Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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197 FXUS65 KRIW 150656 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1256 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 week and 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. Development 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 /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 902 PM MDT Fri Jun 14 2024 Some lingering rain showers and thunderstorms are near KRKS/KPNA thanks to a rogue outflow boundary that is moving northwest. This outflow boundary looks like it has finally stalled just southeast of KPNA, so no new convective development is expected with this tonight as the recent convective activity dissipates. Conditions will remain VFR through the TAF period. Model guidance is now depicting convective development in Natrona and Johnson County Saturday afternoon, which means a chance for storms in the vicinity of KCPR for a couple of hours. Strong surface winds should prevent any rogue outflow boundaries associated with this convection from pushing west and initiating more convection in the area, so thinking is just a short window for thunderstorms at KCPR Saturday afternoon. Wind will increase Saturday morning and become strong across the area through the afternoon. Wind gusts will average 25-35 knots (as high as 45 knots) Saturday afternoon. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Lowe AVIATION...Rowe