JACKSON, Wyo. — A significant heatwave resulted in record high temperatures across Teton County and Wyoming over the holiday weekend. The unseasonably hot temperatures will persist on Tuesday and Wednesday before cooler temperatures finally arrive late in the week. Smoke from wildfires in Idaho will also impact Teton County from time to time this week.
August 30 – September 5 Recap
While most of August was wet and stormy due to an active monsoon, the pattern changed abruptly over the past week as a strong ridge of high pressure took control over the Western U.S. This resulted in a record-breaking heatwave for early September throughout the Western U.S., including Teton County and Wyoming.
Typical high temperatures for the beginning of September are in the mid to upper 70s in Jackson, but we saw highs reaching the upper 80s to low 90s throughout the past week. In fact, the high in Jackson topped 90 degrees for three consecutive days over Labor Day weekend, including a high of 92ºF on Saturday which tied a record for the date.
The three 90+ degree days that Jackson has experienced in early September are more than we experienced in July and August combined – a rare occurrence during a time of year in which we are typically cooling off.
Elsewhere across Teton County, daily record highs were also set in Moran (87ºF), Alta (90ºF) and the Jackson Hole Airport (90ºF) over the holiday weekend. It’s safe to say this was one of the hottest (if not the hottest) Labor Day weekends on record in Teton County.
High temperatures over the past week ranged from 87ºF on August 30 and 31 to 92ºF on September 3, and low temperatures ranged from 37ºF on August 30 and September 2 to 42ºF on September 1. Fortunately, cooler overnight lows and a weaker sun at this time of year (compared to mid-summer) have helped to take an edge off of the heat, compared to if we were seeing similar high temperatures in July.
Despite the relatively cooler overnight lows, we have yet to see an overnight freeze in Jackson, which is unusual for being a week into September. The average date for the first freeze in Jackson is on August 19 (the cut-off date between the last freeze and the first freeze is August 1).
Currently, we are in sixth place for the latest first freezes on record, though we will likely see our first freeze this weekend, which would allow us to avoid the record latest first freeze date of September 17, which was set in 1997 and tied in 2017.
Temperatures aside, high pressure also resulted in a very dry airmass and no rain was recorded across Teton County over the past week.
Forecast for Tuesday (9/6) to Monday (9/12)
The heatwave will continue on Tuesday and Wednesday with highs reaching the low 90s in the Jackson Hole Valley. In fact, there is a chance we could tie (or even break) the all-time high temperature record for the month of September in Jackson on Wednesday, which is 93ºF.
Smoke from wildfires in Idaho has also impacted our area since Monday. While there are many wildfires burning in Idaho, the main culprit for the recent uptick in smoke is the Ross Fork Fire burning in the Sawtooth Mountains just north of Sun Valley.
Smoke has been thickest during the morning hours for the last two days, but seems to be clearing up a bit on Tuesday afternoon (similar to Monday). Smoke has also been thicker in Teton Valley, Idaho compared to Jackson Hole.
On Wednesday, smoke is projected to lessen a bit compared to the previous two days. Winds will also become a bit gusty in the afternoon, and a late-day shower or thunderstorm couldn’t entirely be ruled out ahead of a trough of low pressure approaching from the northwest.
On Thursday, the first of two cold fronts will arrive in the morning, signaling the end of the heatwave. Daytime highs will be about 10 degrees cooler in the low 80s on Thursday, and gusty winds can also be expected throughout the day.
Isolated showers and thunderstorms will also be possible throughout the day, but the best chance of showers will exist east of Jackson Hole along and east of the Continental Divide (Yellowstone, Absaroka, Winds, etc.).
On Thursday night, another cold front will arrive from the north with conditions drying out across Jackson Hole and the Tetons. However, if you have plans in the Wind River Range or any other areas along and east of the Continental Divide, be prepared for some light snow to fall on Thursday night as low as 8,000-9,000 feet.
Despite the welcome cold front arriving on Thursday, unfortunately, smoke is likely to return and may be heavy at times as winds aloft will be shifting to northwest, which will favor more direct smoke transport from Idaho fires into Teton County.
Conditions will dry out on Friday with pleasant temperatures expected as highs reach the low 70s in the valley. However, smoke will likely remain a factor and could potentially result in poor air quality at times.
Heading into the weekend, we will see a gradual warming trend with generally pleasant temperatures expected. The wild card, of course, will be the smoke.
It’s possible that smoke conditions could improve briefly on Saturday as winds shift to due north (instead of northwest), before worsening again on Sunday as winds shift back to northwest. However, confidence is low this far out and the smoke outlook could always change, for better or for worse.
On Monday, we should start to see a pattern shift as a trough of low pressure sets up near the West Coast and moisture from the remnants of Hurricane Kay in the Pacific begins to move northward toward Western Wyoming. Shower chances could arrive as early as Monday afternoon or Monday night.
Next week is looking cooler and more unsettled with subtropical moisture arriving from the southwest along with a series of disturbances from the West. This could result in a period of near-daily shower and thunderstorm chances for most of next week, though confidence is low in the day-to-day details this far out.
Temperatures will be cooler/more seasonal by September standards next week. However, given the subtropical origins of the moisture arriving, it’s likely that this pattern will favor rain across the Tetons and higher elevations for most of the week with only the tops of the highest peaks seeing snow.
However, if and when the trough holds together and eventually moves across the Rockies, then some high elevation snow couldn’t be ruled out toward the end of next week.
Alan Smith, Meteorologist
Town of Jackson Climatology for September 6-12:
Average High: 74
Average Low: 34
Record High: 93 (September 8, 1934)
Record Low: 12 (September 11, 1916)
Precipitation Since Oct 1st: 16.50″ (102% of Average)