11:00 AM | *Pattern change to colder-than-normal begins next week across the central and eastern US...this upcoming pattern change has some staying power*

The upper air pattern will transition by later next week to one that will feature strong high-latitude blocking centered over Greenland and high pressure ridging along the west coast of Canada and the US to Alaska. This kind of upper air pattern is generally quite favorable for the transport of cold air masses from northern Canada into the central and eastern US. Map courtesy ECMWF, weathermodels.com

Overview

Temperatures will climb to well above-normal levels in the central US during the next couple of days and then in the eastern US this Friday and Saturday. However, a pattern change to colder-than-normal begins next week in the central and eastern US and this change looks like it will have some staying power. Numerous teleconnection indices point to an upcoming change in the temperature pattern and an on-going stratospheric warming event supports the idea.

The next several days will feature above-normal temperatures across the central and eastern US, but this pattern will flip next week to one with below-normal conditions. Map courtesy NOAA, tropicaltidbits.com

Remainder of this week

Temperatures will climb to well above-normal levels across much of the central US during the first half of this week and then that warm-up will shift to the eastern states for Friday and Saturday. In fact, temperatures on Saturday afternoon can peak in the upper 50’s-to-middle 60’s in the DC-to-Philly-to-NYC corridor ahead of an incoming cold front. However, the frontal passage will begin a transition to colder weather conditions in the eastern half of the nation that may very well have some staying power.

The teleconnection index known as the Arctic Oscillation will slide deeper into “negative” territory during the next couple of weeks and this is often correlated with high-latitude blocking over the polar region. Plot courtesy NOAA

Teleconnection indices

A look at the teleconnection index known as the Madden-Julian-Oscillation or MJO which tracks a tropical disturbance indicates it will transition during February to “phases” or locations which are normally associated with colder conditions across the eastern and southern US. The MJO is the major fluctuation in tropical weather on weekly-to-monthly timescales and can be characterized as an eastward moving “pulse” of clouds and rainfall near the equator that typically recurs every 30-to-60 days.  The MJO phase diagram illustrates the MJO index through different phases which generally coincides with locations along the equator around the globe.  When the MJO index is within the center circle, it is considered weak and when it is outside, it is stronger and usually moves in a counter-clockwise direction. The different phases of the MJO correlate well with different temperature and precipitation patterns around the world depending on the time of year.  The current forecast of the MJO suggests it will propagate into the “colder” phases of 8 and 1 later this month which usually results in colder-than-normal weather across much of the central and eastern US.

The upcoming change to a colder-than-normal temperature pattern across the central and eastern states is likely to begin next week and it looks like it will have some staying power. These forecast maps are for late February (25th) and feature below-normal temperatures in the eastern half of the nation (right plot of 850 mb temperature anomalies) with high-latitude blocking over northern Canada and Greenland (left plot of 500 mb height anomalies). Maps courtesy ECMWF, Weather Bell Analytics

Other teleconnection indices known as the Eastern Pacific Oscillation (EPO), Pacific North America (PNA), Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) are trending in directions that generally support the idea of colder-than normal temperatures during the middle and latter parts of February across the central and eastern US. Specifically, a pattern that features -EPO, +PNA, -AO and -NAO usually results in high pressure ridging across Alaska and the west coasts of the US and Canada and high-latitude “blocking” across Canada and Greenland…all of which tends to be favorable for cold air outbreaks to make their from Canada into the central and eastern US.

An ongoing stratospheric warming event over the polar region of the northern hemisphere may result in a “split” vortex late this month with one part over the northern US and this can contribute to colder-than-normal conditions over the central and eastern states somewhere down the road this winter. Map courtesy NOAA

Stratospheric warming

Additional support for a pattern change to colder-than-normal for the central and eastern US and one with some staying power comes from an on-going stratospheric warming event over the polar region of the northern hemisphere. This continuing stratospheric warming event has already disrupted the polar vortex this winter season and it looks like it will again.

The red line in the plot indicates actual stratospheric temperatures (at 10 millibar level) which features two “bursts” of warming. A third such “burst” of warming is likely later this month and it very well can result in a piece of the polar vortex to become positioned over the northern US. Plot courtesy NOAA

There has been one spike in stratospheric temperatures that lasted from late November into mid-December and a second burst occurred during the early and middle parts of January. It is this second episode of stratospheric warming that supports the notion of a pattern change to colder-than-normal beginning around the middle of February across the central and eastern US as there is usually a lag time of several weeks (4-6) for an impact on temperature patterns across the US. Looking ahead, there are strong signs for another burst of stratospheric warming later this month that can result in a “splitting” of the polar vortex which is likely tom extend the colder pattern into the month of March.

Any storm threats?

n terms of upcoming storm threats in the central or eastern US, there are signs for a storm system to accompany the front-end of the transition in the temperature pattern early next week. Odds favor an “inland” track early next week which would take a low pressure system to the Great Lakes region and limit snowfall potential to the Upper Midwest/western Great Lakes. If this were to take place in this fashion, the colder air mass would then reach the eastern states on the heels of this system by the middle of next week.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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