196 FXUS65 KRIW 202145 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 345 PM MDT Fri Jul 20 2018 .SHORT TERM...This evening through Monday Dry conditions with clear skies so far this afternoon. Increasing clouds from the south have started and this will be the focus for isolated dry thunderstorms this afternoon. Overnight RH recovery was poor last night over much of Sweetwater County northward toward South Pass, with values in the upper teens to middle 20s. This has led to critical RH values in these areas, along with the Upper Green River basin, southern Lincoln County and areas east of the Divide. A Special Weather Statement was issued earlier this morning to highlight these extremely dry conditions, along with the dry thunderstorms expected this afternoon and evening over southern portions. Strong gusty winds and lightning will be the main threats from these showers, as dewpoint depressions of 40 to 60 degrees are in place this afternoon. CAMs continue to trend downward this afternoon, as CAPE values range between 100-300 J/kg and LI's over 0 to -2. Isolated showers will be possible over the Tetons/Yellowstone early Saturday morning, in advance of the afternoon convection. These showers could linger through 15Z, with additional storms developing over the Absarokas/Wind Rivers after 18Z. A prefrontal trough will enter northern portions by this time, moving out of the forecast area by 06Z Sunday. PW's will increase substantially, with a return of 0.75 to 0.80". Thus, thunderstorms will be more wet than today. Storms will be isolated to widely scattered across the forecast area and end by 06Z Sunday, with a few lingering over southern Sweetwater County. There could be a chance for strong to severe storms over eastern portions of Johnson County Saturday evening, with dewpoints ranging between 50F to 60F, LI's -5 to -8, CAPE values over 3000J/kg and SE sfc winds. By 12Z Sunday, a cold front will progress southward across the forecast area. This should suppress most of the convective activity over southern portions and keep temperatures in the 80s. Dry conditions will be in place for much of the area Monday, in the wake of the cold front. Isolated chances for showers or storms will mainly be over the higher elevations. .LONG TERM...Monday night through Friday Monday night looks fairly quiet as a shortwave exits the region with maybe a few lingering showers over and on the lee side of the Bighorn Mountains. Tuesday will see increased ridging from the south but we will still have enough moisture for some diurnal thunderstorms, mainly influenced by higher terrain. The highest chance will be in the North Big Horn Basin and along the Bighorn Mountains. Wednesday and Thursday become more interesting with a series of shortwaves overriding the ridge and bringing increased coverage of showers and thunderstorms east of the Continental Divide. Thursday night into Friday morning will see the arrival of another weak cold front and more showers and thunderstorms overnight. Friday afternoon expect lingering showers and thunderstorms in the mountains east of the divide. && .AVIATION...For the 00Z TAFS through 00Z Saturday Issued AT 345 PM MDT Fri Jul 20 2018 VFR conditions will prevail through the period. Isolated showers and thunderstorms are expected to continue south of a KCPR-KLND-KBPI line from 00z to 03z Saturday. The main hazard near these showers and storms will be erratic wind gusts of 35-45kts. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Although there will be less wind this afternoon, temperatures will remain hot along with RH values at or below critical values. Isolated thunderstorms may fire in southwestern Wyoming this afternoon or this evening, otherwise expect dry weather. Any shower or thunderstorm could have a strong wind gust, due to the low RH. Mixing and smoke dispersal will generally range from good to excellent. Expect an increased chance of afternoon showers and thunderstorms for Saturday. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...LaVoie LONG TERM...Hulme AVIATION...Hulme FIRE WEATHER...LaVoie |