Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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297 FXUS65 KRIW 251159 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 559 AM MDT Tue Jun 25 2024 .KEY MESSAGES... - Warm above normal temperatures are expected for today. Highs are expected to be cooler compared to the past few days but will still be 10-15 degrees above normal. - Afternoon showers may create strong gusty outflow winds with little to no rain reaching the surface. - Chances for precipitation and cooler temperatures look to arrive by Wednesday. - Thursday may be the best day to see widespread showers and thunderstorms with much needed rain possible. && .DISCUSSION... Issued at 245 AM MDT Tue Jun 25 2024 Another hot day across the Cowboy State is in the books. Some temperatures of note from yesterday, Lander hit 96, Riverton hit 95, Greybull hit 102, Worland hit 99, and Casper hit 97. Unfortunately, even with how above normal these values are there were no records met or broken. Temperatures will begin to trend cooler starting today, as high pressure is pushed out of the region by the end of the week. Warm and dry conditions persist for one more day. Highs today will be in the low 90s east of the Divide and in the mid to upper 80s west of the Divide. Winds will still be breezy at times but not to the same degree as they were yesterday. Isolated showers are possible during the afternoon mainly in parts of northern Park and southern Sweetwater Counties. Due to the dry nature of the atmosphere, most will see virga showers. The one concern is the dryness of the atmosphere which may produce strong outflow winds from these showers. An example of this was seen yesterday at Casper airport, where an outflow created 60 mph wind gusts. While the same degree of gusts are not expected today, they are still a possibility during the afternoon and evening today. As mentioned earlier, change is on the way, with cooler temperatures and chances for precipitation for the second half of the week. The change looks to really kickoff Wednesday, as a potent trough digs across the PACNW. This trough will start to push out the area of high pressure that has been influencing our weather over the past few days. As the high pressure is ushered east, moisture rich air will be funneled north just in time for the trough to start providing favorable dynamics for shower and thunderstorm development. The first real chance for precipitation will come Wednesday afternoon and evening. Current guidance is showing a minimum chance of precipitation ranging from (20-30%) across much of the CWA. The one concern will be the ability of this moist air from the south being able to mix throughout the atmosphere. CAM`s vary of the degree of mixing, with some showing a deep dry layer near the surface inhibiting precipitation from reaching the surface. Others show a more mixed atmosphere, which would be favorable for shower and thunderstorm development along with wetting rain on the surface. If mixing is able to occur there is a chance of seeing some heavy downpours with any showers or thunderstorms that end up developing. This is due to the high PWAT values associated with this moist southern air. Models are showing values of 0.75-1.00 inches with splotches of 1+ inch. So overall for Wednesday there is still some uncertainty regarding the exact impacts but the expectation should be possible showers and thunderstorms during the afternoon and evening. Thursday looks to be the best day to see widespread precipitation over the whole CWA. This is due to better dynamics as the trough over the PACNW nears closer to the region. Another aspect is the ability for moisture to mix throughout the atmosphere. Thursday has the potential to be a very interesting day as the dynamics and moisture is there for possible widespread thunderstorm development. CAM`s are only just starting to reach this time frame, meaning we will have a better idea of the convective environment within the next day or so. As of right now it is looking like the CWA could see widespread showers and thunderstorms develop during the day Thursday. The main concerns from any convection would be strong winds, small hail, frequent lightning and heavy downpours due to the higher than normal PWAT values. Temperatures look to cool behind the trough, as 700 MB temperatures range from 1-7 degrees Friday into Saturday. Overnight temperatures may be chilly in spots those nights, especially west of the Divide where temperatures may flirt with the mid 30s. Overall, the heat and dry conditions linger for another day before a change to cooler and wetter weather. The weekend sees a brief return to warmer weather with another chance of showers and thunderstorms for Sunday/Monday. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 558 AM MDT Tue Jun 25 2024 VFR conditions will prevail through the period. West to northwesterly wind gusts of 15 to 25 knots will occur at most terminals this afternoon. Isolated virga showers are once again expected this afternoon, most likely across southern Wyoming. The main concern with this activity will be isolated outflow winds gusting over 40 knots. Wind and any showers will subside around sunset. An incoming wave will start spreading clouds and a low chance of showers across western Wyoming near the end of the period, but no impacts are expected at this time through 12Z Wednesday. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Dziewaltowski AVIATION...Myers