####018006564#### FXUS65 KRIW 130155 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 755 PM MDT Sun Oct 12 2025 .KEY MESSAGES... - Widespread freezing temperatures tonight with temperatures in the 20s and low 30s. A Freeze Warning is now in effect late tonight/Monday morning across the eastern Bighorn Basin and northern Johnson County. - Precipitation chances (up to 40%) return Monday afternoon across southern Wyoming. Gusty winds, showers, thunderstorms, and mountain snow will accompany the next weather system Tuesday through Thursday. && .UPDATE... Issued at 116 PM MDT Sun Oct 12 2025 The forecast remains mostly unchanged this afternoon with the upper- level trough that brought yesterday's unsettled weather now (19Z) located over eastern Montana. It's associated upper-level jet maximum is roughly located over the Wind Corridor and is contributing to gusty 35 to 50 mph winds across that area. As the entire system progresses east this afternoon, these gusty winds will subside slightly. Cold air advection behind the trough will favor gusty west winds of 20 to 30 mph through sunset this evening. Lingering moisture from the departing system is present across western and northwestern Wyoming, evident on satellite by cloud cover. This moisture will remain over these areas until the evening, and with much colder air and westerly flow, isolated to widely scattered (15%-40% chance) terrain induced showers and mountain snow remains possible through sunset. However, light precipitation could linger across Yellowstone National Park until midnight. As mentioned, cold air has filtered into Wyoming behind the system with temperatures 10 to 20 degrees cooler at 19Z compared to 19Z yesterday. Widespread below freezing temperatures are still forecast tonight with the cold air already in place and clear overnight skies. As for the Freeze Watch area (the eastern Bighorn Basin and northern Johnson County), confidence in how widespread a hard freeze (28 degrees or lower) will be is around 40%. However, given the clear skies and already cold conditions, we went ahead and upgraded the Freeze Watch to a Freeze Warning. Otherwise, the forecast for Monday remains on track with isolated showers across southern Wyoming as southwesterly flow returns to the Intermountain West with weak embedded disturbances aloft. && .DISCUSSION... Issued at 127 AM MDT Sun Oct 12 2025 Thunderstorms are exiting northward into the BYZ CWA as of 06Z. The cold front has passed through Greybull and Riverton and will progress eastward, exiting the CWA by sunrise this morning. Wind gusts of 35 to 45 mph will continue across much of the area this morning, decreasing after 18Z (12 PM). Light precipitation will also continue over northern portions through the morning, with light snow in the higher elevations as well as the Wind River Mountains and Salt and Wyoming Ranges. Isolated showers will then be possible over western portions through the afternoon. A Freeze Watch remains in effect for eastern portions of the Bighorn Basin and northern Johnson County, as temperatures have trended upward closer to 30 degrees and making the chances for a hard freeze less likely. Have continued with the Watch for now, as skies will become clear early this evening. Temperatures across the CWA have trended upward as well, with readings near 30 degrees for most locations east of the Divide. Readings in the teens are no longer in the forecast for the western valleys, although locations in the Upper Green River Basin could still be that cold. Breezy southerly winds return Monday, with isolated showers possible over the southern half of the forecast area. Temperatures will be about 10 degrees warmer west of the Divide, as a result of the southerly winds. This trend continues Tuesday, as a strong closed upper low from British Columbia digs southward just off the West Coast. Southerly winds will be a bit stronger with this digging trough, especially across the Wind Corridor (Rock Springs to Casper). Rain showers will be confined to far western portions of the CWA. Models have come into better alignment and bring this storm closer to the Cowboy State during the day Wednesday. Rain showers will be ongoing over far western portions Wednesday morning, with snow levels ranging between 7500 and 8500 ft over the Tetons due to the proximity of the associated cold front. These showers will become more widespread through the day. Southerly winds will continue to increase, with gusts of 35 to 45 mph likely across much of the area. Coincidentally, this system is progged to play out quite similarly as the current ongoing storm. The cold front will make its way eastward over western portions through the day, quickly making its way across the rest of the CWA through much of the night. There is a chance for high winds (60+ mph gusts) to occur over portions of Natrona County in the wake of the front. This system is not expected to be as cold either, with snow levels ranging between 6500 and 7500 ft Wednesday night as the closed upper low moves over eastern MT by 12Z Thursday. Precipitation chances will continue Thursday, mainly over northern portions, as winds turn more northwesterly. Gusts up to 35 mph will be likely over northern portions of the Bighorn Basin and Johnson County, as well as the Green River Basin and Sweetwater County. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 502 PM MDT Sun Oct 12 2025 VFR conditions expected throughout the period at all TAF sites. Scattered mid to upper level clouds throughout with dry conditions expected. Light winds less than 10kts due to radiational cooling under mainly clear skies. Winds increase a bit after 18Z with daytime heating Monday afternoon, with the peak at RKS up to 25kts and CPR 18kts. Otherwise, all other locations around the 10-12kt range. No other weather elements are expected at this time. 