Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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628 FXUS65 KRIW 022240 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 440 PM MDT Thu May 2 2024 .KEY MESSAGES... - Breezy and dry conditions across Natrona County this afternoon, with a Red Flag Warning in effect through this evening. - A quick-moving weather system will bring a round of moderate snow to the Wind River Range tonight into Friday morning. South Pass and Sinks Canyon will see accumulating snow. A Winter Weather Advisory is in effect tonight through Friday early afternoon. - After a brief warm up this weekend, widespread rain and snow impact the region Monday, followed by another cooler than average work week. && .DISCUSSION... Issued at 250 PM MDT Thu May 2 2024 A longwave trough remains over the region today, and an embedded shortwave will move overhead this evening. Ahead of this shortwave weather system, dry air and breezy conditions for central Wyoming have led to elevated fire weather concerns (see the Fire Weather section for more details). The shortwave weather system moving through tonight into tomorrow (Friday) morning looks to be more robust than in previous model runs. For this reason, snow amounts were increased, mainly for the Wind River Range and southern Absarokas. South Pass looks to get 4 to 6 inches of snowfall, and although much of this may quickly compress given the relatively strong sun leading to warm ground this late in the spring, there were enough signals to justify issuing a localized Winter Weather Advisory for the northeastern side of the Wind River Range. Expect winter travel conditions over South Pass tomorrow morning, and those in Sinks Canyon or Dubois are likely to see a light layer of snowfall in the AM hours. Saturday will bring a brief warm-up to the area, with temperatures about 5 degrees above average. On Sunday, the next weather system starts impacting the western side of the state, bringing mountain snow, valley rain, and much cooler temperatures. Those east of the Divide will have one more day of warmth on Sunday with temperatures about 10 degrees above normal, but it will come paired with strong winds gusting in the 40 to 55 mph range ahead of the cold front. Precipitation spreads east of the Divide Sunday night, and Monday will be wet across most of the state. Mountains could easily pick up another foot or more of snow from this system, especially the Tetons where multiple feet look likely (70% confidence). Lower elevations are likely (60% chance) to see a wetting rain of a tenth or more of precipitation, with the Bighorn and Powder River Basins (northern Wyoming) being favored for the heavier and more widespread rain/snow. This system exits the state Monday night. On Tuesday and into the end of next week, cooler weather prevails under another broad trough. Scattered mountain showers are likely especially during the afternoons, but no other major weather systems are set to impact the state through next Friday. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 439 PM MDT Thu May 2 2024 VFR conditions this evening. A shortwave passes through the area late this evening, with impacts tonight through early Friday afternoon. Precipitation chances (which will most likely be in the form of snow for all sites) begin at KJAC around the start of the TAF period, with the best chances occurring after 06Z/Fri. Models are showing KJAC on the edge of the best snow chances, so timing and categories are hard to narrow down; VFR to IFR is possible. The NBM has peak chances for the worst flight category at about 10Z/Mon (50- 60% chance of at least MVFR). For KBPI and KPNA, snow chances look to be more banded, making it very difficult to pin down a timing and duration of snow. Snow bands pass through the KRKS area around 10Z-14Z/Mon. NBM has the peak chances for the worst flight category at about 12Z/Mon, which lines up well with other high-resolution models. If a snow band does pass, expect a quick drop in visibilities. Snow bands are difficult for models to place accurately in time, so a change in this timing is very possible. Snow impacts begin at KLND and KRIW around 08Z/Mon. The best snow chances continue through most of the morning and should be ending by 18Z/Mon. Though MVFR currently looks to be the most probable category, IFR is possible (20%). Snow may linger at KLND a few hours past 18Z/Mon, which would mean snow could potentially transition to rain for the afternoon if precipitation does linger. 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 250 PM MDT Thu May 2 2024 Critical fire weather conditions currently exist across the lower elevations of Natrona County (Fire Weather Zone 280), with weather stations showing west winds 20 to 30 mph, gusting 35 to 45 mph. Weather models currently show these conditions lasting until about an hour before sunset, which seems reasonable given typical diurnal patterns. With sunset, winds quickly decrease and RH increases. The air mass will be more moist tomorrow with widespread light precipitation and lighter winds, so fire weather concerns are much lower. On Sunday, strong winds and relatively low RH in the 20 percent range could again bring elevated fire weather concerns mainly to areas east of the Continental Divide. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 9 PM this evening to 3 PM MDT Friday for WYZ015. Red Flag Warning until 8 PM MDT this evening for WYZ280. && $$ DISCUSSION...VandenBoogart AVIATION...Wittmann FIRE WEATHER...VandenBoogart