(This article first appeared in the Mountain Weather column in the Jackson Hole News & Guide on Feb. 1st, 2017).

Winter is half over, but already huge!

The first half of the winter season draws to a close on Thursday, February 2nd, Groundhog’s Day. That is the halfway point between December’s Solstice and March’s Equinox. And what a snowy first half it has been.

Recent conversations I have had around town usually come around to mentioning how much snow we’ve had, and how it seems snowier than we have seen in a long time.

It has been a while since we have seen this much snow, but perhaps not as long as you might think. Which begs the question, “how snowy is it?” In this week’s column I will look at how much snow we have received, in town and in the mountains, during the first half of the winter season.

Town Snow

At this point, we have already received enough snow in the Town of Jackson, in December and January alone, to exceed the long-term average total snowfall for the four winter months, December through March. Even if town did not receive any more new snow for the next two months, we’d still end up with an above normal snowfall winter.

In December 2016 we had 34 inches of snow recorded at the Jackson Climate Station. Add to that the 30 inches we had January 2017, and that makes a total of 64 inches in the last two months. The long-term average snowfall in town from December 1st through March 31st is 61 inches.

That is a lot of snow, however, that is nowhere near our record snowfall. The snowiest December ever was in 2008, with 47.5 inches. The snowiest January ever was in 1969, with 56 inches in town.

If you combined the snowfalls for December and January, for those years, here is what you would find: Total snowfall for December 1968 and January 1969 was 82 inches in town. Total snowfall for December 2008 and January 2009 was 87.5 inches.

So, it was only eight winters ago that we had the biggest one-two punch of snow we have ever seen in the Town of Jackson, for a December-January combined snowfall. Almost two feet more snow fell in December 2008 and January 2009 than we had this December-January.

Mountain Snow

I think it is safe to say that the mountains had a very “powderful” December and January. The total snowfall for December and January (through January 28th) was 241 inches at the Rendezvous Bowl weather station (Elevation 9,580 feet) at the Jackson Hole Mountain Resort.

In December of 2016, 153 inches of snow was recorded, nearly doubling the average for December of 81 inches. This was also the second snowiest December in their history, behind the 225 inches that fell during December 1996.

In January of 2017, as of this past weekend, Rendezvous Bowl had recorded 88 inches of snow for the month. That is just ahead of the long-term average January snowfall of 85 inches for that site, but well behind the record January on the mountain of 150 inches set in 1998.

Looking at the combination of big Decembers and Januarys in the same winter: December of 1996 (225 inches) and January of 1997 (126 inches) is still the clear winner for giant snowfall numbers, with a total of 351 inches for the two-month period. Twenty years later, it looks like December 2016 and January 2017 have combined to be the second snowiest, with that 241-inch total.

By the way, that two-month snow total for December 1996 and January 1997 of 351 inches was greater than the long-term average snowfall of 299 inches for December 1st through March 31st at Rendezvous Bowl.

Deep and Cold

Temperatures have been colder than normal these past few months, during almost break we had between snowstorms the last two months, it got down below zero. Colder temperatures keep the snow from settling as much, and every subsequent storm just piles it up deeper.

For valley dwellers, that means snow banks are really high. For skiers, borders and ‘bilers, that means deep coverage up high, with very few rocks showing anymore. This is a snowpack that will likely take a long time to completely melt away this spring.

Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Range for the past 25 years.

Normally at end of the year, I like to review the weather highlights for the past 12 months. However, this December had so much weather to talk about, that I could easily fill this space with the highlights from this past month alone. Which is what I will do. Two weeks from now, in the next Mountain Weather column, I will give you the full review of the weather in Jackson Hole in 2016, with all of its high and low points.

Abundant Snowfall

The buzz about town, and at the ski areas, was how HUGE December was for snow. And it was big, by several different measures.

First, the Town of Jackson had above normal snowfall, with 23 inches recorded, compared to the average in town in December of 17 inches. That number for this December is a little low, because there was a day or two of missed readings due to the Holidays. In reality, town received more than 23 inches in December.

The Jackson Hole Mountain Resort’s Rendezvous Bowl weather station recorded 153 inches of snowfall in December, at the 9,580-ft. elevation. That makes December 2016 the second snowiest December in their recorded history. December 1996 is still the December to beat; it had 225 inches of snowfall, which was the largest monthly snowfall on the mountain, ever. By the way, the average in December at this site is 81 inches.

Mid-mountain, at the 8,180-ft. elevation, had its third snowiest December with 128 inches. December of 1996 and 1977, were number one and two, respectively. Even at the base of the mountain (6,510-ft.) December’s snowfall of 58 inches was 20-inches above the December average of 38 inches.

Also notable: On the last day of December, the settled snowdepth at Rendezvous Bowl was at 90 inches. That is the second deepest December 31st snowdepth ever, behind that big December of 1996, which had 114 inches on December 31st. The 40-year average snowdepth in Rendezvous Bowl on December 31st is 57 inches.

December 2016 and December 1996 were head-and-shoulders above normal for snow at the Jackson Hole Mountain Resort. Question is, will we have to wait another 20 years to see another December like this?

Temperature Swings

The other weather factor that left its signature this December was the temperatures. Wild swings from warm to cold are common, maybe once in a month, but not once a week! We experienced temperature changes in the valley of 40-degrees or more within a couple of days, on multiple occasions.

For example: On December 4th, the high temperature in town was 31-degrees and the low temperature was 21-degrees. Two days later, on December 6th, the high was only 4-degrees, and the low was 21-degrees below zero. That was a 52-degree swing, between the high temperature and the low temperature, in just two days.

The coldest temperature we had in December 2016 was 24-below zero on the morning of December 8th. By the next day the afternoon high temperature was 35-degrees. The day after that, the high was 37 degrees, making for a 61-degree rise in temperature within two days.

The warmest temperature of the month occurred on December 15th when the high reached 39-degrees. The morning low on December 16th was only 35 degrees. Then the very next day, the morning low was 15-degrees below zero, and the high that day was only 8-degrees.

In the end, it was an exceptionally cold December; with average high temperatures almost five degrees colder than normal and average low temperatures for the month were seven degrees colder than the long-term average.

What caused it all?

Most will say that it was La Nina that caused this cold & snowy December. That may have had something to do with it, and that is certainly the preferred short answer.

The longer, more technical answer is, that a zonal or westerly jet stream flow persisted across the Pacific and extended all the way across the Western United States for a good portion of the month.

That jet stream carried copious amounts of moisture inland from the Pacific, and when the jet was south of us, we were colder, and when it shifted north of us it got warm, with rain in the valley.

That jet stream is not continuous anymore, and a complex blocking pattern in the Pacific has slowed the flow and caused a split in the jet stream for the start of the New Year. It’s still a La Nina, that didn’t go anywhere, but the westerly flow and the big snow are on hold until the pattern changes again.

Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for the last 25 years.