FXUS65 KRIW 100155 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 755 PM MDT Fri May 9 2025 .KEY MESSAGES... - Any storm activity has diminished and pushed east and southeast of the Casper/Casper Mountain area out of Natrona County. Quiet overnight to come. - Warm temperatures over the weekend that will lead to elevated water levels due to snowmelt. - Increasing storm chances come Sunday afternoon along with elevated fire weather conditions into Monday as well. - The next system and best chance for a more widespread precipitation event. && .UPDATE... Issued at 142 PM MDT Fri May 9 2025 Isolated convection will continue today, focused mainly on the eastern half of the area off of the higher terrain. This activity will drift to the southeast through the afternoon, ending around sunset. Gusty outflow winds to 35 mph or so will be the main concern. No big changes this afternoon to the upcoming forecast. The weekend will see temperatures warm to near 20 degrees above normal for most of the area. The ridge will begin to move east on Sunday, allowing for the return of more widespread convection chances, especially west of the Divide. There are a couple of resultant weather concerns we are beginning to key in on. One is the potential for rising rivers and streams given the multiple days of above normal temperatures expected this weekend. The other is fire weather conditions as southwesterly winds increase ahead of next week's system. This will first be a concern on Sunday, though Monday will be the day with the strongest wind and lowest humidity. && .DISCUSSION... Issued at 211 AM MDT Fri May 9 2025 The H5 ridge continues to build, and will stretch northward along the Rockies today. The ridge will continue to bring temperatures will above normal in the 70s and low 80s this afternoon. The weak shortwave that's drifting along the northern edge of the ridge will mosey across the Bighorn Range this afternoon, and will tap enough instability from heating of the day to spark a few showers and thunderstorms. Steer flow is toward the southeast, so areas of Johnson and Natrona Counties also have a 20 to 30 percent chance for thunderstorms as well. As was that case assisted, once peak heating wanes and the ridge continues building northward, shower activity will fade away early in the evening. The weekend will be marked by even warmer conditions as the axis of the ridge centers on Wyoming. H7 temps still lead to highs in the mid to upper 70s west of the divide and low to mid 80s east of the divide. Early next week, the ridge gets pushed east by a longwave trough off the PacNW coast. Western WY remains pinned between the two, but the H7 heat ridge holds across the state Monday and Tuesday. Temps will be a few degrees cooler these days, held down by the increasing cloud cover from the approaching trough. Models still having trouble resolving the progress of the trough, with GFS running faster, and EC holding back a bit, but feeding more Pacific moisture into the state. With either solution, there is an increasing potential for an extended period of rain/snow for western WY into midweek. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 404 PM MDT Fri May 9 2025 High pressure will keep VFR conditions at terminals through the period. The ongoing, isolated convection across the eastern half of the area will linger through the afternoon. The best chance for brief terminal impacts will be at KCPR but this will be short-lived, with any showers or storms ending around sunset. Wind will generally be light through the period, though outflow from any showers in the broader area may lead to briefly increased wind gusts through the evening. No precipitation is expected to impactterminals on Saturday. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Myers DISCUSSION...Straub AVIATION...Myers