JACKSON, Wyo. – On Saturday, June 8, a landslide caused a catastrophic road failure at mile 12.8 on Highway 22 on the west side of Teton Pass, halting the main commuter route between Victor and Jackson.
Geological factors likely set the stage for the road collapse, but recent meteorological conditions may have also played a role. Above-average soil moisture, heavy late-season snow, and recent above-average temperatures are all factors to consider.
Two Wet Years in a Row and Above-Average Soil Moisture
The past two years have been wetter than average in the Tetons, and soil moisture is above average as a result. The water year of 2022-2023 (water years begin on October 1) was a heavy winter in terms of snowfall, and we followed that up with one of the wettest summers in years.
During the 2023-2024 water year, we started out dry in late fall and early winter, but rebounded substantially from mid-winter through spring with heavy late-season snowfall.
At the end of May, soil moisture was 20 to 40% above average in the Tetons.
Heavy Late Season Snowfall in May
During the month of May, the Rendezvous Bowl Plot at 9,580 feet received 55 inches of snow, which is well above the 15-year May average of 30 inches and also the second snowiest May in the past 15 years.
Temperatures were also cooler than average in May, which along with the late-season snow we received, meant that there was an above-average snowpack heading into early June.
Above-Average Temperatures and Accelerated Snowmelt in Early June
During the first week of June, we saw an abrupt flip from below-average temperatures to above-average temperatures and mid-summer like warmth. So far this month, temperatures are 5.4ºF above average in Jackson and we’ve had several days with highs in the 80s.
In the two days leading up to the June 8 landslide, the town of Jackson had highs in the low 80s and the Teton Pass west-side weather station at 8,000 feet had highs in the low 70s. Even at 9,000 feet, high temperatures reached the 60s and lows were only in the high 40s to low 50s.
As a result, snowmelt rates accelerated substantially, which may have played a role in destabilizing the already saturated soils. Also, a significant rain event occurred on June 3 with over an inch of rain (on top of snow) measured above 9,000 feet.
Here is a look at temperature anomalies across the Western U.S. so far this month, with red colors over Western Wyoming indicating well-above-average warmth.
Recent Weather – Damaging Thunderstorm Winds on Sunday, June 9
The Teton Pass landslide has been the big story over the past week (if not the entire year), but it was an active week of weather in addition to that as well.
We have had a quiet start to thunderstorm season and we even had some thunderstorm “chances” emerge on Friday and Saturday, but we ended up with very little activity. That all changed on Sunday evening when a line of strong (to arguably severe) thunderstorms moved through from the west.
These storms brought intense winds to both sides of the Tetons with numerous reports of downed trees throughout the valley. The Jackson Hole Airport recorded a wind gust of 58 mph, which is just below the minimum level of 58 mph needed to be classified as a severe thunderstorm.
Given the tree damage, it’s possible that wind gusts exceeded 58 mph in some areas but weren’t measured as we don’t have many weather stations that measure wind in the valley.
Hail also occurred with this storm in Teton Valley where there were reports of damage to gardens.
The line of storms was fast-moving and the duration of rainfall was short, but briefly heavy with rainfall amounts ranging from 0.10 to 0.35 inches across Teton County, Wyo. and Teton County, Idaho.
Recent Weather – Snowmelt Runoff and Flooding
The high snowmelt rates recently have also impacted rivers and streams throughout our region, especially in Teton Valley where more substantial stream flooding has been reported.
The Teton River has experienced flooding in recent days and is currently in a “Minor Flood Stage” near Driggs. The river has likely reached its crest already and is forecast to start gradually lowering by late this week, likely indicating that our snowmelt runoff rates have just peaked.
Upcoming Weather
Warm temperatures and occasional gusty winds can be expected from Wednesday through Friday, but then we may be looking at a mid-June cooldown as we head into early next week.
First, highs will reach the low 80s each afternoon through Friday. We may see just enough moisture for a slight chance of afternoon thunderstorms on Friday, but only light and spotty rainfall is expected at best.
On Saturday, a moisture-starved cold front will move through, with continued mostly sunny skies while highs will be in the mid 70s on Saturday and low 70s on Sunday. Gusty winds can also be expected at times.
Early next week looks more interesting as a deeper low pressure system approaches from the northwest along with a stronger cold front. We will also see a better chance of showers, though it’s uncertain how much rain we’ll receive yet as we are currently right on the southern fringe of projected moisture.
At the moment, it looks like we may only see highs in the upper 50s to low 60s in the valley on Monday and Tuesday, though this is subject to change this far out. Also, depending on how much moisture makes it this far south, snow is not out of the question across the higher elevations.
Also, there is a chance we could see a freeze in the valleys once the system exits around mid-week.
Late next week, temperatures are expected to rebound substantially as high-pressure returns.
Alan Smith, Meteorologist
