Winter Outlook 2012-’13: Unprecedented “El Nino mystery” complicates forecast

Winter 2012-'13 Outlook Headlines:

"This year is totally unique in the 63 years we've been keeping statistics on El Niño. Never before has an El Niño event begun to form in July and August, then quit in mid-September."

-NOAA's Mike Halpert on the unprecedented onset and demise of El Nino in 2012.

El Nino head fake unprecedented "false start" El Nino faded, but regenerating?

Few clear atmospheric trends to shape upcoming winter outlook

Few "oscillation" clues AO, NAO, PDO trends offer little guidance, but recent "blocking patterns" may persist

Condition "neutral" Siberian snow cover near average this fall

Uncharted waters What role will record loss of Arctic Sea ice in 2012 play this winter?

Warmer background hum Decadal trends support warmer winters in Minnesota, especially at night

Wildly variable season snowfall totals in the Twin Cities in the past decade

Weather Lab Winter Outlook 2012-'13: Few clues to hang your hat on

Welcome to November!

The 5 months that can qualify for "winter" in Minnesota are here. Lately it seems our "Forrest Gump" weather patterns in Minnesota are like a "box of chocolates."

You never know what you're going to get.

At this point the view of winter from the weather lab confirms that notion.

I had hoped to get this outlook out last week, but honestly the intense workload from hurricane Sandy got in the way. I was kind of hoping the delay would reveal some more atmospheric clues as to upcoming winter weather patterns. It didn't...except for one possibility.

As always, remember a few things about seasonal forecasts, and use this outlook with caution & amusement.

-I'm not a seasonal weather forecast expert.

-Seasonal weather forecasts rely on clear atmospheric signals, and there are few this winter for the Upper Midwest.

-Seasonal weather forecasts are often barley better than the flip of a coin overall.

-Forecasts leading into last winter were perhaps the most off the mark ever

"For entertainment purposes only" might be the best way to view this winter's outlook. Given the lack of clear atmospheric signals as we turn the corner into winter, my confidence is relatively low at this point as to what winter will bring.

Still it's fascinating to watch these trends unfold, and to discuss them in some level of detail.

So with the preamble and disclaimers complete, here's a bare bones look at the Weather Lab Winter Outlook for 2012-'13.

Key seasonal factors for Winter of 2012-'13:

1) El Nino: Unprecedented "head fake"

It seems the word "unprecedented" is best to describe the wild swings and unusual weather pattern we're seeing in Minnesota the past few years.

That applies to the on again-off again "attempted" El Nino late this summer and fall.

Never before has an El Nino begun to form in the tropical Pacific, and then shut down in the fall.

NOAA elaborates in their Winter Outlook.

"This is one of the most challenging outlooks we've produced in recent years because El Niño decided not to show up as expected," said Mike Halpert, deputy director of NOAA's Climate Prediction Center. "In fact, it stalled out last month, leaving neutral conditions in place in the tropical Pacific."

El Nino winters show about a 70% statistical bias toward milder winters in Minnesota. Without El Nino, the landscape of temperatures in Minnesota this winter is more unclear.

Still the last week seems to have shown some signs of anomalous warming in the tropical Pacific. The latest weekely SST anomalies show a growing area of +0.5C to +1.0C in the tropical pacific.

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Is it just a warm blip that will again disappear? Or is it the start of what may be a "better late than never" El Nino event this winter?

Only time will tell.

At this point I'd say there's still at least 60% chance that some level of El Nino (Pacific SST's +0.5 or greater) may develop this winter. I am still favoring the development of El Nino conditions this winter.

Trend: Favors developing El Nino & milder winter vs. average temps overall

The Oscillations: Little help, but "blocking patterns" may persist

Meet the "oscillations." There's the Arctic Oscillation (AO) the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO) to name a few.

As their names imply, all live in different areas of the northern hemisphere, and operate on different time scales.

We've learned a lot about weather patterns driven by these oscillations over the past few decades, but there's still much more we don't know about these atmospheric "teleconnections."

The AO can be the dominant force in winter weather in the USA & Europe.

The last 2 winters have seen dramatic swings in the phase and magnitude of the AO.

