Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000 FXUS65 KCYS 172338 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 438 PM MST Sun Dec 17 2017 .SHORT TERM...(This evening through Tuesday night) Issued at 215 PM MST Sun Dec 17 2017 Early afternoon water vapor loop showed a split flow aloft with a southern stream low spinning along the AZ/northwest MX border, and progressive northern stream trough bisecting the Dakotas into northeast UT/northwest CO. A surface trough extended from east central MT south along the laramie Range and northern CO Front Range. Low clouds across western NE have cleared out nicely, with some wave clouds west of the Laramie Range. Low level pressure gradient was sufficient for occasional strong west winds between Laramie and Rawlins, with gusts to around 55 mph. The gradient should relax a bit later this afternoon, with winds decreasing somewhat. Temperatures ranged from the mid 20s to mid 40s. The near short term (tonight through Monday) will focus on high wind potential for the WY 106 and 110 zones including Arlington and Bordeaux from late tonight through Monday afternoon. The GFS and NAM CAG-CPR 700/850mb height gradient progs are between 50 and 60m between 09Z and 00Z Monday. Prior runs of the 700mb winds were west 35-40kt, have now increased to 45-50kt. Our Bordeaux local wind probabilities range from 25 to 65 percent for the same time period. Therefore, confidence is growing for a high wind episode from late tonight through late Monday afternoon, and a High wind Watch was issued. Aside from the winds, Monday will be dry with milder high temperatures in the mid 40s to mid 50s east of the Laramie Range, with 20s and 30s to the west. Winds will diminish Monday night and Tuesday, but increase somewhat across the southeast WY wind corridors Tuesday night. It will continue dry during this period, with intervals of mid and high clouds. A weak front tries to slip south into the northern NE panhandle Tuesday where high temperatures will remain in the 40s. .LONG TERM...(Wednesday through Sunday) Issued at 215 PM MST Sun Dec 17 2017 One more mild day across the CWA Wednesday then winter weather arrives Thursday and remains through the weekend. Snow will be the main concern Thursday then very cold temperatures expected after that. An upper trough will dig southeast over the western CONUS Thur with southwesterly flow aloft over this area giving us our last mild day. The arctic front will then drop south across the CWA Thursday evening with snow developing and spreading across the CWA behind it. Much colder Thursday with snow continuing Thurs morning then tapering off Thursday afternoon and evening as the upper trough axis passes by. Models in decent agreement keeping the system more an open and progressive trough so this should keep snowfall amounts down a bit. Still looking like around a foot or so of snow over the higher mtns with a general 2 to 5 inches over the plains by Thursday evening. Friday looking to be cold with the next upper trough dropping south out of Canada, bringing an even colder push of arctic air with it. Should see another round of snow across much of the CWA late Fri into Saturday as the trough digs well into the southwest part of the country. GFS not as amplified with it and as a result keeps QPF going over the CWA through Sunday while the EC is dry. Either way very cold air will settle over the CWA Saturday through Monday with fairly widespread mins temperatures below zero likely particularly Sunday and Monday. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 434 PM MST Sun Dec 17 2017 Dry and milder conditions are anticipated during the next 24hrs which will allow for VFR conditions to prevail. It will be breezy again tomorrow afternoon across most of the TAF sites due to downslope flow. && .FIRE WEATHER... Issued at 215 PM MST Sun Dec 17 2017 Cool to mild temperatures and low-level moisture will preclude fire weather issues through mid-week. Lowest humidities will remain above critical thresholds through the week. Much colder temperatures and accumulating snow are expected later this week. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...High Wind Watch from 2 AM MST Monday through Monday afternoon for WYZ106. High Wind Warning until 5 PM MST Monday for WYZ110. NE...None. && $$ SHORT TERM...MAJ LONG TERM...RE AVIATION...REC FIRE WEATHER...MAJ

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