


Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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903 FXUS65 KRIW 132258 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 458 PM MDT Sun Jul 13 2025 .KEY MESSAGES... - Another pleasant, sunny, warm, and dry July day across the Cowboy State today. - Warm temperatures and dry conditions persist into Monday with increased chances for elevated to near critical fire weather conditions. - A frontal passage with introduce chances for showers and thunderstorms on Tuesday and Wednesday. && .UPDATE... Issued at 1247 PM MDT Sun Jul 13 2025 Little change in regard to the upcoming forecast. Warm summer-like temperatures return to much of the Cowboy State today. Highs range from the upper 80s west of the Continental Divide to the mid to upper 90s east of the Divide. Skies remain mostly clear allowing for plenty of sunshine along with dry conditions. Minimum RH values are expected to be near critical values for portions of the state. However, marginal winds should limit any elevated fire weather concerns. While nearly all of the area will remain dry there is still a small chance (~10%) for a very isolated virga shower. Overall a fairly typical mid July day is expected. A cold front is expected to approach the state Monday, but will remain just out of reach. This allows temperatures to stay warm for another day. Highs Monday are expected to be similar to Sunday with temperatures in the upper 80s west of the Divide and mid to upper 90s east of the Divide. The approaching front creates some scattered showers and thunderstorms mainly across northern Wyoming. Dewpoint depressions will range from 40 to 50 degrees, which may generate isolated strong gusty outflow winds in association with any showers that develop. The front will bring increased winds with a westerly breeze developing during the afternoon. Winds range from 10 to 15 mph with periodic gusts of 15 to 25 mph. These winds combined with low minimum RH values produce elevated fire weather conditions, especially over southern Wyoming. However, with winds remaining mostly marginal the concern for widespread near critical fire weather conditions looks to be low at this time. Tuesday continues to look active as much of the state will see increased chances for showers and thunderstorms. The aforementioned cold front moves across the state Tuesday, gradually trekking south during the day. The best chances for precipitation will be east of the Divide, especially across northern Wyoming. Models do show these showers spreading south into central Wyoming and eventually across the south. However, just how far into southern Wyoming is still to be seen, as there remains some discrepancies among models at this time. Above normal PWATs will move into the area along with the frontal passage. This could create the chance for isolated heavy downpours as showers and thunderstorms develop and move across the state. There does look to be the potential for a few strong storms on Tuesday. Abundant moisture streams into the state with some locations seeing dewpoints in the 50s. Depending on how much sunlight can break through during the first half of the day, CAPE values could reach of 500 to 1000 J/kg if not slightly more. This combines with favorable shear as northeasterly surface flow interacts with upper-level southwesterly flow. Overall, the area of concern looks to be across central and eastern Wyoming where the greatest instability is expected to develop. The strongest storms may be capable of producing strong gusty winds, hail, and heavy downpours. Showers and thunderstorms linger into the late evening hours before gradually dissipating early Wednesday. Cooler temperatures settle over the region Wednesday with highs in the low to mid 80s west of the Divide and the 70s east of the Divide. Warmer temperatures return for the second half of the week as a broad area of ridging tries to build back in. There may be some chances for showers and thunderstorms even with this ridging developing but coverage will be isolated. Warm and mostly dry conditions look to return and persist into next weekend. && .DISCUSSION... Issued at 306 AM MDT Sun Jul 13 2025 All in all, the reasoning in the forecast has changes little from yesterday. Northwest flow will continue to dominate today. Thicknesses continue to climb today though, so it will be a rather hot day today with widespread 90s in the lower elevations East of the Divide. Almost all areas will be dry as well. However, notice the modifier, almost. There will be a very subtle shortwave moving across the area this evening. And this may be just enough to bring an isolated shower or thunderstorm in and near the northern mountains. The chance is very small though, small with a capital S. We have some slight POPs in spots but the chance is at most 1 out of 6 with the vast majority of locations seeing nothing. Things start turning more active next week. A cold front will start approaching the area from the north. It will remain north of the area though, so it will be another hot day with temperature fairly similar to todays. We have two concerns. And it reminds me of one of my favorite songs from the 70s, Fire and Rain by James Taylor. Although starting Monday will should not see sunny days we thought would never end. We will start with fire. With the approaching cold front, the pressure gradient will tighten ahead of it and bring some breezy conditions. Humidity will be very low on this day, falling as low as 10 percent. This brings the possibility of elevated to critical weather into the forecast. Wind looks borderline though. The most likely place to see it would be across portions of Sweetwater, Sublette and Fremont counties in the afternoon. At this time, it is uncertain if we will get 3 hours of wind gusts past 25 mph for Red Flag criteria though. So, we will let the day shift take another look to see if any watches are needed and then we can upgrade tomorrow night if needed. Now for the rain, or more specifically thunderstorm part. Chances of storms will increase but mainly across the northern portions of the state. Chances here range anywhere from 1 in 5 in the lower elevations to 1 in 3 in the mountains. There is not a lot of upper forcing with on this day. However, what we do have are very large dew point depressions (as high as 60 degrees) and inverted V soundings with any afternoon convection being high based, strong wind gusts are possible with any shower or storm, although many may end up bring rain free. The chance of rain increases in the evening and at night as temperatures cool and the atmosphere moistens somewhat. Tuesday and Wednesday still look like the most active days. The models do agree on the northwestern half of the area and areas East of the Divide seeing the best chance of seeing showers and storms, with tapering chances further south. There are still disagreements though on the timing and rainfall amounts of the storms each day, with some models showing Tuesday as the most active day with the system more progressive. Others have it on Wednesday with a slower progression. So, there is still little confidence in the details at this time. Temperatures will be substantially cooler though, especially in northern Wyoming. Some guidance shows Buffalo remaining in the 50s on Wednesday. Don`t know if I believe that with it being the middle of July though. Some areas will be around 30 degrees cooler on Tuesday or Wednesday when compared to Sunday and Monday. Flat ridging should then control the weather for Thursday through Friday and bring near normal temperatures. A few storms may be around each afternoon but most areas should be dry. Above normal temperatures are then favored to return for next weekend. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 457 PM MDT Sun Jul 13 2025 All terminals to be VFR through the forecast period. Late day cumulus fades early Sunday evening with the setting sun. There is a batch of mid-level moisture that leads to isolated virga showers clipping the northwest corner of the state late Sunday evening. A weak disturbance and a bit more moisture arrives in zonal flow Monday afternoon. As a result, convection initiates over the Absaroka Range by early Monday afternoon. Additional convection spreads eastward into the basins late Monday afternoon. For now, have included PROB30 group for KCOD 20Z-24Z/Monday with gusty outflow wind 30-40kts the primary potential hazard given high cloud bases. Surface westerly wind increases to 10-20kts at terminals west of the Continental Divide early Monday afternoon. Gusts will be a tad higher at KRKS. 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 1247 PM MDT Sun Jul 13 2025 Elevated to near critical fire weather conditions will be possible across portions of the state Monday. Minimum RH will be 10 to 15% for much of the region with higher values over northern Wyoming. Winds look to be the main limiting factor with periodic gusts of 20 to 25 mph, but not consistent enough to warrant a Fire Weather Watch at this time. Increasing chances for showers and thunderstorms arrive Tuesday with higher minimum RH values and cooler temperatures. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Dziewaltowski DISCUSSION...Hattings AVIATION...CNJ FIRE WEATHER...Dziewaltowski