Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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925 FXUS65 KRIW 182221 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 421 PM MDT Sat May 18 2024 .KEY MESSAGES... - Elevated fire weather conditions today and tomorrow, with gusty winds up to 40 mph and relative humidity values below 20% - Cool and wet Monday and Tuesday across the area. Snow in the mountains. - Active weather pattern past Tuesday, keeping cool temperatures and precipitation chances through the workweek. && .DISCUSSION... Issued at 1235 PM MDT Sat May 18 2024 Fairly zonal flow today in the wake of the cold front that passed through yesterday and last night. High temperatures will be a touch cooler today as a result, but still in the low 70s for most. A gusty afternoon again, though not as strong as yesterday. A southwest to west wind gusting 25 to 35 mph develops for the afternoon across most locations west of the Continental Divide, and across Fremont and Natrona Counties, as well as the western Bighorn Basin. Today is also dry, with minimum relative humidities (RH) under 20% for most lower elevation locations. The HREF is highlighting Sublette, Sweetwater, Fremont, and Natrona Counties for the lowest RHs, those being around 10%. Elevated fire weather conditions for this combination of wind and dry weather. A Pacific system will be the main weather driver to end the weekend and for the first half of the workweek. Starting with Sunday, flow shifts southwesterly as the trough approaches, with a tightening pressure gradient. Winds begin to increase in the morning, with widespread gusts 30 to 40 mph (80% confidence for this range). RHs again fall below 20% for much of the area, the HREF highlighting Sublette and Fremont Counties with the best chance for lowest values of 10% to 15%. Again, elevated fire weather conditions for Sunday. A little moisture ahead of this system could bring some showers across the area Saturday night through Sunday. Chances range from near 0% to 60% depending on location. The upper-level low tracks eastward Monday, centered on Idaho. This is when the better moisture begins to make it into the Wyoming. Precipitable water values increase to 100% to 150% of normal. Widespread precipitation chances pick up Monday morning and into the afternoon. Snow level around 7000 to 7500 feet will mean snow for the mountains. The low tracks across the state Tuesday, shifting upper level flow as it does. This is important, because by Tuesday morning, favored flow will be for the eastern side of mountains. Through Tuesday, 0.15 to 0.75 inches are possible across much of the area. Of interest will be two locations, one being the mountains, the other for the central area of roughly Fremont and Natrona Counties. Starting with the latter, models are indicated a roughly 30% to 50% chance of Fremont to Natrona County getting more than 1 inch of rain Monday through Tuesday. Being 3 to 4 days out yet, not all high- resolution models are in range, so this can very well change. Overall, this is something to watch in model trends. For the mountains, the focus is on the eastern sides as the low tracks eastward for Tuesday. Although snow begins Monday, rates and amounts ramp up Monday night and through Tuesday. Totals through Tuesday, as of now, are a little over a foot for the eastern Winds, Absarokas, and Bighorns. Again, being a few days out, there can still be some change in exact storm track on how much moisture comes with this system. Will hold off on winter highlights for now, as confidence is not yet high enough in any specific amounts at this range out. There is a little concern when it comes to flooding, namely over the Bighorn Mountains. Some late season snow has kept liquid amounts above normal for this time of year. We have already seen river levels rise as warm temperature melt snow and recent storms bringing precipitation. With the potential another large system (possible QPF 1 to 2 inches), could see more river rises. Past Tuesday, it looks to remain active, with another system in the Wednesday through Friday timeframe. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 421 PM MDT Sat May 18 2024 VFR conditions continue through the next 24 hours, with increasing high cirrus tonight and Sunday. A few light showers are possible late tonight and Sunday for NW WY in the vicinity of KJAC and KRKS. These will bring cigs down some, but should be staying above the 6000ft level, and will be brief in nature. Winds will again jump back up midmorning, with frequent gusts around 25kts. SOme higher gusts are likely at KCPR and KRKS during the afternoon. 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 1235 PM MDT Sat May 18 2024 Elevated fire weather conditions for most lower elevation locations today and tomorrow. Gusts today of 25 to 35 mph are common, with gusts up to 40 mph tomorrow. RH drops below 20% for most locations, with some areas nearing 10% minimum RHs today and tomorrow. Cooler and wetter pattern starts Monday, with widespread precipitation chances through Tuesday. An active weather pattern continues after Tuesday. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...Straub FIRE WEATHER...Wittmann