Winter Outlook 2011-’12: “Wild cards” may decide snow & cold

Autumn leaves are falling and November is right around the corner.

The seasonal reality is, winter is almost here in Minnesota. The 3 coldest months of the year, otherwise known as "Meteorological winter" are December through February.

Several winter forecasts are out. Some of the "Almanacs" and major forecast firms are blaring headlines of "brutal cold and snow" and other wintery weather fare for the Upper Midwest this year.

So, what can we really expect this winter in Minnesota and the Upper Midwest? What factors and variables will determine the seasonal forecast? Which way do they lean? And how reliable can seasonal forecasts be anyway?

So here we go. The MPR Huttner Weather Lab Winter Outlook lies below.

Full disclosure: I'm not a seasonal forecast specialist! I'm a broadcast and synoptic meteorologist (short term forecaster) by training and experience. My winter outlook is purely for entertainment and discussion, and maybe a little bit of fun. Use it accordingly!

Let's review: Winter of 2010-'11:

Simply put, Minnesota got smoked last winter!

Some highlights from 2010-'11 include:

-Dec through Feb temps about -1.8 degrees vs. average

-4th snowiest winter on record with 86.6" season snowfall

-Snowiest winter at MSP in 27 years (98.6" in 1983-'84)

-5th and 15th biggest snowfall events in MSP history last winter

-The "Domebuster" Metrodome collapse- this had to be the symbol of the winter of 2010-11 in Minnesota

-Major "snowmageddon" type blizzards from Minnesota to Chicago and the east coast

La Nina to blame?

Most forecasters and weather observers credibly point to last winter's strong La Nina episode as the culprit for the intense winter last year. Another factor that is gaining credibility is increased Siberian snow cover in the fall of 2010, which some cite as contributing to more frequent cold out breaks in the northern USA in winter.

Whatever the reason, last winter was one for the books... by some measures the most severe winter in Minnesota in decades.

Seasonal Forecasting: The variables

Seasonal weather forecasting has come a long way in the past few decades. There are hundreds of dedicated, brilliant researchers who have spent careers developing and refining techniques which have improved statistical accuracy in seasonal forecast well beyond the proverbial "coin toss."

Still, seasonal forecasting can be dicey to say the least. There are certain atmospheric and oceanic "signals" (like ENSO phases) that can be reliable indicators of jet stream and weather patterns months in advance. Yet, those signals may be reliable only part of the time, for certain seasons and for certain parts of the globe.

2011-'12 Outlook: "Wild Cards" at play

Let's look at the major variables that go into this winter's outlook, how reliable they are, and how they may tend to affect Minnesota's winter weather.

ENSO Cycles: El Nino & La Nina

They get all the headlines, and they have the muscle to shift jet streams and drive weather patterns around the globe.

Last year's strong La Nina episode delivered on promises of extreme winter weather.

This year La Nina is back for an encore in the tropical Pacific. But all La Nina's are not created equal. This winter's event is not predicted to be as strong as last year's "uber La Nina."

Here are the details from NOAA's Climate Prediction Center. (CPC)

"Currently, La Niña is not as strong as it was in September 2010. Roughly one- half of the models predict La Niña to strengthen during the Northern Hemisphere fall and winter (Fig. 6). Of these models, the majority predict a weak La Niña (3-month average in the Nino-3.4 region less than -0.9°C). In addition, a weaker second La Niña winter has occurred in three of the five multi-year La Niñas in the historical SST record since 1950. However, the NCEP Climate Forecast System (CFS.v1) predicts a moderate-strength La Niña this winter (between -1.0°C to -1.4°C) and CFS.v2 predicts a strong La Niña (less than -1.5°C), which rivals last year's peak strength. For CFS forecasts made at this time of year, the average error for December-February is roughly ±0.5°C, so there is uncertainty as to whether this amplitude will be achieved. Thus, at this time, a weak or moderate strength La Niña is most likely during the Northern Hemisphere winter."

Variable: Weak to moderate La Nina

Potential effect in Minnesota winter: Colder & snowier than average

Wild card: Not as strong as last year's La Nina and may produce different atmospheric circulation effects

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Siberian Snow Cover in Autumn: A developing diagnostic tool?

One emerging and "sexy" tool for forecasting winter weather in the USA is anomalies in Siberian snow cover in September and October. The evidence and theory goes like this; Above average snowfal in Siberia in autumn causes shifts in the polar vortex. This can mean warmer than average conditions in the Arctic, and more frequent cold air outbreaks in the northern USA as the cold is displaced southward during winter.

So far in 2011, snow cover has been running near or below average over much of Siberia, especially in western Siberia. The past week has brought significant snow to Sibera, so Siberian snow pack has increased in recent days.

The bottm line? While snow cover is increasing, there seems to be no clear signal that snow cover has been above average in Siberia this fall.

Variable: Average Siberian snow cover this fall

Potential effect on Minnesota winter: Colder and snowier if Siberian snow cover is above average

Trend for 2011-'12: No clear signal for the northern USA

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The Oscillations: NAO, PDO & AO

Seasonal forecasters keep track of multiple regional atmospheric "oscillations" around the globe. These shifts in temperatures and pressure systems around the earth can signal trends for seasonal forecasts.

The Arctic Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation each represent different regions and time scales as the names suggest.

NOAA's winter outlook specifically cites the Arctic Oscillation as a major "wild card" in this winter's outlook.

"For the second winter in a row, La Niña will influence weather patterns across the country, but as usual, it's not the only climate factor at play. The 'wild card' is the lesser-known and less predictable Arctic Oscillation that could produce dramatic short-term swings in temperatures this winter.

