701 FXUS65 KCYS 072303 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 403 PM MST Sun Nov 7 2021 .SHORT TERM...(This evening through Tuesday night) Issued at 252 PM MST Sun Nov 7 2021 The main concern with this forecast package is the timing of the shortwaves and precipitation chances tonight through Tuesday night. Tonight: A very subtle potential vorticity anomaly is expected to skirt the northern sections of our forecast area tonight. This feature is already showing signs of breaking down the upper level ridge based on the latest water vapor loop. Latest surface analysis, were indicating the frontal boundary had reached northern Goshen and Platte counties. Not a lot of cool air behind this boundary, but wind speeds should slacken quite a bit behind this boundary. This combined with limited cloud cover and low dewpoints will allow for good radiational cooling tonight. Some low and mid level moisture will fill in behind this boundary mainly along and northwest of a Rawlins to Lusk line. This moisture combined with some synoptic scale forcing with the right entrance of the upper level jet should support enough lift for some light rain or snow. Not confident in any freezing drizzle at this time, but if the column does not become very saturated in the dendritic growth zone then one could not rule that out. For now, we will let the evening shift take a better look and see if any adjustments need to be made. Otherwise, a much cooler night is in store for the area with even some potential for frost in the southern half of the forecast area. Monday-Tuesday: The weak shortwave will lift northeast of the area fairly quickly on Monday morning resulting in a mostly cloudy and cooler day. Meanwhile, another potential vorticity anomaly is progged to push through the area on Monday night. This system appears to have some weak synoptic scale forcing with some support from the left exit region of the upper level jet and 500-300mb quasi-geostrophic forcing. It could be enough to bring some more snow showers to the higher elevations above 6500ft and light rain to lower elevations, but snowfall amounts should be fairly minimal. Most of the precipitation chances should move out of the picture early Tuesday morning. Tuesday Night: Another shortwave will be on its heels. This system will help increase wind speeds a bit more especially over the wind prone areas of Arlington, I-80 Summit and Bordeaux. Could be enough for some wind highlights especially over the Arlington area. Moisture will be pretty scarce with this system as well, but could be enough to trigger some more scattered rain/snow showers. .LONG TERM...(Wednesday through Sunday) Issued at 252 PM MST Sun Nov 7 2021 Broad upper trough over the CWA for Wednesday. Not a lot of agreement on PoPs forecasts with the ECMWF most bullish on PoPs across our northern CWA in Converse and Niobrara Counties as well as the mountains. SREF in line with the ECMWF while the GFS is the drier solution. Decided to follow the ECMWF/SREF solution and tried to hit our northern counties and western mountains fairly high on PoPs. Next wind event taking shape Friday into Saturday as upper ridge axis shifts east ahead of our next PACNW shortwave. GFS showing us on the subsident southern side of a 140kt jet moving into Montana and northern Wyoming. Graig to Casper 850/700mb height gradients above 60mtrs Friday afternoon into Saturday. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 404 PM MST Sun Nov 7 2021 Dry cold frontal boundary, currently stalled out across the Laramie Range, is expected to continue digging southward and wind speeds lessening behind the line. Main concerns exist into tomorrow with a short wave disturbance pulsing through the region. Combined with some upslope flow, could see some low ceilings east of Cheyenne. Started trending those ceilings downward to MVFR and even IFR for KCDR where upslope flow will be a factor. HiRes model guidance is starting to pick up on these trends, but will need to be evaluated overnight for low clouds. && .FIRE WEATHER... Issued at 252 PM MST Sun Nov 7 2021 Wind speeds have really begun to slacken up ahead of the frontal boundary this afternoon. This has kept us out of the Red Flag territory for the fuel ready zones this afternoon. Low relative humidities continue to be in place, but after this evening we will see much better humidity recoveries tonight as the weak frontal boundary passes through. Cooler and cloudy conditions will be in store through the early part of the week with scattered areas of rain/snow showers. Therefore, we are not anticipating any critical fire weather conditions through mid week. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...REC LONG TERM...GCC AVIATION...MD FIRE WEATHER...REC