KRIW issues Area Forecast Discussion (AFD) valid 2019-12-06T18:27:00Z 728 FXUS65 KRIW 061827 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1127 AM MST Fri Dec 6 2019 .SHORT TERM...(Today through Saturday) The initial focus of the short term forecast period will be the patchy to areas of fog that have especially developed from KBPI to near KPNA. Visibilities in some valley locations have ranged from a quarter to a half of a mile. Expect the fog to dissipate across the area as per the going forecast between the 16Z-17Z time frame and have highlighted the fog with a special weather statement and mentions in the forecast. A surface ridge of high pressure across the western sections of the forecast area, will settle across the forecast area today with a low level southwest flow expected to pick up. Gusty winds in excess of 25 to 30 mph will be possible especially in the wind corridor from northeast of KRKS to KCPR especially after 18Z today. Decent warm advection will also be the focus from KCOD-KBYG and down to KCPR and will trend slightly lower than model guidance values in most areas today and Saturday due to continued snow pack and in valley areas. Southwest winds ahead of the next cold front on Saturday will be into the windy category especially at KCPR and expect some 30-40 mph gusts in Natrona county. The first in a series of short waves will begin to affect western sections of the forecast area on Saturday, as the large upper low off the Pacific northwest coast begins to eject short wave energy toward the forecast area. Mainly light snow is expected to increase in coverage west of the Continental Divide in the warm advection by Saturday afternoon and have continued with increasing precip chances for snow by Saturday afternoon. The timing of increased QPF values across western sections are not expected to occur until after 03Z Sunday, so will not be concerned yet with any advisories/watches yet. .LONG TERM...(Sunday through Friday) Sunday, snowfall increases across the west and also spreads east of the Divide. Western mountains will receive the most snow and southern areas the least. Gusty winds will develop with this system in the mountains and the Wind Corridor from Rock Springs through Natrona county. Snow east of the divide will be heaviest Sunday afternoon as snowfall west decreases, with the heaviest snowfall overall, ending by Sunday evening. Light snow will then linger through the night. As this system is exiting overnight Sunday into Monday morning, a stronger cold front moves through the area and drops highs 10 to 15 degrees cooler. By Monday, most of the area will be dry with only isolated chances remaining in the mountains. Low temperatures will also be 10 to 15 degrees cooler in the morning and every morning through the period. High temperatures will slightly improve through the week, but overall a cold week ahead. Most of the forecast area will be dry through the week, but northwest flow sets up over the area and will keep isolated snow chances over the northern and western mountains through Tuesday. Thursday into Friday will be the next decent shot of precipitation, mainly across the west. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1125 AM MST Fri Dec 6 2019 Conditions have improved at sites leaving VFR/MVFR conditions at most terminals through this TAF period. KBPI will likely keep some low clouds through the period. All sites will have light winds with the exception of KCOD seeing a few gusts around 25 knots through early afternoon and KCPR which will remain breezy through the period. Gusts 20 to 30 knots are expected at KCPR before 12z Saturday, with gusts after 12z approaching 50 knots. Next system will arrive after 18z Saturday, mainly impacting KJAC. && .FIRE WEATHER... Skies will be generally mostly clear east of the Divide this morning, with the exception of valley fog in locations mainly west of the Divide. Southwest winds are expected to increase today across the wind corridor by late this morning. Winds ranging from 25 to 30 mph with gusts up to 40 mph are expected by early this afternoon especially northeast of Rock Springs to Casper locations. Lighter winds are expected for much of the area today. Skies will remain mostly cloudy to overcast west of the Divide through this afternoon. Expect snow flurries to be possible through tonight over the far western mountains and portions of Yellowstone. Clouds and light snow will increase by Saturday afternoon west of the Divide with generally mostly sunny conditions expected east of the Divide. Southwest winds will continue to increase east of the Divide in the wind corridor from northeast of KRKS to KCPR. Southwest winds will range from 25 to 30 mph with gusts to 45 mph across these areas. && .RIW WATCHES/WARNINGS/ADVISORIES... High Wind Warning from 8 AM to 6 PM MST Saturday for WYZ020-022. Winter Storm Watch Saturday evening for WYZ023-025. Winter Storm Watch from Saturday afternoon through Saturday evening for WYZ012-013. && $$ SHORT TERM...Troutman LONG TERM...Bourque AVIATION...Myers FIRE WEATHER...Troutman