2013-'14 Early Winter Outlook
I know it's still July, but some people are already asking about what this winter might bring.
In light of the recent string of unseasonably cool conditions, it would be easy to assume that the colder than normal weather pattern would continue into the Fall and Winter months.
However, that isn't the opinion of the Climate Prediction Center (CPC).
CPC, a branch of NOAA that makes long-range statistical forecasts out to a year in advance is suggesting that we will see another warmer than average winter. Here's a look at their official prediction for the three month period starting in December 2013...
As you can see (denoted by the warm colors and the "A" for above average), they have us and most of the United States in an above average temperature outlook for this coming winter.
Normal temperatures for Louisville during the winter months typically means highs in the 40's and lows in the 20's.
At the same time, CPC is predicting near normal precipitation for our area with below normal precip forecated for the Southeastern US.
For reference, Louisville receives around 10 inches of rain and around a foot of snow on average each winter season.
The Climate Prediction Center uses a number of "indicators" when it comes to putting together it's long range forecasts.
These indicators include such things as the current state and forecated state of sea surface temperatures over the Eastern Equatorial Pacific (known as El Nino/La Nina), the tropical 30-60 day oscillation known as the Madden Julian Oscillation or the MJO, the North Atlantic Oscillation (NAO), the Pacific North Amercian Oscillation (PNO) and current climatological trends.
Among these indicators, the most important are the forecasted state of El Nino/La Nina and current climate trends.
El Nino/La Nina is a preferred indicator because it's predictability is higher than the other climate patterns and can be a very strong signal when either a strong El Nino or La Nina is present.
Currently, the Eastern Equatorial Pacific is experiencing cooler than normal sea surface temps (SST) off the coast of South America on the order of a degree or two below average.
These cooler than normal temps signal that we have entered a weak La Nina period.
We know that historically strong La Ninas produce significantly colder than normal winters across the Ohio Valley and much of the Eastern US.
CPC is showing that come winter, SST's in the Eastern Pacific will likely be near normal indicating neutral conditions.
In the case of a Neutral El Nino/La Nina, then we have little to go on outside of current climate trends and because of the gradual warming that has been taking place over the last few decades, this becomes the key ingredient to the CPC outlooks, which explains their warmer than normal forecast for us this winter.
So what do I think?
Personally, I don't like to forecast anything beyond about 7 or 10 days out simply because our weather models essentially become useless after that and without some sort of strong climate signal to work with (such as a strong El Nino or La Nina) there is very little predictability other than trends... and if there is one thing I know about trends is that they are always trending!
However, with that being said, there is one thing to watch for once we start getting a little closer to the cold season. That is the recent trend of "blocking patterns" in the jet stream.
These blocking patterns have been responsible for several cold outbreaks over the Eastern US since late last year. (Remember, the path of Sandy was the result of a blocking pattern back in the fall.)
A typical blocking pattern over the North Atlantic (sometimes called a Greenland Block) is caused by a break down in the northern branch of the jet stream.
As the jet breaks down, an upper ridge of high pressure anchors itself over the region forcing arctic airmasses to invade the Eastern US.
These blocking patterns can be predicted up to a couple weeks in advance using the NAO or North Atlantic Oscillation as an indicator.
Already, some of the long range climate models are hinting that blocking over the North Atlantic may indeed be a major factor in this upcoming winter.
The latest run of the CFSv2 seasonal climate model ran by CPC is now showing a substantial below normal temperature anomaly over the Eastern US.
This has my attention and is something I will watch closely over the months to come.
WDRB Meteorologist Jeremy Kappell
Email me at firstname.lastname@example.org