880 FXUS65 KCYS 081148 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 445 AM MST Wed Mar 8 2023 .SHORT TERM...(Today through Friday) Issued at 244 AM MST Wed Mar 8 2023 Today...Conditions still have been unfavorable for our current Winter Weather Advisory for freezing drizzle and dense fog from the Southern Laramie Range through Laramie County looking at webcams and surface observations. However, we will closely monitor the situation and if freezing drizzle and dense fog have not materialized by 5 to 6 AM, we will cancel the advisory early. Maximum temperatures still remain below normal with 700 mb temperatures near -5 Celsius and low level upslope east to southeast winds along with cloud cover. The models are likely underdoing areal coverage of snow due to too limited low and mid level moisture coverage, thus will continue with 30 to 60 percent POPS for much of our forecast area. Light snow will increase in coverage, especially along and east of I-25, as the low level southeast upslope lift is enhanced by the approach of the next shortwave trough aloft from western Colorado. Tonight/Thursday...A fairly potent and progressive shortwave trough aloft moves overhead tonight and early Thursday producing decent 300-500 mb and 500-700 mb quasigeostrophic lift of the moist low and mid levels, and producing widespread light to moderate snow, with the areal coverage greatest north of a Douglas to Torrington to Alliance line. The snow looks to quickly end from west to east Thursday morning and early afternoon in the wake of the shortwave trough aloft and with fairly decent subsidence. Projected snowfall totals suggest a borderline situation for Winter Weather Advisories for snowfall for Niobrara County, as well as northern Sioux and Dawes Counties of the northern Nebraska panhandle, where 2 to 4 inches of snow may fall. For now, we have opted to keep an eye on the future development and let our day shift forecasters take another look before issuing a Winter Weather Advisory. In the wake of the passing cold front, decent surface and low level gradients suggest a blustery and cold northwest wind of 25 to 35 mph gusting to 50 mph Thursday afternoon along and east of Interstate 25 and south of a Douglas to Alliance line. Maximum temperatures will still remain cold with 700 mb temperatures near -10 Celsius, yielding high temperatures mostly in the 30s to lower 40s. Thursday night/Friday...A decent warming trend is anticipated for Friday as 500 mb heights aloft rise some 60 meters on zonal flow, with a surface lee trough developing Friday afternoon. With 700 mb temperatures reaching near 3 Celsius, maximum temperatures will reach the 40s to lower 50s. With the models projecting increasing low and mid level moisture, orographic snow showers will spread eastward across and near our Snowy and Sierra Madre Ranges. We will issue a High Wind Watch for the North Snowy Range Foothills including Arlington and Elk Mountain from 6 AM Friday to 6 AM Saturday as the models are projecting 50 to 60 knot winds at 700 mb, along with our local guidance random forecast and 700 mb Craig to Casper height gradients near 70 meters suggesting winds exceeding high wind criteria. .LONG TERM...(Friday night through Tuesday) Issued at 244 AM MST Wed Mar 8 2023 Medium to long range models in decent agreement and show quasi- zonal flow for most of the weekend. A general warming trend is expected with a brief cool down late Saturday through Sunday night. In fact, some of the mildest temperatures we've seen in a while are possible for Tuesday of next week. Models indicate another Pacific upper level trough pushing onshore Thursday and Friday, but this time ejecting east northeast across Idaho and Montana. This solution is reasonable given the current pattern with a strong jet stream along the central Rocky Mountain Region and the northern Great Plains. Any push of cold arctic air seems to be displaced into the eastern Pacific and eastern Gulf of Alaska on the eastern edge of the strong Omega Block currently south of Alaska. As this upper level trough ejects northeast, mainly strong gusty winds are expected across the eastern plains with any precipitation mainly confined to areas west of the I-25 corridor, especially the mountains. Sierra Madre Range and Snowy Range may do very well with this next shot of moderate to heavy snowfall...with 10 to 18 inches possible. Much lower amounts expected in the valleys with even a chance at rain/snow mix down to 6500 feet before the cold front moves across the area. Winds will be the primary concern for most of the lower elevations with gusts over 55 MPH possible Friday night through Saturday night. Models in agreement with 700mb winds of 50 to 60 knots through the potential event along with strong subsidence and favorable near-surface pressure tendencies over the Continental Divide (increasing) in contrast to areas further east across the central plains (slightly decreasing). So far, this looks like mostly an event for southeast Wyoming with western Nebraska missing out on the strongest winds as the peak winds aloft don't move over that area until late at night and the best surface pressure gradient remains west and north of western Nebraska. Increased winds slightly over the previous forecast and trended wind forecast towards the 90th percentile for the wind prone areas. Otherwise, there is a small chance at some thunderstorm activity across western Nebraska Saturday afternoon before FROPA. Models, including the NAM and GFS, are showing LI below -2 with a marginally unstable BL. Models show bands of convection developing near the jet axis ahead of the cold front. Increased prob thunder to around 10 percent, but did not add it into the forecast quite yet. A few cooler days expected Sunday and Monday with highs near or slightly below normal. However, daytime temperatures in the 30s and 40s are much better than what we were experiencing a month ago. Models then show an upper level ridge axis amplifying northward on Tuesday with 700mb temperatures climbing to +2c to +6c. For mid March, this translates to 50s to even middle 60s for high temperatures for most areas...with 40s to near 50 for the areas with lingering snowpack. So maybe a little taste of spring on Tuesday before the next Pacific storm approaches the area for the middle of next week. && .AVIATION...(For the 12Z TAFS through early Thursday morning) Issued at 445 AM MST Wed Mar 8 2023 A strong jet stream will remain over the region today as a Pacific storm system approaches from the west later today. Weather conditions today will not change much compared to 24 hours ago with persistent IFR conditions, especially at night, and occasional light snow and fog/freezing drizzle across the eastern plains. HAZARDS/WEATHER TRENDS: Most of the region will remain in IFR or near IFR (low-end MVFR conditions) this morning including KLAR. KRWL will be the only terminal in VFR until widespread snow develops this evening. Western Nebraska terminals and KCYS will remain in IFR conditions with occasional freezing drizzle and fog at KCYS, and possibly extending eastward to KSNY this morning. A 6 hour window of improving CIGS and MVFR conditions is still expected from 16z today to 02z Thursday due to some surface heating. Otherwise, most terminals will drop to IFR conditions once again after 02z this evening...with light snow and low VIS possible at KRWL, KCDR, and possibly KBFF and KAIA. && .FIRE WEATHER... Issued at 244 AM MST Wed Mar 8 2023 No fire weather concerns are expected for the next week due to a cold, unsettled weather pattern with accumulating snow. Winds are expected to increase across southeastern Wyoming on Thursday and remain strong through Sunday. Temperatures warm Friday and Saturday. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...High Wind Watch from Friday morning through late Friday night for WYZ110. Winter Weather Advisory until 10 AM MST this morning for WYZ116>119. NE...None. && $$ SHORT TERM...RUBIN LONG TERM...TJT AVIATION...TJT FIRE WEATHER...RUBIN