JACKSON, Wyo. – A major winter storm is on track to impact Teton County and Northwest Wyoming on Wednesday and Thursday. The storm will bring heavy snow to the Tetons and snow levels down to the valley floor, with a shot of very cold air to follow.
Winter Weather to Take Hold For the Last Week of October
Following a couple of weeks of mild autumn weather, an abrupt shift to winter conditions is set to take hold.
A powerful trough of low pressure is moving across the Pacific Northwest into the Northern Rockies. Southwest winds will transport abundant moisture into Northwest Wyoming, and temperatures will also plummet on Thursday morning as a cold front arrives with snow levels dipping to the valley floor.
The National Weather Service in Riverton has issued Winter Storm Warnings for the Teton and Gros Ventre Mountains as well as Yellowstone National Park and the Absaroka Range. Winter Weather Advisories (less severe than warnings) are in effect for the Salt River, Wyoming, and Wind River Ranges.
As of midday Wednesday, the storm is already getting underway with snow falling above 8,000 feet and rain falling below. On the west side of the Tetons, snow levels have already dipped slightly below 8,000 feet with webcams indicating accumulating snow at the base of Grand Targhee.
On Wednesday night, snow levels will gradually lower before eventually reaching the valley floor by early Thursday morning as a strong cold front moves through. Snow will continue through the morning hours before tapering off to more terrain-driven snow showers on Thursday afternoon and evening.
Snowfall will be significant across the higher elevations of this storm, ranging from 6-16 inches in the Tetons above 8,000 feet. Significant travel impacts are expected over Teton Pass, Togwotee Pass, and across Yellowstone National Park from Wednesday evening through Friday morning with snow-packed and icy roads.
Strong winds could also lead to areas of blowing snow and reduced visibility. Winds will be out of the southwest on Wednesday and Wednesday night, before veering to more of a westerly direction on Thursday.
The first widespread valley snow accumulations are also expected on Thursday morning, though borderline temperatures will make for a tricky forecast. Generally speaking, snowfall will range from a half-inch to 4 inches in the valley, favoring areas west of the Snake River and north of the airport.
Slushy snow accumulations are also possible on valley roads during the morning hours on Thursday.
Temperatures will be well below average on the backside of this storm with highs only in the 30s on Thursday and Friday in the valleys. A second weaker storm will pass just south of the area on Friday and Saturday, resulting in scattered light snow showers with light accumulations favoring the higher terrain.
Another surge of cold air will arrive on Saturday with this weaker storm, however, and highs will struggle to get above freezing in the valleys with lows on Saturday night falling into the single digits. These values are well below average for late October.
Conditions will dry out from Sunday through Tuesday but temperatures will remain below average with highs in the upper 30s to low 40s and overnight lows in the single digits.
Extended Outlook
Dry and chilly conditions will persist into the middle of next week. A more active pattern is then expected late next week with snow returning to the forecast, both for the mountains and the valley. Similar to last year, we seem to be undergoing another abrupt transition from mild autumn weather to persistent early-season cold and snow.
October Weather So Far (Prior to October 25)
Prior to our upcoming winter pattern, this has been a mild October though precipitation has been above average.
As of October 25, temperatures are running 4.6 degrees above normal this month in the town of Jackson. The temperature has only fallen below 25ºF once so far this month, and we enjoyed several bonus 70ºF days, the last of which occurred as recently as October 21.
In other words, this upcoming cold snap is going to hit hard as we will be going from consistent above-average warmth to well-below-average cold.
Although we had some long dry stretches mid-month, precipitation has been well above average this month. Jackson has received 1.84 inches of precipitation so far this month, and will certainly pass the 2-inch mark with this upcoming system. Average precipitation in October is 1.41 inches.
A wet early October system was responsible for much of this month’s precipitation when 1.52 inches of rain fell in Jackson within the first five days of October.
As far as snowfall goes, the Rendezvous Bowl Plot at Jackson Hole Mountain Resort has received 14 inches so far in October while Grand Targhee has received an impressive 28 inches.
Average snowfall in October at the Rendezvous Bowl Plot is 30 inches, so we’ll see how we stack up at the end of the month following this upcoming storm.
Alan Smith, Meteorologist
