918 FXUS65 KRIW 190031 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 631 PM MDT Tue Jun 18 2019 .SHORT TERM...(This evening through Wednesday) Issued at 210 PM MDT Tue Jun 18 2019 Unstable northwest mid-level flow with ample surface moisture continues again today to produce scattered showers and thunderstorms. Thus far the storms have remained non-severe with possible gusts around 30 mph and brief heavy rain with some small hail. Later this afternoon and into the evening, some storms may become stronger, especially over Johnson and eastern Natrona Counties. SPC has a marginal risk of severe storms for this area. All high resolutions models are indicating that the showers and thunderstorms are likely to continue through the late evening hours as has been occurring the past few days. Skies should remain partly cloudy overnight with temperatures similar to this morning. The pattern looks to shift on Wednesday to more westerly and an upper-level just moves into Washington and Oregon. Surface winds across southern and central WY as well as the higher terrain should increase out of the west. Areas will see 20-30 mph sustained wind with gusts of 40 mph. This flow will also bring drier air to much of southwest WY as temperatures climb a few degrees to the mid 70s to low 80s. A weak boundary is expected to remain along the MT/WY border wednesday. As the left front quad of the jet moves over that area Wednesday afternoon, scattered showers and thunderstorms are expected from YNP eastward to the Bighorns and into Johnson County. SPC already has that area in a marginal risk for severe storms. As the area of convective activity organizes and moves eastward during the late afternoon, expecting the wind across the Bighorn Basin and Johnson County to shift to the north. .LONG TERM...(Wednesday night through Tuesday) Issued at 158 PM MDT Tue Jun 18 2019 Showers and thunderstorms from the weak boundary over Montana will linger in the north Wednesday night through about midnight. Winds in the south will continue to gust through midnight as well, decreasing from west to east shortly afterwards. Clearer skies overnight and Thursday morning followed by increased cloudiness in the afternoon will lead to slightly cooler conditions over most of the area Thursday. Westerly winds will become strong again Thursday afternoon as our next weather system draws nearer. Another round of showers and thunderstorms is in store for the north but southern Wyoming will see dry conditions with humidities in the low 20s. This area will be worth watching as it is approaching near critical fire weather. Friday will see a chance of showers and storms over the north again with isolated activity in the central and south. A cool day with highs mainly in the 60s with some places only reaching the upper 50s. Some snow in the higher mountain elevations of NW WY is possible Friday into Fri night. Saturday will remain on the cool side with 60s for highs. Some afternoon and evening showers and storms will occur due to a weather disturbance in the flow. Sunday will start out dry in the morning, then showers and storms will develop in the afternoon through the evening hours. High temps a little warmer on Sunday. Next Monday and Tuesday may remain unsettled with the chance of showers and storms over the region. High temps will be warmer next Monday and Tuesday with mainly 70s with some lower 80s in places. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 631 PM MDT Tue Jun 18 2019 Showers and thunderstorms will continue through the evening. All terminal sites are expected to see VCTS sometime during the day. Winds will remain fairly light for most areas, except for locally gusty winds near thunderstorms. Some showers may linger over the region through 09Z Wednesday. VFR conditions will prevail at the terminal sites, but a period of MVFR/IFR conditions may occur if a storm directly impacts an airport. Expect moderate to strong westerly winds at most locations Wednesday afternoon. && .FIRE WEATHER... Issued AT 200 PM MDT Tue Jun 18 2019 Scattered showers and thunderstorms in northwest flow will continue late this afternoon into the evening hours, with the stormy activity expected to continue through midnight. Some of the storms may produce gusty outflow over 30 mph along with brief heavy rain and some small hail, and some stronger storms are possible over Johnson and eastern Natrona counties too. More westerly flow will push into WY on Wednesday, bringing slightly drier and warmer air to the southern two-thirds of the state. Sustained winds over the higher terrain and from southern into central WY are expected in the 20-30 mph range. Afternoon humidities are likely in the low 20s in the lower elevations of southern and central WY. A weak boundary along the WY/MT border along with upper level strong winds will cause scattered showers and thunderstorms from YNP eastward to the Bighorns and into Johnson County. These storms should create a north wind push into the Bighorn Basin and Johnson County after 6pm Wed. A larger low pressure system is expected over the northern Rockies Thursday into Friday to bring more wind and precipitation. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...McDonald LONG TERM...Hulme AVIATION...Hulme FIRE WEATHER...McDonald