Sunday, February 20, 2011

Long Range Outlook

Brief Summary:

La Nina will continue to weaken heading into spring. NAO (North Atlantic Oscillation) will generally remain neutral or positive. Although we will see a brief cool down for the start of March, temperatures will remain roughly near or above average. Precipitation will stay near or below average. The chances for a significant snow (over 6") look slim to none.

Digging into the data (technical):

Meteorological winter is about to end (December through February), so it is now time to look at the overall pattern heading into spring. Earlier this winter, we had a strong La Nina, which typically brings mild and dry weather to our region. However, we experienced a strong -NAO (North Atlantic Oscillation), which is when a strong ridge in the jet stream persists over western Greenland and eastern Canada. This brought us cold and snowy weather for December and early January. This ridge eroded in late January, and we have been mild and dry ever since.

La Nina is starting to quickly weaken. In fact, we could be in neutral conditions by May or June. This is a plot of sea surface temperatures, which shows that Nina still exists, but it isn't as strong as earlier this winter. In addition, what you can't see is the water below, which is starting to warm.

Past La Ninas have brought us slightly cooler and wetter weather for March through May. However, this might not be the case this year because La Nina is weakening.

Here is a plot of NAO, which shows negative conditions early in the winter, and then neutral/positive conditions ever since mid January.

There are indications that NAO could turn slightly negative in early March, which would typically get any snow-lover excited. However, the ridge is too far east. I've posted the long range outlook for the upper-level atmosphere (first map), and temperatures for the lower atmosphere (second map). Notice on the first map how the ridge, indicated by the yellow blob, is located east of Greenland. Although this could bring us slightly below average temperatures, it is not in an ideal location for significant snow. Average highs for early March are in the mid 50s and average lows are in the mid 30s. We should generally stay near these numbers for early March. Of course, there will be some fluctuations.

Obviously, there could be some changes to the forecast, however, this isn't looking good for snow-lovers.


Anonymous said...

Aaron great post on the summary. I think many people need to realize the NAO which you summed up really well. Also great point about how La-Nina is weakening, so that even though we may see slightly colder, we get less precip. Thats the key point. Also, Thunderstorm season will be interesting. Also great summary.

Anonymous said...

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Anonymous said...

Keep up the great work CBS6 stormteam