Miguel Pierre

High latitude blocking increasingly likely through November

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Good afternoon! Autumn like weather is in place as we speak across much of the Northeastern United States, with relatively seasonable temperatures. Enjoy it while it lasts. It will feel much more like winter very soon, as an arctic blast is set to arrive from Friday into Saturday. Very quickly, temperatures will fall 15 to 25 degrees below normal for this time of year, with record low temperatures possible over reporting climatology sites in the Northeast states. While this intensity of cold air will be short lived, colder than normal air will remain persistent.

A vigorous polar disturbance inside a shortwave trough will be swinging through the Great Lakes and Northeast tonight and Friday. This feature will amplify into a small closed low over Quebec later on Friday Night. The result will be a frigid airmass from Northern Canada swinging southward with a vengeance and reaching the Northeast USA from Friday into Friday Night. This type of southward movement of polar/arctic air is unusual this early in the season.

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Doug Simonian

Afternoon Video Update: NAO Blocking Signal Grows

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Good afternoon! The well-advertised signal of high-latitude blocking developing in the 2nd half of November continues to grow. It all starts with an amplification and slowing down of a Pacific wave train, which helps to pump latent heat towards the Poles, further leading to ridging extending towards the Poles. Subsequently, this changes the background state of the Arctic to the point where North Atlantic blocking becomes more feasible, and thus the entire Arctic is able to see blocking. This has big implications as we head into late November and December.

We explain and discuss all of this in our latest video update. For more written content regarding the blocking episode please refer to this article. For more context as to why this blocking is so important for cold in the East, please refer to this article.

The next step is figuring out how long exactly this blocking episode will last. We will keep you updated on our findings over the next few days!

John Homenuk

Why is high latitude blocking a key for sustained cold in the East?

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For quite some time now, we have been discussing the critical pieces that go into our Winter Forecast. The puzzle starts with current conditions – from the tropical Pacific to the Atlantic and Indian Oceans and everywhere in between. The current ENSO state has a huge impact on the forecast for any season, so understanding how these processes are impacting the global circulations is key.

There are secondary processes, however, that have a huge impact on the sensible weather experienced throughout the United States on any given day, week, or throughout a month. Understanding how these work are the meat and bones behind any seasonal forecast, and can make or break a forecast – even one that was founded on a correct forecast of larger scale processes (ENSO, etc).

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John Homenuk

Cold risks emerging to end November

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There is something about this time of year that features more fanfare than the rest. Maybe it’s the approach of winter, or the first surge of cold air into the middle latitudes. Either way, it seems that the first week of November almost always features a bit more drama to the forecast than most weeks, and this year is no different. Forecast models have offered hints this week that the pattern may be set to undergo some significant changes as we look towards the end of Autumn. 

As most are aware, the middle latitude pattern in the Northern Hemisphere has been stagnant for quite some time now. Granted, there have been periods of colder than normal air – especially recently in the Northern Plains where departures neared -10 F on a 7 day average. But for the most part, East of the Mississippi River, temperatures have averaged above normal as a Southeast Ridge anomaly has remained stout, owing to La Nina background forcing from the tropical Pacific Ocean. 

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