For anyone living or spending time in Northwest Wyoming in recent weeks, you’ve probably noticed the pattern has been quite active for thunderstorms. Afternoon thunderstorms have been almost a daily occurrence across the Tetons and surrounding mountain ranges over the past couple of weeks.

The North American monsoon has picked up recently, and while it is not an especially strong monsoon this year, the position of high pressure has been such to allow for a favorable flow of moisture in Western Wyoming from the south. Frequent low pressure systems over the Pacific Northwest have also helped to send upper level waves into Wyoming as well to help with thunderstorm development.

If we take a look at the water vapor satellite image, we can clearly see the flow of moisture from the south (image source: College of DuPage).

water vapor satellite image august 7 2019
Water vapor satellite image – Wednesday morning, August 7th, 2019

Thunderstorm Potential Increases on Thursday

We are seeing an influx of monsoonal moisture into the Jackson Hole area today (Wednesday), but the combination of mid to high levels cloud cover this morning and relatively stable air aloft should keep thunderstorm coverage more isolated Wednesday afternoon.

Still, we are likely to see a few showers and thunderstorms fire over the higher elevations Wednesday afternoon, producing brief/light rain, gusty winds, and occasional cloud to ground lightning.

Wednesday night through Thursday, we’ll see a deeper surge of monsoonal moisture arrive, being driven by a low pressure system moving into the Pacific Northwest. Check out the model projected precipitable water anomalies for Thursday afternoon – well above average (image source: weathermodels.com). Precipitable water is a measure of total column moisture from the surface to about 30,000ft, and a good indicator of “fuel” for thunderstorms.

gfs model precipitable water august 8 2019
GFS Model Precipitable Water Anomaly for noon MST (18Z) Thursday (source: weathermodels.com)

As a result, the potential for thunderstorms will increase significantly Thursday afternoon, with frequent cloud to ground lightning and locally heavy rainfall possible. Heads up if you have outdoor plans in the Tetons, Yellowstone, or Wind River Range.

The one possible caveat to the forecast for Thursday is cloud cover. If skies remain overcast from the morning through early afternoon, this could suppress or at the very least delay thunderstorm activity until late in the day. However, if we have early sunshine, then the atmosphere will become ripe for thunderstorm development by midday or early afternoon.

If you’re heading outdoors Thursday, take extra precautions to be off exposed peaks and ridges before noon, and of course bring your rain gear.

Trend toward cooler and drier weather this weekend

Friday will be an in-between day as the deepest monsoonal moisture begins to shift north and east of Jackson Hole, as a trough of low pressure advances inland from the Pacific Northwest. We’re still likely to see some scattered afternoon thunderstorms Friday afternoon, with perhaps a bias toward Yellowstone and the crest of the Wind Rivers, versus the Tetons.

On Saturday, monsoonal moisture continues to decrease. However, a cold front will arrive from the west, which could very well trigger some showers and thunderstorms with light rainfall. Timing looks to be during the afternoon, but this could shift a few hours either direction since we’re still several days out.

Check out the approaching trough of low pressure on Saturday, which will help to scour out the moisture and bring cooler air as well (image source: weathermodels.com).

gfs model height anomaly low pressure system
GFS Model 500-millibar height anomaly for noon MST (18Z) Saturday August 10, 2019

On Sunday, we will see noticeably cooler temperatures, breezy conditions, and increased sunshine. Highs are only projected to peak around 70 on Sunday in Jackson, giving us a taste of early fall. Models still indicate there could be just enough moisture and instability for a low threat of afternoon thunderstorms.

Cooler and drier than average next week, but also windy at times

From Monday through the first half of next week, the drying trend will continue and at this point thunderstorm chances look to be close to zero for a few days. This should be a great time to get out for some bigger outdoor adventure objectives at the higher elevations. The only caveat is that conditions could be quite windy at times since the jet stream will be just north of the area.

Temperatures are projected to be on the cool side of average next week as well, with highs in the 80s in Jackson this week being replaced by highs in the 70s next week. Take a look at the one-week temperature trends projected for Jackson (image source: weathermodels.com).

jackson wyoming 7 day temperature forecast
Jackson 7-day temperature outlook

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