A West to Northwesterly flow aloft over the Western U.S. will yield additional snowfall through this coming weekend. A large area of Low pressure in the Gulf of Alaska, combining with a smaller Low-pressure center currently further out in the Pacific will rotate Pacific moisture across the Cascades, Sierra Nevada, and the northern & Central Rockies.

An area of High pressure also sits off the southern California coast, with a strong jet stream between this High and the Low’s to the north. (Jet Stream is yellow line).

These two Low pressure centers hang around out in the Pacific into the weekend and the jet stream relaxes a bit & winds decrease. Pacific moisture will continue to pulse inland through this weekend. Best periods of snowfall in the mountains appears to be Thursday night and again overnight Friday into Saturday. Best break in precip is during the day Friday.

As time goes on , a Ridge of High pressure builds along the West Coast and more Northwesterly flow aloft brings cooler temperatures over the Rockies this weekend. Extending light snow over the northern & central Rockies through Sunday into Monday.

700mb Maps with Forecast Clouds (gray) & Precipitation (blue-green). Maps from Windy.com

Snowfall Forecasts

Models differ slightly about how much snow will accumulate, but it looks like some mountain areas are favored by this West-NW flow. A few of these models predicted snowfall amounts are shown below.

The first is the high resolution WRF from the Colorado Avalanche Information Center, which shows the greatest amounts in the mountains. Their regular WRF model follows, both examples show snowfall totals from Thursday afternoon to Sunday morning.

The NAM (North American Model) below with total snow accumulations from Thursday afternoon through Sunday afternoon.

Post by MountainWeather meteorologist Jim Woodmencey

Back in early September I did my first outlook for the winter season in this blog. That was just after the Farmer’s Almanacs came out with their predictions. Two of those Almanac forecasts had most of the Mountain West painted under cooler and snowier conditions, overall. Those forecasts don’t change, once they are published in late August. (See their maps below).

The Climate Prediction Center (CPC) forecast that I reviewed from NOAA, that was issued in mid-August, revealed that the western U.S. would be warmer than normal, but was undecided about precipitation. That outlook was non-committal about it being above, below, or normal for precipitation for the three-month period, they gave it “equal chances” for each. No help there. However, the latest update looks a little different.

Latest Look

The newest three-month long-range outlook from the Climate Prediction Center, issued on November 21, 2020, still has western Wyoming under warmer than normal conditions for December, January and February. This is still in direct contrast to both Farmer’s Almanac temperature forecasts.

The precipitation forecast from the CPC has now shifted to placing Northwest Wyoming & western Montana under about a 55-percent chance of having above normal precipitation. That’s somewhat more encouraging.

Most of the Pacific Northwest, northern Utah & northern Colorado are riding the 50-percent chance of above normal precip line.

El Nino Situation

The El Niño Southern Oscillation, or ENSO, is one of many indicators long-range forecasters use to decide what the general conditions for the winter season might be across the Northern Hemisphere.

The ENSO actually has three different phases: El Niño, La Niña and Neutral. Sea surface temperatures in the Equatorial Pacific determine the current phase of the ENSO.

An El Niño is occurring when sea surface temperatures are warmer than normal. A La Niña is occurring when temperatures are colder than normal. Neutral ENSO conditions (No Niño) occur when temperatures are near normal, usually when transitioning between the El and La phases.

In general, during an El Niño Winter the northern tier of the United States experiences warmer than normal temperatures and below normal precipitation. At the same time, the southern tier of the United States is usually cooler with above normal precipitation.

During a La Niña Winter the opposite is true, the northern tier of the United States usually experiences a cooler and snowier winter, while the southern tier is usually warmer and drier.

Neutral or No Niño Winters, could go either way. And the ENSO forecast for this winter is for Neutral conditions in the Equatorial Pacific.

ENSO Current status: “Surface temperatures in the east-central tropical Pacific were near to above average in October 2019, but the atmosphere did not react to the warmth. Sub-surface heat that spread across the basin in mid-September was dispersing. Thus, of the three possible outcomes—return of El Niño, La Niña, or neutral—forecasters give neutral the highest odds (70% chance) of continuing through winter.”

What’s it all Mean for JH?

Last winter was a weak El Niño, and pretty much the entire western U.S had a cooler and wetter winter. Jackson Hole was above normal for snowfall, after a record February. That wasn’t supposed to happen.

Historically, from snowfall data for the past 44 winters at the Jackson Hole Mountain Resort, El Niño’s have produced more below normal snowfall winters here than above normal (10 below and 4 above). La Nina’s have produced more above normal snowfall winters than below normal (10 above and 4 below).

