216 FXUS65 KCYS 280355 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 955 PM MDT Sat Apr 27 2024 .KEY MESSAGES... - Significant mountain snow is expected in the Snowy and Sierra Madre ranges, with total snowfall accumulations of 1-2 feet likely in the Snowys through Sunday morning. Winter Weather Advisories and Winter Storm Warnings have been issued. - Confidence is increasing in snow levels lowering sufficiently for heavy snow above 7500 feet over the South Laramie Range and I-80 Summit. However, uncertainty remains with the overall travel impacts due to the heaviest snow occurring during the daytime hours. A Winter Weather Advisory has been issued. - Widespread rain and high-elevation snow will impact a large portion of southeast Wyoming and the western Nebraska Panhandle through Sunday morning. Rain may change to snow as far east as the I-25 corridor into Cheyenne Saturday night, with minor accumulations possible on grassy surfaces. && .UPDATE... Issued at 953 PM MDT Sat Apr 27 2024 Getting dense fog on WYDOT webcams just west of Cheyenne this evening. Reports as low as a tenth of a mile on WYDOT sensors. Decided to issue a Dense Fog Advisory through 8 AM Saturday. Updates sent. && .SHORT TERM /THROUGH MONDAY/... Issued at 217 PM MDT Sat Apr 27 2024 Winter Weather Advisories and Winter Storm Warnings remain in effect for the South Laramie Range until midnight tonight and the Sierra Madre and Snowy Ranges through tomorrow afternoon for periods of moderate to heavy snowfall. So far the Sierra Madre Range has received approximately 4 to 10 inches, with 10 to 13 inches in the Snowy Range and almost 6 inches of snow at Crow Creek in the South Laramie Range. All that being said, the storm is going nearly exactly as expected. As the low has shifted further east in southern Colorado, the moisture tap for the Sierra Madre Range has mostly ended, so they may only see an addition 1 to 3 inches of snow. This shift has heavily favored the Snowy Range and South Laramie Range as the winds turned east, providing direct upslope flow and increased surface moisture right into the eastern slopes. An additional 2 to 6 inches of snowfall is possible with the closer to 2 to 3 inches along the Interstate 80 corridor between Cheyenne and Laramie. Here in Cheyenne, as a heavier band moved up from Colorado, we briefly changed over to snow, but will likely continue to see a rain-snow mix through the afternoon as these bands move through. By this evening, the low is expected to eject northeast, continuing to wraparound moisture into the Nebraska panhandle and keeping rain showers/thunderstorms around, but overall cut the moisture off along and west of Interstate-25. Sunday as the low continues to eject northeastward, an additional, messy, weak shortwave embedded in the flow follows right behind it. This shortwave may kick off a few showers and maybe a rumble of thunder west of the Laramie Range. These showers and thunderstorms will likely remain weak and not produce much substantial precipitation as the main forcing and moisture will have moved east. As skies begin to clear Sunday afternoon, high temperatures may reach well into the 50s outside of the mountains. As this messy, quasi-zonal flow begins to take back over winds will likely be increasing due to the mainly downslope west winds, drying the air out quickly. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Issued at 217 PM MDT Sat Apr 27 2024 WPC clusters are showing a weak upper level ridge building over the area on Monday before a strong upper level trof dives southeast into the northern Rockies on Tuesday. The models are showing quite a bit of variability on temperatures on Monday ahead of the trof, but this could be fairly dependent on the cloud cover. The latest GFS tends appears to show very limited cloud cover moving into the area on that day. Therefore, this limited cloud cover combined with downsloping winds, we are leaning towards the 75th percentile of the NBM. These gusty downsloping winds will most provide milder conditions Monday night as well with the higher gusts taking place in our wind prone areas of Arlington and Bordeaux Monday night. This strong upper level trof is also expected to drive a fairly strong front through the area from the west to east late Monday night into Tuesday morning. The front appears to be mostly dry with a few showers possible, but the main threat will be the strong bora type winds. We did bump up wind speeds on Tuesday for most locations to reflect this potential. In fact, I would not be surprised to see a few more places than the wind prone areas reach high wind criteria for a short while after the frontal passage. Wednesday-Friday looks very cool and unsettled as more shortwaves ride through the upper level trof in the northern Rockies. Quite a bit of uncertainty on the strength of these shortwaves moving through the trof, especially with the ECMWF looking much more amplified than the GEM/GFS on Thursday into Friday. Meanwhile, the general consensus of the WPC clusters are not really latching on to that more amplified signal yet. Ahead of the trof, it looks more favorable for more showers and thunderstorms on Thursday. However, depending on how amplified this trof becomes we may have to contend with the potential for another rain/snow mix on Friday. Stay Tuned! && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 555 PM MDT Sat Apr 27 2024 A soggy overnight will lead to widespread IFR conditions for terminals east of the Laramie Range. IFR conditions will mainly be caused by stratus, leading to low CIGs for the majority of the overnight and into Sunday morning. Widespread light to moderate rain can also be expected tonight into tomorrow morning, especially in the Nebraska panhandle. Some snow may mix in. Visibility drops possible in moderate rain. Conditions improve Sunday afternoon, but scattered showers will be possible. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Winter Weather Advisory until 6 PM MDT Sunday for WYZ112. Winter Storm Warning until 6 PM MDT Sunday for WYZ114. Winter Weather Advisory until midnight MDT tonight for WYZ116. Dense Fog Advisory until 8 AM MDT Sunday for WYZ116>118. NE...None. && $$ UPDATE...GCC SHORT TERM...LEG LONG TERM...REC AVIATION...SF