Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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914 FXUS65 KRIW 151722 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1122 AM MDT Sat Jun 15 2024 .KEY MESSAGES... - Elevated fire weather risk Saturday afternoon and early evening. - Cooler temperatures and increasing precipitation chances Sunday night through Wednesday. - Dry and warming trend by end of the coming week into next weekend. && .DISCUSSION... Issued at 1232 AM MDT Sat Jun 15 2024 IR currently depicts the low that affected the CWA push further east into the Great Plains with another low over the Pacific northwest. Highly meridional upper level flow southwesterly aloft across the upper Rockies. A couple sporadic rain showers are dissipating with a mainly dry Saturday ahead. A weak frontal boundary will continue to slide slowly east through the CWA throughout the day Saturday. This could spark a couple isolated thunderstorms along and east of the I-25 corridor with better ingredients for severe weather further east in the state and beyond. Thunderstorms are progged to develop near the CWA line with CYS after 20Z with the FV3 extending this line through Sweetwater County. Confidence is low at this point (<15%), and even if so, they will push east quickly within an hour or two. The main story for Saturday will be elevated fire weather conditions in the afternoon and early evening time frame. With the aforementioned front, the gradient will tighten to around 6-7 mb across the CWA. As a result, expect wind gust to over 40 mph from Sweetwater County through the Rattlesnakes and along the I-25 corridor. Other points east of the Divide to include the Wind River and Bighorn Basins, expect gusts up to 30-35 mph and less than 25-30 mph to the west. Relative humidity values will be in the 10-25 percent range, lowest for Sweetwater County but with green-up ongoing. confidence is low on any widespread fire concerns. Otherwise, winds will diminish towards sunset with radiational cooling and subside to less than 10-15 mph after midnight heading into Sunday morning. The next system coming from the Pacific northwest will slowly progress east towards the CWA and deepen due to increasing divergence aloft. PVA anomalies look to effect northwest portions of the CWA first early Monday morning expanding eastward throughout the day. Precipitation chances increase across northern portions of the CWA with models in better agreement this last set of runs with this northern progression. Light snow is possible for higher terrain above 7-8kft across Yellowstone and northern Absarokas for overnight and early morning hours, with rain showers lower and further east. Best chance looks to be late Monday and much of Tuesday with the PVA set across this area before quickly exiting northeastward into Montana and the upper Great Plains into Wednesday as the low becomes more progressive at that point in time. Accumulation amounts are still of low confidence, but nothing stands out in any models for a great impact at this point in time. Regardless, cooler temperatures can be had up to 10 to 15 degrees below average by Tuesday. Next up, will be a more ridging to more zonal pattern through the remainder of the work week and into next week. Subtle disturbances look to still perpetrate through the upper level pattern sparking some weak precipitation chances for higher terrain pushing into some lower valleys and basins but of minimal impacts. A warming trend is in store for this period back to average temperatures by Thursday and above for this time of year by the weekend with low 90s possible east of the Divide for some. All in all, rainfall amounts do not look that great for the first half of the work week, but will be the best chance for the wider spread amounts for the northern half of the viewing area. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1122 AM MDT Sat Jun 15 2024 All terminals to be VFR through midday Sunday. The main aviation concern will be gusty west to southwest surface wind of 15-35kts that develops and becomes widespread between 18Z-21Z/Saturday in the wake of an east-moving shortwave. These winds persist until around sunset Saturday (02Z-03Z/Sunday) with lingering west to northwest 10-15kt winds for many areas until 06Z-09Z/Sunday. Otherwise, the shortwave tracking across central Wyoming Saturday morning has been producing pockets of showers and gusty outflow wind. The tail end of this shortwave will be draped from around KCPR to KRKS by mid-afternoon. Convection that forms along this boundary in the vicinity of these terminals moves quickly to the southeast by 23Z/Saturday. Remaining terminals are dry with no impacts. There is a patch of mid-level moisture that will lower mid-cloud decks overnight with a hint of embedded light showers over northwest Wyoming. Again, no impacts with any weak convection that may develop. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Lowe AVIATION...CNJ