1:55 PM | *Just can’t shake off the cold air outbreaks into the central and eastern US through at least the middle of April*

A classic “high-latitude blocking” pattern is unfolding in the northern latitudes with very high heights aloft compared to normal across northern Canada and Greenland. Map courtesy NOAA, tropicaltidbits.com

Overview

One thing a snow lover in the central and eastern US is rooting for during the wintertime is a “high-latitude blocking” pattern in the upper part of the atmosphere as it is often favorable for sustained cold air outbreaks and potentially accumulating snow.  One way meteorologists can monitor the likelihood for this type of weather pattern is to track a teleconnection index known as the North Atlantic Oscillation (NAO).  If this index falls into “negative” territory for a sustained period of time during the wintertime – a snow lover’s dream – it is often associated with sustained colder-than-normal weather in the eastern and central US and an increased chance for accumulating snow.  Here we are now into the month of April and the largely absent “-NAO” pattern this winter season has finally arrived with “high-latitude blocking” likely for the next week or two across the northern latitudes. This may not lead to snow this time of year – although stranger things have happened – but it does signal the likely continuation of cold air outbreaks into the central and eastern US through at least the middle of April.

The teleconnection index known as the North Atlantic Oscillation (NAO) is in and will stay in “negative” territory to the middle of the month and this signals additional cold air outbreaks for the central and eastern US. Plot courtesy NOAA.

Details

Low pressure has pushed off the east coast today and is seemingly now on its way to the open waters of the Atlantic without any further influence on the NE US or Mid-Atlantic.  It will not, however, continue in this northeasterly direction for much longer before it encounters a blocking pattern in the upper part of the atmosphere that will lead to an unusual movement over the next few days as this system will be forced to retrograde back towards the Northeast US. One of the teleconnection indices that provides some information about the chances for “high-latitude blocking” is known as the North Atlantic Oscillation (NAO) and it is now in “negative” territory and should remain there for several days which is supportive of the idea of a blocking pattern that features strong high pressure ridging near Greenland, Iceland and northern Canada.

The current colder-than-normal air mass in the eastern third of the nation will stick around for the next few days and then another cold air outbreak is possible in the same area later next week. Maps courtesy NOAA, tropicaltidbits.com

Conditions will remain unsettled over the next few days across the NE US and Mid-Atlantic because of the atmospheric roadblock this offshore storm is going to encounter with plenty of clouds and a very noticeable increase in winds on Thursday and Friday.  In addition, there will be a band of clouds and showers that will rotate around the low and drop southwestward later tomorrow into early Friday from the NE US to the Mid-Atlantic.  Finally, this low pressure system is likely to make a final exit over the weekend to the open waters of the Atlantic and this will lead to much more settled conditions in the NE US and Mid-Atlantic with milder temperatures going into the early part of next week.

Additional cold air outbreaks are likely across the central and eastern US into the middle of April. Maps courtesy NOAA, tropicaltidbits.com

Looking ahead, with a continuation of a blocking pattern and a -NAO, the prospects for additional cold air outbreaks are quite strong.  In fact, there are signs for multiple cold air outbreaks that will originate in northern Canada and drop southeastward into the central and eastern US between now and at least the middle of the month.  While there will be cold air outbreaks for the next couple of weeks, this doesn’t mean there won’t be spells of warmer-than-normal weather.  In fact, it looks quite mild from later this weekend into the middle part of next week, but cold blast #2 is likely to arrive late next week and more such outbreaks will likely follow into mid-April. 

If only we had this pattern in the wintertime (i.e., if you like cold and snow).

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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