.S. this weekend, reminiscent of the “polar vortex” outbreaks from the last two winters. Compared to the multi-day blasts of cold that were common in early 2014 and 2015, this will be more of a glancing blow, but stout breezes will push wind chills far below zero in many areas.


Figure 1. Surface air temperatures in °F predicted by the 12Z Wednesday run of the GFS model for 7:00 pm ET on Saturday, February 13, 2016. Image credit: Levi Cowan, tropicaltidbits.com.

The brief blast of Arctic chill is partially an offshoot of rapid changes in the Arctic stratosphere. Temperatures there shot up to near-record highs this week, scrunching the stratospheric polar vortex toward Europe. An equally quick cool-down is expected over the next week or two, which should allow the vortex to shift toward its more typical position centered near the North Pole. Meanwhile, the flow at lower levels will remain northerly from polar regions into the eastern United States, and a sprawling surface high will push from the Canadian Arctic all the way into the U.S. Northeast by the weekend.


Figure 2. Wundermap depiction of wind speeds at the 250-mb jet-stream level (about 34,000 feet above sea level) at 06Z (1:00 am EST) Wednesday, February 10, 2016. Winds are shown in knots; multiply by 1.15 for miles per hour.

Basking in February warmth
Another player is the strong upper-level ridge that’s forcing the jet stream from the eastern Pacific to split before it reaches the coast. This ridge--more akin to the Ridiculously Resilient Ridge of the last several winters than to a classic El Niño pattern--has brought sunshine and extremely mild weather throughout the U.S. West, shutting down winter rainfall. Temperatures on Tuesday soared to 85°F at Monterey, California, and into the 90°F range across the Los Angeles area. Santa Ana’s toasty high of 95°F tied its monthly record for February.

In Washington state, upper-level readings were the warmest for February in more than 60 years of recordkeeping (see Figure 3). The mildness at elevation led to “one of the strongest inversions I have ever seen here in Seattle,” said longtime resident Cliff Mass (University of Washington) in his weather blog. It was a full 23°F warmer just 1640 feet above Seattle (less than the height of the world’s tallest skyscrapers) than in the city itself. Sea-Tac Airport ended up setting a record high of 63°F, but just by one degree.


Figure 3. The view from atop Seattle’s Space Needle on Tuesday morning, February 9, 2016, showing the fogged-in city overtopped by sunny, milder air. Image credit: Space Needle Cam, courtesy Cliff Mass.


Figure 4. Since 1948, radiosondes have measured temperature at upper levels of the atmosphere. Shown here are daily readings at the 850-mb level (about a mile above ground) for Quillayute, WA, near Seattle. Record highs and lows for each date are shown by red and blue traces respectively. The temperature of 16.6°C (61.9°F), recorded at 12Z Tuesday, February 9, 2016, and shown in the black dot, was the warmest observed above Quillayute for any February or March day on record. At the surface, Quillayute’s high of 73°F on Tuesday tied the record high for February, in data going back to 1966. Image credit: NOAA Storm Prediction Center and Cliff Mass.

Record cold aloft on its way--but at the surface, not so much
This weekend is likely to see some of the coldest air ever observed aloft over the Northeast in the 60-plus-year period with radiosonde data available (beginning in 1948). Temperatures at the 850-mb level, about a mile above ground, are projected to tumble by Saturday to readings as low as -32°C above Buffalo, NY, and -30°C over Burlington, VT, with even colder readings possible over the Adirondacks (see Figure 5). The Buffalo temperature at 850 mb would be on par with the all-time low from the radiosonde dataset.

