JACKSON, Wyo. — A change to the weather pattern is coming this week as a surge of monsoonal moisture arrives from the south. Thunderstorm coverage will increase as a result, including the potential for active cloud-to-ground lightning and locally heavy rains. Outdoor enthusiasts including hikers and climbers should plan accordingly.
When it comes to thunderstorms, rainfall can be hit or miss and there are often competing factors that can inhibit or prohibit the development with widespread thunderstorms with wetting rains. While available moisture will be in place this week, there will be some obstacles as well. The bottom line is that thunderstorm and lightning risk will be elevated for hikers and climbers this week, while the question of whether or not we see widespread beneficial rain remains to be seen.
High-level clouds are already increasing on Monday afternoon as the leading edge of the moisture is arriving. However, high pressure in place along with southerly flow is resulting in hot temperatures. As of 3 p.m. Monday, temperatures had risen into the low 90s in the Jackson Hole Valley.
Monday Afternoon and Monday Night Outlook
A few showers will be possible later on Monday afternoon and into early evening, but initially, little rainfall is expected.
The amount of thunderstorm activity that develops later Monday remains to be seen as there are conflicting factors at play. Increasing moisture and ripples in the upper atmosphere are factors that would favor thunderstorm development, but flat layers of clouds arriving over Western Wyoming could have a stabilizing effect and suppress thunderstorm activity.
Storms that develop on Monday afternoon and early evening will likely be on the “drier” side as moisture will just be starting to increase. As a result, there are concerns for lightning-triggered wildfires in the area, not to mention the gusty winds that typically accompany dry thunderstorms.
Due to these factors, the National Weather Service has issued a Red Flag Warning for fire danger for Teton County and nearly all of Western Wyoming for Monday afternoon and evening.
As monsoonal moisture filters into the area, scattered showers and thunderstorms will continue possible during the later evening and overnight hours and should produce locally higher rainfall rates compared to the initial afternoon storms. In other words, if you’re camping, make sure to leave your rain fly on.
Tuesday Outlook
Moisture levels and humidity will be significant across the area on Tuesday with more clouds and better rain chances expected. Widespread cloud cover with scattered light showers (and perhaps a thunderstorm) will be possible through the first half of the day on Tuesday. The early cloud cover should also result in both mild morning temperatures and cooler afternoon temperatures.
Initially, the extensive cloud cover may suppress stronger and more widespread thunderstorms from developing, but if and when we see any clearing by the afternoon, then heating from the sun combined with ample moisture should allow for scattered or widespread thunderstorms to develop.
The only limiting factor could be if extensive cloud cover lingers for most of the day and inhibits thunderstorm development. But the potential is certainly there for strong thunderstorms (by our standards), frequent cloud-to-ground lightning, heavy rainfall rates and significant runoff on steep slopes. Storm motions on Tuesday will be west/southwest to east/northeast.
The good news is that fire danger will be lower on Tuesday due to higher relative humidity levels and wetting rains that accompany thunderstorms. Still, we’ll have to keep an eye out for rogue lightning strikes that occur away from rainfall and thunderstorms, which will still present a minor threat for lightning-triggered fires.
Mid to Late Week Outlook: Wednesday – Friday
On Wednesday, we should see more clearing in the morning, allowing for temperatures to heat back up into the mid to upper 80s. Scattered thunderstorms will also develop in the afternoon with the potential for localized downpours.
Thursday looks like another active day for thunderstorms – more so than Wednesday – thanks to a disturbance arriving from the southwest. Ample moisture will remain in place, resulting in a threat for heavy rainfall with thunderstorms.
On Friday, a drying trend will begin, resulting in more isolated thunderstorm coverage along with lighter rainfall.
Teton County: Potential Rain Amounts (Next 5 Days) for Areas that Experience Showers/Thunderstorms
Weekend Outlook
The drying trend will continue over the weekend with lower humidity and more isolated thunderstorm activity. Any storms that develop will likely be of the drier variety, which will result in a return of fire concerns unless rainfall earlier in the week is significant and somewhat widespread.
Temperatures will remain above-average this weekend with highs in the upper 80s.
Smoke and Fire Conditions
As for smoke conditions this week, it will vary day by day and even hour by hour. Generally speaking, Monday afternoon and Tuesday should be less smoky, with perhaps a bit more smoke arriving on Wednesday. Changing winds and rain/thunderstorm activity will result in fluctuations in smoke activity.
Heading into the weekend, we may see a trend toward more smoke and reduced visibility and air quality. Winds aloft will be transitioning to west/southwest during this time, allowing for more direct smoke transport from large fires in Southern Oregon and Northern California.
Closer to home, there are no ongoing significant fires near Jackson Hole, but there are a couple of fires in the region to keep an eye on.
The Goose Fire located west of West Yellowstone has burned 6,258 acres and is only 21% contained. This fire has contributed to smoke in Jackson Hole at times when winds have been out of the north.
Last Friday, the Shale Creek Fire started in the Kemmerer Ranger District of Southwest Wyoming, located southeast of Afton and due east of Cokeville. So far, this fire has consumed 75 acres.
Outlook for Next Week
Following a drier weekend, another surge of monsoonal moisture will be possible early next week. This would lead to another increase in thunderstorm activity along with the potential for wetting rains and perhaps some temporary smoke relief.
Alan Smith, Meteorologist
