JACKSON, Wyo. – A dry thunderstorm pattern will be in place through Friday with typical storms producing gusty winds and little rainfall, with an increased potential for lightning-triggered fires. On Saturday and Sunday, moisture levels will increase with the potential for thunderstorms to produce locally heavy rain.
A Very Dry August So Far
Teton County received virtually no rainfall during the first 12 days of August, which is a big change from the past few Augusts, which were quite wet (especially early in the month).
The North American Monsoon has been on a hiatus during the past few weeks, during a time of year when it is typically the strongest.
Despite the lack of moisture, the weather has been very comfortable for outdoor recreation, and wildfire smoke has been almost nonexistent so far this summer, which is a welcome change from last year.
Last Wednesday, the high in Jackson hit 88ºF, but then a cold front moved through later in the week, resulting in three days of early fall-like conditions.
From Friday through Sunday, the high in Jackson only reached the low 70s each day, and we also briefly dipped down to freezing on Sunday morning – the first freeze of the season, and a couple of weeks ahead of the average first freeze in town.
In recent days, summer heat has returned with a high of 89ºF recorded in Jackson on Tuesday. However, clear nights with limited cloud cover tend to lead to chilly overnight valley temperatures by this point in the year, now that the days are getting shorter.
Upcoming Weather Pattern
The North American Monsoon is finally showing some signs of life, and thunderstorms are returning to the picture in Jackson Hole as a result.
Initially, we are experiencing a weak monsoon pattern from Wednesday to Friday as only limited amounts of moisture will reach our area. The downside is that gusty winds and low relative humidity at the surface are also characteristics of this pattern.
Warm air and a lack of moisture in the low levels of the atmosphere will result in a mainly “dry” thunderstorm setup, with most storms producing only brief light rain and strong wind gusts.
Not the kind of setup you want to see when fire danger is “very high”, and also a reason why the National Weather Service issued a Red Flag Warning on Wednesday.
On Thursday and Friday, non-thunderstorm winds do not look as strong compared to Wednesday, and relative humidity may be a touch higher. But we are still looking at a dry thunderstorm setup (only some highly localized, brief downpours at best), and the potential for lightning-triggered fires will very much remain a concern.
Thunderstorm coverage should be fairly isolated on Thursday and Friday, with most of the action happening during the afternoon… unlike the surprise morning thunderstorm over the Tetons on Wednesday that was likely triggered by a robust shortwave trough moving across the area.
On Saturday and Sunday, a deeper surge of monsoonal moisture will arrive from the south/southwest as a low pressure trough sets up west of our area.
This will likely result in an uptick in thunderstorm coverage on both days, along with better potential for storms to produce locally heavy rain. If you have outdoor plans, be aware of the increased thunderstorm threat and be sure to pack a rain jacket.
The 7-day rainfall projection from the European Ensemble Model does have a decent amount of rain showing up for our area compared to recent weeks. Again, Saturday and Sunday have the highest potential for meaningful rain across the area, but in a hit-or-miss thunderstorm pattern, we’ll see what happens.
During the first half of next week, a drying trend is expected as monsoon moisture retreats to the south.
However, longer range models are in good agreement in projecting another surge of monsoonal moisture by the weekend of August 22nd-24th, and lasting into the week of the 25th.
This is still a ways out, of course, and a lot can change between now and then. But it’s a more consistent monsoon signal than we have seen at any point this summer, so it will be something to keep an eye on moving forward.
As far as temperatures go, they should generally be seasonal over the next couple of weeks (average highs in the low 80s) with some minor fluctuations. This weekend, we will likely see some cooling with better moisture in place, followed by a warming trend early next week when drier weather returns.
Alan Smith, Meteorologist
