JACKSON, Wyo. – The past week has been cool and wet in Jackson Hole with below normal temperatures. However, the cool spell is beginning to break with high temperatures warming up into the 60s late this week and into the 70s next week.
Recent Weather Conditions
The first two weeks of May were warmer than normal, but this past week has been wet and chilly, with most areas picking up anywhere from one to two inches of precipitation in the past seven days.
From May 2nd through 12th, the high temperature exceeded 60º in Jackson on every single day, and the high temperature exceeded 70º on seven of those 11 days. But just when you thought that summer was here, the atmosphere reminded us that it is still May in Wyoming.
From May 13th through 20th, the high temperature only reached 60º on one day, and was below 60º on the other seven days. On three days, the high temperature did not get out of the 40s in Jackson.
Overall, temperatures are still running 1.9º above normal for the month of May as a whole, but the last week has been consistently below average. The average high and low during the month of May are 61º and 33º for perspective, though the averages rise to 66º and 37º by May 31st.
For most of the past week, we saw scattered light rain showers but one heavy precipitation event occurred in the Jackson Hole Valley on Saturday and Saturday night. The town of Jackson recorded 1.18 inches of rainfall during a 24-hour period, which is the most we’ve seen in 24 hours so far this year.
In fact, this was the highest single-day precipitation total in the town of Jackson since March 2, 2024, when we received 1.30 inches of precipitation (and 16 inches of snow) in 24 hours.
The mountains have received several shots of snow in this pattern as well. Given the cooler temperatures, snowmelt has slowed over the past week compared to prior weeks. Currently, snowpack in the Upper Snake River Basin, which includes the Tetons, is 88% of average.
Upcoming Weather Pattern
Wednesday has featured mostly sunny skies and lingering chilly temperatures. We will start to break out of this cool snap later in the week as a ridge of high pressure begins to build in from the south.
From Thursday to Sunday, high temperatures will rise well into the 60s each day, which is close to average for this time of year.
The pattern will also start to dry out, but there are a couple of minor exceptions.
On Thursday, a disturbance will pass north of our area, resulting in a slight chance of afternoon showers and thunderstorms. Available moisture looks like a limiting factor right now, but if moisture transport is a little bit higher than expected, then our chance of afternoon storms would increase.
Another weak disturbance with somewhat higher moisture levels will arrive on Saturday, resulting in scattered afternoon showers and thunderstorms. Rainfall amounts should be light, but cloud-to-ground lightning is possible, so heads up if you have outdoor plans.
On Monday, a more significant warm-up will take hold with highs rising into the 70s. For most of next week, highs are expected to be in the 70s as well.
Sunday and Monday will feature only a slight chance of afternoon showers/thunderstorms. However, thunderstorm chances may rise around the middle of next week as a stronger disturbance is projected to track across the Pacific Northwest and Northern Rockies.
Here is the 7-day rainfall projection from the European Ensemble Model, which indicates light amounts expected for Western Wyoming while Eastern Wyoming will receive heavier rainfall.
Looking further out, high pressure is expected to become established as the dominant pattern heading into the final days of May and the first days of June with above-normal temperatures and below-normal precipitation expected.
Summer Weather Outlook
Seasonal outlooks should always be taken with a grain of salt, as there are many factors that can’t be anticipated weeks or months in advance. But there are a few factors we can look at that can offer us some clues about what may be more or less likely, even if it just slightly tips the odds one way or another.
Heading into the summer of 2025, confidence is that we will have ENSO Neutral conditions, meaning that neither El Nino nor La Nina is expected. Neutral summers tend to favor high-pressure ridging over the Western U.S, more so than a normal summer, which favors above-normal temperatures.
Another factor that can influence summer weather is snowpack over the Southern Rockies – primarily Utah, Colorado, New Mexico, and Arizona.
Snowpack on May 1st was well below normal across this region. This increases the likelihood of an early and strong subtropical high-pressure ridge to develop over the Southwest and move northward, since more of the sun’s energy is used to heat up the land in May/June rather than melting the mountain snowpack (which there is less of than usual).
However, an early and strong subtropical high-pressure ridge over the Southwest tends to result in a stronger Southwest Monsoon, as winds blowing clockwise around the high-pressure ridge pull in moisture from the Gulf of Mexico and South Pacific Ocean into the Southwest during July and August. Moisture intrusions can also reach Western Wyoming.
For Jackson Hole and Western Wyoming, the big picture setup this year favors a hotter and drier than normal early summer in June and early July, and a fairly active monsoon season in late July and August, which could potentially result in heavier rainfall and more frequent thunderstorms.
September tends to go either way in ENSO Neutral + Low Southern Rockies Snowpack years in terms of precipitation, therefore, confidence is lower compared to June, July, and August.
Overall, above-normal temperatures are favored for most of the summer, with the one exception being August, when near-normal (or at least equal chance of above or below normal temperatures) temperatures are favored during the peak of monsoon season.
A hot and dry start to the summer could potentially lead to an active fire season in Western Wyoming, though if we were to experience an active mid to late summer monsoon with above normal rainfall, that could help. At the same time, increased lightning could also lead to fires, so it’s a double-edged sword when it comes to monsoon moisture.
Unfortunately, an active fire season is projected across the Pacific Northwest, where below normal snowpack and drought conditions exist, along with an even stronger signal pointing at above normal summer temperatures. As a result, this increases our risk of wildfire smoke transport into our area.
But I will issue one more reminder that seasonal forecasts, while interesting, still contain an inherent level of low confidence (much more so than short to medium-term weather forecasts), so anything is possible.
Alan Smith, Meteorologist
