FXUS65 KRIW 090412 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1012 PM MDT Wed Jul 8 2026 .KEY MESSAGES... - Scattered rain showers and isolated thunderstorms will slowly taper off this evening, with most activity done by 9 PM MDT. Until then gusty outflow wind of 45 to 55 mph will remain possible. - Warming trend through the weekend with a downward trend for thunderstorm activity as drier air moves into the region. - The hottest weather of the year arrives this weekend, with many all-time record high temperatures possible. The best chance of all time record high temperatures will be Sunday afternoon. - The extremely hot and dry conditions will result in near- critical fire weather conditions for the end of this week into early next week. && .UPDATE... Issued at 1230 PM MDT Wed Jul 8 2026 More clearing from the overnight hours than yesterday that will give way to a bit better instability from Sweetwater to Natrona Counties. Radar is starting to increase in activity off the Uintas that will eventually push into southern Sweetwater County in the next hour and expand north and east through the remainder of the afternoon. Eastern Fremont to Natrona Counties will be of concern from 1600-1800L pushing east of the CWA by 1900L. The other area of note continues to be Johnson County for later in the afternoon before sunset with storms coming in off the Bighorns from Montana. However, the instability may not be quite as high with HiRes models completely missing the early morning convection that rolled in from Yellowstone straight east into Johnson County that looks to be finally dissipating as it moves into eastern portions of the county. Main threats still will be outflow winds as per usual over 50 mph being possible. Dewpoint depressions don't look quite as good as yesterday but severe gusts always still possible, even with the green blobs out of radar range. Heat still on for the weekend into next week with NBM still pinging the widespread triple digits, stay tuned! && .DISCUSSION... Issued at 245 AM MDT Wed Jul 8 2026 I have a question for you this morning. What do these things have in common: gas pressure and volume, supply and demand and speed and travel time. If you answered inverse relationships, you would be right. And that is what we will have over the next week, as the temperature goes up, the chance of convection goes down. Today will be somewhat similar to yesterday. Another shortwave will be moving through the area. We also continue to have fairy steep low and mid level lapse rates. Instability values are also decent, with some portions of the area (mainly the northeastern portions of the area) having over 1000 J/Kg of CAPE and lifted indices as low as minus 5. There will be one difference though, and this will be a trend over the next few days. And that is that precipitable water values are a lower than yesterday, especially West of the Divide. But even East of the Divide, values are 10 to 20 percent lower. It is still around 130 percent of normal though. As a result, it will be another day anywhere from a 1 in 5 to 2 out of 5 chance of a shower or thunderstorm, with the best chance in the afternoon and evening and across northern and far southern Wyoming. The lowest chance will be across the west with less than a 1 in 10 chance. Temperatures will be similar to yesterday, near to somewhat above normal. As for any stronger storms, the best chance would be over Johnson County where there is a marginal risk, with strong wind gusts and marginally severe hail the main threats. Strong wind gusts will be a threat with any shower or thunderstorm though, even further west where dew point depressions will be larger. The downward trend in convection continues on Thursday asdrier works a little further east. There will still be some convection around, but most would be confined to East of the Divide again and especially in Johnson and Natrona Counties where the deepest moisture will remain. Temperatures look largely similar to today. The inverse relationship really begins on Friday as ridging over the desert southwest begins to push northward with rising heights and temperatures aloft. This is the day when below normal precipitable waters will push across the entire area. We can't rule out a stray shower or thunderstorm, mainly over the northern mountains, but even here the chance is less than 1 out of 5. Temperatures will also begin to really rise, with the normally warmer spots seeing high temperatures approaching 100. It is Saturday when we really begin to throw some coal into the blast furnace, otherwise known as a death ridge. Heights across the area will climb to over 5950 meters at 500 millibars, and bring definitely the hottest weather of the year. The NBM ensemble gives a greater than 1 out of 2 chance of high temperatures above 100 degrees in locations 5200 feet or below, with a nearly 100 percent chance in the warmer spots likely from Thermopolis up to Greybull. All locations below 6500 feet have a 4 out of 5 chance of temperatures over 90 degrees. Some records will likely fall on this day. With the dry air in place and warm temperatures aloft, the chance of convection looks just about nil. However, the heat looks to peak on Monday. This mornings guidance shows 700 millibar temperatures climbing as high as 24 degrees celsius. This combined with nearly full sunshine will lead to one of the hottest days in quite a while. Ensemble guidance shows a nearly 100 percent chance of high temperatures over 100 degrees below 5500 feet, and places like Rock Springs, Green River and even Jackson have a greater than 1 out 3 chance of high temperatures over 100 degrees. When we go up to 105 degrees, ensemble guidance gives a greater than 4 out of 5 chance of this from Thermopolis to Greybull, with Riverton even having a 1 out of 2 chance. And going up even further, to 110, there is a 2 out of 5 chance a place like Greybull or Worland could reach this temperature. We could see some all time high temperatures fall on this day as the 5980 500 millibar ridge will be centered just about over Wyoming. We should begin to take a couple of degrees off of the highs on Monday as the ridge retreats to the east just a bit. However, most areas below 5500 feet will again have at least a 1 in 2 chance of high temperatures above 100 degrees. And with the ridge moving East, some moisture, mainly of the mid level variety will begin to come around the back side of the ridge. A couple of storms are possible on Monday, but chances increase more on Tuesday and into Wednesday. With the low levels remaining rather dry, these thunderstorms would produce more wind than rain though. Convection should be on the isolated side though with most locations not seeing one on any given day. Temperatures will drop somewhat from the blast furnace levels of the weekend, but look to remain above normal through the middle of next week. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1000 PM MDT Wed Jul 8 2026 VFR conditions prevail over the next 24 hours for most sites. A few isolated showers linger this evening, but these should largely end by midnight (09/0600Z). Mid-level cloud decks hang around in central Wyoming overnight into the morning hours, and by mid-morning, CPR could see some virga (light showers evaporating before they hit the ground). These could lead to some unexpected gusts from variable directions at (and above) CPR during the morning hours. During the afternoon hours, LND and RIW each have a slight chance (PROB30 groups added) of afternoon thunderstorms with erratic, gusty (35 to 45 kt) winds. Other sites have a smaller but non-zero chance of an isolated storm nearing the airport, so added BKN and OVC decks at these sites to hint at the possibility. RKS now looks to remain south of the better lift, so removed the PROB30 at that location for the 06Z set of TAFs. Any isolated storms and showers quickly end after sunset Thursday. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Lowe DISCUSSION...Hattings AVIATION...VandenBoogart