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... Freeze Warning from 3 AM to 9 AM MDT Monday for WYZ004-006-010. && $$ UPDATE...Gerhardt DISCUSSION...LaVoie AVIATION...Lowe ####018006342#### FXUS65 KBYZ 130156 AFDBYZ Area Forecast Discussion...Updated National Weather Service Billings MT 756 PM MDT Sun Oct 12 2025 .KEY MESSAGES... - Frost/freeze for most areas tonight. Most locations will see morning temperatures in the mid to upper 20s. - Light snow accumulations (1-3") may impact US-191 north of Big Timber to Judith Gap for Monday morning commute. - 30 to 60 percent chances for precipitation return, from Tuesday night through Thursday evening. High elevation snow accumulations possible (above 7000ft). - Mainly dry and warmer next weekend. && .DISCUSSION... Today through Sunday... Broad upper level trof is centered over SW Canada this afternoon, with a couple of lobes of stronger energy rotating around its periphery. The eastern lobe, that brought significant precipitation (0.25 to 1.25 inches) to the area late Saturday into this morning, is lifting northeast of the area at this time, taking precipitation chances with it. Residual energy/instability combined with a few breaks in the clouds will keep scattered showers and maybe a rumble of thunder in the forecast for western mountains and foothills this afternoon into early this evening. Additional shower chances will persist over far SE MT associated with exiting jetstream energy. As we go into tonight the second piece of energy drops down the west coast and deepens. This pattern adjustment brings increasingly divergent flow aloft over the area as well as pulling in easterly low level upslope flow in the low levels. The upper level divergence combined with the low level upslope winds set up a good precipitation producing period overnight into tomorrow over the western mountains and foothills, possibly extending eastward as far as a Columbus to Roundup line. Models are advertising 2 to 3 inches of snowfall possible late tonight through late Monday morning along the US-191 corridor from north of Big Timber to south of Harlowton (Melville vicinity). For Harlowton the probability for at least an inch is sitting at 46%, with an 18% probability for 2+ inches. So, the main concern with this light snowfall is mainly with travel impacts Monday morning. The Metro-model is a bit wishy-washy with how road temperatures will respond overnight, showing temperatures getting down to 32 around 4 am and staying right there through late morning. This suggests there will be snow accumulating on road surfaces (US-191) around sunrise, but not as much as models are thinking will fall in this area. Contemplated a Winter Weather Advisory for this area given the early season nature of this snowfall, but just not seeing enough accumulation at this point to pull the trigger. However will continue to advertise the potential for some locally slick travel in that area for tomorrow mornings commute. Morning lows will be chilly with most areas looking at mid to upper 20s. Cover any tender vegitation that you are trying to keep going a bit longer into the fall. Bundle the kids up warm for school tomorrow morning and leave a bit of time to scrape the windshield and get the car warmed up. Upper low continues to sag south away from the area Monday turning the corner over Arizona and beginning to head our way late Tuesday. This will make for a mainly dry afternoon Monday and a dry day on Tuesday. As the upper low moves closer, expect stronger upper level dynamics to develop over western zones Tuesday night into Wednesday morning with increasing precipitation chances (30-60%), spreading eastward to encompass the forecast area by Wednesday evening. Upper trof lingers over the area through Thursday evening with continued strong widespread precipitation potential (most areas looking at around half an inch of precipitation possible). With this system arriving from the southwest, it will be warmer than this weekends system and have higher snow levels. Snow levels start out around 9500 feet Tuesday night, dropping to 8500 feet Wednesday afternoon, and finally down to around 7000 feet Thursday morning. Currently looking at 4 to 8 inches of snow above 7000ft, with the heaviest amounts really sticking above 8000ft based on latest guidance. Upper low exits to the east Friday with breezy westerly (downslope) winds drying things out for the area. Ridging builds in behind the system for a warmer and mainly dry weekend. Chambers .AVIATION... Rain/snow showers, becoming all snow can be expected along the western foothills (KLVM through K3HT) into Monday morning. Snow will gradually diminish through mid-day Monday. Low stratus will develop and impact areas from KBIL to KSHR and areas west tonight through mid-day Monday. Fog is possible through the morning hours at KSHR. As a result, MVFR/IFR conditions are anticipated at these sites as well as mountain obscurations over south central MT. Lower confidence exists for fog across eastern MT (KMLS, KBHK), but a 20% chance is still forecast (dependent on cloud cover). TS/STP && .PRELIMINARY POINT TEMP/POPS... Mon Tue Wed Thu Fri Sat Sun ----------------------------------------------------------- BIL 030/044 033/051 039/054 041/055 040/058 038/057 038/062 21/B 11/B 45/R 66/R 43/R 32/R 12/R LVM 024/039 026/052 032/051 032/052 031/055 029/055 032/060 52/S 22/O 67/R 76/R 43/R 42/O 13/R HDN 028/051 032/055 036/057 039/054 037/060 035/057 034/064 10/U 11/B 45/R 76/R 53/R 42/R 11/B MLS 028/052 039/061 042/061 041/054 038/058 035/057 034/064 00/U 11/B 35/R 66/R 43/R 21/B 01/U 4BQ 028/055 041/064 044/068 042/054 038/058 036/054 036/063 00/U 11/B 23/T 65/R 32/R 22/R 10/U BHK 022/052 035/057 038/059 040/055 035/056 032/055 031/061 00/U 11/N 23/T 65/R 42/R 21/B 00/U SHR 023/052 030/061 036/063 034/054 032/058 029/055 030/064 00/U 21/B 34/R 76/R 43/R 42/O 11/U && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$ weather.gov/billings