400 FXUS65 KRIW 280409 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1009 PM MDT Sun Jul 27 2025 .KEY MESSAGES... - The warm and dry weather continues Monday, but with less wind. A weak, dry cold front will push southward over northern portions, resulting in slightly cooler temperatures in Johnson County and the Bighorn Basin. - Elevated to near-critical fire weather conditions will also continue Monday. - A pattern change begins Tuesday and lasts through the end of the week, as a surge of monsoonal moisture returns over the area. This will result with cooler temperatures and an increased chance of showers and thunderstorms. && .UPDATE... Issued at 1230 PM MDT Sun Jul 27 2025 No major changes to today`s forecast. The main focus is on the elevated to critical fire weather over central and southern portions of Wyoming. RH recovery overnight will be poor across many areas, with maximum overnight RHs 20 to 35 percent. Most places remain dry this afternoon, though an isolated (15%-20%) shower or storm could pop-up over far northern Yellowstone or the Absaroka Range, especially for the northern range. Over the northern Bighorn Range, the chances are 10 to 15 percent. Tomorrow will likely see the peak heating for the week, before a system pushes in mid-week, bringing cooler and wetter conditions. && .DISCUSSION... Issued at 321 AM MDT Sun Jul 27 2025 On this last Sunday morning of July, the reasoning of the forecast remains similar to yesterday. Ridging will remain over the area today and bring another hot and, in some locations, breezy day. The question is about potential fire weather. Just about all areas will have at least elevated fire weather, given the very low humidity with many locations having single digit humidity this afternoon. The main question is about wind once again. Wind does not look quite as strong as yesterday since there will be no shortwave moving through, limiting mixing more. The 700 millibar winds are also around 5 to 10 knots less than yesterday. However, some locations still look critical. For guidance, we used the NBM ensemble of probability of wind gusts past 25 mph. For the most part, we used a chance of 3 out of 5 or higher this afternoon and this gave southern Lincoln County, Sweetwater County and the Green and Rattlesnake Ranges the best chances. So, Red Flag Warnings were hoisted in these areas from 12 pm to 8 pm. We thought about Natrona County, but wind looks lighter here and anything would be isolated. The Wind River Range has some but on the west side for the most part, which does not have critical fuels yet as well as portions of the Salt and Wyoming Range. However, these are in the highest elevations and a lot are above the timber line. Fremont County had a thought to, especially eastern portions, but again, here we thought it would be isolated. As for convection, with higher heights and a lack of moisture, chances would be very small. The main location would be the far northern mountains but even here the chance is less than 1 out of 5. Temperatures look similar, with widespread 90s east of the Divide and 80s in the lower elevations west of the Divide. Monday looks like another hot and mainly dry day. There will be the first indications of a change in the pattern though. For one, somewhat more humid air will return east of the Divide. Critical humidity is still likely for most (below 15 percent), but most places will see at least in the double digits. The increasing moisture may also touch off a few thunderstorms, especially in Johnson County where humidity will recover faster. But again, coverage remains less than 1 out of 5. Temperatures will remain hot in most locations, similar to today`s highs. Wind will also be down a few ticks, so fewer places may have fire weather highlights (far southwestern Wyoming has the best chance). Tuesday is when the pattern really begins to change. Monsoonal moisture will begin to surge back into the area and increase the chance of showers and storms. The return has slowed a bit this morning, however areas east of the Divide still have anywhere from 120 to 150 percent of normal of precipitable water values. Things could set interesting this day as we have both a marginal risk of excessive rainfall and severe thunderstorms on this day. For Tuesday, this would be mainly east of the Divide, as areas to the west should have one more mainly dry day. Wednesday and Thursday are the days when the deeper moisture moves across most of the area and brings the best chances of more widespread showers and storms. Wednesday may be the most active day, with the highest precipitable waters and best low level easterly flow that will bring in deeper moisture and initiate upslope flow along the eastern peaks. Placement of the storms is impossible to pinpoint at this time, but things look rather active through Thursday. By the end of the week, drier area may try to push in, cutting the coverage of the showers and storms. Temperatures will fall to below normal levels by Tuesday and remain there through Thursday with the increased cloud cover before recovering to near normal levels for next weekend. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1000 PM MDT Sun Jul 27 2025 Clouds will gradually scatter out through the rest of the night, with mostly SKC skies by sunrise. Skies will remain hazy, as smoke from wildfires in UT and AZ continues to surge northward over the state. Most of the smoke will be shunted eastward through the day. There will be a 20% of virga showers over the Absaroka and Wind River Mountains and western portions of Sweetwater County during the afternoon. KCOD is the only terminal that could be impact from this activity at this time. Winds will generally be light, except west of the Divide, where gusts up to 20 kt will occur in the afternoon. A cold front will push south over northern portions during the day, turning winds more northerly in its wake. The front will push toward the Divide in the evening, With winds turning easterly at KRIW and KLND between 03Z and 06Z. 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 321 AM MDT Sun Jul 27 2025 A combination of humidity falling into the single digits and a gusty southwesterly breeze will bring critical fire weather to southern Wyoming again this afternoon. Elsewhere, wind should remain below critical threshold but humidity will remain very low, in the single digits as well. The most likely locations for near critical fire weather east of the Continental Divide will be Fremont and Natrona Counties. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 8 PM MDT this evening for WYZ277-279- 289. && $$ UPDATE...Wittmann DISCUSSION...Hattings AVIATION...LaVoie FIRE WEATHER...Hattings