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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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595 FXUS65 KRIW 172310 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 510 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 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 with wind the main hazard with this next compact shortwave across the state. Going forward, monsoonal moisture weakens throughout the weak, 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 /00Z TAFS THROUGH 00Z MONDAY/... Issued at 510 PM MDT Sat Aug 17 2024 Showers and thunderstorms associated with a surge of monsoonal moisture will continue to push east-northeast through the evening. East of the Divide terminals (KLND, KRIW, and KCPR) will be impacted by these showers and thunderstorms during the first 3 to 6 hours of the TAF period. Gusty winds of 30 to 40 kt are the main threat with these showers and storms. Winds will decrease to mostly light (<10 kt) and storms will exit the region through the overnight period. Mostly clear skies and light winds will then start Sunday morning. Winds across the south (most notably KRKS) will see west winds start to increase late in the morning. Similar gusty southwest winds will occur near KCPR in the morning after sunrise. Showers and thunderstorms then become possible by mid- to late- afternoon across most terminals. PROB30 groups have been included for these showers and thunderstorms. 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...Hensley/LaVoie FIRE WEATHER...Myers