It’s almost too fitting. For much of the winter, meteorologists and hobbyists alike spend countless hours attempting to forecast and predict the likelihood of high latitude blocking development. This year, stratospheric warming events were expected to kick off changes that would eventually lead to the development of said high latitude blocking, and change our pattern to a cold and snowy one. While the pattern turned cold and snowy for sure, the high latitude blocking never came to fruition. In fact, the NAO stayed positive for much of the winters duration.
Well, it’s finally here. Just in time for Spring.
Higher than normal heights and, in fact, a closed mid level ridge, developed into Central Canada and the NAO region during the latter part of this week. This forced the development and expansion of an upper level low from the Central Great Lakes into the Northeast United States. The sensible weather impacts were felt quickly — it’s already in the 40’s outside and, tonight, temperatures will fall into the 30’s. Freeze Warnings have been issued for parts of interior New Jersey.
Let’s back up a bit: What exactly is high latitude blocking? The name, in its simplicity, is quite descriptive. When meteorologists reference “High latitude blocking” they are, in fact, speaking of “blocking” in the high latitudes.
Essentially “blocking” ridges, or sometimes even just above normal mid level heights, can develop in the higher latitudes from Canada into Greenland and the North Atlantic. These ridges, or higher than normal heights, can act to do several things that have major impacts on our areas weather. First, they slow down the pattern around them. Depending on the strength of the blocking, the pattern can slow so much that it can force other surrounding disturbances to phase and retrograde (See Hurricane Sandy). If the blocking isn’t quite that strong, the pattern can still slow down to support major storms (See, Blizzard of December 26 2010).
Subsequently, high latitude blocking often aids in displacing cold air from the typical areas of Northern and Central Canada southward into the United States. Think of the atmosphere as a wave pattern — and then imagine ridges in those waves over Western, Northern, or Eastern Canada. The cold air that is typically there is forced underneath those ridges, into the United States.
And so here we are — after a winter spent waiting for high latitude blocking, we finally have it. What does this mean for our Spring weather? Essentially — it means that Spring will be taking a hiatus for at least 7 to 10 days. The high latitude blocking will force multiple upper level troughs underneath it, into the Central and Eastern United States. This will keep below normal temperatures locked into our area for the foreseeable future.
In addition, an active stream of disturbances crashing into the United States from the Pacific raises some eyebrows for a potentially phased upper level low; or significant rain event, possibly including a coastal storm. Forecast models have hinted at this possibility as early as Day 7 — as the blocking forces multiple disturbances underneath it into the Central and Eastern United States. Phasing of these disturbances would eventually lead to a moisture surge and potentially coastal development with prolonged rain and wind in our area.
But, we digress. That’s a discussion for the medium range as we draw closer. For now, we can say with confidence that temperatures will run below normal for the next several days. The 70’s and 80’s which we were teased with over the past weekend have turned out to be exactly that: A tease.