Summary
We will see more sunshine during the first part of the day on Friday followed by widely scattered afternoon t-storms with storms moving S to N. Sat looks like a near repeat with widely scattered afternoon t-storms. From Sun to Wed, an uptick in shower/t-storm activity is expected followed by a possible brief drying trend late next week. Valley highs in the low 70s this weekend & 60s next week.
Short Term Forecast
A cluster of strong thunderstorms developed across the Star Valley area and moved into the Southern Jackson Hole Valley and Southern Teton Range on Thursday evening.
The southern part of the Tetons and JH Valley saw a good soaking along with frequent lightning with the cluster gradually weakening as it moved north across the Tetons. The town of Jackson picked up a half-inch of rain.
Forecast for Friday:
Valley fog early on Friday morning will gradually dissipate as the morning progresses with more sunshine expected region-wide through the morning hours compared to Thursday.
We have seen some drier air working its way into our area from the south as the low pressure system from previous days moves northward into the PNW. However, enough lingering moisture along with daytime heating/instability will result in a good chance of thunderstorms this afternoon – though coverage looks more scattered in nature.
I wouldn't rule out a storm as early as 11am, but the highest threat of storms will be after 1pm. Storm chances will linger into the evening before drying out overnight. Storms will move from south to north and could produce brief downpours.
One possible limiting factor to Friday's storm potential is that models are hinting at a stable layer at around 20,000 feet above sea level moving in mid to late afternoon. Instability will be high in the lower levels of the atmosphere, supporting strong updrafts, but whether or not the stable layer (or cap) aloft will be enough to inhibit thunderstorms is a question mark.
Storms chances look roughly equal region-wide across Northwest Wyoming, though I suspect chances/coverage will be a bit higher from Alpine north to Yellowstone with comparatively lower chances/coverage south of Alpine and Bondurant where drier air will be moving in from the south.
Forecast for Saturday:
Saturday looks like a near repeat to Friday with scattered afternoon thunderstorms expected once again. I wouldn't rule out a storm as early as 11am-noon, but the highest threat will be after 1pm. Storms will move in a south-to-north direction and could produce brief downpours.
Similar to Friday, I'm also seeing hints of a stable layer/cap moving in mid-afternoon around 20,000 feet. Once again, there is a question as to whether or not this will inhibit thunderstorm development, or if updrafts are strong enough to weaken the cap and break through.
A chance of storms will linger into early Saturday evening before drying out overnight.
Forecast for Sunday:
A new slow-moving trough of low pressure will move into the Southwest U.S. near the California/Nevada border, with an uptick in moisture and energy arriving from the south/southwest.
As a result, we will likely see an increase in thunderstorm activity during the afternoon hours compared to Friday and Saturday. Heavy rain will also be possible with stronger storms.
Bottom line: The weekend is looking nice overall with seasonally warm temperatures and abundant sunshine during the morning to midday hours. But thunderstorms will be a possibility each afternoon, with Sunday being more active than Friday and Saturday.
Extended Forecast
Outlook for Monday, June 12 to Sunday, June 18:
Monday looks like another active day with a good chance of showers and thunderstorms – most likely in the afternoon/evening hours but also possible in the morning & overnight hours.
Winds aloft will be out of the southeast with a trough of low pressure centered over Southern Utah, which will likely favor Star Valley, Pinedale, and the Southern Tetons/valleys, but we'll see how this looks on Monday's forecast.
On Tuesday, we will be in between the low pressure system across the Southwest and a new approaching trough from the northwest, with a possible shift in winds to west/northwest (blowing from the west/northwest). However, significant moisture is projected to remain in place, which should result in another active day with good chances of showers/thunderstorms.
The trough of low pressure from the northwest is projected to move across our area on Wednesday (and possibly early Thursday), resulting in a chance of showers/thunderstorms at all hours of the day. We should also cool down a little bit, though a significant cooldown is not anticipated at this time.
Behind this trough, we may dry out briefly late next week. However, another trough is expected to approach from the northwest late next week, and it may dig a bit further south before reaching our area, potentially tapping into deeper moisture and leading to a return of thunderstorm chances by the weekend of the 17th-18th.
Thanks so much for reading and have a great weekend! Next update on Monday (June 12).
Alan Smith
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