JACKSON, Wyo – Hot, dry and windy conditions have settled into Teton County to start this week after several days of cool and wet conditions. Following this break in the pattern, a storm system will arrive on Wednesday and Thursday, bringing rain, thunderstorms and snow to high altitudes as well as cooler temperatures.
Recap September 13-19
Last week started hot and dry, but then moisture from the remnants of a Pacific hurricane rolled in, bringing measurable rainfall every day from Tuesday evening through Sunday morning. Temperatures were also much cooler during this trend compared to an abnormally warm start to the month for the season.
The city of Jackson recorded a total of 0.81 inches of rain over five days last week. Recorded and estimated rainfall totals in Jackson Hole ranged from half an 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 numerous times in the past week, although snow levels remained quite high. Snow levels dropped to around 11,000 feet on Thursday and dipped briefly to around 10,000 feet on Friday and Saturday, but accumulations were minimal and short-lived up to those elevations.
By the time the skies cleared up a bit over the weekend (especially Sunday), only the shady aspects of the higher peaks had obvious snow cover. In other words, the high altitude hiking season is not over yet, but the climbing routes on the highest peaks will face snow and ice this week.
Conditions finally cleared on Sunday and Monday with warmer temperatures and sunny skies. Another benefit of last week’s rain is that it has dampened fire activity in the West, so the skies are much cleaner at the start of this week.
Last week, high temperatures in Jackson ranged from 60°F on September 16 to 24°C on September 19, and lows ranged from 30°F on September 13 to 44°F on September 16.
Forecast from Tuesday (20/09) to Monday (26/09)
The week ahead will feature a cool, 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 following (including this weekend). Winds will also be gusty for much of the week.
Tuesday we will see another beautiful day with peaks reaching the upper 70s in the valley. However, there will be a little more cloud cover compared to Monday and the winds will also be quite strong, especially in the afternoon.
Wednesday will start with dry conditions in the morning with increasing clouds in the afternoon as we approach a low pressure system. It will be another balmy 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 Wednesday afternoon and evening. Some of the thunderstorms that develop could be stronger with frequent cloud-to-ground lightning, heavy showers, hail and possible gusty winds.
On Wednesday evening the showers will become more widespread and will continue throughout the night. Snow levels will start high at around 12,000 feet before gradually dropping to around 10,000 feet at sunrise Thursday morning.
Thursday will be much cooler and wetter as a cold front moves through the region. Periodic showers will continue throughout the day and a few thunderstorms are also possible. Peaks will only reach the upper 50s in the valley.
Snow levels will also be lower on Thursday, generally ranging from 9,000 to 10,000 feet. Any accumulation below 10,000 feet is likely to be short-lived, while areas between 10,000 and 11,000 feet could pick up a few inches of wet snow.
Periods of light showers will continue through Thursday evening, before finally easing after midnight and before sunrise Friday morning. Once the showers clear, a hard freeze is likely on the higher elevations.
On Friday, conditions will begin to dry out as the storm system exits to the east, leaving us in a cooler, drier airmass with waning clouds and highs into the low 60s in the valley.
The weekend looks generally calm, but a minor disturbance passing north of the area will bring another uptick in the winds on Saturday. A few light showers are also possible north of Jackson Hole (including Yellowstone), but there is only a very small chance that the disturbance will spread far enough south to bring any shower activity to the Tetons and Jackson Hole .
On Sunday and Monday, high pressure will build over Intermountain West, bringing mostly sunny skies, warmer temperatures and lighter winds. Peaks will peak in the 70s in the valley.
The first half of next week looks very pleasant with dry and sunny conditions expected as well as highs in the 70s.
During the second half of next week and in the last days of September, we may see a weaker system approaching with a chance of showers at some point, but we are unlikely to see a system major with heavy rainfall. Temperatures are also expected to cool slightly next weekend.
Alan Smith, Meteorologist
Climatology of the city of Jackson from September 20 to 26:
Medium top: 69
Medium Low: 30
High record: 87 (September 25, 1956)
Record low: 5 (September 26, 1956)
Precipitation since October 1: 17.31″ (102% of average)