Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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523 FXUS65 KRIW 210841 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 241 AM MDT Fri Jun 21 2024 .KEY MESSAGES... - An isolated shower or thunderstorm before sunrise this morning. Precipitation dissipates by the mid morning. - Another round of showers and thunderstorms develop during the late morning becoming widespread and intensifying by the early afternoon. A few strong to severe storms will be possible this afternoon, especially in parts of Johnson and Natrona Counties. - Hot and dry weather returns for the end of the weekend and through much of the upcoming week. Highs may near 100 degrees in parts of the CWA by Sunday. && .DISCUSSION... Issued at 240 AM MDT Fri Jun 21 2024 Showers and thunderstorms continue to develop across the state early this morning. Convection is expected to remain weak, with some capable of producing small hail, heavy rain, gusty winds, and frequent lighting. A few may linger towards sunrise but the majority will dissipate before than. The week concludes with seasonable temperatures, partly sunny skies, and the chance for afternoon showers and thunderstorms. June has been rather dry across many parts of the Cowboy State with little to no rainfall in places. The good news is some much needed moisture looks to make its way into the region today. Unfortunately, this moisture will come in the form of convective showers and thunderstorms. Figuring out where convection develops and this moisture ends up is like throwing a dart at a dartboard with a blindfold on. So even though we may see some widespread convection occur this afternoon, there will be places who see little to nothing and places who see a much needed dose of rain. This convection is due to a weak shortwave moving across the Inter- Mountain West today. A strong high pressure over the southeastern CONUS will funnel gulf moisture into the region. Combine this warm gulf moisture with the favorable dynamics from the shortwave and you get widespread showers and thunderstorms. The 06Z SPC convective outlook has upgraded parts of WY to Slight/Marginal chance for severe thunderstorms. Parts of Natrona and Johnson counties have a (50-70%) chance of seeing thunderstorms and will likely be the spot with the best chance for strong to severe thunderstorm development. The remainder of the state has a (20-50%) chance of seeing thunderstorm development but a lower chance of seeing stronger storms. There are a few things to be concerned about with any strong to severe storms that do develop. These concerns are small hail (possibly nearing 1 inch in the strongest storms), strong gusty winds, frequent lightning, and heavy downpours. There is a small chance for some flooding to occur depending on the track of the storms that develop this afternoon. PWAT values are high for this time of year, ranging from 0.75 to 1.00 inches which is around 150- 200% above normal. Now to summarize how today looks to play out, a few showers and thunderstorms linger till around sunrise. During the morning, skies will remain patchy in areas but the sun will likely break through at times. High temperatures are forecast to remain slightly below normal for today. By the mid-late morning, convection is expected to start developing across the southwestern CWA and gradually move northeast. Showers and thunderstorms will become more widespread and likely begin to intensify by the early afternoon. The best chance for strong to severe storms will be in parts of Natrona and Johnson Counties during the mid to late afternoon. Most of the convection will move out of the CWA by the mid to late evening with a few lingering showers until midnight. The weekend will see a return of warm and mostly dry weather as a potent area of high pressure builds back into the region. Temperatures return to the 80s and even 90s for Saturday with some of the warmest temperatures arriving by Sunday. Models are showing parts of the Bighorn and Wind River Basin having a (40-70%) chance of seeing 95 or higher temperatures. These warm above normal temperatures are expected to persist through the upcoming week with many seeing highs of 90+ degrees for much of the week. This trend towards hot and dry weather really highlights the importance of rain from the showers and thunderstorms that develop this afternoon, as we may not see another chance of precipitation for a while. There will likely be elevated to near critical fire weather conditions as we head into the end of the weekend and the first half of the upcoming week. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 933 PM MDT Thu Jun 20 2024 Scattered rain showers and thunderstorms have developed in central Wyoming this evening. These rain showers and thunderstorms will impact KCPR/KRIW/KLND for a few hours overnight before shifting north toward KWRL later tonight into Friday morning. Have prevailing -SHRA and VCTS at KCPR through 07Z/Fri and TEMPO groups with -SHRA at these other terminals where convection will be more isolated tonight. Wind direction varies greatly across the area and this will continue through Friday afternoon. The main weather system will push through Friday afternoon, which will lead to widespread convection. Current thinking is convection will begin developing around 18Z/Fri and travel east, exiting the area by 02Z/Sat. Thunderstorms will be strong Friday afternoon, with strong outflow/downdrafts likely (80%) and isolated severe wind gusts/large hail possible (10-20%), especially near KCPR. Very little convective activity is expected near KJAC, so only have a period of VCSH Friday afternoon. At all other terminals there is a PROB30 group with -TSRA and variable gusty wind. Conditions will be mostly VFR, but MVFR conditions appear likely (70%) at times Friday afternoon as showers and storms move through the area. The strongest storms will be able to drop VIS down to IFR, especially if they produce hail. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Dziewaltowski AVIATION...Rowe