Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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701 FXUS65 KRIW 090819 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 219 AM MDT Sun Jun 9 2024 .KEY MESSAGES... - Showers and thunderstorms will move over western portions by midday, becoming widespread through the afternoon. Stronger thunderstorms could produce strong to severe wind gusts and large hail. - Isolated to scattered (20-30%) thunderstorms will remain possible across the CWA Monday, but are not expected to be as strong. - Dry conditions return Tuesday with temperatures remaining above normal. Widespread showers and thunderstorms could return by Friday. && .DISCUSSION... Issued at 214 AM MDT Sun Jun 9 2024 An upper level ridge will shift eastward over western portions of the CWA this morning. A shortwave trough is also already moving onshore over OR/CA this morning. These features will allow an area of subtropical moisture, currently over the Great Basin and marked by showers as of 130 am, to reach western portions by 18Z. Precipitable water (PW) values will increase across the CWA today, ranging between 0.6 and 1.0 inches, with the lower end of these values staying over southern portions. This is still within the 90th percentile (0.66"), with 0.9" as the daily max for June 9th. Gulf moisture (from the Gulf of Mexico) will also add to this moist environment, advecting into eastern portions through the afternoon. This will culminate in dewpoints in the low to mid 50s for most areas east of the Divide, CAPE values of 1000 to 1500 J/kg and LI`s of minus 4 to minus 6 across much of the CWA. SPC has kept the northern half of the Cowboy State under a Marginal Risk for severe thunderstorms today. Strong to severe wind gusts and large hail will be the main threats from the stronger thunderstorms, with locally heavy rain being a threat as well due to the abnormally high PWs. Thunderstorms will continue through the evening becoming more isolated after midnight, with showers remaining possible through the night along and north of an Afton-Riverton-Kaycee line as the trough begins to move over western WY Monday morning. Temperatures west of the Divide will be about 5 degrees cooler Monday. with isolated to scattered thunderstorms remaining possible across much of the CWA. Strong to severe storms are not expected, as the trough keep the most unstable elements over eastern portions of the state. Gusty west-northwest winds will be widespread across the forecast area, due to the resulting pressure gradient from the passing trough. Dry conditions will return Tuesday, as a transitory ridge moves over the region. A more zonal flow pattern will be in place Wednesday, before a ridge, from a strong high center over AZ/NM, rebuilds over the Northern Rockies Thursday into Friday. Showers and thunderstorms could return to the area Friday, as an upper level low from the Desert Southwest surges northward. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1008 PM MDT Sat Jun 8 2024 VFR conditions expected at all TAF sites for the entirety of the period. Light winds and mainly clear skies to start and overnight. Increasing storm chances after 18-20Z for all locations from northwest to southeast throughout the afternoon and evening. KRKS will be last to see storm activity, but all locations have PROB30 categories with confidence low, as sporadic as these storms will be. Otherwise, relatively light winds outside of any outflows with increasing clouds in the afternoon and towards the end of the period. Improving skies and dry conditions towards the end of the period and overnight into Monday morning. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .HYDROLOGY... Issued at 214 AM MDT Sun Jun 9 2024 Rivers and creeks will remain on the high side today at Action Stage or below, but look to remain steady for now. SnoTel sites above 9000 ft remain below 10 inches of SWE and continue to drop. At this rate, the remaining snow at these sites could be gone in the next couple of days. The notable exception is sites in the Tetons and portions of Yellowstone NP, where 20-30 inches remain on the ground. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...LaVoie AVIATION...Lowe HYDROLOGY...LaVoie