JACKSON, Wyo. — Monsoonal moisture working its way into Western Wyoming will result in an uptick in thunderstorm activity across the Tetons and Yellowstone this weekend. However, conditions will dry out in time for the Fourth of July itself on Monday with seasonally warm temperatures along with breezy winds expected throughout the weekend.
A little bit of monsoonal moisture (associated with the North American Monsoon over the Southwest U.S.) has arrived already as of early Friday, which coupled with an upper air disturbance resulted in several rounds of thunderstorms tracking over the Tetons starting early Friday morning.
A similar pattern will remain in place for the remainder of Friday with scattered thunderstorms re-developing from time to time. Rainfall rates will generally be light (or briefly moderate) during Friday’s storms, and the storms will also be fast-moving from west to east.
However, active cloud-to-ground lightning and gusty winds can be expected with Friday’s thunderstorms. Highs on Friday will top out in the upper 70s to low 80s in the valley, depending on the extent of the cloud cover associated with this thunderstorm activity.
On Saturday, more abundant monsoonal moisture will arrive from the south, and a more active thunderstorm day is expected as a result.
There is a slight chance of showers and thunderstorms early in the day on Saturday associated with an upper air disturbance, and the best chance of morning activity will be over Yellowstone.
As the sun heats up the lower levels of the atmosphere, thunderstorms will become more likely in the afternoon and coverage should also be greater compared to Friday. Storms on Saturday will be capable of brief heavy rain, frequent cloud-to-ground lightning, small hail, and gusty winds. In other words, be prepared and keep your eyes on the skies if you have outdoor plans.
Highs on Saturday will top out in the upper 70s to low 80s in the valley once again.
On Sunday, we will start to see a decrease in moisture over the course of the day, but a stronger upper air disturbance is also expected to arrive early in the day and should interact with lingering moisture and instability to result in a chance of showers and thunderstorms.
This will include a threat for morning thunderstorm activity with the best chance likely occurring around midday to early afternoon. Sunday’s thunderstorms should be less numerous and less intense compared to Saturday, and storm chances should also decrease by later in the afternoon and into Sunday evening as drier air starts to work its way in from the west.
Highs on Sunday will reach the low 80s and winds will also become gusty during the afternoon out of the southwest.
For the Fourth of July on Monday, a much drier airmass will be in place and thunderstorm chances will be close to zero as a result. However, winds will be quite strong throughout the day, so please be careful with campfires, fireworks, etc. Fire danger is moderate right now, but there is a 99-acre fire burning in the Bondurant area currently.
Highs on Monday will reach the upper 70s to low 80s in the valley. Evening temperatures around the time fireworks begin in Jackson will be in the upper 50s to low 60s.
Beyond the Fourth of July, a strong ridge of high pressure will build over the Rocky Mountains and Intermountain West later next week. This will result in a transition to hot and dry weather across Jackson Hole with high temperatures pushing 90 degrees by the end of next week.
Alan Smith, Meteorologist
