FXUS65 KRIW 011733

AFDRIW



Area Forecast Discussion

National Weather Service Riverton WY

1033 AM MST Sun Nov 1 2026



.KEY MESSAGES...



- A weather system crosses the area today into tomorrow and

  brings periods of rain to many along with some mountain snow. 



- Gusty to strong wind likely (greater than a 3 out of 4 chance)

  the eastern half of the area on Monday, with the strongest

  wind in Johnson and Big Horn Counties.



- More tranquil weather returns for the rest of the workweek

  except for a chance of showers Wednesday.



&&



.DISCUSSION...

Issued at 136 AM MDT Sun Nov 1 2026



The weather has cooperated for the most part for evening activities 

for Halloween. We are now entering what I call the 151 days (or 152 

if it is a leap year) of winter in western and central Wyoming. This 

is when we usually start expecting more wintery precipitation than 

rain. I say usually because the past couple of winters have been 

unusually warm and dry. We will have the precipitation, and there 

will be some snow, but not really in the lower elevations. Going to 

try something different tonight with the discussion, I will discuss 

the overall weather pattern over the next couple of days first with 

the players. Then, I will focus on the three main impacts, 

precipitation amounts, potential snowfall and amounts and finally 

potential for strong to high wind in portions of the area.



The low that will be bringing the precipitation today is now moving 

onshore in northern California and will open a trough crossing the 

Rockies late tonight and into tomorrow. The latest model trends have 

been downward somewhat though with QPF, with the bulk remaining to 

the south over Utah, Colorado and Arizona. We will see some here 

though, with the heaviest precipitation in the west through midnight 

tonight, tapering off after midnight after the trough axis passes 

through the area. For areas East of the Divide, although there will 

be some showers around this morning, the most numerous should be 

tonight through Monday morning. Lee cyclogenesis will occur over 

eastern Colorado late today and then the low will strengthen as it 

moves northeastward into the Northern Plains states. This will 

likely bring some wrap around moisture that will keep precipitation 

going somewhat longer. However, it will also introduce a dry slot 

that could keep amounts down somewhere. And this complicates the 

rain and snow forecast somewhat. And finally, with the deepening 

flow, the pressure gradient will tighten across the area. This will 

bring the likelihood of strong wind to much of the area and 

potentially high wind to portions of Johnson County. These main 

impacts should end Monday evening as the low moves away to the east.

Now for the individual forecast elements.



Precipitation amounts...As was stated earlier, these have trended 

down somewhat with core of the moisture remaining to the south. 

However, all areas should see some precipitation. The wettest areas 

at this time look to be 1) Far southern Wyoming, which will be 

closer to the core of the deeper moisture; 2) The western facing 

slopes in the western mountains with a period of favorable 

orographic flow and 3) Favored northerly upslope flow areas East of 

the Divide like the Wind River Basin south of Riverton and the 

Lander Foothills, around Casper, the southern end of the Bighorn 

Basin and the eastern Bighorns. As a counter, the least amounts 

would be in 1) far northern Wyoming, which will be away from the 

core moisture and 2) Areas of downslope, like the eastern Bighorn 

Basin, the northern Wind River Basin and the Green River Basin. 

However, there are still model differences on the placement of the 

heaviest rain and the potential dry slot. Other differences are with 

the amount of wrap around, as some have it further west than others.

As for amounts, most areas have at least a 1 in 2 chance of a 

quarter inch of QPF or more, with the exception of the 

aforementioned downslope areas. As for greatest chance of three 

quarters of an inch or more, this would be mainly in the 

aforementioned upslope areas. Some areas will likely see more than 

an inch of QPF through the system though. Most should end by sunset 

Monday, with all precipitation finished by sunrise on Tuesday. 

CONFIDENCE IN AMOUNTS...Moderate to low.



Snow...For the most part, this looks like only the mountains for 

this. Snow levels remain fairly high through this afternoon, ranging 

from 8000 feet in the far west to 9500 to 10000 feet in eastern 

portions of the area. The cooler air then works in as flow turns 

north, falling as low as minus 3 to minus 4 by Monday afternoon. 

This would drop snow levels down to 7000 to as low as 6500 feet. 

However, the deepest moisture would be out of the area by then. 