But the surface air mass cascading southward from Canada doesn’t fully mirror the coldness that’s present higher up, and it won’t be strong enough or long-lasting enough to allow surface temperatures to plummet as they otherwise might. While it’ll be unquestionably frigid this weekend in the Northeast, there will be few if any monthly record lows at the surface, and even daily record lows may be hard to come by. For example, at Burlington, VT, the current WU-predicted high of 3°F on Saturday and low of -8°F on Saturday night would fall well short of the record low maximum for Saturday (-3°F, from 1979) and the record low for Sunday morning (-19°F, from 1987). Compare this to last week in Burlington, when record daily highs were set on four consecutive days (Feb. 1 through 4). Of course, those highs—which included 54°F on Feb. 3 and 4--were far more pleasant and less extreme-feeling than what Burlington will experience this weekend.


Figure 5. As shown by this Wundermap, temperatures at the 850-mb level (about a mile above ground) projected by the 06Z Wednesday run of the GFS model will be close to the lowest ever observed by radiosonde across parts of the Northeast. The yellow region over the Adirondacks corresponds to predicted values colder than -34°C (-29°F) about a mile above sea level at 10:00 pm EST Saturday, February 12, 2016.

A teeth-chattering flashback
Like the strong ridge in the West, this weekend’s cold pattern in the Northeast will serve as a brief echo of the last several winters. In early 2015, recurrent upper-level troughs and back-to-back-to-back snowfall led to weeks of misery in Boston and gave New York and Vermont their coldest January-to-March period on record. Still, the readings that winter weren’t so much brutally low as consistently low.

“In Boston, we haven’t seen a temp colder than -3°F since 2004 (when we hit -7F),” noted weathercaster Eric Fisher (WBZ/WSBK). “The coldest we could manage last winter was -3°F, and we didn’t set a single daily record low. The cold was more of the extremely persistent kind than the one-off shocking variety.” Fisher added that Boston has seen only nine subzero nights in the last 20 years. The latest WU forecast brings Boston down to –4°F by Sunday morning.

Wind chills will add to the impact of this weekend’s fierce cold, especially in the wake of what’s been a quite mild winter overall. Wind chill readings in the range of -10°F to -20°F may spread across the Boston area on Saturday night. The windiness is a hint that this frigid air mass isn’t planning to hang around for long. By Monday, return flow from the south will be putting a significant dent in the cold. Temperatures will be back to near the seasonal average by Tuesday, but still cold enough to pose a potential winter weather hazard as low pressure organizes near the mid-Atlantic coast early next week. The brunt of this nor’easter may end up offshore, but as with several recent storms, coastal areas could easily get slapped with heavy, windblown snow--or heavy rain, if temperatures recover quickly enough. Freezing rain and/or sleet may also become a concern over the mid-South if enough mild air is wrapped around the developing nor’easter. Models are still struggling with this storm, but it’s certainly one to watch.


Figure 6. The expected Northeast cold stands out amid unusually warm temperatures almost everywhere else in this hemispheric map of projected surface temperatures relative to seasonal averages at 03Z Sunday, February 14, 2016 (10:00 pm EST Saturday). The map is based on the 18Z Wednesday run of the GFS model. Image credit: Climate Reanalyzer/University of Maine.

More to come?
Long-range forecasters are debating whether the Northeast is likely to see many more rounds of intense cold this winter. Judah Cohen (AER) expects relatively cold readings to predominate from late February into March across the midlatitudes of North America and Eurasia. “The perturbation of the [polar vortex] is likely to dominate the evolution of the temperature variability across the Northern Hemisphere (NH) for the duration of winter,” said Cohen in a February 8 blog post.

This outlook would be in line with the tendency in recent years toward intense winter cold outbreaks in northern midlatitudes, including the northeast U.S.--a development that Cohen and others have associated with depleted Arctic sea ice. However, it would run counter to the typical outcome during strong El Niños of relative mildness across the northern U.S. and Canada. WU blogger Steve Gregory sees the El Niño signal returning full force within a few days, perhaps assisted by a favorable phase of the Madden-Julian Oscillation. “While it is still far from a certainty, we should see a return to above normal temps in the east and below normal in the west, along with increased chances of precip along the west coast in about 10 days,” Gregory said in a Monday blog post.

We’ll have our next post by Thursday evening.

Bob Henson