989 FXUS65 KRIW 282140 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 340 PM MDT Wed Jun 28 2017 .SHORT TERM...(This evening through Thursday) Issued at 126 PM MDT Wed Jun 28 2017 First line of convection moving into the nw early this afternoon ahead of upper circulation moving into wcntrl MT with fairly strong thermal trough extending swd in the mid levels. Also approaching next jet streak moving into Oregon attm. Nose of this jet may add some upper support later this afternoon into this evening as it starts moving ewd later. Strong to possibly severe storms are still expected the this afternoon and early evening across the nw. As this first line gets farther east, it will hit some better low level moisture and lower lcls so idea of some strong/svr storms in the ern Bighorn Basin over to Johnson is still good. Other areas across the west and north half could see strong to marginally severe due to both hail and wind (spreads increasing to 40-45 already at noon) and with front pushing s/se across the area. Storms will last well into the evening and even after midnight, especially east of the divide. On Thursday, cold trough axis moves across the area with much cooler air and considerable showers and thunderstorms for the west and north half. Cold enough for snow in the nw mtns and even down to the floor in Yellowstone National Park during convective showers (snow pellets). Quite chilly in the park with much of the day only in the 40s above 7K feet. Even the lower elevations east of the divide will mostly see 60s behind the next front. Even though the instability is not as great as today, the cool mid levels and decent sfc dp will still create a favorable environment for more tstms in this nw flow (and next cold front). Quite cool/chilly behind this trough Thursday night with mainly 40s east of the divide and upper 20s to 30s west. Mostly dry Friday with the potential for some building showers/isold storms off the nrn mtns. Shortwave ridge moves ovhd Saturday for a warmer day with an approaching shortwave late in the day or early evening. Enough heating to fire some isold storms across the nw and north with gusty wind and maybe some small mtn hail. Spreads increase so strong wind gust threat will be there with any storm, especially across the lower elevations. .LONG TERM...(Thursday night through Wednesday) Issued at 126 PM MDT Wed Jun 28 2017 The middle of the weekend will see a departing weak ridge to the east, while a shortwave trough moves into western WY from the Pacific Northwest. The disturbance should bring scattered showers and isolated thunderstorms to western and northern WY from Saturday night through Sunday night, as it moves slowly eastward. Temperatures will warm slightly on Sunday, but moreso on Monday and Tuesday as the upper level high pressure over the southwest US strengthens. Still forecasting some isolated thunderstorms mainly over the mountains Monday and Tuesday, with a better chance across northern WY Monday evening as a weak wave moves across MT. Tuesday evening on the Fourth of July may see more typical diurnal thunderstorms for natural fireworks. Wednesday looks to be a continuation with less convective activity, although the NE areas may see a weak boundary move south. Overall, the strongest winds during the period should occur from thunderstorm outflow as the surface pressure gradient weakens from the weekend into the early part of the week. && .AVIATION...(For the 00Z TAFS through 00Z Thursday afternoon) Issued at 340 PM MDT Wed Jun 28 2017 Shortwave trough moving through the area early this evening in westerly flow, with scattered showers and thunderstorms. Primary threats this evening are gusty winds over 40 kts along with small hail and brief heavy rain. VFR conditions generally, with local MVFR possible under and around storms. The convective activity is likely to continue through 03z-06z/Thu tonight core of the disturbance moves through from 00z-03z/Thu. Lingering showers likely as well after 06z/Thu across northern WY. After a few hours of some relative calm, another shortwave trough will approach the area from the north-northwest, mainly along and east of the divide. Showers likely around KCOD starting at 15Z/Thu. By 18Z/Thu, instability and cooling in the mid levels should allow scattered to widespread thunderstorms as well. General flow Thursday will be W- NW across SW WY, and west becoming northerly east of the divide. Some local areas may see heavier precipitation on Thursday,. such as KCOD and KLND. Showers to linger until about 06Z/Fri. && .FIRE WEATHER... Issued AT 126 PM MDT Wed Jun 28 2017 All fuels are currently in green-up and below critical levels for all locations. Fire danger remains low across all mountain areas...but will continue somewhat elevated in the afternoons across the lower elevations east of the Divide over portions of southern and central WY. These areas with elevated fire concerns will generally coincide with low afternoon RH values and/or gusty winds...through Friday. Winds west to northwest 15 to 25 mph into this evening...north to northwest 10 to 20 on Thursday...and north to west 5 to 15 on Friday...today and Thursday with higher gusts in the afternoons and especially near stronger showers/storms. This afternoon and evening, we will see isolated to scattered storms producing brief heavy rainfall, hail to 1 inch and strong gusty outflow winds of 40 to 55 mph...especially across portions of the northern half of Wyoming. This unstable pattern will continue through Thursday night. Smoke dispersion will be good to excellent each afternoon and evening. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...Skrbac LONG TERM...McDonald AVIATION...McDonald FIRE WEATHER...Skrbac |