JACKSON, Wyo. — We’re coming out of another active weather period across Northwest Wyoming with numerous thunderstorms and abundant rainfall over the past several days, along with a dip in temperatures. However, over the rest of this week and into next week, we will see our first real extended stretch of summer-like weather.
June 14-20 Recap
A slow-moving low pressure system resulted in another active weather weekend across the Tetons and Jackson Hole that continued into the early part of this week.
We’ve been in a weekly cycle featuring active weekend weather for quite some time now. In case you’re wondering, Jackson has received measurable rainfall at least one day every weekend (Saturday or Sunday) since the beginning of May.
Last week started out similar to this week with chilly temperatures coming out of the weather pattern than produced the flooding in Yellowstone and severe thunderstorm wind damage around Jackson Hole. However, we saw our warmest temperatures of the year so far later in the week with highs in the 80s.
Conditions turned unsettled and also very windy over the weekend as a trough of low pressure set up to our west, resulting in thunderstorms (and a fantastic lightning show) over the Tetons on Friday night followed by clouds, gusty winds, and isolated showers on Saturday.
Conditions then turned wet on Sunday as a series of strong thunderstorms with frequent lightning and heavy downpours moved through from the south, starting on Sunday morning and continuing into Sunday evening.
A cold front also arrived on Sunday with much cooler temperatures. Periods of showers and thunderstorms continued to move through on Monday and light snow fell above 8,000 feet with the Tetons revealing dustings of snow during breaks between showers/storms.
A funnel cloud was also observed near Driggs/Tetonia on Monday, or more specifically a “cold air funnel”. Cold air funnels form after a cold front has moved through when temperatures are very cold aloft but solar radiation heats the surface enough to result in an unstable atmosphere. Winds near the surface and aloft can differ enough in this post-frontal airmass to result in rotation, allowing a funnel cloud to form. Cold air funnels are typically harmless and rarely ever reach the ground.
The Jackson weather station received 0.59 inches of rain over the past week, nearly all of which fell between Sunday morning and Monday evening. Observed and estimated rain totals were similar throughout Teton County and Yellowstone, generally ranging from a half-inch to three-quarters of an inch of rain, possibly approaching an inch across some of the higher elevation areas.
This rain was more beneficial compared to last week, as it provided us with good moisture but without the significant flooding issues that occurred last week.
Temperatures were all over the place during the past week with three days of highs in the 50s in Jackson, one day with a high in the 60s, and three days with highs in the 80s.
High temperatures ranged from 53ºF on June 14 to 86ºF on June 17, and low temperatures ranged from 30ºF on June 16 to 47ºF on June 19.
Forecast for Tuesday (6/21) to Monday (6/27)
We got a nice taste of summer late last week, but it will arrive for real this week with no significant cool snaps on the horizon.
Tuesday morning is starting out chilly with areas of fog and low clouds. However, this low cloud cover will quickly mix out as the day progresses and it will turn into a beautiful day with highs reaching the low 70s in the valley under sunny skies. Winds will also be light for a change.
Temperatures will start out near freezing in the valley on Wednesday but will warm up quickly with highs in the upper 70s under mostly sunny skies. Winds will pick up a bit out of the southwest during the afternoon, but overall, it looks like a wonderful day to get outside.
The weather will turn slightly more unsettled late this week as some moisture associated with the North American Monsoon (which has started much earlier than usual) attempts to work its way into the Tetons from the southwest.
Thursday will be warmer with highs in the low 80s along with breezy afternoon winds, but isolated thunderstorms will become a possibility later in the afternoon and into the evening. Isolated showers will remain possible overnight as well, but any rainfall be light and spotty.
Friday is more uncertain as a disturbance will be passing to our north and a cold front will arrive from the north at some point.
Depending on the northward/southward extent of the disturbance and the timing of the cold front, moisture could increase enough ahead of the front to result in an uptick in showers or thunderstorms. Or, the cold front could arrive early enough in the day to “push” the moisture southward and keep us dry.
Weather models are in poor agreement on how Friday’s pattern will play out, but we can at least expect a slight chance of showers on Friday morning followed by a better chance of showers/thunderstorms on Friday afternoon and a drying trend on Friday evening. Rainfall amounts should be light overall, and temperatures will cool off into the 70s for highs with breezy winds also expected.
The weekend is looking quite nice as drier air will be arriving behind Friday’s cold front. Highs on Saturday will reach the mid 70s in the valley and winds will likely be on the stronger side in the wake of Friday’s disturbance. However, thunderstorm chances look minimal with only a slight chance of a stray afternoon storm developing over the higher elevations.
On Sunday, we will see slightly warmer temperatures with highs near 80 along with lighter winds under mostly sunny to partly cloudy skies. Thunderstorm chances will increase on Sunday afternoon compared to Saturday, but activity looks to be fairly isolated at this time with any storms producing only light rain.
Monsoonal moisture will increase over the Great Basin this weekend and is projected to work its way toward the Tetons from the northwest on Monday (as opposed to the south or southwest) and this could result in an uptick in thunderstorm chances over the Tetons on Monday afternoon. Northwest winds aloft are less favorable for storms to “survive” upon reaching the valley, with a better chance of storms over the Northern JH Valley compared to town. However, we’re still far enough out that the details could change.
Warm temperatures with relatively frequent afternoon thunderstorm chances can be expected for most of next week with a ridge of high pressure taking hold over the Western U.S., while moisture associated with an active monsoon pattern over the Southwest U.S. will continue to work its way into Jackson Hole from time to time.
Overall, temperatures are expected to be above average for most of next week with highs getting into the 80s in the valley most days. Thunderstorm and rain chances will fluctuate from day to day.
Alan Smith, Meteorologist
Town of Jackson Climatology for June 21-27
Average High: 77
Average Low: 38
Record High: 95 (June 26, 1988)
Record Low: 22 (June 25, 1953)
Record 24-Hour Precip: 0.85″ (June 26, 1965)