JACKSON, Wyo. — Warm, dry and windy conditions have taken hold across Teton County to start this week following several days of cool and wet conditions. Following this break in the pattern, a storm system will arrive on Wednesday and Thursday, resulting in rain, thunderstorms and high elevation snow along with cooler temperatures.
September 13-19 Recap
Last week started out warm and dry, but then moisture from the remnants of a Pacific hurricane arrived, resulting in measurable rainfall each day from Tuesday night to Sunday morning. Temperatures were also much cooler during this pattern compared to an unseasonably warm start to the month.
The Town of Jackson recorded a total of 0.81 inches of rain over five days last week. Recorded and estimated rainfall totals across Jackson Hole ranged from a half-inch to an inch last week, while estimated rainfall totals in the Teton Range were between an inch and 1.25 inches.
The higher peaks of the Tetons were also dusted with snow on numerous occasions last week, though snow levels remained fairly high. Snow levels dipped to around 11,000 feet on Thursday and briefly lowered to around 10,000 feet on Friday and Saturday but accumulations were minimal and short-lived down to these elevations.
By the time the skies cleared a bit over the weekend (especially on Sunday), only the shaded aspects of the highest peaks held any obvious snow cover. In other words, high elevation hiking season is not over yet, but climbing routes on the higher peaks will be dealing with snow and ice this week.
Conditions eventually cleared out on Sunday and Monday with warmer temperatures and sunny skies. Another benefit of last week’s rain is that it put a damper on fire activity across the West, and skies are much cleaner early this week as a result.
High temperatures last week in Jackson ranged from 60ºF on September 16 to 76ºF on September 19, and lows ranged from 30ºF on September 13 to 44ºF on September 16.
Forecast for Tuesday (9/20) to Monday (9/26)
The upcoming week will feature a cool and wet storm system on Wednesday and Thursday with mostly sunny skies and drier conditions in the days leading up to this system and in the days after (including this weekend). Winds will also be gusty for much of the week.
On Tuesday, we’ll see another nice day with highs reaching the upper 70s in the valley. However, there will be a bit more cloud cover compared to Monday and winds will be quite strong as well, especially in the afternoon.
On Wednesday, we’ll start out with dry conditions during the morning hours with increasing clouds during the afternoon as a low pressure system approaches. It will be another mild but windy day with highs in the mid 70s in the valley.
Instability ahead of this system will result in scattered showers and thunderstorms developing on Wednesday afternoon and evening. Some of the thunderstorms that develop could be on the stronger side with frequent cloud-to-ground lightning, heavy downpours, hail, and gusty winds possible.
On Wednesday night, showers will become more widespread and will continue throughout the overnight hours. Snow levels will start out high at around 12,000 feet before gradually lowering to around 10,000 feet by sunrise on Thursday morning.
Thursday will be much cooler and wetter as a cold front works its way through the area. Off-and-on showers will continue throughout the day and a few thunderstorms are possible as well. Highs will only reach the upper 50s in the valley.
Snow levels will also be lower on Thursday, generally ranging from 9,000-10,000 feet. Any accumulations below 10,000 feet will likely be short-lived, while areas in the 10,000-11,000 foot range could pick up a few inches of wet snow.
Light and intermittent showers will continue into Thursday evening, before eventually tapering off after midnight and prior to sunrise on Friday morning. Once the showers clear, a hard freeze is likely across the higher elevations.
On Friday, conditions will begin to dry out as the storm system exits to the east, leaving us in a cooler and drier airmass with decreasing clouds and highs in the low 60s in the valley.
The weekend is looking generally quiet, but a minor disturbance passing north of the area will result in another uptick in winds on Saturday. A few light showers are also possible north of Jackson Hole (including Yellowstone), but there is only a very small chance of the disturbance tracking far enough south to bring any shower activity to the Tetons and Jackson Hole.
On Sunday and Monday, high pressure will build over the Intermountain West, resulting in mostly sunny skies, warmer temperatures and lighter winds. Highs will top out in the low 70s in the valley.
The first half of next week is looking very nice with dry and sunny conditions expected along with highs in the 70s.
During the second half of next week and into the final days of September, it’s possible we could see a weaker system approach with a chance of showers at some point, but it’s unlikely that we’ll see a major system with heavy precipitation. Temperatures should also cool off slightly late next week.
Alan Smith, Meteorologist
Town of Jackson Climatology for September 20-26:
Average High: 69
Average Low: 30
Record High: 87 (September 25, 1956)
Record Low: 5 (September 26, 1956)
Precipitation Since Oct 1st: 17.31″ (102% of Average)