####018005041#### FXUS65 KCYS 192129 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 329 PM MDT Fri Apr 19 2024 .KEY MESSAGES... - Freezing Drizzle and Dense Fog will be the main concerns tonight especially between Cheyenne and the I-80 Summit. - Snow will be more favorable in the southern panhandle tonight where accumulation will range from 1 to 2 inches. - Much warmer temperatures are expected for Sunday through Thursday. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 254 PM MDT Fri Apr 19 2024 A very tricky forecast is expected tonight especially with the models now showing the higher QPF shifting south of the border into northern Colorado. This will be setting the stage for the potential of more freezing drizzle/ice accumulation/fog across the I-80 corridor from the I-80 summit to Cheyenne. The latest NAMNEST soundings seems to have the best handle on the current satellite trends with the thicker cloud deck in place. The models have also been shifting the entrance region of the upper level jet currently over the northern Nebraska panhandle further south into the southern panhandle this evening and overnight. As a result, we are looking at the best synoptic scale forcing across northern Colorado which is the area that has the best potential for lift to reach the dendritic growth zone. The latest water vapor loop is also showing some higher clouds starting to move in from southwest Wyoming. This may induce some seeder feeder light snow showers this evening. However, the best low level warm air advection appears to be overnight and tomorrow morning which will most likely moisten up the saturated boundary layer and start the freezing drizzle and fog again. The better synoptic scale forcing does appear to enter the I-80 corridor between Pine Bluffs Wyoming and Sidney tomorrow morning as the shortwave pushes off to the east, but it should be fairly shortlived with amounts generally less than 2 inches. Since we are looking at a greater potential for freezing drizzle/fog tonight between the Cheyenne and the I-80 summit we did issue and Winter Weather Advisory for that area since temperatures will be well below freezing overnight along with colder ground temperatures, but ground temperatures should warm quickly by mid morning on Saturday as the higher sun angle kicks in. The snow, fog and freezing drizzle should be tapering by early afternoon, but would not be surprised to see some dense fog develop Saturday night with continued response to upslope flow. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Issued at 254 PM MDT Fri Apr 19 2024 An active pattern through early next week will keep near daily chances for rain/snow showers and warmer temperatures. Sunday warmer air quickly makes its way into southeast Wyoming and western Nebraska as upper-level ridging makes its way back into the area. However, Monday a quick shortwave ejects eastward along the northern fringes of the forecast area, dropping temperatures a few degrees as a boundary drops to near the WY-CO state line. This boundary is then pushed eastward Tuesday into Wednesday, resulting in increased precipitation chances, particularly along the I-80 corridor between Laramie and Sidney. Wednesday afternoon a boundary develops along the Laramie Range before moving eastward. With increased moisture moving up the Central Plains from the Gulf and a few hundred J/kg of CAPE, thunderstorms are not out of question Wednesday afternoon and evening. Thursday is where long range models begin to really differ significantly in their solutions with the ECMWF bringing a weak shortwave embedded in the flow, while the GFS brings a much more potent shortwave in ahead of the main low pressure system. Overall the end of the week looks to bring cooler temperatures with higher precipitation chances, starting as rain and potentially transitioning to snow over the weekend. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1123 AM MDT Fri Apr 19 2024 IFR conditions persist at KCYS with freezing drizzle continuing for the next few hours before lifting with MVFR to VFR conditions briefly anticipated before dropping once again to IFR with snow showers late tonight into early tomorrow. KLAR and KSNY may also experience light rain/snow showers late tonight into early tomorrow. Elsewhere across southeast Wyoming and western Nebraska will remain VFR with CIGS near 5kft sticking around until later this afternoon/early evening. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Winter Weather Advisory from 8 PM this evening to noon MDT Saturday for WYZ116. Winter Weather Advisory from 11 PM this evening to noon MDT Saturday for WYZ117-118. NE...None. && $$ SHORT TERM...REC LONG TERM...GCC/LEG AVIATION...LEG