Last winter's AO & NAO were strongly positive. The result? The 4th mildest winter on record and a scant 22.3" season snwofall.

The previous winter saw just the opposite. A strongly negative AO presided over temps -3F as MSP got buried under 86.6" of snowfall...the 4th snowiest winter on record.

In October the AO trended negative, and produced the first colder than average month in Minnesota since May 2011.

A negative AO tends to produce the type of 'blocking patterns" we say with Hurricane Sandy's unprecedented track. That can mean big north-south undulations in the jet stream that can bring alternating warm and cold snaps for Minnesota...and the potential for some big snow storms if enough cold air is present.

Unfortunately we can't forecast the AO more than about 2 weeks out. Current forecast trend more positive as we head into November. But overall there have been a lot of changes in AO phase this year.

I am leaning toward that trend continuing, a trend and I think that has the potential to produce significantly more snowfall that last winter's "stuck" positive AO phase.

Trend: Changeable AO/NAO this winter. Periodic negative phases will favor a few arctic more outbreaks and a few bigger snow storms in the Upper Midwest. Overall trend favors more snowfall than last winter.

Siberian Snow Cover: No clues

Lately some climate watchers have locked onto trends in Siberian snow cover in the fall as a clue to the upcoming winter forecast in the USA & Europe. The theory goes, if there's above average snowfall & snow cover in Siberia in fall, look out for a harsh winter in the USA.

This fall, snow cover in Siberia has run pretty close to average... give or take.

There has been a slight positive trend in snow cover over northwest & central Canada this fall, which has me a little concerned (hopeful?) that a jet stream may want to develop over the Rockies early this winter and speed into Minnesota.

If that SW-NE oriented jet sets up, we could see more frequent rain/snow systems aiming at Minnesota in the next 60 days.

The rain would be a great thing for soils before freeze up. The snow could get us an early start on winter snowfall totals.

Overall snowfall trends don't seem to point to a clear direction for the upcoming winter.

Trend: Near average Siberian snow cover this fall gives few clues to USA winter. Slightly positive snow cover in Canada may favor wetter pattern (rain or snow) in November & December for Upper Midwest?

Uncharted (Arctic) Waters: How will record Arctic Sea ice loss in 2012 play out?

We've just witnessed another unprecedented event in the Arctic in 2012. The record low in Arctic Sea ice peaked in September.

We've lost a full 70% of ASI volume since satellite observations began in 1979.

As I pointed out earlier today with Hurricane Sandy, there are some studies suggesting that a warmer Arctic makes blocking patterns more frequent.

This may allow more frequent dips in the jet stream over North America and the USA thus winter...and that may mean more arctic outbreaks than last year.

WxUnderground's Jeff Masters elaborates.

Francis et al. (2009) found that during 1979 - 2006, years that had unusually low summertime Arctic sea ice had a 10 - 20% reduction in the temperature difference between the Equator and North Pole. This resulted in a weaker jet stream with slower winds that lasted a full six months, through fall and winter. The weaker jet caused a weaker Aleutian Low and Icelandic Low during the winter, resulting in a more negative Arctic Oscillation (AO), allowing cold air to spill out of the Arctic and into Europe and the Eastern U.S.

Thus, summers with high Arctic sea ice loss may increase the odds of cold, snowy winters in Europe and the Eastern U.S. In my April 2, 2012 blog post, Arctic sea ice loss tied to unusual jet stream patterns, I discuss three additional research papers published in 2012 that argue for a major impact of Arctic sea ice loss on Northern Hemisphere weather in fall and winter, with sea ice loss causing an increase in the probability of negative-AO winters.

Trend: Record low Arctic Sea ice this summer may lead to more frequent cold air intrusions into the Midwest this winter compared to last winter.

Solar cycle peak: favoring a more positive AO?

This one may have a smaller impact that many other factors, but I found it interesting that the coming peak in Solar Cycle 24 may play a role in favoring a more postitve AO.

Again Jeff Masters expoundes:

Another major influence on the AO and winter circulation patterns may be the 11-year solar cycle. Recent satellite measurements of ultraviolet light changes due to the 11-year sunspot cycle show that these variations are larger than was previously thought, and may have major impacts on winter circulation patterns. A climate model study published in Nature Geosciences by Ineson et al. (2011) concluded that during the minimum of the 11-year sunspot cycle, the sharp drop in UV light can drive a strongly negative AO pattern, resulting in "cold winters in northern Europe and the United States, and mild winters over southern Europe and Canada, with little direct change in globally averaged temperature."

