JACKSON, Wyo. — High pressure will result in warm and dry conditions early this week and we will also see periods of light smoke from fires in Idaho and California. Monsoonal moisture will arrive late this week, resulting in mountain thunderstorms on Thursday and Friday with just a slight chance of a storm over the Southern Jackson Hole Valley around town.
July 19-25 Recap
The past week was warm and dry with above-average temperatures, though it was not quite as hot as the previous week.
High temperatures in Jackson were very consistent, ranging from 84ºF on July 25 to 89ºF on July 22. Low temperatures ranged from 38ºF on July 20 to 55ºF on July 23.
Friday was the only day over the previous seven days with any showers and thunderstorms in the area, most of which occurred during the morning hours as a disturbance moved through. However, these were “dry” storms that only produced a trace of rainfall in Jackson.
While the three-month period from April to June was wetter than average across Teton County, July has been exceptionally dry so far, even by our standards. The Town of Jackson has only received 0.05 inches of rain so far this month. Average July rainfall is 1.12 inches.
Areas further north have received more rainfall this month, including Moran who has picked up 0.31 inches since July 1 – but this is still well below average.
Forecast for Tuesday (7/26) to Monday (8/1)
A strong ridge of high pressure is centered over the West Coast currently with a heatwave ongoing across the Pacific Northwest. The core of the heat will remain west of Jackson, so we will continue to see above average but not exceptionally hot temperatures.
Dry and stable air associated with the high pressure ridge will lead to mostly sunny skies and relatively light winds on Tuesday and Wednesday. Highs will reach the mid 80s on Tuesday before warming up into the upper 80s on Wednesday. The only chance of storms on Tuesday and Wednesday will be east of the Continental Divide where there are higher moisture levels.
Our skies have turned a bit hazy due to light smoke arriving from fires in Idaho and California, but air quality is currently in the “Moderate” range.
There are not any significant influxes of smoke forecasted at this time which is good news. However, that can always change if there are any new fire starts upwind of Jackson, or if ongoing fires in California and Idaho were to exhibit extreme fire behavior and growth at any point.
On Thursday and Friday, the weather pattern will turn a bit more active as high pressure starts to weaken a little bit, allowing for some monsoonal moisture to sneak into the area. This will result in a good chance of mountain thunderstorms on both Thursday and Friday.
Steering winds aloft will be light on Thursday and Friday from northwest to southeast, and this will likely keep most of the storm activity anchored to the Tetons and surrounding mountain ranges with lower chances of storms drifting into the valley.
The Town of Jackson will only see a slight chance of storms on Thursday and Friday as northwest winds aloft are unfavorable for storms and precipitation over the Southern JH valley, while the Northern JH Valley around Jackson Lake and the Palisades/Alpine area further south will stand a better chance of seeing a storm than Jackson.
Storms that develop over the Tetons will be moving slow enough that locally heavy rain will be possible along with frequent lightning. So if you’re hiking in the Tetons, be prepared for storms that could persist for longer than usual. Friday’s storms will have a better chance of producing wetting rains compared to Thursday once the monsoonal moisture has become a bit more established.
Heading into the weekend, drier air will return leading to a reduced threat of thunderstorms. An afternoon storm still couldn’t be ruled out on Saturday and Sunday, but the threat appears marginal at this time.
As far as temperatures go, we will see a slight cooling trend on Thursday and Friday, before warming up again on Saturday and Sunday – possibly reaching 90ºF in the valley on Sunday.
Early next week, monsoonal moisture will begin to creep back into the picture but the timing is uncertain. We could see a little bit of moisture sneak in as early as Sunday (hence the slight chance of thunderstorms), but the leading edge of this moisture arrival is more likely on Monday if not later.
Extended Outlook
Next week is looking more interesting as high pressure migrates eastward into the Southern Plains and a trough of low pressure sets up over the Northwest.
South/southwest winds in between these features could potentially transport significant amounts of monsoonal moisture into our area. This would result in more widespread thunderstorm activity across Teton County mid to late next week with the potential for wetting rains.
Temperatures will also trend cooler next week with highs currently projected to reach the low 80s in the valley most days, which is close to average for early August.
Alan Smith, Meteorologist
Town of Jackson Climatology for July 26 – August 1
Average High: 83
Average Low: 42
Record High: 96 (July 31, 2000)
Record Low: 27 (July 29, 1959 and July 30, 1966)
Precipitation Since Oct 1st: 12.84″ (89% of Average)
