JACKSON, Wyo. – Subtropical moisture arriving in advance of an approaching low pressure system will result in a good chance of thunderstorms from late Wednesday afternoon through Thursday morning. Cooler and drier conditions will prevail on Friday, followed by a warm-up this weekend.
Recent Weather Conditions
Following a mid-June cold snap that resulted in record low temperatures last Wednesday, we have since warmed up significantly with highs in the 80s over the past several days. The two hottest days during this stretch were on June 23 and June 25 when we hit 87ºF in Jackson.
So far this month, temperatures are running 3.2ºF above average in the town of Jackson and 3.7ºF above average at the Moran weather station near Jackson Lake.
We also did not receive any rainfall during the previous seven days. We have only received 0.46 inches of rain in the town of Jackson so far this June, which is well below average. Average rainfall during the month of June is 1.59 inches.
Thunderstorm Chances on Wednesday-Thursday
We will briefly see a more active pattern during the middle of the week. A trough of low pressure is approaching our area from the Pacific Northwest, while subtropical moisture is moving into our from the south ahead of this trough. This moisture is associated with an early onset of the North American Monsoon.
Early cloud cover has suppressed early afternoon thunderstorm chances on Wednesday, but increasing moisture, instability, and atmospheric dynamics along with better surface heating will result in a better chance of thunderstorms during the late afternoon and evening hours.
There is also a good chance of thunderstorms during the overnight and morning hours on Thursday, which will coincide with the best dynamics of the approaching trough. We will have some elevated instability during the morning hours, which refers to instability aloft that is not dependent on surface heating from the sun (which is typical of a more common afternoon thunderstorm setup).
Thunderstorms will be scattered in nature and fast-moving, with storm motions varying from WSW>ENE to SW>NE. Storms will be capable of producing frequent cloud-to-ground lightning, brief heavy rain, pea to marble size hail, and locally strong wind gusts of 40-50+ mph.
Despite the uptick in moisture, fast storm motions and scattered coverage will limit rainfall amounts with most areas seeing a trace to 0.2 inches. Stronger storms or training of thunderstorms (i.e. multiple storms tracking over the same area) could potentially result in highly localized rainfall of a half-inch or more.
Drier air will arrive on the backside of this system by midday Thursday with a drying trend expected through the afternoon. Temperatures will be a little cooler on Thursday afternoon with highs in the mid 70s and gusty winds are also expected.
East of Jackson Hole, thunderstorm chances will be higher across Central and Eastern Wyoming including a threat for strong to severe thunderstorms.
Upcoming Pattern – Friday (June 28) through Thursday (July 4)
Cooler and drier conditions will prevail behind the mid-week weather system on Friday with highs in the low 70s under mostly sunny skies. Winds will also remain on the breezy side, making for a comfortable afternoon to hit the lower-elevation trails.
On Saturday, high pressure will rebuild over the Central Rockies and we will warm right back into the low 80s. Sunday will be even warmer with highs in the mid 80s. Average highs at the end of June are in the upper 70s for perspective.
On Sunday and Monday, another trough of low pressure will approach from the Pacific Northwest. We may see just enough moisture arrive for a chance of isolated showers and thunderstorms on either or both days.
So while we do have some rainfall chances over the next week, rainfall amounts will be light and spotty except for maybe some isolated areas on Wednesday night/Thursday.
Here are projected rainfall totals over the next 7 days, representing the average of 50 simulations of the European weather model.
Temperatures will also cool off briefly on the backside of this system on Monday and Tuesday with highs in the 70s. By the Fourth of July next Thursday, warmer and drier conditions will return with highs in the 80s.
For the remainder of the Fourth of July weekend (July 5-7), a generally hot and dry pattern is expected with highs well into the 80s.
Alan Smith, Meteorologist
