Grand Targhee

000
FXUS65 KRIW 011009
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
409 AM MDT Sat Aug 1 2026

.KEY MESSAGES...

- A very hot weekend is on tap with many locations in the lower
  elevations seeing highs over 100 degrees. Some locations may
  set records for the hottest August temperature, especially on
  Sunday.

- Elevated to critical fire weather is possible through Tuesday,
  with Sunday and Monday being the days of greatest concern.

- A cold front will drop much of the area Sunday night and
  Monday, bringing relief from the heat early next week,
  especially in northern and central Wyoming.

&&

.DISCUSSION...
Issued at 1237 AM MDT Sat Aug 1 2026

We are now officially two thirds of the way through meteorological 
winter (it runs from June through August). And, unless you've been 
living under a rock, it has been a hot one. Some of our major 
climate sites have had their warmest July on record. This includes 
Lander, which has records going back to 1892. And this looks to 
continue this weekend. However, we may have some welcome relief on 
the way for portions of the area early next week.

However, we will have to run the heat gauntlet this weekend before 
we get to the relief. (Was waiting to throw the word gauntlet in, I 
loved that video game back when I was a teenager in the 80s.) 
Anyway, the reasoning for the forecast for the weekend remains the 
same as yesterday. Another heat dome will build northward over 
Wyoming and bring a couple of days of very hot and in some cases 
record breaking heat. We will still have 700 millibar temperatures 
climbing to 21 to 22 celsius on both Saturday and Sunday, and 
this translates to all lower elevations seeing high temperatures
at least in the 90s. For today, most elevations below 5000 feet
have at a minimum a 1 out of 2 chance of high temperatures over
100 degrees, with the lower elevations of the Bighorn Basin 
(generally below 4000 feet) having a 1 out of 2 chance of high 
temperatures over 105. Sunday still looks like the warmest day, 
as a gusty southwesterly breeze develops ahead of a cold front 
dropping toward the area from Montana. This should allow 
temperatures to be a few degrees warmer, with locations having 
at least a 1 in 2 chance of highs over 100 now under 5500 feet. 
And in the areas most prone to the downslope warming, like the 
Wind River Basin, southern Bighorn Basin and even around Casper,
could be even warmer. The National Blend of Model ensembles 
give at least a 1 in 3 chance of highs of 105 below 5000 feet in
these areas. This is the day when some all time highs for the 
month of August may be set. It does not look quite as hot as on 
July 12th though, so all time record highs should be safe for 
most. The one that may be in jeopardy is the Sweetwater County 
airport, where we could reach the all time record high of 98. 
With this, we will keep the heat advisories going as is. As for 
precipitation, I can't completely rule out a very isolated virga
shower over the mountains, but the chance is less than 1 out of
10 and was left out of the forecast.

The other concern on Sunday will be fire weather. Humidity will will 
be very low through the weekend, falling under 15 percent for many 
areas and many of the lower elevations seeing relative humidity in 
the single digits. Wind should remain light to moderate on Saturday. 
The gusty southwesterly breeze then develops on Sunday, bringing
the possibility of critical fire weather. The low humidity is a
slam dunk, the wind is still borderline in some areas though. For
now, we will keep the fire weather watch going and let the day 
shift take another look.

As for Monday, those of your who are Gen X or older may remember an 
commercial for antacid where it asks how do you spell relief? Well, 
the relief from the heat will be spelled C-O-L-D F-R-O-N-T. It will 
drop slowly into northern Wyoming Sunday night, reaching the 
Continental Divide during the day on Monday. This will bring some 
cooler temperatures, generally about 15 to 20 degrees cooler than on 
Sunday. A few places in far northern Wyoming may have a brief taste 
of September, with high temperatures only in the 70s. It will remain 
rather hot across southern Wyoming though. In addition, with the 
front in the area, a gusty breeze will continue. With the cooler 
temperatures and somewhat higher humidity across northern Wyoming, 
fire weather should drop below critical. However, with the gusty 
wind and humidity around 10 percent continuing in southern Wyoming, 
critical fire weather should continue another day. So, we will 
continue the fire weather watch. The one thing the front will not 
bring is moisture. We can't completely rule out a shower over the 
far north, but the chance is less than 1 out of 10. 

Mainly dry weather looks to continue through much of next week as 
well. A weak shortwave may bring a stray shower or storm to northern 
Wyoming Tuesday evening, but the chance is less than 1 out of 5 
given the lack of moisture. The general trend for much of next week 
will be for the ridge to build back northward and bring warmer 
temperatures back to the area. Above normal temperatures look likely 
toward the end of next week and next weekend, but extreme heat looks 
unlikely at this time, just temperatures running a few degrees above 
seasonal averages.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 409 AM MDT Sat Aug 1 2026

VFR conditions will prevail through 12Z Sunday as high pressure 
builds over Wyoming. We can't rule out a stray virga shower over the 
mountains, but the chance is less than 10 percent. Most locations 
East of the Divide will see wind remain at 12 knots or less. In 
vicinity of KBPI, KPNA and KJAC, some gusts to around 18 knots will 
be possible after 20Z until sunset after the wind decouples. 
Otherwise, expect a mainly clear sky with nothing more than some 
passing high clouds.
&&

.FIRE WEATHER...
Issued at 1237 AM MDT Sat Aug 1 2026

Today will be a hot and dry day across the area. Relative
humidity will fall under 15 percent for most locations. However,
wind should remain light to moderate except for the northwestern
mountains where fuels are not critical. However, elevated fire
weather is likely this afternoon. An approaching cold front will
bring a gusty south to southwesterly breeze and combined with
humidity falling into the single digits will bring a good chance
of critical fire weather on Sunday across much of the area,
continuing in southern Wyoming on Monday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 10 PM MDT Sunday for 
WYZ003>006-010-011-013-016>020-023-025>030.

Fire Weather Watch from Sunday afternoon through Sunday 
evening for WYZ275-276-282-283-285.

Fire Weather Watch from Sunday afternoon through Monday 
evening for WYZ277>279-289.

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings
FIRE WEATHER...Hattings