607 FXUS65 KCYS 182322 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 420 PM MST Fri Feb 18 2022 .SHORT TERM...(This evening through Sunday) Issued at 230 PM MST Fri Feb 18 2022 Visible Satellite loop across the Front Range shows mid to high clouds moving southeast across the area under northwest flow aloft. Some lower clouds will likely sneak into Niobrara and Dawes county over the next several hours as a weak boundary shifts south and stalls. Can't rule out a few rain/snow showers near this boundary with enough convergence in the low levels, mainly near Lusk, Harrison, and Chadron. Showers should be short-lived and brief with clearing skies after midnight. Otherwise, strong winds this morning across the Wind Prone areas have subsided with gusts dropping below 45 mph. Expect these winds to continue to decline this evening; but this lull in the winds will be brief as all models are showing low to midlevel pressure gradients increasing between midnight tonight and early Saturday morning. Gusts over 50 mph can not be ruled out prior to sunrise Saturday along I-80 between Rawlins and Laramie. Primary forecast concern this weekend will be another round of strong gusty winds, not only for the Wind Prone areas but possibly spreading into the high valleys and immediate high plains zones near the Laramie Range. Models show the Arctic front near the Canada/US border gradually drifting south into Idaho, Montana, and the Dakotas late Saturday and Saturday night. Further south, a 115 knot upper level jet axis will gradually shift south into Wyoming. Pressure gradients from the surface up to 500mb will also increase Saturday through Saturday night. Most models show a core of 700mb winds between 50 to 70 knots across most of southeast Wyoming extending east into western Nebraska. Models also show the typical mountain wave signature at 700-500 mb, which is further confirmed on the 12z 700mb OMEGA fields. Greater confidence in high wind criteria west of Interstate 25 compared to the eastern zones. Therefore, due to increasing confidence with timing, upgraded the Arlington and Elk Mountain zone to a High Wind Warning for gusts around 75 MPH. Bordeaux, the Laramie Valley, and the I-80 Summit also look good, but since the timing of the winds appear to be later in the day, or possibly Saturday night, decided to hold off on those upgraded for now since there are some subtle timing differences on the onset of the winds. Thought about extending the High Wind Watch further north to including northern Carbon, Shirley Basin, and Converse County, but after coordinating with nearby offices will hold off since it appears pretty marginal. Not as confident with high winds east of Interstate 25 since subsidence is not all that strong and peak 700mb winds are not colocated with the best subsidence. Low level lapse rates could also be better with more substantial mixing. Regardless, still expect it to be windy across far eastern Wyoming and into most of western Nebraska Saturday and Saturday night. Mild temperatures are still forecast for this weekend with highs well into the 50s to maybe low 60s on Sunday for the lower elevations. Increased high temperatures on Sunday ahead of the front since guidance typically has a cold bias during the daytime pre-FROPA. .LONG TERM...(Sunday night through Friday) Issued at 114 PM MST Fri Feb 18 2022 The main focus of the long term forecast is a substantial and prolonged outbreak of arctic air expected beginning Sunday night and continuing through the work week. Accumulating snowfall is likely Monday through Tuesday morning, with light snow possible through Thursday. A broad trough is expected to dive down along the coast of British Columbia into the Northwest CONUS on Sunday. A strong surface high will also push down the eastern side of the Rockies, ushering in the coldest air of the season towards our area. Frontal passage is currently expected roughly between midnight and sunrise on Monday morning, so a midnight high is likely for Monday. During the daylight hours, temperatures are likely to remain fairly steady or even drop as the arctic airmass deepens through the day. Northeast winds will help saturate the lower atmosphere through the morning on Monday, leading to snow filling in from northwest to southeast as the day progresses. A period of pretty good snowfall rates is possible with model soundings showing a saturated isothermal layer in the dendritic growth zone Monday afternoon near Cheyenne. Much colder and drier air pushing in Monday night is likely to slow down snow rates, but light snow will remain possible. For totals in the first round, looking like we might approach advisory criteria in several areas, with the mountains most likely. A secondary shortwave is then expected to dive down slightly further south and west than the initial wave on Tuesday into Wednesday. The 12z model suite has shifted slightly north with the best ascent for this second round, so nudged PoPs up slightly all the way through Thursday morning. With moist SW flow aloft, the Sierra Madre mountains would have the highest odds of snowfall continuing through the middle of the week. The Tuesday-Thursday timeframe will continue to be watched for the possibility that light snow continues across a broader portion of the area, but confidence is quite low at this time. The cold temperatures may be the most significant story with this event. 700-mb temperatures could bottom out around -25C Tuesday morning, which will lead to some of the coldest temperatures of the season. Strong consistency among the ensembles boosts confidence in extreme cold, with the worst Monday night into Wednesday. Tuesday's highs may struggle to get out of the lower single digits, and record low maximums look likely. The record low maximum for Cheyenne is 11F. Even some low minimums may be challenged. Cheyenne's record low on Tuesday and Wednesday is -13F. This is currently close to the lower end of ensemble guidance, but certainly a possibility to keep watching closely. The bitter cold and dreary weather is likely to continue Wednesday, with single digits highs possible once again. The upper level trough finally starts to clear out by Thursday, which will start to weaken the arctic air. Currently expect some moderation Thursday, but we should be still significantly below average. Much more uncertainty introduced late in the week regarding how quickly the trough will clear out and how much we will be able to warm. && .AVIATION...(For the 00Z TAFS through 00Z Saturday afternoon) Issued at 420 PM MST Fri Feb 18 2022 W-NW surface winds will remain gusty at times early this evening before diminishing, only to come back up again Saturday afternoon. Weak front slips south into eastern WY and far northwest NE this evening with CIGS declining to MVFR at KCDR and KAIA through late tonight. This front will to the north and east by early Saturday morning with CIGS improving to VFR. W-SW surface winds will become gusty Saturday morning and continue into the afternoon. Gusts of 30 to 40 kt will be prevail. Stronger winds and mountain wave turbulence will develop in the vicinity of the higher terrain in southeast WY through the day Saturday. && .FIRE WEATHER... Issued at 144 PM MST Fri Feb 18 2022 No fire weather concerns this weekend through next week. It will trend a little warmer with increasing winds, but fuels should remain wet or snow covered. For next week, a strong arctic cold front will push south across the Front Range and adjacent plains Sunday night and Monday, resulting in periods of additional snowfall and a very cold last week of February. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...High Wind Warning from 5 AM Saturday to 11 AM MST Sunday for WYZ110. High Wind Watch from late tonight through Sunday morning for WYZ106. High Wind Watch from Saturday afternoon through late Saturday night for WYZ107-115-118-119. High Wind Watch from Saturday morning through Sunday morning for WYZ116-117. NE...None. && $$ SHORT TERM...TJT LONG TERM...MN AVIATION...MAJ FIRE WEATHER...TJT