Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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321 FXUS65 KRIW 280807 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 207 AM MDT Fri Jun 28 2024 .KEY MESSAGES... - Cooler today. Gusty afternoon winds and dry air bring elevated fire weather conditions. A front moves through this afternoon and evening, bringing a gusty north wind to the Bighorn Basin and Johnson County. - Elevated fire weather conditions Sunday, with above average temperatures, gusty winds, and very dry air. - A weather system moves through late Sunday into Monday, bringing cooler temperatures and the chance of rain, mainly for northern Wyoming. && .DISCUSSION... Issued at 205 AM MDT Fri Jun 28 2024 A bit cooler today, with highs sitting near, to slightly below, average for the end of June. Highs are forecasted to be in the low 70s to about 80 degrees for the lower elevations. An upper-level low sits near the Montana/Canada border today, tracking eastward. This keeps a tight pressure gradient. As a result, afternoon winds gusting 30 to 40 mph are common across Sweetwater County and portions of Central Wyoming. Western Wyoming has gusts more in the 15 to 30 mph range. As the trough continues eastward, it drops into northern Wyoming in the afternoon and evening. This brings a northward shift in the wind direction for places like the Bighorn Basin and Johnson County. Gusts to 40 mph are possible as this front- like feature passes through. This front makes its way down into Natrona and Fremont Counties in the evening. For rain chances today, almost everywhere remains dry with the moisture from yesterday pushed to our east. An isolated shower or storm is possible over far southeast Sweetwater County as the last of the moisture exits. A few showers may also form over the Absarokas or northern Bighorn Mountains, but should be of little impact if they do form. The final point about today is elevated fire weather conditions. The dry air brings afternoon relative humidities (RH) down to the lower to middle teens across much of Sweetwater, Fremont, and Natrona Counties. Combined with the gusty wind described above, elevated fire weather conditions are in place this afternoon. A Rangeland Fire Danger Statement (RFD) is in place this afternoon and evening for those mentioned counties. A ridge begins to build in for Saturday. This has two main impacts. The first is that the winds will be much lighter. The second is warming temperatures. No rain is expected at this time, though an argument could be made for a stray shower in southern Sweetwater County during the afternoon. For Sunday, ridging continues, but will be on the way out as a trough over the Pacific Northwest approaches the area. This increases the pressure gradient once again, with a gusty west-to- southwest afternoon wind. With the ridge in place a couple days, very dry air is also a factor. Afternoon RHs 8% to 15% look to be common across most of the area. Current models have 700mb temperatures in the 16 to 19 degree Celsius range, translating to middle 90s to around 100 degree surface temperatures east of the Continental Divide and highs in the middle 80s to low 90s west of the Divide. These temperatures would be around 10 degrees above average. All of this adds up to an elevated fire weather day. That aforementioned trough moves through late Sunday. Some scattered showers and thunderstorms are possible over northern portions of the area and southeastern Sweetwater County Sunday evening. The trough`s passage overnight brings cooler temperatures for Monday, (closer to average) as well as continued rain chances, mainly across the northern half of the area. The rest of the week hinges on the development of a high over the western U.S. Depending on its strength and position will determine how low pressure systems move through the area. Currently, there is potential for some low rain chances through the rest of the workweek, mainly for the northern half of the area. This has low confidence at this time. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 931 PM MDT Thu Jun 27 2024 VFR conditions expected for all TAF sites for the entirety of the period. Diminished winds with a northerly component behind a weak cold front overnight into Friday around 10kts or less. Decreasing clouds in wake of the shortwave. Increasing winds not as strong up to 25-30kts, highest at CPR, with daytime heating and mixing to the surface. With that comes some mid level clouds that will lift towards sunset after 01-03Z. Winds will decrease as well around 10kts due to radiational cooling as skies clear into the overnight hours through Saturday morning. Any precipitation will be well east and southeast of RKS with no other weather elements expected at this time. 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 205 AM MDT Fri Jun 28 2024 Elevated fire weather conditions today. Minimum RHs between 10% and 15% for much of Sweetwater, Fremont, and Natrona Counties. A Rangeland Fire Danger Statement (RFD) is in effect this afternoon for those counties. Elsewhere, RHs down to around 20%. Gusty west winds pick up late morning for the Wind Corridor. Afternoon gusts 30 to 40 mph. A front brings a north wind shift to the Bighorn Basin and Johnson County this afternoon, with gusts to around 40 mph possible. This pushes down into Fremont and Natrona Counties this evening. Dry conditions continue for Saturday, but winds are much lighter. Elevated fire weather conditions return for Sunday, with RHs in the upper single digits to low teens for much of the area. Gusty winds also return, with high temperatures around 10 degrees above average. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...Lowe FIRE WEATHER...Wittmann