The Web Site and Blog of Ted Keller

Milder Days Ahead, North Atlantic Oscillation

6-10 Day Temperature Forecast

Welcome Winter!

Thursday was probably the most winter-like day we’ve had so far this winter.  Temperatures fell all day, wind chills were in the single digits and snow continued to fly well into the afternoon in many parts of the Ozarks.  Springfield’s official snow measurement was 0.6″.  January’s total is 0.7″.  This season, 1.1″  There were reports of a few 1″ plus totals peppered mostly across areas north and northeast of Springfield.

It looks like our low temperature this morning stopped at 13 degrees which is about as cold as the coldest we’ve had so far this season.

Trends

We’re heading back up in temperature this weekend. Expect a return of forties and fifties to last into Monday.

The cold air I referenced last week has been building in Canada.  While it will be making some inroads into the northern and northeastern U.S., we here in the Ozarks will have another “chunk” (cold front) of cold air coming in Monday night and perhaps a few weaker cool fronts after that in what will amount to a cooler but still mild pattern of weather for us and much of the southern U.S. next week.

North Atlantic Oscillation

There is an index which meteorologists follow (one of many) called the North Atlantic Oscillation (NAO).  It measures the difference in pressure between higher latitudes (closer to the north pole) and lower (closer to the equator).  When the index runs positive, it means that there an unusually large difference in pressure. Negative values indicate lower pressure differences.

If one analyzes the pressure over the northern Atlantic over a long period of time, it becomes clear that a so-called”semi permanent” low pressure area shows up near Iceland and it fact bears the name of that island nation “the Icelandic Low”.  But like so many long-term averages, there is often significant departure from year to year or season to season.

For the past two Decembers, the Icelandic low has taken a hiatus.  The NAO has been strongly negative meaning the low was weak or replaced by higher pressure.  This sent lots of cold air southward into the U.S. where it energised the storm track and provided enough cold air for snowstorms. Like this one in 2010 in the northeast and of course our major two snows last February on the 1st mostly affecting Missouri and on the 9th targeting northwest Arkansas and northeast Oklahoma. 

This December, the index has been strongly positive meaning a strong low which keeps the arctic air bottled up at higher latitudes.  It shows up to the north but doesn’t have a path directly into the central U.S.  As a result, the country has been mild in particular the northcentral U.S. which has been much above normal and setting temperature records.

There is every indication that this pattern will continue for much of January.  All patterns can and do break or shift, even temporarily, so we’ll keep watching for when that might happen.

Until then, mild and dry are the two weather words!

 

 

 

 

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