Saturday, August 31, 2013

North Atlantic Oscillation 2013-2014 Winter Forecast

This is the forecast for the North Atlantic Oscillation in the winter of 2013-2014 by The Weather Centre.

The North Atlantic Oscillation is an index known by a few, but unknowingly adored by snow lovers along the Eastern Seaboard. It can also be the source of fantasies for those in the Midwest. Regardless of where you live, chances are, when the term 'Nor'easter' comes up, it's due to the North Atlantic Oscillation.

The North Atlantic Oscillation (henceforth may be referred to as the NAO) is an atmospheric index that is determined by the pressure differences between a body of high pressure in the Atlantic and a body of low pressure over Greenland. The NAO has two phases- positive and negative. In the positive NAO, these two areas of different pressure are maximized, with the high pressure getting higher and the low pressure getting lower. The positive NAO results in warmer than normal temperatures for some in the Eastern US, and an unfavorable snow environment for many east of the Mississippi River. In the negative NAO, the low pressure over Greenland is weakened, sometimes to the point of where high pressure takes over that area. In similar fashion, low pressure over the Atlantic weakens, and the results for those in the United States are remarkable. The negative NAO sets up a pattern conducive for the formation of the 'Nor'easter' system that brings significant snow (and sometimes rain) to many in the Northeast US. The negative NAO can also bring snowstorms to the Midwest and Ohio Valley, but the negative phase is most renowned for its Nor'easter formation potential.

Now, I gathered two analog years in my Preliminary winter forecast I issued in June. I indicated my prime analog was the winter of 1962-1963. Since the release of that forecast, new data has strengthened the argument for 1962-1963 as being my top analog. Because this analog has been strengthened by new evidence, it remains my primary analog.

Shown above is a map of the mid level atmospheric flow in the winter of 1962-1963. Yellows and reds indicate high pressure, while blues and purples depict low pressure. We want to look towards Greenland at this point. When we find that land mass, we see an abnormally large area of high pressure in and just to the east of Greenland. If you recall in my explanation of the NAO, high pressure over Greenland indicates the formation of the negative NAO. Consequently, low pressure anomalies have developed over much of the Eastern and Central US. It is likely that, should my primary analog verify, the NAO would remain negative for the majority of the winter.

Despite the favorable analog positions, rather iffy sea surface temperatures and long range model forecasts tell me it will most likely not be extremely negative- a moderately negative NAO is more probable.

Here is my forecast for the North Atlantic Oscillation.



Anonymous said...

Andrew I live in Des Moines IA, do you see this winter resembling 2009-10 winter at all? That year we had above average snow and well below average temps.
Thanks for all your hard work!

Anonymous said...

What do you think about the NOAA winter forecast?

Andrew said...

Anonymous at 10:28: 09-10 is not currently one of my analog years, but cold and above normal snowfall could end up happening in the Des Moines area.

Anonymous at 1:28: I do not believe that is the NOAA's actual forecast; that appears to be the forecasting system the NOAA uses. Regardless, I don't agree with the temperature outlook right now- for what it's worth, I have never seen a long range NOAA outlook like the one on your link show below normal temperature anomalies in the last 3 or 4 years.

Robert brubaker said...

Whar was your criteria to take the winter of 1963 as basis? We know it was the coldest winter in the last 70 years at least.
The Atlantic tripole is in negative phase and the QBO is not sure to turn in easterlies at 40-50 hPa until the end of winter.
So, I think it is exagerated so speak about a very cold winter.

Best regards,
Robert B.

Rosco said...

Looks like any forecast of colder than average weather for winter 2013/14 in the continental US is proving to be justified and it is still only December.

Who is looking forward to February with anticipation ?