JACKSON, Wyo. — A significant change to the weather pattern is set to occur as much cooler and wetter weather arrives from Wednesday through Sunday. The pattern will greatly reduce fire danger, but will also result in less than ideal backcountry conditions for climbers and backpackers.
As of late Tuesday afternoon, gusty southwest winds have developed ahead of this system along with a round of thunderstorms tracking over the Tetons. There are some fire weather concerns due to lightning activity and strong winds, but hopefully, rainfall and cooler temperatures in the days to follow will alleviate these concerns.
Cooler temperatures and wetting rains on Wednesday and Thursday
Scattered showers and thunderstorms on Tuesday night will become more numerous during the day on Wednesday behind a cold front that moves through early in the morning. Off-and-on showers and thunderstorms can be expected throughout the day with showers and storms generally moving in a south to north direction.
The latest models are coming in stronger with Wednesday’s showers and thunderstorms and we can expect to see some locally heavy downpours as a result. Temperatures will be much cooler on Wednesday as well with highs only in the 60s in the valley and in the 40s at 9,000-10,000 feet, so be prepared for cold and wet conditions if you’re hiking in the Tetons.
The low-pressure system will keep us in a moist southerly flow through Wednesday night and Thursday with additional showers expected throughout the day on Thursday. Weather models are struggling a little bit to get a handle on the progression of this system and whether or not significant rainfall bands set up over Teton County or too far east – this admittedly adds an element of uncertainty to Thursday’s forecast.
Even so, at this time additional wetting rains continue to look like a good bet on Thursday and rainfall amounts could end up being even higher compared to Wednesday. Lightning activity will decrease on Thursday compared to Wednesday, but some embedded thunderstorms will remain possible. Thursday also will be the coolest day of this pattern with highs only in the low 60s in the valley.
In addition, southerly flow and abundant energy with this system will limit the rain shadow effect of the Tetons on both Wednesday and Thursday, and the difference in precipitation totals in the Tetons versus the valley will not be as much as usual. That means the Jackson Hole Valley, including the town of Jackson, should see good rainfall totals out of this system.
As the system moves across Western Wyoming on Thursday night, winds aloft will transition to west/northwest with continued lighter showers favoring the Tetons through midday or early afternoon on Friday. The valley will see lighter rain totals during this period as the wind shift will result in a Teton rain shadow effect.
Cooler temperatures will prevail on Friday, however, with highs in the 60s.
Projected Rainfall Totals
Given the dynamic nature of this storm system, there is some uncertainty as to rainfall totals and geographic distribution. But generally speaking, we should see healthy rain totals ranging from 0.5-1.5 inches in the Tetons and 0.4-1.2 inches in the Jackson Hole Valley.
Mountain ranges east of Jackson Hole including the Gros Ventre, Wind River, Absaroka and Beartooth Ranges should see even higher amounts.
Here is the rainfall forecast for the Greater Teton and Yellowstone Region through 5 a.m. Friday morning along with a blended model projection map below:
- 0.8-2.4 inches – Wind River Range, Absaroka Range
- 0.6-1.8 inches – Gros Ventre Range, Salt River Range, Togwotee Pass, Beartooth Range
- 0.5-1.5 inches – Teton Range and Yellowstone
- 0.4-1.2 inches – Jackson Hole Valley, Star Valley
- 0.3-1.0 inches – Teton Valley (ID)
Snow on the higher peaks?
Colder air arriving with this system is likely to result in snow falling across the higher peaks of the Tetons and surrounding ranges, especially on Thursday.
On Wednesday, snow levels should generally stay above 11,500 feet, which of course still means the highest peaks of the Tetons will see snow. Colder will then arrive on Thursday with snow levels falling to 10,500 feet in the Tetons and even lower across the Beartooths and Wind Rivers, who could see snow levels dipping to 9,500 feet on Thursday night and Friday morning.
This is just a reminder that snow can fall in the mountains during any month of the year, even during what has been an otherwise hotter than average summer.
What about the smoke situation?
The smoke has been terrible in Jackson Hole and Western Wyoming early this week. This system should help some, but unfortunately, smoke transport models are projecting smoke from California fires to become entrained into the southerly flow around the low pressure system.
As a result, we will likely still be dealing with smoke issues on Wednesday and Thursday, even in spite of the rain. However, smoke density should not be as high and the air quality should improve somewhat.
Check out the projected smoke levels near ground level for Wednesday afternoon:
Once the system moves across the area on Thursday night, we should see better smoke relief on Friday. It may be short-lived, though, as southwesterly flow returns in the days to follow which could bring more smoke from California.
Another cool/wet storm system this weekend
We will see a break in the action late Friday and into early Saturday, but then a second weaker storm system will approach from the northwest.
We still have to work out the details of this storm since it’s several days away, but another period of cool temperatures with widespread showers and thunderstorms is likely sometime during the Saturday afternoon through Sunday afternoon timeframe.
Rain amounts from this system are expected to be less compared to Wednesday/Thursday, but it still offers another opportunity to pick up beneficial moisture – at the expense of your weekend outdoor plans.
High temperatures over the weekend will range from the upper 60s to low 70s in the valley depending on the timing of the system. If you’re backpacking or climbing, then additional light snow couldn’t be ruled out over the higher peaks (generally above 10k or 11k) – especially in the Winds – along with generally wet and cold conditions.
Next week, we will transition back into a dry pattern along with a warming trend that should take us through the end of August.
Alan Smith, Meteorologist
