9:00 AM | ***50+ mph winds on Saturday with snow showers and even snow squalls...big warm up Monday-to-Wednesday...multiple signs point to the return of winter weather after next week's warm up***

A stratospheric warming event will unfold over the next couple of weeks and will tend to make the overall weather pattern turns colder again in the eastern states. The polar vortex will transition from an extension over the western states at day 5 (left) to over the eastern states at day 10 (middle) and by day 15 (right), the polar vortex will be split apart as depicted by the NOAA GFS forecast. Maps courtesy NOAA

Overview

The powerful winds of late Thursday night and early Friday will diminish on Friday night; however, the next strong system will produce 50+ mph wind gusts on Saturday in the northeastern quadrant of the nation and there can be snow showers and even heavier snow squalls. After that, there are signs for a big time warm up in the eastern states in the Monday, Tuesday and Wednesday time period with temperatures likely to climb into the 50’s and 60’s.  There are also signs, however, that next week’s warm up will be a temporary break from winter weather and that there will be a resurgence of winter weather as we get to late next week and beyond. In fact, an evolving stratospheric warming event and the trending pattern of Pacific Ocean teleconnection indices suggest that winter’s wrath could hang around well into the month of March across the eastern states with additional cold air outbreaks and multiple new snow threats.

A vigorous wave of energy pushes into the northeastern states on Saturday and it will result in 50+ mph winds gusts, snow showers and even heavier snow squalls. Map courtesy NOAA, tropicaltidbits.com

Active weather on Saturday…warm up next week

An impressive upper-level wave will deepen on Saturday as it drops to the southeast across the Great Lakes and into the northeastern part of the country. The overall pressure gradient field will tighten during the day as this system moves overhead and winds will respond accordingly and could gust past 50 mph by later in the day. In addition, the atmosphere will become quite unstable on Saturday and this is likely to result in some snow shower activity and perhaps even a few heavier snow squalls. One note of concern, it is possible that if a heavier snow squall were to occur, it could be mixed with rain in the I-95 corridor, and the combination of the rain and melting snow on pavement could result in some icing as temperatures likely drop sharply afterwards.

After a chilly and quieter day on Sunday, it’ll turn noticeably milder on Monday, President’s Day.  In fact, the warm up that begins on Monday is likely to continue in the eastern US for a few days with daily high temperatures in the DC-to-Philly-to-NYC corridor likely to be in the 50’s and 60’s. It looks like colder air will return to the eastern states by late next week and there are likely to be additional cold air outbreaks during the latter part of February and the first half of March along with multiple new snow threats.

A big-time warm up is coming to the eastern states in the first half of next week (Monday-to-Wednesday), but winter is sure to make a return later next week and beyond. Map courtesy NOAA, tropicaltidbits.com

Signals for a resurgence of winter after the temporary warm up

-Stratospheric warming event

One of the reasons to believe the winter is not coming to an end next week in the eastern US has to do with an unfolding stratospheric warming event.  Sudden stratospheric warmings (SSWs) are among the most impressive dynamical events in the physical climate system.  During the winter months in the polar stratosphere, temperatures are typically lower than minus 70° Celsius. The cold temperatures are combined with strong westerly winds that form the southern boundary of the stratospheric polar vortex which plays a major role in determining how much Arctic air spills southward toward the mid-latitudes. This dominant structure is sometimes disrupted in some winters or even reversed. Under these circumstances, the temperatures in the lower stratosphere can rise by more than 50°C in just a few days. This sets off a reversal in the west-to-east winds and the collapse of the polar vortex. In response to the stratospheric warming (and associated layer expansion) at the high latitudes, the troposphere in turn cools down dramatically (with layer contraction) at the high latitudes. This tropospheric cold air can then be transported from the high latitudes to the middle latitudes given the right overall weather pattern.

Stratospheric warming (oranges) can be seen in the northern latitudes during this 30-day loop of analyzed 10 millibar temperatures and anomalies. Each frame is an eleven-day mean, centered on the date indicated in the title, of 10 millibar temperature and anomalies from the NOAA/NCEP Climate Data Assimilation System (CDAS). Contour interval for temperatures is 4 degrees (C), anomalies are indicated by shading. Anomalies are departures from the 1981-2010 daily base period means.

Computer forecast models suggest a stratospheric warming event will indeed take place during the next couple of weeks with a splitting of the polar vortex on the table. The location of the polar vortex and its axis orientation have already played important roles this winter season with regards to temperature patterns across the nation. For example, during the month of December, the polar vortex tended to “stretch” in a northeast-to-southwest direction extending out over the western part of the nation.  This contributed to a colder-than-normal month of weather in the western US while it was warmer-than-normal across the eastern US.  In early January, the polar vortex shifted its orientation axis to a northwest-to-southeast direction and it extended out over the eastern states which contributed to a colder-than-normal weather pattern for the bulk of the month. This evolving stratospheric warming event looks like it will result in a stretching of the polar vortex back to a position where some of it will extend overhead into the eastern US – likely resulting in colder-than-normal weather as we head from late February into the month of March.

When the Eastern Pacific Oscillation (EPO) is in negative territory, the overall pattern generally favors the transport of cold air masses from northwestern Canada into the central and eastern US.

-Pacific Ocean teleconnections (+PNA, -EPO)

Some other support for the idea that winter will hang on in the eastern US as we head into March comes from a couple of Pacific Ocean teleconnection indices known as the Pacific-North American (PNA) and the Eastern Pacific Oscillation (EPO). Cold air masses that form over the northwestern part of Canada and Alaska have a much easier time of making their way into the eastern US if the PNA is in positive territory and if the EPO is in negative territory. Indeed, the forecasted trends in both of these indices is in the appropriate direction to become more favorable for cold air outbreaks into the eastern states after next week’s warm up from late February into March.

The Pacific North American (PNA) teleconnection index will drop into negative territory for a short time next week, but then will trend positive as we close out the month of February. Plot, data courtesy NOAA

With respect to the PNA pattern, when it is in positive territory, there tends to be a ridge of high pressure over the west coast of the US or the Great Basin region.  This tends to result in a flow of cold air from eastern Alaska and northwest Canada into the central and eastern portions of the CONUS.

The teleconnection index known as the Eastern Pacific Oscillation (EPO) will flirt with the neutral zone over the next few days, but then will trend back down into negative territory as we move from late February into the month of March. Plot courtesy Weather Bell Analytics (Meteorologist Joe Bastardi, Twitter), NOAA

With respect to the EPO, when it is in negative territory, there tends to be a ridge of high pressure over eastern Alaska, the Gulf of Alaska and far northwest Canada. This pattern tends to establish a flow of Arctic air from Alaska (and possibly even from Siberia across the pole) into the central and eastern portions of Canada and then ultimately into the central and eastern portions of the CONUS.

Stay tuned…it is looking more and more likely that fellow Pennsylvania prognosticator Punxsutawney Phil had the right forecast in early February for six more weeks of winter.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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