FXUS65 KRIW 080822 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 222 AM MDT Sun Sep 8 2024 .KEY MESSAGES... - High pressure keeps temperatures on the warm side the next few days. Isolated (15%-30%) storm chances over western Wyoming today. - A breezy afternoon Monday, with elevated to critical fire weather concerns. - A larger weather system impacts the area Wednesday through Friday, with widespread precipitation chances, (including mountain snow) cooler temperatures, and windy conditions. && .DISCUSSION... Issued at 220 AM MDT Sun Sep 8 2024 High pressure over the area will keep temperatures on the warm side once again today. Highs peak about 5 to 10 degrees above average today, sitting around 80F west of the Continental Divide, with mid- 80s to low 90s east. An upper-level shortwave passes through the northwest portion of Wyoming this afternoon and evening. This should help spark a few showers and thunderstorms, namely along and west of the Divide. Have kept chances on the order of 15% to 30% from about 2pm MDT until shortly after midnight, though the best chances occur before 8pm MDT. Not expecting any severe storms today, with the biggest threat being outflow winds up to 40 mph. Of note, however, are the dew point spreads nearing 50 degrees, which indicate there could be some outflow gusts around 50 mph. The ridge flattens a bit for Monday as long wave trough passes through Canada. Temperatures remain comparable to today. A tighter pressure gradient and a shortwave moving through will increase afternoon winds. Models have trended up with these winds from a couple days ago. Widespread gusts of 15 to 25 mph occur for the lower elevations. Being westerly flow, locations east of mountains could see some enhanced winds coming from those higher elevations, more on the order of 30 to 40 mph. With afternoon relative humidities (RH) of 10% to 15% for much of the lower elevations of Natrona and Johnson Counties, elevated to critical fire weather conditions are possible (60%). Wind will be the point of lower confidence on this event. Gusts around 25 mph are possible, meaning marginal for critical fire weather conditions. Will let day shift look at models trends and decide if the Fire Watch needs upgrading. Some afternoon convection is also possible, (15% to 30%) with recent high-resolution models highlighting most of these chances for the southern half of the area. Tuesday looks quite similar to Monday. Winds looks to lessen some, so for now, fire weather concerns are low. Another shortwave moving through could bring some isolated (15% to 30%) showers and storms along and west of the Divide Tuesday afternoon and evening. An approaching low could keep these rain chances going through Tuesday night. The next big weather system will be that mentioned upper-level low. For Wednesday, Wyoming will be in pre-frontal southwest flow. For locations favored in southwest flow, such as the Wind Corridor, gusts 30 or 35 mph are currently forecasted. Elsewhere, it will still be breezy. Precipitation chances will also spread east of the Divide. The main system pushes through Thursday and Friday. Models are in more agreement with the front starting to push into western Wyoming Thursday morning, moving east of the Divide Thursday afternoon and evening. 700 mb temperatures are still looking around the 2C mark, with some near 0C temperatures over far northwest Wyoming. Translating this to the surface, west of Divide locations see highs near 60 degrees to around 70 Thursday. On Friday, after the front passes through the whole area, highs will be in the 60s west of the Divide, with lows 70s east. Western valley places, like Jackson, will be in the mid 50s. Snow levels currently look to drop to around 9500 feet for Friday morning, so expect mountain snow. In summary, Wednesday through Friday can be characterized by cool, wet, and windy (feeling like fall, anyone?). Temperatures begin to rebound into next weekend as the low moves out. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 949 PM MDT Sat Sep 7 2024 Smoke from Wildfires in ID, OR, and the Fish Creek Wildfire in northwest WY will continue to plague the area. This smoke will lead to minor reductions in VIS at several terminals. Reductions in VIS will mainly stay above MVFR criteria, but smoke from the Fish Creek Wildfire will be more dense since it is originating in the area. KPNA has the best chance (40%) of MVFR VIS and would occur Sunday morning after sunrise if it does occur. For terminals not impacted by smoke, conditions will remain VFR through the TAF period. Virga showers will develop across southwestern WY late Sunday afternoon into Sunday evening, which will lead to gusty outflows/downdrafts at times for terminals west of the Continental Divide. Wind will remain light until Sunday afternoon for all terminals and gusty at terminals west of the Divide from Sunday afternoon until 02/03Z. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 220 AM MDT Sun Sep 8 2024 Limited fire weather concerns today as winds remain on the light side (generally 10 mph or less). Afternoon RHs are 10% to 20% for most of the area. Elevated to critical fire weather possible (60%) Monday. A Fire Weather Watch has been issued for fire zones 280 and 281, the lower elevations of Natrona and Johnson Counties. Wind could be the limiting factor, with current models indicating around 25 mph afternoon gusts. Widespread afternoon RHs 10% to 20% are expected. && .RIW WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch from Monday afternoon through Monday evening for WYZ280-281. Air Quality Alert until 1 PM MDT Monday for WYZ012>016-025. && $$ DISCUSSION...Wittmann AVIATION...Rowe FIRE WEATHER...Wittmann