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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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108 FXUS65 KRIW 201023 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 423 AM MDT Sat Jul 20 2024 .KEY MESSAGES... - The weather pattern will keep the same weather conditions across the Cowboy State through this weekend into next week. This means hot, afternoon showers and storms, and fire weather concerns. - Saturday looks to be a more active convective day with widespread rain showers and thunderstorms across the area. The main threat will be gusty wind from outflow boundaries and downdrafts, but brief heavy rain and frequent lightning will be threats as well. - In terms of temperatures it has been hot, but not oppressively hot. This will continue to be the case as high pressure remains centered over Nevada through this weekend. - A shift in the ridge/high will occur by the middle of next week, which means temperatures will, once again, jump up near triple digits east of the Continental Divide and near 90 degrees F west of the Continental Divide. && .DISCUSSION... Issued at 149 AM MDT Sat Jul 20 2024 With the high centered over Nevada the Cowboy State remains on the periphery of its effects. This has allowed for subtle shortwaves to drop down from the north. This is especially true for today (Saturday) as model guidance is depicting a little more consequential shortwave dropping down into the Cowboy State. Subsequently, model guidance shows more coverage of convection compared to the last few days. As such, expect numerous outflow boundaries to form as convection gets going late in the morning in the mountains thanks to the added lift from the shortwave and diurnal upslope flow. PWAT`s are respectable around 0.75"-1" across the area, so there will be sufficient moisture for heavy rainfall with the strongest storms, but overall the atmospheric profile doesn`t look conducive for flash flooding. Forecast soundings show too much dry air in the column and (no surprise) show moderate inverted v signatures. Wouldn`t be surprised if there were a couple of gusts close to 50 knots this afternoon. It certainly doesn`t take much here to get that kind of wind, especially this time of year. The shortwave will also bring northerly wind to the area this afternoon, which combined with more cloud cover/convection will limit high temperatures this afternoon. Expect, on average, around 5 degrees F cooler than yesterday. The pattern shouldn`t change much into next week as the dominant high slowly shifts east by the middle of next week. There will be continued chances for isolated to scattered rain showers and thunderstorms each afternoon and some pockets of mid-level energy move through the Cowboy State. Gusty wind will be the main threat with any convection that develops. By Wednesday model guidance is showing 700 mb temperatures approaching/reaching 20 degrees C over the area. With that kind of warmth moving overhead it is almost a certainty that several locations east of the Continental Divide will rise back into the triple digits. The good news is this looks to be temporary as model guidance has a trough pushing the high to the south down into the Desert Southwest late in the week. Don`t get your hopes up, however; getting a dominant high/ridge to move that much in the peak of summer is no easy feat, so model guidance may be overestimating the response of the high as the trough tries to push it south. Regardless, heading into the middle of next week fire weather concerns will increase as temperatures rise, RH drops, and isolated storms bring more lightning. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 420 AM MDT Sat Jul 20 2024 Prevailing conditions will remain VFR through the TAF period, although brief reductions to MVFR are possible with the strongest convection this afternoon. A weak shortwave will drop down into Wyoming this afternoon, which will aid in the development of convection. This should result in more widespread rain showers and thunderstorms than the area has experienced the last few days. In addition to this, a shift in wind direction becoming northerly/northeasterly will occur this afternoon. To account for the convection there are PROB30 groups with VRB gusty wind and -TSRA at all terminals Saturday afternoon. The timing is subject to change and very difficult to pinpoint as numerous outflow boundaries will interact causing rain showers to develop erratically and possibly linger at certain terminals well into this evening before ending after midnight. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 149 AM MDT Sat Jul 20 2024 Convection will be the driving factor behind fire weather concerns in the short-term. Fire starts from lightning have been cropping up over the last couple of weeks as fuels have been drying thanks to mostly dry conditions and hot temperatures. Wind is not a primary concern in the sense that synoptic flow will remain weak, but plentiful outflow boundaries from convection will continue to pose a risk to ongoing and new fires. This will be the main threats through this weekend into early next week, but temperatures will rise, which will result in falling RH by the middle of next week. Wind will be the saving grace, again, since high pressure that is bringing the hotter/drier air will keep wind light in general. Convection will decrease in coverage, but is not likely to cease altogether, so new fire starts from lightning will remain a threat through next week. && .RIW WATCHES/WARNINGS/ADVISORIES... Air Quality Alert until 1 PM MDT this afternoon for WYZ001-012- 013. && $$ DISCUSSION...Rowe AVIATION...Hattings FIRE WEATHER...Rowe