A “FRONT-LOADED” WINTER SO FAR
We’ve seen a lot of ups and downs during the first two months of “Meteorological Winter” (December & January). In my winter forecast, I had predicted that December would be the coldest and snowiest month of the winter compared to normal. As it turned out, the last week of December and the first week of January were not only cold. That period was also one of the coldest such periods on record.
Since the brutal cold overlapped two months, neither one will look especially cold in the future. December only ended up about 1.4 degrees below normal. And January has only been less than 2 degrees below normal, with an unseasonably mild week coming to end the month. We call early cold and snow, followed by mild weather as a “front-loaded” winter. The big questions are the following. Will the severe winter weather return in February and/or March? Will there be a consistently severe pattern during that time?”
SIGNS OF PATTERN CHANGE
There are many things we look at to try to predict general weather patterns a month or more ahead of time (no one can make specific day-to-day forecasts with any accuracy beyond a couple of weeks). These indicators include what is going on in the Atlantic and Pacific Oceans, the Arctic, Siberia and Eurasia on the other side of the world, and even in the stratosphere (the layer above the one we usually talk about, where the “weather” happens). There are many acronyms, such as ENSO, NAO, AO, PNA, EPO, MJO, and more that we look at. I’ll try to simplify it a bit.
The most significant things this winter seems to have been the PNA, EPO, and MJO. We have talked a lot about the AO (Arctic Oscillation) and NAO (North Atlantic Oscillation) in previous winters, but neither has been a significant factor so far this winter.
On the other hand, the PNA (Pacific-North American Oscillation), combined with the EPO (East Pacific Oscillation), and the MJO (Madden-Julian Oscillation) were directly related to our super-cold two week blast. You can get the details and see the maps on other “weather weenie” sites.
THE MJO (MADDEN-JULIAN OSCILLATION)
There are a few good sites that explain the MJO, and you’re free to Google them, but you are hereby warned: this is really complicated and scientific stuff.
Here’s the bottom line: the MJO goes through phases 1-8, and they tend to relate to weather patterns around the world. The U.S. effects are below:
It is no surprise that the MJO was in the colder phases 8, 1, and 2 during our extreme cold spell in late December/early January. We have been in the warmer phases 4 and 5 recently. So, we’re heading toward another round of cold. But how cold? We look at other indices for that.
THE PNA (PACIFIC-NORTH AMERICAN OSCILLATION)
This is a blocking pattern that is very important in setting up Arctic air invasions deep into the U.S. Here is a map showing average January temperatures when the PNA is considered “POSITIVE”:
Notice the extreme warmth compared to normal in Alaska and Western Canada. And now look at the actual map of temperatures compared to normal for our “super-cold” two week period:
That’s a pretty close correlation. It makes you want to look for forecasts of a +PNA.
THE EPO (EAST PACIFIC OSCILLATION)
The EPO was a significant driving force during the super-cold blast that ended around January 7th. It’s crucial to see how it will change during the rest of winter.
While a +PNA favors cold around here, a +EPO favors the opposite:
The +EPO favors warm air in Canada and much of the U.S., and colder than normal air in Alaska. So a –EPO would favor the opposite.
I’ve talked about the European model many times-it’s the proven best in the world overall. And using “ensembles” of the European (running the model 51 times under slightly different conditions) is even better for longer range forecasting. I call it “The Best of the Best”. Here is what the BOB shows:
(Charts courtesy of weathermodels.com and Ryan Maue)
The EPO clearly goes negative in early February, and if the model is right, it stays negative even into March! The green line is the average, and the gray areas represent reasonable possibilities. So, there’s no guarantee of a –EPO, but it sure looks likely.
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The same model as above, only with a different oscillation. This time, the PNA is predicted to be near neutral for the first half of February, and then it gets more positive. The gray shows a close call until Feb. 16th.
THE BOTTOM LINE
Between the coming phase of the MJO and the clearly –EPO, it sure makes sense to predict a return to significant cold in February-possibly lasting into March. But the PNA is borderline, and that is what makes it far from a sure bet. Plus it’s still not clear just HOW COLD it will get around here.
We’re not talking about a couple of bitter cold days here. If the PNA goes positive, it could be a sustained cold pattern moving in. Stay tuned.