The winters of 2009 - 2010 and 2010 - 2011 both occurred during a minimum in the 11-year sunspot cycle and fit this pattern, with strongly negative AO conditions leading to cold and snowy winters in northern Europe and the Eastern U.S. There was more solar activity during the winter of 2011 - 2012, which may have contributed to the fact that AO conditions reversed, ending up positive. The coming winter of 2012 - 2013 will have even more solar activity than last winter (Figure 3), potentially increasing the odds of a warm, positive-AO winter in northern Europe and the United States.

Trend: Coming peak of Solar Cycle 24 may favor more positive AO and a potentially milder winter.

Background Hum: Decadal trends favor warmer winter in Minnesota.

Behind all the short term and seasonal trends and fluctuations are distinct, decades long trends toward milder winters in Minnesota. Think of it as the elevator "Muzak" paying in the background of all the seasonal "teleconnections" plates spinning in the air.

The latest set of 30-year averages that came out last year shows Minnesota winters are now 2F to 4F warmer. than just a few decades ago.

The biggest temp increases are at night, in winter.

Last winter's record warmth continued this trend.

Our warming climate is a bigger picture factor that seems to buck, and even trump all other factors that want to produce a colder than average winter.

Recent data shows Minnesota is the 3rd fastest warming state in the USA, and that warming has accelerated since 1970.

Trend: Decadal trend of warming in the Upper Midwest favors milder than average winters.

Weather Lab Winter Outlook 2012-'13: The specifics

I agree with NOAA that this will be one of the most difficult winter seasons in recent memory to forecast. There just isn't any clear, distinct trend or piece of data to hang your weather hat on this winter.

Based on everything I'm looking at this fall, longer term trends, current atmospheric teleconnections and the law of averages...I think the hopefully obvious safe play is to forecast more snow and cold than the 4th warmest winter on record in Minnesota last year, but probably not the 86.6" "blitz" we saw in 2010-'11.

Yes, there's a hole as big as a Mack Truck to drive through between the extremes of the past 2 winters in Minnesota. We'll probably end up somewhere in that gaping hole.

Still I can't help but think we may be in for some surprises this winter. Why should this winter be any different in producing the gamut of "unprecedented" swings we've seen the past few years.

Confidence is not high this winter...but here's my best crack at the winter of 2012'-13 for the Twin Cities & beyond.

Overall trends:

I expect bigger week to week and month to month fluctuations this winter compared to last winter in both temperature and snowfall.

Snowfalls and cold arctic outbreaks will likely be punctuated by milder weeks that may eat away at snow cover this winter.

The overall character of this winter should be colder and snowier than last year.

Temperature: (December-February) Milder than average

Overall I am leaning toward a winter that's still warmer than average, but noticeably colder than last winter.

MSP & most of Minnesota +1F to +3F (December through February)

I also think we'll many more sub-zero night that last winter's paltry 3...but far fewer than the longer term average of 39. At this point I'd lean toward 10 to 15 nights below zero in the metro this winter.

Snowfall: (Total season snowfall) Near average

40" to 50" for the Twin Cities metro area.

If you have to pin me down on a number...I'll pick 42.5" for MSP Airport.

I think there will be enough cold air to generate higher snowfall totals in northern Minnesota this winter. I could see some 50" to 70" totals up north.

The long term average season snowfall for the metro dating back 125 years is 45.6".

Again, confidence is not high this winter. The biggest thing I'll be watching the next few weeks is the possible development of El Nino in the Pacific. If a full blown El Nino does develop, it will increase my confidence in another milder than average winter this year.

The other factor is the extent of late November & early December snowfall and snow cover in Minnesota. If we get some decent snowfall early, it's going to favor a colder temp bias as we head into the teeth of winter. If not, temps will tend to run warmer than average as we head towared Christmas.

Overall this should be a better winter for snow & winter "enthusiasts" than last year.

As we say in the weather biz...stay tuned!

PH