JACKSON, Wyo. – Anomalous warmth has persisted across Western Wyoming with temperatures running 12ºF above normal in Jackson so far during the month of December. A storm on Wednesday produced wet snow up high, a 60 mph wind gust at the Jackson Hole Airport, and 0.79 inches of rain in the town of Jackson.
Recent Weather
The past week has been remarkably warm for this time of year. We had a five-day streak without an overnight freeze in the town of Jackson from December 9-13, which is impressive considering that our average high temperature is below freezing at this time of year.
Also, we hit 50ºF in town on four of the past seven days, and are currently on a nine-day streak with a high of at least 40ºF. For perspective, the 15-year average high during the month of December is 30ºF.
Following a series of storms during the first 10 days of the month, a drier pattern emerged from December 11-16.
Normally, we would be thinking about inversions and cold valley temperatures during dry spells at this time of year, but not in this case, due in part to a lack of snow cover and due to the lack of any cold airmasses at the end of the last storm prior to this dry spell.
On Wednesday, a strong storm arrived, producing snow in the mountains, rain in the lower valley, and powerful winds at all elevations.
A wind gust of 60 mph was recorded at the Jackson Hole Airport and a wind gust of 90 mph was recorded at the top of the tram at Jackson Hole Mountain Resort.
One of the main drivers of this wind event was a cold front that moved through early on Wednesday afternoon. Anomalous warm air was in place ahead of the cold front with colder/more seasonal air behind the front. The sharp temperature and pressure gradients separating these airmasses have resulted in very strong winds.
Early indications are that 6 inches of wet/dense snow fell at Jackson Hole Mountain Resort on Wednesday, with 3 inches at Targhee and 3 inches at Snow King.
Heavy rain fell in the town of Jackson on Wednesday morning, with an impressive total of 0.79 inches from early morning to midday.
Here is the 7-day weather summary for the town of Jackson:
For perspective, the average high and low in Jackson on December 17 are 30º and 9º.
Also, note that the 0.26″ rain total for December 17 was measured at 7 a.m. Since that time, an additional 0.53″ of rain fell, bringing the storm total to 0.79″.
Upcoming Weather Pattern
Get ready for a wild, stormy, windy, and wet weather pattern that will bring a lot of snow to the higher elevations, but wetter, Sierra cement-type snow and mixed precipitation to the valleys.
The storm track is about to turn more active, but the anomalous warmth is not going anywhere, at least not for more than brief respites.
Here are the projected departure from average temperatures through Monday, December 22.
On Thursday, we will briefly be colder in the wake of Wednesday’s cold front. A storm will arrive on Thursday afternoon that will bring heavy snow to the Tetons, and initially some accumulating snowfall to the valley.
However, a warm front will arrive on Thursday night, and snow will eventually change back over to rain in the valley.
On Friday, snow will continue to fall in the mountains with primarily rain in the town of Jackson and over the lower valley, though snow could mix in at times and higher valley areas near the base of the Tetons may continue to see wet snow. Strong winds can be expected on Friday as well.
We will see another brief cooldown on Saturday in between storms, with another strong storm expected from Saturday night through Monday. This storm will feature a southwest flow with subtropical moisture streaming across California and into Western Wyoming.
Precipitation will start out as snow in the valley on Sunday morning, but then will change over to rain from Sunday afternoon through Monday. In fact, snow levels are currently projected to range from 7,000 to 8,000 feet on Sunday and Monday, which is not ideal for our ski resorts.
Big picture, we are looking at a lot of moisture and a lot of snow above 8,000 feet over the next week. But it won’t be the typical Teton powder that we are famous for, and we will struggle to build any sort of low-elevation snowpack due to frequent rain and warm temperatures.
Here is a 7-day snowfall projection from the European Ensemble Model, which represents the average of 50 simulations.
Looking further out, a similar pattern is expected to continue through the holidays with frequent storms, above-average precipitation, and continued well-above-normal temperatures.
As a result, we are likely looking at additional significant snowfall at mid to high elevations, which will help boost the higher elevation snowpack. But in the valley, we may continue to see alternating periods of rain and snow.
NOAA’s 8-14 day outlook highlights this pattern well.
Alan Smith, Meteorologist
