Bill’s Blog: The factors that play into the winter forecast


Streaming on Bill, Terri, Ellen, Matt and Emily dig into the data to provide the winter weather outlook.

GRAND RAPIDS, Mich. (WOOD) — For the coming winter, odds favor temperatures to be slightly warmer than average, precipitation to be above average and snowfall to be near average.

First, a look back at last winter (2019-20). November was 5.5 degrees cooler than average (and nearly 10 degrees cooler than November has been so far this year).

After that, the trend reversed. December 2019 was 4 degrees warmer than average and January 2020 was a whopping 6.9 degrees warmer than average. February was only 0.7 degrees warmer than average.

The coldest temperature of the winter was +4 degrees on Feb. 14th and 15th.

Snowfall in Michigan last winter and difference from average

Precipitation (rain and melted snow/sleet) was above average last winter (+2.53 inches for December through February in Grand Rapids), but season snowfall was below average (53.5 inches for Grand Rapids).

That was because a higher percentage of our precipitation fell as rain because temperatures were warmer. With the warmer air, there was a decided lack of lake-effect snow last winter.

Flint (53.7 inches) got more snow than Muskegon (51.9 inches) last winter! While snowfall was below average in West Michigan, it was above average in eastern Michigan (+6.3 inches in Flint and +1.2 inches in Detroit) and also above average in Upper Michigan, where it was cold enough for lake-effect snow (Marquette +5.3 inches and Sault Ste. Marie +13.6 inches). Tamarack in the U.P. recorded 301.1 inches for the winter of 2019-20.

Global sea surface temperatures Nov. 25, 2019.

The first place I look when making a seasonal forecast is the global sea surface water temperatures. The map above shows the sea surface temperature difference from average for Nov. 25, 2019.

Yellow, orange and red indicate areas where the water temperature is warmer than average. Blue indicates areas where the water temperature is cooler than average.

You can see a lot of yellow in the equatorial and Northern Hemisphere latitudes and cooler-than-average water around 30 degrees to 60 degrees south in the Southern Hemisphere. There was warmer-than-average water around most of North America and that was a significant factor in the relatively warm winter than much of the U.S. recorded.

Now let’s look at current sea surface water temperature difference from average:

Sea surface temperature anomaly map – Nov. 19, 2020.

The dark blue along the equator west of South America stands out. That is called La Nina.

When the wind increases along the equator, it stirs up colder water from well below the surface and that’s what’s happened during the past year. When we have La Nina, there is often (not always) a rather dominant winter pattern:

Typical Winter Pattern during a moderate to strong La Nina.

We have an upper level ridge over the northern Pacific Ocean, a mean position of the polar jet stream from British Columbia across the Plains and Ohio Valley and northeast up into New England. This pattern favors dry weather across much of the Southern U.S.: lots of sunny, mild days for vacationers and snowbirds in Arizona, Texas and Florida. Wet weather is favored across the Pacific Northwest, Ohio Valley and parts of the southern Great Lakes.

Worth noting is that while the sea temperatures have cooled along the equator. The sea-surface temperatures around the U.S. and much of North America are similar to last winter, warmer than average.

La Nina difference in snowfall from average.

Here’s a comparison of snowfall during a La Nina Winter in Grand Rapids compared to an average of all years. This is interesting. There’s slightly below average snowfall in December and January and then the snowplow drivers work overtime in February.

North American Snow and Ice Cover

We also look at early snow cover in Canada and Siberia. Air coming off that snow cover will likely be cold.

You can see earlier snowfall across Upper Michigan, northwest Wisconsin and Minnesota has melted. Snow covers most all of Canada (north of 49 degrees latitude). Lake Winnipeg has frozen over and Hudson Bay is starting to freeze over.

Some of the polar bears are already on the ice of Hudson Bay, where they are being tracked.

There is a solid snow cover over Siberia that already extends south to cover much of Mongolia and Northern China. There is also snow cover over much of Finland, Sweden and Norway. When there is early and thick snow cover across Russia (Siberia), odds favor a colder and snowy winter in the Great Lakes.

Very cold air can on rare occasions come over over the North Pole and down into North America especially after Christmas). This is known as the “Siberian Express.”

CFSv2 Temperature Forecast for Decembere 2020 – February 2021

There are several computer models that try to forecast our weather out months in advance.

Above is the temperature forecast for December through February from the CFSv2 model. It’s not too different from the typical La Nina pattern, with warmer than average temperatures over the South and East and cooler than average temperatures from Minnesota to Washington state.

