JACKSON, Wyo. – The Tetons have received 26-34 inches of snow over the past week, but a warm storm involving subtropical moisture has resulted in rain as high as 8,000 to 9,000 feet on Wednesday. Well-above-average temperatures will prevail from late this week into early next week.
Recent Weather
We had our first true taste of winter last week as a series of strong storms impacted the area. Colder temperatures ahead of the storms also led to improved snowmaking conditions, which helped Jackson Hole Mountain Resort and Grand Targhee to open up for the season after a delayed start.
The series of storms from December 4-8 produced 20-30 inches of snow across the higher elevations of the Tetons.
The town of Jackson also saw its first significant snowfall of the season, with 6.4 inches of snow recorded during this same period.
But, just when you thought winter was here to stay, anomalous warmth returned to the area this week.
As a ridge of high pressure intensified over the Western U.S., a powerful atmospheric river (plume of subtropical moisture) reached the Pacific Northwest with moisture extending far enough south to reach this area.
Atmospheric rivers typically involve subtropical moisture, warm temperatures, and strong winds, and we have seen all of this over the past couple of days.
Snow levels quickly rose above the valley floor, and light rain has been falling in town along with gusty westerly winds, which created a strong rain shadow effect east of the Tetons and led to lighter amounts in town. Heavier rain has been falling at the base of the Tetons, with heavy, wet snow falling up high.
The Tetons picked up 4-10 inches of wet, dense snow on Tuesday, with snow levels (the rain/snow line)initially ranging from 7,000 to 8,000 feet. However, snow levels rose even higher on Wednesday, likely peaking around 8,500 to 9,000 feet, though first-hand observations will be needed to confirm this.
It is very unusual to see rain fall at elevations this high during the core winter months of December to February.
Here is the 7-day weather summary for the town of Jackson:
For perspective, the average high and low in Jackson on December 10 are 31º and 11º.
Despite the warm-up this week, we have seen a net snowpack growth across the mid to high elevations, thanks to last week’s snowy pattern. In the past 7 days, snow depth has increased from 18-23 inches at 9,000 feet on December 3 to 42-47 inches on December 10.
Upcoming Weather Pattern
We are about to head into a 5-day dry spell after this warm, wet storm as high pressure intensifies over the Western U.S.
No cold air pushes are arriving behind this storm, so we will hang onto well-above-average temperatures for late this week and into early next week, while the Eastern U.S. will be colder than average.
On Thursday and Friday, scattered cloud cover and gusty winds will persist with highs in the 40s and lows struggling to get down to freezing.
On Saturday and Sunday, more sunshine can be expected along with lighter winds and colder overnight temperatures dipping into the teens in the valley.
Normally at this time of year, high pressure with clear skies and light winds would mean temperature inversions holding all day long in the Jackson Hole Valley. However, given our now lack of snow cover in town and the lack of any preceding cold air pushes, it’s questionable whether or not that will happen.
Depending on whether or not we see any inversions hold through the afternoons, highs could range from the 30s to 40s. Either way, it’s above-average for this time of year, and mountain temperatures will be even warmer compared to average, with highs in the upper 30s to near 40 and overnight lows barely getting below freezing.
On Monday, temperatures will remain mild, but we may see an increase in clouds and winds. The next storm is possible as early as Tuesday, though it may be another warm storm with wet/dense snow up high and a rain/snow mix in the valleys.
Here is a 7-day snowfall projection from the European Ensemble Model. If you’re looking for snow and more winter-like conditions in the near term, head to the Canadian Rockies or to the Eastern U.S.
The good news for skiers and snow lovers is that the pattern is looking more favorable once we get beyond about December 16th. In fact, the second half of next week and into the week of Christmas looks to feature a more trough-dominant signal over the Northwest U.S., potentially opening the door up to stronger and more frequent storms.
Most longer-range models have a strong wet signal showing up for our area beyond December 16.
Temperatures are still a question mark, however. It looks like this stubborn warm airmass over the Western U.S. is going to be tough to break down, so we may see some warm storms initially with rain possibly mixing in at times in the valley. Over time, we should see a gradual cooling trend, however.
Alan Smith, Meteorologist
