Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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178 FXUS65 KRIW 141726 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1126 AM MDT Sun Jul 14 2024 .KEY MESSAGES... - Above normal temperatures continue today. - Isolated showers and thunderstorms will again bring the potential for strong outflow winds gusting 50 to 60 mph this afternoon and evening. - Elevated to near-critical fire weather conditions are expected through this evening. - Smoke from western US wildfires will continue to move in causing hazy skies at times. - Slightly cooler temperatures and better rain chances move in for Monday. && .DISCUSSION... Issued at 423 AM MDT Sun Jul 14 2024 Today is the last of several consecutive days of high temperatures peaking well above normal. The expansive area of high pressure responsible for the heat continues to rotate to our south, now centered over the Colorado-New Mexico border. One notable difference for today is the increased availability of moisture which will continue to advect in as it rotates around the high. Current guidance suggests fairly widespread PWAT values of 0.8" to nearly 1" later this evening. Combined with a stronger shortwave moving through the flow, the moisture will lead to better coverage of showers and thunderstorms today. One caveat with the high temperature forecast is that the increased clouds and outflow potential may end up keeping several locations a little cooler than previous days - though only marginally. Other than a few weak morning showers, convection will begin developing in earnest by early afternoon across southwestern Wyoming and then expand quickly east of the Continental Divide. Given the increased moisture, there will be a better chance of rain reaching the ground today. The best chance for this to happen will be across the higher terrain of northwestern portions of the area where dewpoints will be slightly higher (upper 30s to 40s). However, the more widespread impact from the convection will again be strong outflow winds gusting up to 60 mph given the still dry boundary layer and high LCLs; we`ll still see plenty of virga showers. Forecast soundings continue to show the classic inverted V look for today, as well as DCAPE values over 1000 J/kg for most of the area. Fire weather concerns continue as well given the heat, low humidity, and outflow wind potential. Additionally, with instability a little higher today we may see more lightning than previous days. Smoke from western US wildfires that are flaring up will continue to filter in as it rotates around the high, likely making the mountains appear a little hazy. Showers and thunderstorms will linger through the evening across northern Wyoming and eventually come to an end overnight. However, another round of convection is expected on Monday as the high is flattened somewhat by a large trough to our northeast. With increased cyclonic flow across the area and continued moisture availability, this activity will be widespread again, with an even better chance of rain reaching the ground given dewpoints in the 40s for most locations. However, we`re still looking at a relatively dry lower atmosphere. This will lead to a continued strong outflow wind threat - though more in the 40 to 50 mph range. Otherwise, temperatures will trend further down on Monday though still around or just above normal. Tuesday looks very similar, though shifting the better precipitation chances east of the Divide. Further out, ensemble cluster guidance continues to favor the ridge strengthening again to our south. This would keep temperatures on the warm side and precipitation chances a bit more limited. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1125 AM MDT Sun Jul 14 2024 Difficult forecast. Isolated showers and thunderstorms occur this afternoon and evening. All sites will have a 20% to 40% chance of a shower/thunderstorm today. Whether a location gets rain or not, wind gusts will be the main threat. Gusts 30 to 50 mph from outflows may occur at any site whether a thunderstorm occurs or not. A few of the stronger storms may produce outflows greater than 50 mph. Most TAF sites have TEMPO groups to account for thunderstorm chances, but mainly for variable and gusty outflow concerns. Showers/thunderstorms begin to decrease this evening. KJAC holds chances through about 06Z/Mon. Winds decrease overnight. Another chance of showers/thunderstorms occurs near the end of the TAF period, for Monday afternoon. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... Issued at 423 AM MDT Sun Jul 14 2024 Elevated to near-critical fire weather conditions will continue today given the low humidity, hot temperatures, and gusty outflow wind potential. However, we will also see a better chance of rain reaching the ground today, and areas directly under these isolated cells could see a wetting rain. Increased instability will also lead to an uptick in lightning potential today. As with previous days, outflow wind gusts could briefly reach up to 60 mph this afternoon. Humidity recovery will be better tonight in the wake of today`s activity. && .RIW WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 10 PM MDT this evening for WYZ004>006-010- 011-017-018-020. && $$ DISCUSSION...Myers AVIATION...Wittmann FIRE WEATHER...Myers