Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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470 FXUS65 KRIW 011924 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 124 PM MDT Sat Jun 1 2024 .KEY MESSAGES... - High-based convection producing gusty outflow wind 40 to 50 mph will be the primary hazard across southwest and central Wyoming through sunset Saturday. There is a 20 percent chance of wind gusts 50 to 55 mph. - A ridge of high pressure boosts daytime high temperatures to much above normal for the period Wednesday through Saturday. - The above normal temperatures allow for an active mountain snowmelt throughout much of the coming week. Foothill creeks and streams will see daily diurnal rises. The most notable rises are expected in smaller tributaries of the Snake River and the northern Bighorn Range. && .DISCUSSION... Issued at 124 PM MDT Sat Jun 1 2024 An active cumulus field stretches from a shortwave in northern Nevada into southwest Wyoming early Saturday afternoon. Midday webcams indicated generally virga from this weak convection given a dry sub-cloud layer. In fact, the upstream KSLC 12Z sounding showed a moist layer around 14K feet AGL. Soundings and temperature-dew point spreads potentially approaching 50F lend credence to the possibility of 45-55 mph convective outflow wind gusts across southwest Wyoming later Saturday afternoon. Thermodynamics and bulk shear become more favorable for intensification after 3pm Saturday. After initial development over southwest Wyoming, CAMs show some consistency in bringing these showers into Fremont and Natrona Counties early Saturday evening. Overall, high-resolution ensembles indicate a 20 percent chance of 50+ mph gusts during the 3pm to 9pm timeframe within these regions of the forecast area. The mid-level moisture plume lingers overnight as the upstream shortwave traverses the forecast area. This combination leads to lingering light showers over the aforementioned areas into Sunday morning. Gusty outflow wind remains the primary hazard although lesser speeds of 30 to 40 mph would be most likely peak gusts. A secondary shortwave follows on the heels of this first wave, reaching the western border Sunday morning. Instability looks weak Sunday and mainly confined to central and southern sections through early afternoon. As this shortwave crosses the region, further stabilization comes to central Wyoming. In general, convection looks to wane by early evening. Nonetheless, scattered showers are expected across the region throughout the day. The upper-level flow backs to the southwest Sunday night and Monday in response to the next upstream shortwave. This provides a steady increase in mid- level moisture across western Wyoming Monday morning. Dynamics and deepening moisture favors more widespread convection across the northwest-quarter of the state Monday afternoon and evening as the shortwave approaches and treks just to our north. This track enables lingering convection over the far north late Monday night into Tuesday morning. One concern for Monday is the potential for rain-on- snow in the western mountains, which would enhance snowmelt runoff in the higher terrain feeding the Snake Basin. For the most part, QPF in the far west mountains ranges from one-third to two-thirds of an inch Monday and Monday evening. Higher totals could fall in the mountains of the Teton Range and southwest Yellowstone National Park. This situation bears watching given the rising water levels associated with snow melt Saturday and Sunday. Tuesday finds west-northwest flow aloft across the forecast area as the shortwave moves into the Northern Plains. Breezy west to northwest wind prevails into the evening hours. Any convection would be confined to the far north. Daytime highs will be slightly above normal. A building ridge over the Great Basin and West Coast allows for these temperatures to climb beginning Wednesday. Daily high temperatures will be approximately 10F above normal Wednesday through Saturday leading to widespread 80s for most lower elevation locales. Ensembles continue to depict a weak low in the Desert Southwest circulating moisture north on the backside of the ridge late in the week. Friday and Saturday appear to be the most likely days for some of this sub-tropical moisture to reach Wyoming and initiate late day convection. Above normal temperatures, especially from Wednesday onward, allow for active high-elevation snowmelt to continue. Much of the remaining snowpack is above 9K feet, but there are certain areas where lower snow still remains. As a result, the most notable rises are expected in smaller tributaries of the Snake River and the northern Bighorn Range. For the most part, foothill creeks and streams see daily diurnal rises that will need to be monitored. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1112 AM MDT Sat Jun 1 2024 Prevailing VFR conditions through the TAF period. Isolated showers and thunderstorms will be around this afternoon and early evening. The best chances (30% to 50%) occur at KLND and KRKS. Lesser chances (15% or less) occur at most other sites though. Given the lower chances, other sites do not have rain chance mentioned in TAFs. KCPR would be the most likely, with about 15% to 20% chances between roughly 23Z/Sat and 03Z/Sun. High-resolution models are very inconsistent with rain placement, so confidence is low at this time. These showers, especially in the vicinity of KCPR and KRKS (but could occur at most sites this afternoon) could bring strong outflows, the highest potential gusts being 40 to 50 mph. These winds will be the biggest threat through this evening. Some low rain chances (15% to 30%) move into western Wyoming between 06Z/Sun and 12Z/Sun, with KJAC being the potential impacted terminal there. 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...CNJ AVIATION...Wittmann