JACKSON, Wyo. – Multiple clusters of thunderstorms tracked across the Tetons and Jackson Hole Valley on Tuesday, producing rainfall amounts of 0.3 to 1.0 inches across Teton County, including 0.49 inches in the town of Jackson and 0.94 inches at Jackson Hole Mountain Resort.
Recent Weather
Following a 10-day stretch of dry weather, Tuesday’s pattern delivered some much-needed rainfall to the area.
Tuesday’s storms were not “monsoonal” in nature. Rather, a potent trough of low pressure originating in Canada deepened over the Northern U.S. Rockies on Tuesday, with Pacific moisture reaching our area from the north and the west.
Warm air in the low levels of the atmosphere, cooler air aloft (steep temperature lapse rates), and the uptick in moisture resulted in an unstable atmosphere conducive to thunderstorms.
Also, strong westerly winds aloft and consistent upper-level dynamics associated with the trough resulted in numerous thunderstorms developing and tracking across the Tetons from west to east.
The first round of storms on Tuesday afternoon produced light rain and gusty winds as low-level moisture was lacking initially. But as deeper moisture arrived, storms began to produce heavy downpours later on Tuesday afternoon and especially on Tuesday evening.
Rainfall was widespread across Teton County, with totals ranging from 0.3 to 1.0 inches in most areas.
Jackson Hole Mountain Resort and the Teton Range saw the heaviest rainfall amounts, with all four rain gauges at JHMR recording amounts between three-quarters of an inch and an inch of rain. The Raymer Plot at 9,657 feet received the highest rain total of 0.94 inches.
Thunderstorm rainfall is often hit-or-miss in the summer, and we saw just the right combination of moisture, instability, and upper-level “energy” to produce widespread rainfall that led to many “hits” across the area.
The town of Jackson received 0.49 inches of rain on Tuesday, which is the highest 24-hour rain total (in town) in the month of July since 2018.
This is also more rain than what fell in the entire month of June (0.37 inches). For the month of July as a whole, the town of Jackson has received 0.87 inches so far, which is actually above average (July is the only month of the year in which average precipitation is less than an inch in Jackson).
While we could certainly use more consistent rain later this summer, this was a nice bonus following a dry early summer season.
Leading up to Tuesday, we had been in the middle of a dry spell since the Fourth of July. This included several hot days with highs in the upper 80s to low 90s. Jackson had its first two 90-degree days of the season over the past week, including a high of 91ºF on Sunday.
The chart below shows recorded high and low temperatures and rainfall over the previous 7 days in Jackson:
Upcoming Weather Pattern
On Wednesday and Thursday, a return to dry and sunny weather will occur in the wake of Tuesday’s system. High temperatures will reach the low 80s on Wednesday and mid-80s on Thursday in Jackson. Winds will also become gusty on Thursday as a disturbance passes north of the area.
On Friday and Saturday, monsoonal moisture will arrive from the south, resulting in a good chance of scattered afternoon thunderstorms. This looks like a relatively modest monsoon “surge” with hit-or-miss thunderstorms, but locally heavy downpours will be possible under stronger storms.
The pattern is less certain from Sunday through the middle of next week. Another trough is projected to deepen over the Northern Rockies with monsoonal moisture retreating south of our area.
But if the trough deepens far enough south across Idaho and Wyoming, then we could see enough Pacific moisture arrive for afternoon thunderstorm chances. If the trough remains centered further north, then thunderstorm potential would be lower. Weather models are currently in poor agreement on this pattern.
For now, a low to moderate potential for afternoon thunderstorms from Sunday through next Wednesday is warranted.
The European Ensemble Model, which represents the average of 50 simulations of the European weather model, projects relatively light rain amounts across our area over the next 7 days.
Looking further out, a drying trend is expected during the second half of next week (July 24-27, roughly speaking).
During the final few days of July, some longer-range models are hinting at an uptick in monsoonal moisture from the south, which would lead to increased thunderstorm potential. However, confidence is low this far out.
Alan Smith, Meteorologist
