>> Friday, November 16, 2012
Well, there were lots of disappointed snow fans across the Southeast last Winter, but a new Winter approaching brings new hope of the white stuff for snow lovers around the region.
Let's delve into a few factors..... first of all, the ENSO cycle.
Conditions through the Winter will likely be ENSO neutral, as the El Nino many expected has simply failed to materialize. You can see on the charts below that most modeling takes values to neutral or even negative by Spring.
IRI/ CPC modeling:
The NAO might be the single biggest influencing factor in the temperature regime around here. There is no magic bullet, but the NAO definitely plays a huge role. Last year, a mainly +NAO led to a warm Winter overall in our part of the country. The previous Winter, the NAO remained in the negative state for much for the time, equating to an overall cold Winter.
What about this Winter? Well, over the past several months, the NAO has tended to be negative more often that not. I also like to look at how the NAO and AO behave during the month of October. You will notice that this October, we had a -NAO for much for the month.
This can make or break a Winter Outlook, but my thinking at the moment is that we will continue to tend to see a -NAO through the Winter, more often than not. If that is the case, that will mean ridging and blocking around Greenland, colder temps in the eastern US, and a more favorable setup for Winter weather-producing storm systems.
Much the same as the NAO, you will notice we had a -AO for much of October. If a -AO, there is arctic air readily available to be tapped into the eastern US.
Let me state that again.... an incorrect forecast for the NAO/ AO stage can quickly bust a Winter Forecast....that is what happened to mine last year. So, this is a very important factor.
Finding some ENSO analog years.....these are the 4 main Winters a looked at in terms of analogs.
Below is the temp anomaly and precip anomaly maps for each of those Winters.
There are other considerations as well, such as the PDO, the QBO, and the solar cycle among others, but I won't spend any time here discussing those. But those factors were considered as well.
One big item this forecast hinges on is the idea that the overall blocking tendency the atmosphere has shown recently will continue to some extent through the Winter. That is one baseline of the forecast. Another key component is the NAO to trend negative, at least at times.
With that in mind, for the Southeast US, I will go for a near to slightly below average temperature trend for the Winter as a whole. I will go with slightly above average precipitation for a good chunk of the Southeast.
Remember, the temperature portion of the forecast is December through January.
As for snow, remember the snowfall portion of the Winter forecast is first flake to last flake, regardless of month. Many mountain areas have already seen some good snow amounts for this time of the season.
So, the general idea is above normal snowfall for the mountain areas from NC on northward. I will go with near average snow for the foothills and the Piedmont of NC into the Upstate of SC and north Georgia and the Tennessee Valley. See the map below.