Winter Outlook: Higher “Winter Misery Index” ahead?

Let's face it weather fans. Minnesota winters are not what they used to be.

We've gotten off pretty easy with winters in the past 20 years. In fact, the past 3 winters fall toward the mild category on the Winter Misery Index. Yes, here in Minnesota we like to quantify our winter misery. Or recent lack thereof.

It's been 4 years since what many of us would call the last "real winter" in Minnesota. It seems we're statistically overdue for a more rigorous winter. So will Minnesota get a respectable blast of cold and snow this year? As the Magic 8-ball would say, some "signs point to yes."

Quantifying Minnesota's milder winters

The Minnesota DNR Climate Working Group's Winter Misery Index (WMI) shows a clear trend toward milder winters. The WMI assesses cumulative points for cold and snow in winter.

The Winter Misery Index (WMI) is an attempt to weigh the relative severity of winter when compared with winters of the past. The WMI assigns single points for daily counts of maximum temperatures 10 degrees F or colder, and daily minimums of 0 degrees F or colder. If the minimum temperature drops to -20 degrees or colder greater, eight points are attributed to that day. Snowfall totals of one inch or greater in a day receive one point. Four-inch snowfalls generate four points for the day, an eight-inch snowfall receives a whopping 16 points. To quantify the duration of winter, one point is tallied for every day with a snow depth of 12 inches or greater.

A look at the past 20 winters clearly shows the trend toward less severe winters in Minnesota.

• The past 3 winters have been mild. (WMI at or below 55 points.)

• The last "severe" winter in the Twin Cities was 4 years ago in 2013-14. (WMI 207 points)

• 9 of the past 20 winters (45%) fall in the low moderate or mild category.

• Just 3 of the past 20 winters (15%) fall into the severe category.

• The last 2 winters were the 6th and 8th warmest on record in the Twin Cities.

Bottom Line: The long term trend strongly favors milder winters in Minnesota.

Snow Trends: Less snow, more rain and ice

Overall snowfall trends in Minnesota are also on the downswing. Our last winter with above average snowfall in the Twin Cities and much of Minnesota was 4 years ago. The Twin Cities picked up a respectable 69.8" that season.

The 30-year average snowfall at MSP Airport is 54.4 inches. A look at the past 13 winters shows a strong trend toward less snow.

• 10 of the past 13 winters have produced below average snowfall. (Brown below)

• Just 3 of the past 13 winters have produced above average snowfall. (Blue below)

Milder winters mean more of our winter precipitation falls as rain and ice instead of snow. Minnesota now gets 3-times more winter rain and ice than we did in the 1970s.

Bottom Line: Winters are trending less snowy overall in Minnesota.

Seasonal forecast factors: La Nina

As I've written many times before, there are several factors seasonal forecasters evaluate for winter season outlooks. ENSO cycles probably show the most skill and predictive value for North American winter. Tropical Pacific sea surface temperatures are running blue (cooler than average) this fall.

Model forecasts lean toward La Nina conditions (-0.5C or colder) this winter. I pulled this clip from NOAA's latest ENSO discussion released Thursday. A La Nina Advisory is in effect. NOAA puts the chances for a La Nina flavored winter at 65% to 75%.

Synopsis: La Niña conditions are predicted to continue (~65-75% chance) at least through the

Northern Hemisphere winter 2017-18.

During October, weak La Niña conditions emerged as reflected by below-average sea surface

temperatures (SSTs) across most of the central and eastern equatorial Pacific Ocean. For the remainder of the Northern Hemisphere fall and winter 2017-18, a weak La Niña is

favored in the model averages of the IRI/CPC plume (Fig. 6) and also in the North American MultiModel

Ensemble (NMME) (Fig. 7).

The consensus of forecasters is for the event to continue through

approximately February-April 2018. In summary, La Niña conditions are predicted to continue (~65-75%

chance) at least through the Northern Hemisphere winter (click CPC/IRI consensus forecast for the

chance of each outcome for each 3-month period).

La Nina winters statistically tend to produce colder than average jet stream patterns over the northern tier of the U.S.

[image]

In Minnesota La Nina winters tend colder than average about 70 to 80 percent of the time.

La Nina winters favor above average snowfall, especially in northern Minnesota.

NOAA

Bottom Line: The La Nina event this winter favors a colder and snowier winter for Minnesota.

Out on a limb

Seasonal weather forecasts are like crawling out on a long tree limb. Hopefully you don't get sawed off.

Two years ago I forecast a mild El Nino winter. That worked out perfectly. Last year's pattern gave me less confidence going in. I forecast a slightly warmer than average winter. That was too conservative. Last winter was 6 degrees warmer than average.

The truth? Our pronounced long term winter warming trend in Minnesota is making it tough to get a good old-fashioned winter anymore. We still get one every 3-4 years it seems. And we're due.

Basically I see this winter as a battle between two trends.

1. The statistical trend for colder and snowier winter in La Nina years.

2. The long-term trend for milder winters in Minnesota due to climate change.

So here's my best estimate at a winter outlook. Confidence is medium this year.

• Colder and snowier than last winter, which was the 6th warmest on record in Minnesota.

• Temps for meteorological winter (Dec-Feb) 2016-17 should land between 0 (average) to 3 degrees warmer than average across Minnesota.

• Snowfall in the Twin Cities likely between 40 and 50 inches. (30-year average is 54.4")

• Northern Minnesota may see snowfall totals of 60" to 70"+ this winter.

• Snow cover should be more persistent this winter than the past 3 years.

• A colder than average November is freezing lakes earlier. Better news for Pond hockey events this winter?

• Look for at least one Polar Vortex outbreak on your national newscasts this winter.

• I can see between 15 and 22 sub-zero nights in the Twin Cities this winter. (Average is 24)

• The Twin Cities will likely get close to or hit -20F this winter.

Overall I expect a more rigorous winter than the past 3 years. Maybe we can earn our reputation as the Frozen Tundra back again during Super Bowl week? How do you think this winter will go down?

Stay warm. And stay tuned.