Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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462 FXUS65 KRIW 160715 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 115 AM MDT Mon Sep 16 2024 .KEY MESSAGES... - More active weather Monday as an upper level system pushes closer to the area with widely scattered rain showers and a few isolated thunderstorms. - A cold front pushes through Tuesday with more scattered rain showers and isolated thunderstorms. Severe wind gusts are possible across eastern counties east of the Bighorns. - Cooler temperatures and continued unsettled weather through the rest of the week and into the weekend with another system. && .DISCUSSION... Issued at 1250 AM MDT Mon Sep 16 2024 IR currently depicts ample cloud cover across much of the area west of the Divide. Radar shows some light rain showers pushing north off the Winds that short term models have it slowly dissipating with its progression through the Absarokas. The main upper level low will continue to slowly progress eastward over the Sierra Nevada deepening with increasing divergence aloft. This has allowed for ample diffluence over the CWA, especially west of the Divide where stronger PVA is expected. A shortwave will kick off the low up the ridge through the CWA through the late morning to afternoon and evening hours. More widely scattered rain showers and a few isolated thunderstorms are expected west of the Divide by mid afternoon after 2PM. The ARW was best throughout the activity Sunday and is also more aligned with the FV3 in coverage as the HRRR is heavily over doing it with more east of the Divide. A further eastward wave will clip Natrona County and Casper towards late afternoon after 5-6PM but with much of the activity further east into Cheyenne`s area with better ingredients for any severe convective activity. Otherwise, shower activity will continue overnight into Tuesday off and on west of the Divide as the aforementioned low nears from the southwest. More widespread activity once again, spreading east of the Divide through the afternoon hours. A cold front associated with the low will push through from around noon in the west to 5-6PM to the east across the CWA. Winds will turn westerly with initial gusts over 30-35mph in some areas before subsiding into the overnight hours. Severe activity could occur along the triple point area as the front moves over the Bighorns across the I-25 corridor and points east. Wind gusts up to 50-60 mph the main threat as the low becomes more progressive the further east it gets. Mountain snow is likely for much of the higher terrain areas of the CWA with the Winds and Tetons seeing the most but still only light in nature for a couple inches or so. As the low kicks off to the northeast and opens back into a wave, the jet digs another low off the Pacific northwest coast through the Sierra Nevadas in similar fashion. Models are in some disagreement on how far south this one goes but will be closed off and deepening with its slow eastward progression. The further south it digs, the less of an impact to the CWA it will be. Regardless, an unsettled pattern will continue through the entirety of the week and into next weekend as well. The EC usually handles these longer term outlooks better and has it more south than others as the main PFJ remains north to support it as a weaker finger to the south keeps it south. Time will tell, but what can be had will be cooler and more seasonable temperatures for the long term forecast with 50s west of the Divide and 60s to low 70s to the east. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1008 PM MDT Sun Sep 15 2024 An active weather pattern means more chances for rain showers, thunderstorms, and strong outflow boundaries on Monday. Tonight a few rain showers will pass through western WY, with a TEMPO for - SHRA at KJAC from 07-11Z. Other terminals should stay dry and VFR tonight into Monday morning. Southerly flow will increase on Monday as an approaching upper-low moves into the region. Sustained wind will average 10-20 knots, with gusts of 20-30 knots. Convection will develop in the afternoon, with the best chances for terminals west of the Continental Divide and KCPR. All terminals have a good chance (50%) of strong outflows/downdrafts during the afternoon/evening hours. Monday evening into Monday night convection will hang around the low, so KJAC/KBPI/KPNA may have rain showers and thunderstorms continue. Wind will decrease substantially around sunset (01-02Z) for all terminals, but will remain around 7-12 knots through the evening hours. Conditions will remain VFR for all terminals through the TAF period, with the exception being if/when thunderstorms directly impact a terminal. If/when this occurs brief reductions in VIS to MVFR/IFR will result. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 1250 AM MDT Mon Sep 16 2024 Elevated fire weather conditions Monday with southerly gusts up to 25-30 mph for much of Sweetwater County and across the Rattlesnakes as well. Higher low level moisture content expected in this area with increasing shower activity seeing relative humidity values in the 25 to 35 percent range. Areas of lower humidity in the 15-20 percent range along the I-25 corridor will see wind speeds below 15-20 mph. Otherwise, less fire weather concerns the remainder of the week with more unsettled weather and cooler temperatures. The only thing of note will be a shift in winds out of the west to north of west behind a cold front that will push through Tuesday afternoon. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Lowe AVIATION...Rowe FIRE WEATHER...Lowe