It's that time of year again weather fans!
Everyone from the National Oceanic and Atmospheric Administration to private forecasters to the almanacs are rolling out winter forecasts with much anticipation. Will the dreaded polar vortex return? Snowmageddon-the sequel? A blissfully mild El Niño driven winter?
Place your bets.
The MPR News Weather Lab is in the process of putting together my winter outlook for Minnesota, which I will post next week.
Just like last year at this time, the upcoming outlook for winter is presenting mixed signals. As you might expect, the resulting winter forecast outlooks are all over the map.
Heads or tails?
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Here's a little seasonal forecasting secret. Winter outlooks are usually barely better than the flip of a coin.
Last winter? Let's face it, nobody -- including me -- predicted the coldest winter in 35 years. One trend I did highlight a year ago that favored a colder winter last year was the extent of Siberian snow cover last fall.
October Siberian snow cover is the newest and sexiest emerging area of research as a potential predictor of winter weather in the northern hemisphere. The simplified theory goes something like this.
Extensive fall snow cover in Siberia produces higher pressure patterns near the surface.
This higher pressure, in turn, assists in generating a "surface-to-stratosphere wave activity flux event."
The connections with the stratosphere can drive the Arctic Oscillation into a negative phase.
Negative AO phases tend to produce more frequent Arctic outbreaks into the central and eastern U.S.
This October, Siberian snow cover is running at near record levels. MIT's Judah Cohen is one of the lead proponents of using Siberian snow cover as a winter forecast tool. Mashable's Andrew Freedman writes about the extensive Siberian snow and Cohen's latest interpretation.
The winter as a whole may be a cold and snowy one in the East and in parts of Europe, that is, if a rapid buildup of snow cover across Siberia is any indication. Judah Cohen, who is the director of seasonal forecasting at the private weather company AER, the extent and rate of expansion in Siberian snow cover during the month of October is a reliable indicator of winter weather thousands of miles downstream, in parts of North America and Europe.
This year, Cohen says, Siberian snow cover got off to its fastest start since he started tracking the index in 2000. “I think that’s something that’s notable,” Cohen said.
On the other hand, the National Oceanic and Atmospheric Administration (NOAA), relying on predictions of a weak El Nino event to develop during the winter, issued a winter outlook that calls for warmer-than-average conditions in parts of the eastern U.S.
Cohen called NOAA's reliance on the El Nino prediction to make its winter outlook "questionable," since the event is expected to be weak and may not have much influence on U.S. winter weather.
There is a split between Cohen's forecasting methods, along with the seasonal forecasts coming from other private companies, including The Weather Channel and AccuWeather, and the government's outlook.
If the AO trends negative again this winter, more extended polar vortex outbreaks could be in the cards.
El Niño or El No-ño?
The early money was on a developing El Niño and a milder than average winter for Minnesota and much of the northern U.S. But so-called warm El Nino/Southern Oscillation conditions have been halting, and slow to develop in the tropical Pacific this year.
That has changed slightly in recent weeks. Tropical sea surface temperature anomalies have been increasing. There's a lot more orange and red popping up in the equatorial Pacific maps.
Note the more consistent ribbon of recently developing positive sea surface temperature anomalies near the equator.
That may just be the start of the El Niño signal many have been looking for.
Forecasts still call for a 60 to 65 percent chance of a weak to moderate El Niño to develop in the next 60 days.
If El Niño develops as expected, it will be very interesting to see how winter circulation patterns in the northern hemisphere evolve.
Will El Niño produce a milder than average split flow jet stream over the U.S. this winter? Or will the near record Siberian snow cover trigger a negative phase AO circulation that could overwhelm the effects of a weak El Niño?