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Here’s why a cold, wintry pattern will continue

We know, it’s been relentless. But we warned you of this. The past two to four weeks have featured a near constant parade of storm systems with winter weather, as well as bitter cold both during the systems and surrounding them. The pattern has been “locked and loaded” as meteorologists like to say. The atmosphere has settled into a routine, and it’s one that continues to dislodge arctic air farther south than usual while maintaining an active jet stream of energy. This has resulted in countless chances for snow with a train of storm systems moving across the country into very cold air. In terms of snowfall, New England has benefited the most — many weather stations are running toward all time snowfall records.

A breakdown and overview of the hemispheric setup offers us some clues as to why this pattern has become so relentless, and why it’s likely to continue for at least another 7 to 10 days before any hint of moderation. As meteorologists, long term forecasting is rarely as straightforward as “colder than normal with the potential for snow”. But the next 7-10 days offer just that.

In the mid and upper levels of the atmosphere, this pattern has been driven by a large ridge on the west coast — extending northward into British Columbia and times — and a resulting large trough on the East Coast of the United States. This west coast ridge has seen multiple levels of amplification — and not surprisingly, when it is more amplified, a colder more amplified pattern develops in the East. Working in tandem with this West Coast ridge has been a very active Pacific Jet stream, sending  disturbance east through the Pacific Ocean and over the top of said ridge.

GFS ensemble mean showing positive height anomalies with a ridge on the west coast into the Northern Pacific.

GFS ensemble mean showing positive height anomalies with a ridge on the west coast into the Northern Pacific.

What the pattern has lacked in terms of high latitude blocking over the North Atlantic and Greenland, it has compensated in volume of activity. There have been multiple disturbances traversing the country each week, with continued shots of cold air.  This doesn’t look to change over the next 7-10 days. Forecast models, in fact, are in good agreement that further amplification of ridging in British Columbia up toward the Northern Pacific (into the EPO index region) will occur. This helps to dislodge cold air southward through Canada into the Northern 1/3 of the United States.

Both the GFS and ECMWF ensemble means continue to harp on the idea of this pattern continuing over the next 7 to 14 days. With cold air being pushed southward from Canada, and an active Pacific Jet continuing to send disturbances into the United States, the chances for wintry weather should continue through at least the end of February. Individual storm threats, however, will be harder to focus on until they get closer into the range of forecast models. As we have seen over the past several weeks, forecast models can be wildly inconsistent in patterns such as this one. They will struggle to iron out the intricate details of the pattern that ultimately will have huge impacts on our sensible weather.

GFS Meteogram for NYC showing the temperature getting above freezing only one day in NYC in the next 10.

GFS Meteogram for NYC showing the temperature getting above freezing only one day in NYC in the next 10.

Temperature wise, there is solid agreement among both operational and ensemble forecast guidance that below normal temperatures will completely dominate the forecast. Many forecast models don’t bring NYC above 35 degrees for the next 10 days. The above image, from the GFS operational model run this morning, only takes NYC (Central Park) to 37 degrees for a few hours next week. Otherwise, temperatures are generally in the teens and 20’s.

And again, while individual snow threats will remain fuzzy until we get closer to them, seeing the amplitude and agreement among the ECMWF and GFS ensembles through Days 7-10 gives us increased confidence that colder than normal air will continue — and we’re fairly confident that snow threats will make their way into the forecast as well.

Spring is only 31 days away.

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