JACKSON, Wyo. — August has been an active month for Teton County so far with frequent rounds of rain and thunderstorms. That trend will continue this week as monsoon moisture hangs around, resulting in near daily rounds of showers and thunderstorms.
August 16-22 Recap
We are in a persistent pattern right now featuring daily rounds of afternoon and evening thunderstorms. Weak winds aloft have resulted in spotty and erratic movement of thunderstorms with hit-or-miss rainfall.
The Town of Jackson received its biggest thunderstorm “hit” on Monday evening as frequent lightning, hail and brief heavy rain pelted the town with 0.20 inches of rain recorded.
Looking back further (since I was out of town last week), rainfall has been impressive this month and fire danger has been significantly reduced as a result. Over the weekend of August 13-14, a strong thunderstorm produced very heavy rainfall in the Town of Jackson with 0.86 inches of rain recorded, most of which fell in under an hour.
Jackson has now received over three inches of rain during the month of August, which is well above average. The culprit has been a very active monsoon season across the Southwest U.S. with moisture from this pattern streaming northward into Wyoming on a frequent basis over the past few weeks.
High temperatures over the past week ranged from 82ºF on August 20 to 89ºF on August 17, while low temperatures ranged from 43ºF on August 17 to 48ºF on August 22.
While frequent storms and rainfall have made for some refreshing and comfortable evenings lately, low temperatures have been unusually mild due to the added moisture in the atmosphere which has kept overnight temperatures from dipping too low.
The historical average low in Jackson for the month of August is 40ºF, and by late August, average lows are in the upper 30s. However, we have yet to see a low temperature dip below 40ºF in August 2022, which is unusual for this late in the month now that the days are getting shorter.
Forecast for Tuesday (8/23) to Monday (8/29)
A weak but slow-moving area of low pressure over the Northwest U.S. along with continued monsoonal moisture will keep Jackson Hole in a relatively active pattern this week with near daily rounds of thunderstorms through at least Saturday.
On Tuesday, a minor disturbance has already resulted in a quick round of showers that moved through earlier this morning. Increasing sunshine behind this disturbance will heat up the atmosphere, and will support another round of afternoon thunderstorms.
Tuesday’s storms may end up being more isolated in coverage compared to recent days, but brief downpours will remain possible under stronger storms along with active cloud-to-ground lightning. Storms on Tuesday will be slow-moving and erratic but will generally move from west to east.
On Wednesday, an upper air disturbance will approach from the southwest but it may not arrive until late in the day. Ahead of the disturbance, we will see just a slight chance of thunderstorms during the early afternoon hours, with a better chance of storms late in the day.
Scattered showers and thunderstorms will also remain possible through the overnight hours on Wednesday night when “energy” from the disturbance will be strongest, despite the lack of solar heating which typically fuels thunderstorm development.
On Thursday, scattered showers will be possible during the morning hours, followed by a better chance of thunderstorms during the afternoon.
Storms on Wednesday and Thursday will generally move from west to east or east/northeast and will be faster-moving compared to recent days. However, brief downpours will remain possible under stronger storms.
High temperatures from Tuesday through Thursday will reach the low to mid 80s.
Conditions should dry out on Thursday night, but then another disturbance will arrive on Friday, resulting in another day of scattered afternoon thunderstorms. Temperatures will also be a little cooler with highs in the upper 70s.
Over the weekend, a trough of low pressure will move across the Northern Rockies, but this should actually scour out much of the monsoonal moisture that has been in place. Still, we could see enough lingering moisture along with energy from the trough to result in isolated showers and thunderstorms on Saturday. Gusty winds can also be expected with highs in the upper 70s.
A cold front is expected to arrive later Saturday night or Sunday, with slightly cooler and drier conditions expected behind the front during the day on Sunday. A stray shower or thunderstorm couldn’t entirely be ruled out on Sunday at this time, but the threat is low as conditions are looking pretty dry. However, strong winds will also be possible behind the front on Sunday.
Winds will be lighter on Monday with temperatures warming up slightly. A slight chance of a thunderstorm can’t be ruled out at this time as some lesser amounts of monsoonal moisture may sneak back into the picture next week.
Extended Outlook
Drier conditions with above-average temperatures are expected for most of next week as a ridge of high pressure strengthens over the Western U.S. However, we may see limited amounts of monsoonal moisture arrive at times, which could result in occasional isolated thunderstorm chances – but likely less than recent weeks.
There are some hints that we could see a low pressure system from the Pacific approach near or over Labor Day weekend, which could potentially cool temperatures off a little bit and introduce shower/thunderstorm chances. However, a major fall-like cooldown appears unlikely at this time.
Alan Smith, Meteorologist
Town of Jackson Climatology for August 23-29:
Average High: 79
Average Low: 38
Record High: 94 (August 27, 1924 and August 29, 1934)
Record Low: 18 (August 28, 1960)
Precipitation Since Oct 1st: 15.96″ (103% of Average)
