671 FXUS65 KRIW 261801 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1101 AM MST Sun Jan 26 2020 .SHORT TERM...This afternoon through Monday night Conditions will be similar today, compared to Saturday. The transitory ridge axis is over the ID/WY border, continuing to shift eastward as it weakens through the day. Precipitation from an approaching shortwave and upper level southwest flow will move over far western portions by midday. Snow will be ongoing across this area through tonight, before beginning to subside by midday Monday. Light snow will remain possible over the far west Monday afternoon and night. Snow will spread across the remaining areas west of the Divide after sunset this evening. This activity will make its way east of the Divide late tonight/early Monday morning. Some locations may have a rain/snow mix, as temperatures could be a couple degrees above freezing and snow levels range between 6000 and 7000 feet. The focus for snow will shift east of the Divide by Monday morning, along and east of a Cody to Jeffrey City to Casper line. This snow will be heavy and wet and likely to melt on contact or have a hard time accumulating, as temperatures rise into the middle to upper 30s. Heavy accumulations are not expected, but wet, slick conditions are likely. Snow and/or rain will shift to Johnson/Natrona counties by the afternoon, before finally ending after sunset Monday evening. Snowfall totals of 1 to 2 inches are expected across all by far western portions, with most locations in these areas staying under 1 inch. 2 to 4 inches will occur the western mountains, with the Tetons receiving 5 to 10 inches. Most of this will occur tonight. .LONG TERM...Monday night through Saturday Issued at 350 AM MST Sun Jan 26 2020 The extended forecast continues to show an active pattern with a series of shortwaves poised to traverse the region as we remain in an onshore Pacific flow pattern. On the heels of the shortwave that will be moving out early Monday afternoon, another shortwave pushes across the state Tuesday into Wednesday. There continues to be less confidence with this event regarding snow amounts east of the Divide than the previous system, though there is confidence for snow increasing across the west beginning Tuesday. The energy with this wave is expected to split, as we have seen with previous recent shortwaves in this pattern, and be concentrated to the south in CO, UT and AZ and northwest in MT and the Dakotas. The back side of this event may see some energy move across WY, so PoPs in eastern Sweetwater and Natrona counties and in the Big Horns were increased slightly between 12Z Wed and 00Z Thurs. North/northwest upper flow will continue towards the end of the period, with another embedded shortwave likely bringing more snow to western Wyoming on Thursday. Models suggest modest ridging will set up by the weekend which would bring a reprieve from the snow, although there are hints at a more significant system arriving the following Monday. && .AVIATION...For the 18Z TAFS through 18Z Monday West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals The next round of snow and low clouds will develop after 19Z in the mountains and far west valleys and continue through 12Z Monday. This would include the KJAC terminal forecast. Mountains will become frequently obscured by 00Z through 15Z Monday. Snow and low ceilings will develop over the rest of SW WY between 00Z and 03Z and continue through 12Z. This would include KBPI, KPNA, and KRKS terminal forecasts. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals VFR conditions will occur through most of the forecast period. Late tonight into Monday morning, areas from KRIW and KLND east to KCPR will see lowered cigs and vis as snowfall develops in those region. Most impacts will occur between 12z and 18z Monday for those locations. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Snow will return to far western Wyoming this afternoon, spreading to southern portions by this evening. Snow will spread east of the Divide late tonight/early Monday morning, ending from northwest to southeast through the afternoon. Accumulations will remain light, with temperatures rising above the freezing mark in the Bighorn Basin and zones 280/281. Gusty southwest winds will continue over zones 280/289 this afternoon. Winds will increase over zone 279 by Monday morning, as snow ends across the zone. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...LaVoie LONG TERM...Fisher AVIATION...Myers FIRE WEATHER...Straub