Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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089 FXUS65 KRIW 062332 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 532 PM MDT Mon May 6 2024 .KEY MESSAGES... - Deepening low pressure in northeast Wyoming will continue to generate very gusty west to northwest wind through Tuesday. - Western mountain snow has been limited Monday. However, another round of precipitation is expected late tonight and Tuesday. - The area of low pressure shifts back south Tuesday night and Wednesday, setting the stage for more widespread rain during the daylight hours. There is the potential for lower elevation light snow in upslope-favored locations late Wednesday night. && .DISCUSSION... Issued at 255 PM MDT Mon May 6 2024 Satellite imagery is showing an impressive upper-level low reforming over northeast Wyoming early Monday afternoon. In fact, WPC mentioned that this system may threaten monthly low pressure records for the region. Instability has remained to our east, while 500mb southeasterly flow fed moisture into portions of central and northern Wyoming through midday before the upper low wrapped up and switched the flow to the northwest. Precipitation was heaviest in Johnson and Natrona Counties where 0.75 to 1.25 inches fell over a 6-hour period. Elsewhere, the corresponding pressure gradient has generated widespread 40 to 50 mph gusts, particularly in those locations favored by northwest flow and along the I-80 corridor. The heavier snow anticipated over the far west mountains has not materialized as the best moisture was well to the east. As a result, much of the western snow has been confined to mountain areas along and just east of the Continental Divide. The tight pressure gradient favors continued gusty west to northwest wind through Monday evening. Gusts of 40 to 55 mph persist, especially in the central Wind River Basin, the I-80 corridor, and northern Johnson County. Wind speeds increase in northern Johnson County Monday evening as the low strengthens on the Plains. Favorable 700mb wind of 50+ knots and the anomalous nature of this low lend credence to the potential of high wind around Buffalo Monday evening into early Tuesday morning. Most high-resolution guidance keeps gusts just below warning thresholds, but Buffalo is susceptible to northwest wind. The gradient decreases enough that speeds should drop below high wind criteria by sunrise Tuesday. Elsewhere, speeds take a downturn beginning late Monday evening. However, this decrease will be short-lived as mid- level winds mix to the surface by midday Tuesday. Westerly wind speeds will be less than those seen today, so no highlights anticipated. As for precipitation, the overall trend will be to shift showers to the east tonight. Precipitation continues to pinwheel southward across areas east of the Continental Divide as it wraps around the developing low pressure system. The southward extent of the precipitation shield has generated advisory snow amounts over Casper Mountain today along with the Bighorn Range. The precipitation shield shifts slowly north and east by mid-evening Monday as the low tracks slowly into the western Dakotas. This should confine rain and snow showers to mainly the Bighorns and Johnson County by midnight Tuesday with decreasing chances through early Tuesday morning. Current highlights for the aforementioned mountain locales are on track and look good. Wrap-around precipitation and a more favorable mid-level orographic flow aids mountain snowfall in the far west mountains late tonight and Tuesday. QPF amounts were too high Monday and there is concern that terrain effects are again inflating QPF totals tonight and Tuesday in the western mountains. This is most pronounced over the Teton Range. For now, have continued the winter storm warning for the Tetons, but storm totals have been tempered accordingly. The best chance for any accumulating light snow in the far west valleys would be late tonight into Tuesday morning. As for Tuesday, the best chance for precipitation will remain across the far west mountains and valleys in favored west to northwest flow aloft. Instability is sufficient to produce isolated thunderstorms during the afternoon in the west. While thunder is less likely elsewhere, there is still enough instability and moisture to generate scattered showers during the afternoon. After a short respite Tuesday evening, the pesky upper low begins to pinwheel and push into the northern forecast area early Wednesday morning. Shortwave energy and a favorable northerly flow provide cooler air and increasing upslope flow across central Wyoming by late afternoon, overnight, and even into Thursday morning. A new round of winter highlights may be needed for the Absarokas, Bighorns, and east slopes of the Wind River Range to account for this potential. Additionally, a difference of a few degrees or a few hundred feet of elevation, along with precipitation intensity could lead to lower elevation snowfall Wednesday night. These light accumulations would be most possible in Natrona and Fremont Counties. In general, conditions dry from northwest to southeast through the day Thursday into Thursday evening as the low sags south and east. Temperatures remain unseasonably cool both Wednesday and Thursday. The overall trend Friday through Sunday will be toward warmer and drier conditions. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 532 PM MDT Mon May 6 2024 An upper low pressure system will continue to rotate through the region over the next 24 hours. As a result, very strong winds will persist through much of the period at all terminals. KRIW and KRKS will see the strongest winds with gusts to 45kts continuing into the evening. Some guidance suggests that KRIW may hold onto the 40 to 45kt gusts through 06Z to 08Z before decreasing to 35kts through the rest of the night. Other terminals will see wind gusts 25 to 35kts through much of the period. Winds will once again increase at all terminals by midday Tuesday to similar speeds/gusts as what occurred today. Also associated with the broad low pressure are scattered showers. KJAC may see persistent light snow showers through much of the period. VFR conditions should prevail, but cigs will occasionally drop to MVFR (FL025 to FL030) throughout the afternoon with Vsby hovering between 5SM and P6SM. Other locations west of the Divide will see lesser chances (less than 20% chance) of showery activity, though MVFR cigs may occur intermittently through the period. KCPR will see the showers and MVFR conditions end over the first hour or so of the period. VFR should prevail at all other terminals through the period. Mountain obscurations will be prevalent through the period across the region. 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... Winter Weather Advisory until 6 PM MDT Tuesday for WYZ001. Winter Weather Advisory until 11 PM MDT this evening for WYZ008-009-022. High Wind Warning from 6 PM Tuesday to 6 AM MDT Wednesday for WYZ010. Winter Storm Warning until 11 PM MDT Tuesday for WYZ012. High Wind Warning until 9 PM MDT this evening for WYZ019- 028>030. && $$ DISCUSSION...Jones AVIATION...Hensley/Rowe