"The evolving La Niña will shape this winter," said Mike Halpert, deputy director of NOAA's Climate Prediction Center. "There is a wild card, though. The erratic Arctic Oscillation can generate strong shifts in the climate patterns that could overwhelm or amplify La Niña's typical impacts."

The Arctic Oscillation is always present and fluctuates between positive and negative phases. The negative phase of the Arctic Oscillation pushes cold air into the U.S. from Canada. The Arctic Oscillation went strongly negative at times the last two winters, causing outbreaks of cold and snowy conditions in the U.S. such as the "Snowmaggedon" storm of 2009. Strong Arctic Oscillation episodes typically last a few weeks and are difficult to predict more than one to two weeks in advance."

The Pacific Decadal Oscillation (PDO) tracks shifts in temperature patterns in the North Pacific Ocean. PDO has a warm and cool phase which can affect USA weather. The PDO is much longer term, with phases that can last 20 to 30 years.

PDO is currently negative, which means cooler water along the Pacific Northwest. This can mean an active jet stream, and frequent storms in the northern USA.

The NAO tracks the strength and positions of pressure systems along Iceland and the Azores. If the NAO becomes negative, the United States could experience more troughs (Arctic outbreaks) in the eastern USA. Last year, the NAO went negative several times.

The North Atlantic Oscillation, (NAO) is more complicated because it is temporary and can only be predicted in a couple of weeks. The NAO may be the biggest game changer this winter.

Variables: NAO, AO & PDO

Potential effect on Minnesota winter: Negative phases of AO, NAO & PDO can cause arctic outbreaks.

Trend for 2011-'12: No definitive signal at this time

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Decadal Trends: Our changing winter climate?

Juxtaposed over the technical and dynamic factors that may control winter weather are so called decadal trends, which lean strongly in favor of milder winters with less snowfall for Minnesota.

Some facts from the past decade include:

-7 of the past 10 winters have featured significantly below average snowfall in the metro, (70% bias toward less than average snow in the past 10 years)

-In those years the average winter snowfall has been 33.6"

(Roughly 22" below the 30 year average of 55.9"!)

-6 of the past 10 winters have featured above average temperatures

(60% bias toward milder than average winters the past 10 years)

-Minnesota winter nights got a lot milder in the past 30 years! (1981-2010 data set) Overnight low (minimum) temperatures in January average a full 2 to 4 degrees F warmer than the previous 30 year (1971-2000) data set.

The bottom line is, winters are trending milder in Minnesota, and while averages are made up of extremes on both ends, you can't ignore the background trend when looking at the potential for two colder and snowier than average winters in a row.

Variable: Decadal trends in winter temps and snowfall in Minnesota

Potential effect on Minnesota winter: Milder winters temps (especially at night) and a apparent bias toward lower winter snowfall totals.

Trend for 2011-'12: Increased odds for a milder winter with less snow than 2010-'11

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Trends toward average:

Okay, so this is not a strong scientific principle, but there may be a kernel of truth here. While we could have two colder than average "snowmageedon" winters in a row, "averages" might suggest otherwise.

-MSP recorded 86.6" of snow last winter

-There has never been back to back 80" snowfall winters on record at MSP

-Weather often tends to move to the other extreme or back toward average after one extreme is reached

Variable: Weather trends toward the average over time

Potential effect on Minnesota winter: Trend back toward average

Trend for 2011-'12: Tendency for closer to average temps & snowfall this winter

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Wolly Bear Factor: Weather Lab consensus = milder winter!

Okay this is totally unscientific and it's all folklore fun. Both my observations of Woolly Bears this fall and my conversations with other observers show a consensus that there's far more brown on the Woolly Bears than last year!

Weather folklore says that means a milder winter. Most experts seem to agree that there's no credible science behind the Woolly Bear Winter Forecast, but it's fun to think about. Can the mighty Woolly outforecast NOAA's & Accuweather's in Minnesota this winter?

Place your bets!

Bottom Line: Huttner Weather Lab Winter Outlook 2011'-12

Okay here we go....gulp!

Like every good weather forecast, this one a combination of science, art, common sense and "feel." (and hopefully dumb luck!)

Winter Outlook Dec 2011 through February 2012 (for MSP Airport location)

Temperatures: Near Average (+ or - 1 degree overall)

Here's my thinking on temps. This year's la Nina is not likely to produce the same sustained jet stream patterns as last winter. I agree with NOAA that there is likely to be a high degree of variability in temperature swings this winter. Overall my guess is that we'll have one cold month, one mild month and one near average.

Snowfall: Season snowfall total 50" to 60" at MSP Airport

Yes it's a 10" forecast range, but we actually saw that much variability on single storms in the metro last season! My thinking here is that we may see more numerous Alberta Clipper like systems than last year that dump 1"- 3" type snows.

I also think we'll get another big storm or two this year that could produce some 12" snowfall totals close to home, but it's unlikely that we'll see two of the top 15 heaviest snowfall events in MSP history again in the same winter. That really boosted our totals last year.

Overall I see snowfall as being somewhere near our average season snowfall of 55" in the metro. If anything, the surprise may be we end up on the low side again this year as we have 6 of the past 7 winters.

Possible highlights and notable events:

-Wild temperature swings this winter from extreme cold to mild in just a few days

-Shifting and volatile jet stream patterns bringing frequent weather changes

-One or two major arctic outbreaks with -40 in northern MN and -20 in the south

-One or two major "thaws" this winter

-Possible "bare ground" at some point in winter after a major thaw?

Major hope...an early spring next year!

So what do you think?

Place your bets in the comments, and let me hear your snowfall predictions for MSP this winter. Let's see if our MPR "snowfall forecast consensus" can beat the pros.

Stay warm and enjoy all the vigor and beauty that a Minnesota winter has to offer this year!

PH