Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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386 FXUS65 KRIW 092318 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 518 PM MDT Sun Jun 9 2024 .KEY MESSAGES... - Showers and thunderstorms will continue this afternoon and evening, most numerous across the northern half of the area. Strong wind gusts and brief, heavy rain are the main concerns with this activity. - Monday will see continued isolated showers and thunderstorms. - Warmer and drier conditions expected Tuesday through most of the week. Elevated river and stream levels will continue. && .DISCUSSION... Issued at 236 PM MDT Sun Jun 9 2024 Scattered showers and thunderstorms are ongoing across much of Wyoming in response to the arrival of a shortwave trough riding along the upper level ridge. This activity is expected to expand eastward through the afternoon with the best coverage across the northern half of the area. With both Pacific and Gulf of Mexico moisture advecting into the area, there will be fairly decent moisture available for convection (107% of normal per 12Z sounding at RIW). Accordingly, instability will increase through peak heating, with MLCAPE values generally peaking in the 500-1000 J/kg range (with some caveats - such as the Bighorn Basin which will miss out on deeper theta-e advection). The best environment will be across eastern portions of the area which will see MLCAPE rise to the 1000-1500 J/kg range. Given the well-mixed boundary layer, strong, gusty winds are the main concern, though large hail can`t be ruled out with any stronger storms. As the current convection wanes this evening, another shortwave will push into western Wyoming. This will bring another round of showers and thunderstorms overnight, most focused on northern and western portions of the area. This round could bring a little more rain accumulation, though this is very dependent on individual cell locations. A quarter to half an inch is not out of the question from any one cell, though most of the area will see much less. This activity will wane by sunrise. Monday will see additional showers and thunderstorms develop in the afternoon as the next wave clips northern Wyoming. Accordingly, most of the activity will be focused on areas east of the Divide. Strong wind will be the primary concern again, with a lower hail threat as well. Otherwise, an increased surface pressure gradient will make for a gustier west to northwest wind for most of the area Monday afternoon. Further ahead, weak ridging to fairly zonal flow will take over. Accordingly, warmer and drier conditions are favorable Tuesday through at least Thursday. Ensemble cluster guidance is hinting at increasing troughiness by the weekend. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 516 PM MDT Sun Jun 9 2024 Widely scattered showers and thunderstorms continue across the region through the early part of the evening. Localized MVFR conditions are expected during thunderstorms. Gusty and erratic winds, small hail, and locally heavy rain are also possible with stronger storms. TEMPO groups are included in the TAFs to cover the best chances of showers and thunderstorms. Shower and thunderstorm chances significantly decrease after 06Z, but hi- res models continue to suggest that isolated showers and weak thunderstorms may continue across the north and west through much of the night. Have omitted any mentions of TS or SH after 06Z though due to low confidence in coverage and location of any lingering shower and t-storm activity. KJAC, KCOD, and KWRL have the best chance (20%) of any lingering showers or thunderstorms after 06Z. Winds increase across the region late Monday morning, with westerly winds gusting 20 to 30kts across most west of the Divide terminals and northerly winds gusting 20 to 25kts at most east of the Divide terminals through the afternoon. Additional showers and thunderstorms will be possible Monday afternoon, but will be much more isolated than Sunday`s activity, and thus have only included mentions at KCPR where the best chances (30%) for any of these showers or storms exists. 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...Myers AVIATION...Hensley HYDROLOGY...LaVoie