Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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999 FXUS65 KRIW 191828 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1228 PM MDT Sun May 19 2024 .KEY MESSAGES... - Elevated to critical fire weather conditions today, with gusts up to 40 mph and relative humidities 10% to 20%. - Wet and cool Monday and Tuesday. Some locations east of the Divide may see (40% to 60% chances) over an inch of rain. - Mountains see snow, the heaviest occurring Monday night through Tuesday. Over a foot is possible. Expect impacts to travel over mountain passes. - Unsettled weather pattern continue to end the week. && .DISCUSSION... Issued at 1226 PM MDT Sun May 19 2024 Southwest flow today ahead of the next weather system. Gusty winds up to around 40 mph develop across much of the area, continuing through the afternoon. Relative humidities (RH) drop below 20% for many lower elevation locations, with near 10% for some. These two factors lead to elevated to critical fire weather conditions today. Isolated (15% to 50%) showers moves across the area, mainly for far northern Wyoming and southern areas, where the best leading moisture and jet support is. A rumble of thunder is possible with these. The advancing upper low, and associated cold front, push into Idaho tonight. This low tracks across Wyoming through Tuesday and will be the main weather driver the next couple days. For Monday, precipitation chances will be increasing, even before sunrise as moisture enters the state. The best chances (15% to 40%) Monday morning begin across southwest Wyoming, where jet support will help initiate showers. Chances spread through much of the area through the morning, however. Widespread chances of 30% to 80% chances for the rest of Monday. Highs Monday will only be in the 50s for most, about 10 degrees below normal. The low tracks eastward Monday night into Tuesday. This brings heavier precipitation to roughly the Fremont, Natorna, and Johnson County areas, as well as the eastern Wind River, Absaroka, and Bighorn Mountains. Starting with those lower elevation counties, rain total amounts for Monday and Tuesday (most of which occurs Monday night through Tuesday afternoon) have a 40% to 60% chance to be above 1 inch. A few favored locations, such as near mountains where upslope is favored, is closer to a 70% chance. Current forecast has just under an inch to about an inch for the lower elevations of roughly Fremont, Natrona, and southern Johnson Counties. Elsewhere across the area, totals are generally less than half an inch. For the mountains Monday through Tuesday, the big day will be Monday night through Tuesday as east to northeast flow favored upslope on the eastern side of the mountains. By Tuesday night, snow amounts on the eastern slopes of the Winds, Absarokas, and Bighorns could be a foot or more. Expect winter travel conditions if going over the passes in these areas. Will hold off issuing any winter highlights given the heavier snow won`t start until Monday night. Snow amounts in these areas have been fairly consistent run-to-run. Tuesday will be cold day, with many places around the 50 degree mark for the high, about 20 degrees below normal. Wind does not appear to be a big factor Monday or Tuesday with this storm. Transitory ridging Wednesday brings less precipitation chances and slightly warmer temperatures, just a little below normal. Another system looks to impact the area Thursday/Friday, with low confidence as models have disagreement on the details. In any case, the end of the week looks to remain unsettled, with cool and wet weather. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1113 AM MDT Sun May 19 2024 VFR conditions continue today with SCT midlevel CU bubbling up this afternoon. Main issue today is gusty winds, with plenty of southwest gusts of 25 to 30kts through this evening. Winds decrease overnight, and should stay light into the day Monday. Some shower activity will begin to develop for the southern half of the state overnight, and gradually shift northward during the day Monday. Cigs with this rain will lower to near MVFR levels during the afternoon Monday. && .FIRE WEATHER... Issued at 1226 PM MDT Sun May 19 2024 Elevated fire weather conditions today. Wind gusts to 40 mph occur over most of the area today. RHs will be down to 20% or lower for many locations. The Wind River and Green River basin see RHs down to around 10%. Conditions start improving this evening. Wet and cool starting Monday, with precipitation chances through the rest of the week. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...Straub FIRE WEATHER...Wittmann