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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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777 FXUS65 KRIW 162050 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 250 PM MDT Fri Aug 16 2024 .KEY MESSAGES... - Elevated to critical fire weather conditions through sunset this evening for portions of central and southern Wyoming. - Monsoonal moisture returns west of the Divide tomorrow afternoon, with scattered afternoon showers and thunderstorms expected Saturday through Monday. - Temperatures about 5 degrees above seasonal averages through the weekend. - No major weather systems or weather pattern changes through the end of next week. && .DISCUSSION... Issued at 246 PM MDT Fri Aug 16 2024 The jet streak that caused some overnight and morning showers and weak thunderstorms is slowly moving northeast and out of the state this afternoon. Isolated precipitation currently over the Bighorn Basin, Bighorn Mountains, and Johnson County will soon move out of the area, leading to mostly clear skies and minimal precipitation this evening through mid-day tomorrow. Afternoon mixing will bring mid-atmosphere breezes down to the surface across southern Wyoming, and combined with the dry air mass in place, fire weather conditions will be critical, leading to a Red Flag Warning for portions of the state through 8 PM MDT this evening. The large-scale upper-level ridge will amplify over the weekend, bringing warmer temperatures to the region, but no exceptional heat is forecast. The southwesterly jet stream will remain just west of Wyoming, and vorticity maxima moving through the flow are likely to cause enhanced periods of lift and increased shower and thunderstorms activity, especially west of the Continental Divide starting Saturday afternoon. Moisture in this flow pattern will be monsoonal in nature with high PW, so the stronger storms could cause brief heavy rain (less than 10% chance for any given location) and isolated flash flooding, especially over southwestern Wyoming where soils are slow to absorb incoming moisture. WPC highlights this same threat, showing a Marginal Risk for excessive rainfall over the Saturday through Monday timeframe. The weather pattern changes little in the Tuesday through Friday timeframe. A trough over the Pacific Northwest will keep southwesterly flow in place over Wyoming, and isolated to scattered afternoon thunderstorms will be commonplace. Temperatures fluctuate between near normal and about 5 degrees above normal for the work week. A larger and more impactful trough looks to edge into Wyoming next weekend, but details on this system are still of very low confidence. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1032 AM MDT Fri Aug 16 2024 VFR conditions are expected for the entirety of the TAF period. Some gusty winds at RKS and CPR with the stronger gradient to the south for these areas. Some mid level clouds to the north with low confidence storms on station at COD and WRL between 21-23Z with initiation. TEMPO groups are carried here with the isolated nature of these storms that will completely push northeast by the next cycle run. Otherwise, light winds and clearing skies overnight and into the rest of the period with no other weather elements 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. && .FIRE WEATHER... Issued at 246 PM MDT Fri Aug 16 2024 Relative humidity in the lower to mid teens and winds gusting 20 to 30 mph will bring critical fire weather to portions of Sweetwater, Fremont, and Natrona Counties this afternoon and evening. Red Flag Warnings are in effect through sunset for the driest and breeziest locations. Elsewhere, winds will likely be lighter and RHs above critical thresholds. No thunderstorms are expected this afternoon or evening for the Red Flag Warning area. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 8 PM MDT this evening for WYZ279-289. && $$ DISCUSSION...VandenBoogart AVIATION...Lowe FIRE WEATHER...VandenBoogart