Neutral or No Niño’s have also produced more below normal snowfall winters than above normal snowfall winters, but by a smaller margin (9 below and 6 above).

What’s really interesting is, two of those six above normal No Niño winters were the two snowiest winters on record at the Jackson Hole Mountain Resort, the winter of 1996-97 and the winter of 2016-17.

Based on those stats, an optimist would be rooting for another one of those record-breakers during this winter’s No Niño. The pessimist would say chances are less than 50/50 for an above normal snowfall winter.

I already know how many optimists there are in Jackson, just count how many season ski passes have been sold so far.

Post by: Meteorologist Jim Woodmencey

This article first appeared in the Jackson Hole News & Guide on Sept. 11, 2019

I get it all the time, starting in late August, when I am the grocery store, out hiking on the trail, from people passing in the opposite direction while on my mountain bike. I can’t seem to go anywhere this time of year without being asked, “What kind of winter are we going to have?”

I realize it wouldn’t look good professionally if I simply replied, “I don’t know”. But to be honest, I really don’t know. Mainly because I haven’t been thinking about snow, especially when it was still 80-degrees and sunny outside.

With all that asking, I decided I better sit down and see what the long-range outlooks are saying. So, for this week’s column, I’ll provide you with three individual outlooks for Winter 2019-20 for the Rocky Mountain region. And also review what they said about last winter’s weather (2018-19), so you may gauge their accuracy.

Farmers Forecasts First

There are two main weather Almanacs available, both with a long history of weather prognostications, the Farmers’ Almanac and the Old Farmer’s Almanac.

The Farmers’ Almanac is calling for “Frigid and Snowy” for all of Montana, Wyoming and Colorado this coming winter. That sounds good for us. Utah comes under the heading of, “Cool, and Normal Precipitation”.

Last winter, The Farmers’ Almanac’s forecast for Wyoming was, “Teeth-chattering cold and Snowy”. Fact is, it actually was much colder than normal in Jackson last winter, along with above average snowfall, mainly due to the record snowfall we had in February 2019.

The Old Farmer’s Almanac’s outlook for this coming winter says exactly what you would want to hear if you are a winter sports enthusiast, “Low Temps, Deep Powder”. That forecast is valid for southern and central Idaho, most of western Wyoming and Colorado, as well as, all of Nevada and Utah.

The Old Farmer’s also has northern Wyoming and all of Montana under a forecast that says simply, “A Parade of Snowstorms”. Seems like a can’t-miss situation for Jackson Hole!

How did the Old Farmer’s Almanac do with last winter’s prediction for our area? Their forecast for Winter 2018-19 was, “Mild and Snowy”. OK, so they missed on the temperatures, but nailed it by saying “Snowy”.

Climate Prediction Center

I could pretty much cut and paste the forecast from last winter from the Climate Prediction Center (CPC), a division of NOAA, and plug it in here for this coming winter.

The CPC’s latest prediction for December 2019 through February 2020, issued on August 15th of this year, calls for a 55-percent chance of warmer than normal temperatures over western Wyoming. Bucking the cold trend the two almanacs are predicting.

The CPC also has western Wyoming under what they call “Equal Chances” for above normal or below normal precipitation for Winter 2019-20. Not nearly as encouraging as the two Farmers forecasts.

If you are keeping score, the CPC was wrong about temperatures last winter, it was not warmer than normal, it was much colder than normal. Their prediction on precipitation was also non-committal last year, “Equal Chances”.

Come on CPC! Stick your neck out and go one way or the other. Call it “above” or “below” normal precip, you still end up with a 50-percent chance of being right!

No Nino

One of the final indicators of winter weather is the ENSO forecast, the El Nino Southern Oscillation. Last winter we were in a weak El Nino and were not supposed to be cold or snowy.  Based on that predictor, we should have seen warm and dry conditions in the northern Rockies. It was quite the opposite.

This winter, the “consensus” among NOAA’s ENSO forecasters is that the current “Neutral” conditions in the Equatorial Pacific, which began in July, will continue through the Northern Hemisphere Winter 2019-20.

What does that mean for us? Absolutely nothing. Why do I say that? Because, we have had above normal snowfall in the mountains for the last 5 out of 6 winters, while under El Nino, La Nina, and No Nino (Neutral) conditions. Therefore, at this point I have to discount the ENSO as an indicator.

Any Other Questions?

There you have it, that’s everything I know about how this winter might shape up. So, the next time someone asks, “What’s kind of winter are we going to have?”, I can simply answer, “Haven’t you read my column in the Jackson Hole News and Guide?”

Jim is the chief meteorologist at mountainweather.com and has provided a weather forecast for Jackson Hole and the Teton Range for over 25 years.