There could be some snowflakes mixed in or possibly a brief period 

of wet snow in a place like Dubois, Meeteetse or areas along US 20 

26 like Hiland, but accumulation would be slim to none. Most 

mountains will see at least some accumulation though. The amount we 

are most concerned with is 6 inches, which is needed for most 

advisories. In the western mountains, this is largely restricted to 

the highest elevations, so we will not issue highlights here. The 

southern Absarokas have a 1 in 2 chance, but these are in areas with 

no population and no impact. The Wind River Range does but we 

already have an advisory for the western Wind River Range. I thought 

about extending it to the eastern Winds but will hold off for now. 

The other area of concern is the Bighorn Range, mainly the northern 

portion west of Buffalo and northward. There is an area of a greater 

than 1 in 2 chance of over 12 inches but it is in a relatively small 

area with few people of impacts. In addition, the worst impacts 

would not be until after midnight tonight. So, we will hold off of 

issuing highlights for now. One complicating factor is the potential 

for strong wind to increase impacts, we will touch on that in the 

next section. And finally, we have Casper Mountain. There could be a 

period of upslope flow here, but a lot depends on how much wrap 

around moisture is present. Almost all snow here would be on Monday, 

so we will hold off on any potential highlights for now. There is a 

1 in 2 chance of 6 inches or more above 8500 feet on the highest 

portions of the mountain. Almost all snow should end by sunset 

Monday.

CONFIDENCE IN AMOUNTS AND PLACEMENT...Moderate.



Wind...Wind should remain fairly light through the day today except 

for the favored southwest flow areas, even here is nothing unusual 

for Wyoming though. The main time of concern will be from later 

tonight after the flow turns northward and the pressure gradient 

tightens, especially across northern Wyoming. There will be around 

12 to 14 millibar pressure gradient from the eastern border of 

Wyoming to Greybull. The 700 millibar winds are also rather 

impressive, increasing to 50 knots across Johnson County from 12Z to 

21Z on Monday. The NBM ensemble guidance gives a greater than 4 out 

of 5 chance of wind gusts past 55 mph across northern Johnson 

County. With this, we will hoist a high wind watch for this area 

starting at 3 am and ending at 5 pm Monday. I also gave thought to 

one for Bighorn County, but with the chance less than 1 out of 2 and 

the main chance in the higher elevations I held off. The day shift 

will have to watch this though and a warning may be needed if the 

wind speeds trend up. Most areas east of a Cody to Riverton Line as 

well as portions of southwestern Wyoming have at least a 1 in 2 

chance of gusts past 40 mph so most places will see a blustery and 

cool day, it will definitely feel like November in Wyoming. Wind 

should decrease after sunset Monday as the low moves away and the 

pressure gradient decreases.

CONFIDENCE IN WIND SPEED AND TIMING...Moderate to high.



Tuesday sees a return to more tranquil weather with somewhat warmer 

temperatures. The next potential maker will be a fast moving low 

moving in for Tuesday night into Wednesday. There is a rather 

substantial model spread on this though, with some bringing some 

showers to the state Wednesday and others keeping the system south 

of the area as high pressure builds in from the north. Riding should 

then bring mainly dry weather for the end of next week with near to 

somewhat above normal temperatures.



&&



.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...

Issued at 1027 AM MST Sun Nov 1 2026



Rain and mountain snow have been persistent at KBPI/KPNA this

morning, but have been hesitant to move into the rest of the

region. Trends are starting to finally bring precip and low

clouds into western and central Wyoming during the next couple

hours, aviation conditions will deteriorate the rest of the day.

Once rain starts at an airport, cigs will lower to at least 1500

ft, with lower cigs likely overnight at all sites. Improvements

will be slow in coming, likely starting at far western sites

after 12Z Monday.



Cold front still expected by 06Z tonight, with north winds

gusting near 25kts for sites east of the Divide, and northwest

winds gusting 20 to 25kts at times between 06Z and 12Z.



Please see the Aviation Weather Center and/or CWSU ZDV and ZLC 

for the latest information on smoke, icing, and turbulence 

forecasts.



&&



.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory from 1 AM to 9 AM MST Monday for 

WYZ009.



Winter Weather Advisory from 3 PM to 5 PM MST Monday for 

WYZ009-015.



High Wind Warning from 3 AM to 3 PM MST Monday for WYZ010.



Winter Weather Advisory until 5 AM MST Monday for WYZ014.



Winter Weather Advisory from 8 PM this evening to 9 AM MST 

Monday for WYZ015.



&&



$$



DISCUSSION...Hattings

AVIATION...Straub