


Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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615 FXUS65 KRIW 151824 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1224 PM MDT Wed Oct 15 2025 .KEY MESSAGES... - Showers and isolated thunderstorms today. Gusty outflow winds and small hail are possible, mainly around Natrona County. - A cold front moves through tonight, bringing precipitation chances and colder temperatures. - Snow occurs for the mountains through Thursday night. Winter weather travel is likely across mountain passes. Snow levels could be as low 6500 feet, though most snow occurs above 8500 feet. && .UPDATE... Issued at 1223 PM MDT Wed Oct 15 2025 Not much change with the overall forecast through the next 48 hours or so. With the low clouds over the Bighorn Basin and Johnson County this morning, have lowered high temperatures around 5 degrees, to the mid-to-upper 50s. The cold front is still on track to move through tonight, lowering snow levels. Snow amounts for the western mountains have come up slightly, but are still only around 8 to 11 inches at the highest peaks of the Teton, Wind River, and Salt River Ranges. The highest peaks of the Bighorns (above 9500 feet) could see up to about 9 inches, but this is too localized for any highlights. The Bighorn mountain passes (Granite and Powder River) should see 3 to 5 inches. Otherwise, mountains should generally see up to 8 or 9 inches. Snow levels should lower enough for some light snow over the lower elevations west of the Divide, including Big Piney, Pinedale, Kemmerer, and Rock Springs. Flakes are possible in Star and Jackson Valleys. Lowest snow levels should occur Thursday morning, being 6700 to 7000 feet. && .DISCUSSION... Issued at 253 AM MDT Wed Oct 15 2025 The question of the day continues to be what will happen with the upper level low that is now swirling over California and will move toward and over the Cowboy State over the next 36 to 48 hours. And the good news is that there is more agreement in the model guidance this morning, although there are some differences in the exact track that will make a difference in potential precipitation amounts (try saying those three words fast five times, a bit of a tongue twister). Well, let us dive in. We currently have a few areas of mainly light showers moving northward across the area. A couple of thunderstorms are also noted, but nothing strong and these are mainly in Idaho. Today looks like it will be inverse of yesterday, when we had more shower coverage in the morning and then decreasing in the afternoon. Showers should become more numerous in the afternoon as the low gets closer to the area. And this is where we still have some uncertainty with the track of the low. Some guidance, like European model, show the low moving further south, which would bring a better chance of showers across central Wyoming this afternoon and tonight. Others, like the GFS, bring the low around 75 miles further north, and this could bring a dry slot into central Wyoming, keeping things largely dry. For now, we kept some POPS in the area but chances are generally less than 1 out of 3 in any given area before better chances move in later Wednesday night as the low makes a closer approach. The most numerous showers will be across western Wyoming though. And, there could even be a few stronger thunderstorms. CAPE is rather limited, only around 300 J/Kg at the most. However, lifted indices drop to around minus 3 in the afternoon across portions of Johnson and Natrona County. There will be decent upper level divergence and some direction shear as well. Nothing widespread is expected but there could be a few more feisty storms. The Storm Prediction Center agrees and has issued a marginal risk for Natrona County. The other concern is snow. Few problems are expected through the daylight hours today, as snow levels should remain above 8500 feet and even above this still warm ground and borderline temperatures should melt snow on roads. A cold front will press across the area tonight and drop snow levels to around 7000 to 7500 feet by Thursday morning and possibly as low as 6500 feet in some areas East of the Divide as 700 millibar temperatures may fall as low as minus 4 to minus 5. As for the advisories, they still look reasonably so few changes will be made this morning. The areas with at least a 1 out of 2 chance of 6 inches of snow or more are covered by the advisories for the most part. I do have a small concern that some portions of the Bighorn range may receive 6 inches or more but these would be the higher peaks and therefore impacts would be limited. The steadiest precipitation still looks to fall in the 18 hour period from late tonight through Thursday afternoon, with showers later Thursday as the low moves away to the south and east. As for total precipitation, most areas north of a Kemmerer to Casper line have at least a 1 out of 2 chance of a quarter of an inch or greater over the next 24 hours. The highest amounts still look to be in northwestern Wyoming, with a least a 1 out of 2 chance of greater than three quarters of an inch of QPF over the same time period. Most guidance is showing Friday as a dry day with ridging over the area. Another fast moving cold front will move in from the north on Saturday. There continues to be differences in guidance in regards to shower chances though. For now, we leaned toward the drier end since the front is of continental origin and doesn`t have a lot of moisture to work with. Drier and warmer weather then returns on Sunday. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1030 AM MDT Wed Oct 15 2025 Lingering IFR ceilings at COD/CPR that will lift in the first couple of hours of the period. Otherwise, VFR conditions for all other locations with a slight breeze west of the Divide gusting up to 18kts. RKS will see the strongest winds up to 30kts through the peak heating of the afternoon. Lowering mid level ceilings west of the Divide ahead of the next system and associated cold front. MVFR conditions with light rain after 06-07Z and IFR conditions possible after 12-13Z Thursday morning. This will spread east of the Divide after 05Z for COD and 10Z for other locations with CPR after 04Z due to showers out of south central portions of the state. These low IFR to MVFR conditions with light rain will last through the end of the period extending into the next TAF cycle Thursday afternoon. Improving conditions will not occur until overnight into Friday morning as precipitation ends west to east after sunset Thursday. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 PM this evening to 11 PM MDT Thursday for Wyz008-012-014-015-024. && $$ UPDATE...Wittmann DISCUSSION...Hattings AVIATION...Lowe