688 FXUS65 KCYS 111129 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 529 AM MDT Thu Oct 11 2018 .SHORT TERM...(Today through Friday night) Issued at 236 AM MDT Thu Oct 11 2018 Temperatures will be warmer today as the cool surface airmass over the plains moves southeast and return flow allows for some milder air to filter back over the CWA. Mainly dry as well today though a few rain/snow showers should develop around the mtns this afternoon as the next upper shortwave approaches the CWA from the north. This system will pass across the CWA tonight bringing some rain and snow showers though accumulations should be limited to the higher mtns where about 2-4 inches is expected. Should finally see some sunshine Friday in the wake of the shortwave with dry northwesterly flow allowing temps to warm mostly into the 50s outside of the mtns. Not quite as cool Friday night with downslope flow behind a weak surface trough that will move over the plains. .LONG TERM...(Saturday through Wednesday) Issued at 236 AM MDT Thu Oct 11 2018 The models are fairly consistent in showing the stubborn upper level ridge across the eastern Pacific which will continue to allow more shortwaves to dive south out of Canada. One of the stronger waves is progged to move through our forecast area on Saturday. The models are showing some decent vertical motion/moisture up to 500mb which should be deep enough to favor growth of ice crystals in the dendritic growth zone. There will also be some low level instability behind the front which may also favor some snow bands. This will all be dependent on the strength of the low level gradient associated with the frontal boundary. At this point, it appears like the models are trending colder with temperatures behind this front which may setup some strong gradients as it pushes through Saturday. The FV3/ECMWF are showing this front pushing into northern Colorado by 00Z Sunday. QPF amounts from the National Blend of Models is showing 1 to 3 inch snow amounts by Saturday Evening mainly across the plains with amounts up to 10 inches in the Snowy Mountain Range. If this snow pans out, we could be looking at a really cold night setting up on Saturday night into Sunday morning especially if the cold air advection continues to surge. The ECMWF is showing a 1035mb surface high tracking into Wyoming on Sunday which is pretty cold for this time of year. We did lower temperatures a bit on Sunday morning compared to the superblend model. These cold temperatures will linger through the day Sunday with the surface ridge parking over the state Sunday night. This will most likely be our coldest night of the season with low temperatures approaching 10 to 15 degrees in the plains, and perhaps single digits in the mountains. The upper level ridge will finally begin to embark on the region early next week which will allow us to warm up along with some drier conditions. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 513 AM MDT Thu Oct 11 2018 Latest look at the IR loop was showing some high clouds starting to develop across the I-80 Summit towards KCYS. These clouds may prevent dense fog from forming at KCYS. As a result, we are going to be conservative on ceilings and visibility dropping. However, I am bit more concerned at KAIA and KBFF where the visibility and ceilings have begun to drop during the last hour or so. These sites may need to be watched. However, it may be rather shortlived as the high clouds continue to spread eastward. The rest of the sites should remain in the VFR category this morning. Meanwhile, a fairly distinct shortwave will move through the forecast area this afternoon and evening. This shortwave will kick off a few scattered showers this afternoon/evening and will most likely cause ceilings to drop to the MVFR category especially at the Nebraska TAF sites. && .FIRE WEATHER... Issued at 236 AM MDT Thu Oct 11 2018 Generally cool to mild temperatures will continue through this weekend. A couple disturbances will bring some rain and snow to the area mainly today and again on Saturday. These factors will keep fire weather concerns very low. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Dense Fog Advisory until 9 AM MDT this morning for WYZ116-117. NE...None. && $$ SHORT TERM...RE LONG TERM...REC AVIATION...REC FIRE WEATHER...RE