It is finally time for the 2014-2015 winter outlook to be released. Remember, as with all seasonal forecasts, confidence is low and nothing is etched in stone so to speak. Below, I will go into more detail as to the factors that are pointing me in the direction of the final forecast. I’ll try to keep it as non-geek friendly as possible but there are some parts that will be a little technical.
One important factor in determining what conditions any given winter will bring is something called the El Nino Southern Oscillation which refers to the temperature of the water off of the Pacific coast of South America. When this area of the ocean heats up more than normal, an El-Nino event takes place. When this area doesnt heat up as much, a La-Nina event takes place. A weak to moderate El-Nino event is nearly unanimously agreed upon by the models for this winter.
Here are the model forecasts for SST anomalies off of South America (SST anomalies are how much warmer or colder the water temps are compared to average).
El-Nino usually means warmer than average temps and less than normal precip over the Northern US and Cooler and wetter than normal conditions over the Southern US. Keep in mind however that warmer than normal temps doesn’t mean we will be basking in 50’s all winter long. The average temperature for the months of December, January, and February in Portland is 25.5F. Even a temperature of 25.6F would be above average. Same goes for snowfall. The point is just because it will be a warmer than average or drier than average doesn’t mean that there won’t be cold outbreaks or big snows.
North Pacific SST’s
While El-Nino a very important factor in determining winter conditions, it is certainly not the only one. The record cold and snow of last winter was caused in part by warm SST’s in the North Atlantic which caused ridging over Alaska and subsequently pushed cold air into the Eastern US.
Here are the SST anomalies for October 2-9th 2013. Notice the pool of warm water in the North Pacific east of Japan. This pool of warm water moved slowly east and spent most of the winter sitting off Alaska. This winter, a similar setup is underway except the warm pool is already firmly parked off of Alaska and is much greater in size and strength.
SST anomalies from October 8-15th 2014. Notice the expansive area of warmer-than-normal SST’s near Alaska. I see this as a big red flag that supports cold outbreaks this upcoming winter.
Current Snow Growth
Believe it or not, it is already snowing hard across the high latitudes of the Northern Hemisphere. Lets take a look at the snow growth this year compared to years past.
These maps represent October snow cover over the last six years. Notice that we are WAY ahead of schedule this year. Compare that to years past and notice that last year’s snowy winter was preceded by similar snow growth over the Northern Hemisphere. The warm and not snowy winter of 2011-2012 was preceded by well below normal snow growth.
Here is the snow growth anomaly for 10-17-14 (the latest image available). Notice the above normal snow growth over Siberia and west-central Canada and below normal snow growth over Alaska. Also important to note is the below normal snow growth on either side of Greenland (Greenland isn’t shown because, for now, there is still snow there all year round). This pattern, along with the SST anomalies we talked about earlier favor western ridging like last year and a blocking high over Greenland (What prevented last winter from being even snowier was the quick storm motion caused by lack of blocking). The setup outlined here does in fact favor a snowy winter for New England.
I want to end with the official forecast from NOAA’s Climate Prediction Center. I agree with them for the most part however I think they are basing their forecast too much off of El-Nino. While at least a weak El-Nino looks likely now, remember, it wasn’t too long ago when forecasts called for a ‘Super El-Nino’ to develop this winter.
Based off of the information I have presented above, I think that we will see a near normal winter in terms of temperature – El-Nino should keep the bitter cold mostly in Canada – and a slightly above average winter in terms of snowfall. The CPC outlined their concern for an active Atlantic storm track in their precip outlook and I wholeheartedly agree. While I doubt this winter will be a record-setting one for our area for cold temps, I equally doubt its potential to be warm and snowless.
The active Atlantic storm track and the blocking pattern is already kicking into high gear with a nor’easter on tap for most of this upcoming week. I’ll try to get an update out tonight but if not, count on it tomorrow morning.