Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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479 FXUS65 KRIW 182115 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 315 PM MDT Tue Jun 18 2024 .KEY MESSAGES... - Cool and breezy weather continues as the trough slowly exits this evening. - Ridging redevelops Wednesday, prompting a warming trend that will persist through the weekend. First triple-digit temps of the season are possible Sunday and Monday. - There is a 30 to 40% chance for widespread showers and isolated thunderstorms east of the Divide Friday. && .DISCUSSION... Issued at 311 PM MDT Tue Jun 18 2024 Wild and Wonderful Wyoming graced us with a dusting of snow last night and this morning across the mountains and some portions of the western valleys and Yellowstone National Park. Temperatures have since warmed above freezing this afternoon with some sunshine poking through the clouds as the trough exits, and that snow has mostly melted as I write this around 230 PM. Additional showers and high elevation snow showers will remain possible through the rest of the afternoon and evening as the trough slowly exits. PoPs are only around 20 to 25% and mainly isolated to the northern half of the region and showers have remained isolated through the day. Breezy winds will also continue to persist with the trough, but will decrease this evening towards sunset. Wednesday, ridging begins to become re-established across the region and thus a warming trend will begin. Temperatures will return to near normal values by Thursday across the region. With the ridge, much direr air also moves in for Wednesday and Thursday and RHs will reach critical values both days across much of the region. However, winds will be light and thus, fire weather concerns are limited. The warming trend will not be limited though. Temperatures continue to warm through the weekend and by Sunday and Monday we could be looking at our first triple-digit temps across portions of the region. Model indications are that the heat will not last forever, but will stick around at least for a while. Both GFS and ECMWF solutions prog a trough bringing some relief for the later half of next week, but confidence on widespread cooler and wetter weather remains low. With the ridge building, there is little hope for a widespread soaker between now and then either. Our best opportunity for wetting precipitation will come Friday as a southerly push of Gulf moisture moves up into WY with the help of a weak shortwave. Latest forecast trends have decreased QPF, and indicate that "widespread" could be instead "widely scattered", and given dry air and little surface moisture to enhance PWATs, I would tend to agree with the drying trend suggested by the latest model solutions. Furthermore, instability will be limited and models indicate that inhibition could outweigh instability for much of the region through Friday afternoon, which would limit thunderstorms somewhat. That being said, I have left 30 to 50% PoPs across the region for Friday, and I will not discount the potential for some stronger storms to develop Friday afternoon if we can get a few cells to break the cap. Localized flash flooding may also be a possibility as winds will be light, leading to a chance for slow- moving or training cells, particularly across the eastern and northern portions of the CWA. After Friday, however, precipitation chances return to near zero as the ridge intensifies through the weekend. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1142 AM MDT Tue Jun 18 2024 Showers will increase after 18Z over northern portions of Wyoming affecting mainly KJAC and KCOD. Mountain tops may be obscured at times with some snow showers. Main aviation concern is west winds gusting 20 to 25 kts this afternoon. Skies will generally clear this evening, with light and variable winds returning. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Hensley AVIATION...Tesar