Wet pattern expected late this week and over the weekend

JACKSON, Wyo. — Jackson Hole has enjoyed a nice stretch of weather recently with highs in the low 70s over the past couple of days. However, a slow-moving storm system will bring several days of wet and unsettled weather over the second half of the week.

Tuesday will be the last truly nice day for a while with highs in the 70s and no rain expected. Wednesday will then be a transition day as a large trough of low-pressure approaches from the west.

Conditions will start out nice on Wednesday, but clouds will increase during the afternoon as moisture arrives from the southwest, and scattered showers and thunderstorms will develop during the afternoon and evening hours.

In other words, not a washout – but if you’re recreating after work, be prepared for a possible round of thunderstorms, as many of the ingredients (moisture, unstable atmosphere, upper atmospheric “energy”, and a favorable southwest flow) will be in place.

The low-pressure system will then stall west of Jackson Hole for several days, resulting in a prolonged stretch of unsettled weather and southerly flow from Thursday through Sunday.

The moisture arriving from the south will have origins in the warm subtropical South Pacific Ocean. As a result, we should expect heavier downpours in Jackson Hole compared to what we’ve seen in recent weeks.

The challenge of forecasting these “stalled out” low-pressure systems has to do with the daily timing of showers and thunderstorms. The bottom line in a pattern like this is that rain will be possible at all hours of the days and nights from Thursday through Sunday, though the heaviest showers are more likely in the afternoons and evenings when the atmosphere is most unstable.

The latest model trends indicate that Friday is favored for the heaviest and most widespread rainfall, while Thursday and Saturday should feature more intermittent (but still locally heavy) showers.

The southerly winds associated with this system will limit the rain shadow effect of the Tetons, which happens when winds out of the west or northwest encounter the Tetons at a perpendicular angle. As a result, the valley will see frequent showers and occasional heavy downpours in addition to the higher elevations.

During the Wednesday through Saturday timeframe, Jackson Hole will remain in the “warm sector” of the low-pressure system – meaning temperatures will be relatively mild and snow levels will be high as a result.

More specifically, snow levels should remain at 11,000 feet or higher from Wednesday through Saturday for the most part, but could briefly dip to 10,000 feet or lower at times. Still, this will need to be monitored – for example, if the stalled front were to shift slightly farther east into Western Wyoming than what models are currently projecting, then lower snow levels will be possible.

On Sunday, the low-pressure system should finally get moving and sweep across Western Wyoming Wyoming, resulting in another uptick in showers. A cold front can be expected with this feature as well, leading to cooler temperatures and falling snow levels – possibly down to pass level on Sunday night.

Cooler temperatures will prevail on Monday with possibly some lingering showers. We may not see much of a break after this system either as long-range models are hinting that another storm system could approach sometime next week.

The early call for total rain/precipitation amounts from this storm system is 1-2 inches for the Tetons from Wednesday through Sunday and 0.5-1.5 inches for the Jackson Hole Valley. Stay tuned to future forecasts for adjustments moving forward.

While the rain will not be ideal for outdoor adventures, we badly need the moisture as Teton County and Western Wyoming are currently in a drought. Precipitation so far in May has been less than 50% of average in Teton County, continuing the dry trend experienced since the beginning of March.

Alan Smith, Meteorologist

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