481 FXUS65 KCYS 271109 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 409 AM MST Sat Nov 27 2021 .SHORT TERM...(Today through Sunday night) Issued at 323 AM MST Sat Nov 27 2021 The main concern with this portion of the forecast is how much temperatures will drop tonight and gusty winds returning to the wind prone areas late tonight into Sunday. Latest water vapor loop was showing a subtle shortwave moving through Montana. This feature will continue to slide southeast this afternoon into far eastern Wyoming and the Nebraska panhandle. Unfortunately, this disturbance will not contain much in the way of moisture except for higher cloud decks above 10kft which will tend to keep temperatures on the cool side today. This cloud deck is progged to clear out this evening after the shortwave passes southeast of the area. After the cloud deck scours out, we may see temperatures tumble in the Nebraska panhandle overnight due to the surface high yielding to strong subsidence and ideal radiational cooling. As a result, we have dropped temperatures a few degrees from the previous forecast in the Nebraska panhandle overnight. Meanwhile, the Arlington and Elk Mountain areas will see the wind pick up fairly quickly mainly after midnight in response to tightening height gradients, good subsidence, 700-600mb winds speeds and directions becoming more ideal along with good pressure falls in the northern Plains. With this in mind, we went ahead and issued a High Wind Watch for the Arlington area from midnight through 6pm Sunday. Would not be surprised to see the wind speeds pickup late Sunday morning into the afternoon across the Bordeaux and the I-80 Summit in response to strong subsidence and the lee side trof breaking down. These wind speeds should begin to slacken somewhat on Sunday night in response to slightly lower wind speeds in the 700-600mb layer, but it may be shortlived as the height gradients try to pick up again later Sunday night. Overall, temperatures will rebound nicely on Sunday with afternoon highs climbing back into the 50s and 60s. .LONG TERM...(Monday through Saturday) Issued at 323 AM MST Sat Nov 27 2021 The long term period continues to be dominated by large-scale ridging over the central and western CONUS. Main forecast challenges will be winds and the timing of weak cold fronts. On Monday, a broad ridge will be located over the western US with the axis positioned near the Rockies. The higher winds aloft on the east side of the ridge are expected to gradually lift off to the north and east by Monday, so the high wind threat will be on the decline. However, wind prone areas still are expected to remain elevated into Monday. Underneath the ridge, 700-mb temperatures will again climb to around +5C with mostly sunny skies, leading to very warm afternoon temperatures. Some stations could come within a few degrees of record highs for the day. On Tuesday, a shortwave embedded in NW flow will traverse across the region, dragging a surface cold front with it. This looks mainly dry yet again. There is a slight chance that some preciptiation sneaks into the mountains and our northern counties with increasing cloud cover Tuesday morning, but kept PoPs below the threshold to show up in the forecast for now as only a few ensemble members show any QPF at all. Temperatures behind the front will be closer to normal for this time of year, dropping perhaps 5-10C off of Monday's highs. Went on the lower end of guidance for Tuesday's highs, following the previous forecast. Pressure gradients are expected to drop off behind the front, reducing the high wind threat for Tuesday. The wind prone areas may see only a brief reprieve from the threat for high winds as gradients look to increase again Tuesday night into Wednesday morning as the ridge builds back into our region. This will push the upper level jet across the CWA and back to the north and east. Will have to watch this period for wind headlines again. There is strong model agreement on a very strong ridge broadening over the western US for Wednesday and Thursday leading to dry weather and much above average temperatures continuing. The month of December looks to begin with temperatures more typical of early October than early December. There is some disagreement in just how far the jet stream will get pushed off to the north though. The GFS solution centers the ridge over Colorado and Utah, which would push the jet well to the north over Montana and Canada and limit our wind threat. The ECMWF keeps the ridge axis further west and thus the winds a little closer. Major forecast uncertainty is introduced by the end of the period. Guidance varies wildly starting on Friday, with some (e.g. deterministic GFS) showing the ridge backing off the west coast and allowing a trough to slip down the eastern slopes of the Rockies. This would bring dramatically colder air and even a chance for precipitation, but this solution is not well reflected in either the ensembles or other deterministic guidance. For an example on the forecast uncertainty, the GFS ensembles have a spread of about 10F for Thursday's high temperatures, but this increases to about 35F for Friday's highs. Have kept the forecast as a blend of these extremes for Friday and Saturday, but this period will be watched closely to see if the persistent ridge will finally relent, or if this will turn into yet another short lived, dry cold front. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 423 PM MST Fri Nov 26 2021 Wyoming TAFS...VFR. Wind gusts to 35 knots until 03Z, then gusts to 25 knots at Cheyenne until 08Z. Nebraska TAFS...VFR. Wind gusts to 22 knots at Scottsbluff until 02Z. && .FIRE WEATHER... Issued at 323 AM MST Sat Nov 27 2021 Much cooler air is expected to push into the area today as high pressure builds across northern Plains. This will allow for relative humidities to gradually recover this afternoon compared to yesterday. However, warmer temperatures and more windy conditions will return to the area on Sunday and Monday with near critical fire weather conditions. Afternoon humidities will once again drop into the 20 to 25 percent range both Sunday and Monday mainly along and east of the Laramie Range. Gusty west to northwest winds are also anticipated on both of those days with some gusts of 20 to 25 mph. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...High Wind Watch from late tonight through Sunday afternoon for WYZ110. NE...None. && $$ SHORT TERM...RE LONG TERM...MN AVIATION...RUBIN FIRE WEATHER...RE