CFSv2 model precipitation forecast for December 2020 thru February 2021

Here’s the CFSv2 model forecast for precipitation for December through February. It is also forecasting dry conditions across the southern U.S. from California to Carolina. It has wetter than average weather in the Pacific Northwest, Ohio Valley east to New England.

NOAA/NWS Winter Temperature Forecast

The official National Weather Service winter forecast is out and it looks very much like a typical La Nina Winter, warm in the South and cool from northwest Minnesota to Washington state.

NOAA/NWS Precipitation Forecast

The NWS precipitation forecast also follows a typical La Nina pattern: dry in the south and wet from the Great Lakes westward across the Northern U.S.

Back to La Nina. This is a monthly record of El Nino (numbers in red), La Nina (numbers in blue) and times when it’s neutral (La Nada) in black. The latest number is for August through October at 0.9, but it will surely be a blue number for September though November and through the winter.

We can look back through the records to see when we had similar numbers. I want to focus on 2010-11. The La Nina was stronger at this time in 2010, but there are other similarities that I found.

Hurricanes of 2010 in the Atlantic

In 2010, we had a very active hurricane season with 12 hurricanes and five major hurricanes and just like this year, a significant number of tropical storms impacted Central America.

That year, November was warmer (+3.4 degrees above average) and sunnier than average (40% sun versus an average of 28%) in Grand Rapids.

November 2010 had just 0.1 inches of snow in Grand Rapids, while here in 2020, we’ve had just 0.2 inches (very similar). In 2010, we had 11.4 inches of snow in December (below average), 21.2 inches in January (near average), then we got dumped on in February 2011.

Groundhog Day Blizzard – pic. from Tony Van Dyke

Do you remember the Groundhog Day Blizzard of 2011? Grand Rapids had 17.2 imches of snow in two days (Feb. 1 and 2). We ended the month with 38.2 inches of snow, the second highest ever in Grand Rapids for any February.

We did have spring that year. It was 68 degrees on St. Patrick’s Day and we had a nice 52% of possible sunshine in March.

Killer Tornadoes of 2011

Two more notes on 2010-2011. While 2010 was a very active hurricane year, the two years that followed were also active hurricane seasons in the Atlantic. The map above shows where tornadoes caused fatalities in (mainly the spring) of 2011. It was truly a deadly year, with 553 fatalities and 5,370 injuries. There were 6 EF-5 twisters and 17 EF-4 tornadoes. That compares to no EF-5 tornadoes and just 6 EF-4 twisters in 2020. The map above shows (by red dot) where the killer tornadoes were in 2011. Of special note was the Joplin MO EF5.

Back to topic. This is my guess (yes, it’s an educated guess, but a guess nonetheless) for this winter:

Temperatures for December through February will be 1 degree warmer than average. Lake Michigan is still relatively warm and will sit at 39 degrees Farenheit for a week or more as the lake overturns. As colder air comes down, this should result in lots of cloud cover (I call it the “stratus quo”) in early to mid-winter.

I think we’ll have above average precipitation given the moderate strength of La Nina and the preferred storm track up the Ohio Valley.

The Forecast: Snowfall totals are slightly below average, with a nod to the warmer oceans around us, warmer Lake Michigan and a mild start to winter here in November. I’ve got 68 inches for Grand Rapids, 66 inches for Kalamazoo, 55 inches for Battle Creek, 79 inches for Muskegon and 85 inches for Holland.

Final note: According to WeatherRate, which rates the quality of our forecasts, this summer we had the most accurate seasonal forecasts we’ve ever had since they’ve been keeping records. We didn’t get much severe weather (STILL no tornadoes in Lower Michigan this year! Woo-hoo!) and we had lots of sunny, warm days that were pretty easy to forecast.

As we enter winter with the storm track through the Ohio Valley and Great Lakes, that makes forecasting more difficult. This means a very slight miss in the storm track can mean a big difference in precipitation type and intensity. We’ll have chances for mixed precipitation storms with narrow bands of freezing rain and we’ll certainly have a chance of a bigger snowstorm this winter — hopefully not quite as impactful as the Groundhog Day Blizzard, but still a significant snow event (think area-wide snow day!). We’ll also have a better chance of severe weather next spring — not just in Michigan, but throughout the U.S.

As always, thanks for reading my blog and for watching Storm Team 8.



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