Sunday, January 01, 2012

The Fail Of December & What's In Store For January

December was a collective fail of forecasting from us locally.  Temperatures finishing over five degrees above average, cold shots that had less bark to them than a Maltese, and a pattern that failed to behave like a "typical" La Nina resulted in a month where most forecasters swung and missed...and probably should earn The Price Is Right treatment for their efforts.

That includes us.   We went for "average", which would have worked if the average temperature were five or six degrees higher and featuring a blend of such "wintry" months as December 2001 and December 2006.

Why didn't we get the pattern that most everyone expected?    One factor was a definite lack of high latitude and arctic blocking.    Below are maps of the 500 mb level of the atmosphere and the anomaly to what is considered "normal" for the atmospheric pattern between December 1st and 25th.  The first map is last year's look of the middle atmosphere...the second is this year's.  Red shading is higher heights (ridges of high pressure) aloft, blues and purples are troughs.

 Last year featured a trough in the Eastern US while the arctic and Greenland both featured blocking ridges of high pressure aloft...your "classic" -NAO and -AO look.  The result for us was our coldest December in ten years, followed by a cold January as the pattern stayed locked in this look through much of the month.  Despite occasional relaxation in the pattern and a few mild days sprinkled in, much of December and January featured colder than average temperatures.   This year, those ridges of high pressure aloft aren't there...we have troughs in the high arctic and a ridge of high pressure in the Central Atlantic and off the Southeast US.  To make matters worse, the Pacific has flipped on its head as well, with a ridge of high pressure in the Gulf of Alaska as opposed to a trough...another unfavorable look.  The result is a warm, snowless month as the pattern has either remained zonal or featured southwesterly winds aloft and at the surface.

Some look to the stratosphere as part of the culprit in this.  Temperatures in the highest reaches of our atmosphere have run colder than average over the past month.  The idea behind the stratosphere is that a cold stratosphere supports a warm surface (with a warm stratosphere supporting cold surface and mid level conditions).  There are times where this doesn't always line up perfectly but the past few years have worked out pretty well....and this December is featuring the opposite look in the stratosphere compared to a year ago  (see below).

That may change as we work into January...there have been occasional hints of a stratospheric warming spike at some point in computer modeling.  If that happens, we'll gradually see the pattern flip (if the "opposites" concept maintains serve) as the stratospheric warming takes a couple of weeks to migrate to lower atmospheric pattern shifts.  January will shape up as a bit more volatile in terms of temperatures compared to December -- we're already going to see that bottoming of the thermometer later this week for a couple of days.  However, warmer air will return for a few days late this week and into the coming weekend.  The second week of January looks milder than this coming week although temperatures may not be terribly warm.   If the potential stratospheric temperature shift takes place, we probably will lock into a cooler pattern late in the month.

We don't foresee January as a six degree above average type of month in temperatures...but the idea of it being significantly colder than average is appearing to be far less likely as well.

Strike two for many of us in the forecasting realm!

Forecaster Doug Melegari contributed content to this article.