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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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218 FXUS65 KRIW 180420 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1020 PM MDT Sat Aug 17 2024 .KEY MESSAGES... - Increasing monsoonal moisture today with widely scattered thunderstorms expected this afternoon and evening. - Storm activity will be a bit further east of the Divide Sunday. - Continued active but weaker pattern throughout the week with more seasonable temperatures expected. && .DISCUSSION... Issued at 1235 PM MDT Sat Aug 17 2024 Current IR depicts the ridge of higher heights extending in from the south to southeast as monsoonal moisture starts to pump more northeastward across the Rocky Mountain West. Radar shows increasing activity across Utah currently pushing northeast towards far reaches of southwest Wyoming. Areas along the border should start to see activity cross over by 2-3PM, spreading northeast into the rest of the afternoon and evening hours. Flooding concerns are at low confidence at this point with the bulk of the stronger instability and vort max in northern Utah pushing into Idaho. PWAT values less than half an inch at this point for areas of deep southwest Wyoming, but something to keep an eye on for a more localized threat. Otherwise, stronger winds are the main concern as 40-50 mph gusts are possible with the strongest cells as they push out of northeastern Utah. Currently any reports are calling for these values to be max at this point where as the further northeast these get, the weaker of an environment to flourish in. With moderate steering flow speeds, expect faster moving storms in a multicell structure making for the aforementioned lower flood threat and higher in the wind department. Modest CAPE and lapse rate values at best, indicate a lower end severe threat as these storms enter the CWA but these far reaches of the area will be the most to be concerned with. Otherwise, these storms will progress towards the Winds by 5-6PM with uncertainty on if these will hold together and make it into the Wind River Basin and beyond towards sunset into the overnight hours. Some models indicate this occurring but others not so much. Thus, confidence is low, and even if this occurs, little to no threats will occur with them. Areas along the Wind Corridor stretching to Casper and the I-25 Corridor will see these storms hold better together southeast of the Winds, but again any stronger threat will be diminished with the setting sun and loss of stability into the overnight hours. These will push east out of the CWA by the early Sunday morning hours with another round expected for Sunday afternoon and evening progressing further east of the Divide as the monsoonal push furthers itself into eastern portions of the CWA. Similar threats expected Sunday with wind the main hazard with this next compact shortwave across the state. Going forward, monsoonal moisture weakens throughout the week, although a continued active pattern with the upper level low ongoing across the Pacific Northwest. This will continue to weaken the upper level high with increasing divergence aloft as it moves more east into the southeastern portions of the US. Otherwise, the aforementioned low will slowly fill and push east finally kicking out to the east by Saturday of next week. Seasonable temperatures and winds expected throughout as well. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1010 PM MDT Sat Aug 17 2024 Virga showers will continue to end through the first couple of hours of the TAF period. Winds have already subsided across much of the area, however winds of 15 to 20 kt will continue/develop at KCPR and KRIW through 12Z respectively. The winds at KRIW will subside by 16Z, while the winds at KCPR gradually decrease through 19Z and turn more north-northwest. Showers and thunderstorms will develop across areas west of the Divide and the Bighorn Basin between 19Z and 21Z, spreading toward the northeast through 00Z. Confidence is low on the timing of these storms, so have left PROB30 groups for impacted terminals for now. These storms are expected to cross into the Wind River Basin after 00Z, possibly impacting KLND/KRIW through 05Z. Any remaining showers/thunderstorms will be isolated toward the end of the TAF period, as gusty outflow winds continue across the forecast area. Gusts of 20 to 30 kt are expected with the storms Sunday, although isolated gusts of 40 to 45 kt cannot be ruled out. 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 357 AM MDT Sat Aug 17 2024 Elevated fire weather conditions are expected for much of the area this afternoon ahead of surging monsoonal moisture that will arrive to southwestern Wyoming around noon. This will bring showers and thunderstorms mainly west of the Divide, as well as strong southwesterly wind that will eventually move east of the Divide late this afternoon and evening. While humidity will increase notably, the wind will likely arrive suddenly and could cause issues for ongoing fires. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Lowe AVIATION...LaVoie FIRE WEATHER...Myers