Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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066 FXUS65 KCYS 240840 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 240 AM MDT Tue Sep 24 2024 .KEY MESSAGES... - Above average temperatures and dry conditions expected Wednesday onwards. && .SHORT TERM /THROUGH THURSDAY/... Issued at 230 AM MDT Tue Sep 24 2024 Latest GOES Nighttime Microphysics RGB shows mid-level cloud cover across east-central WY through the NE panhandle associated with the earlier shortwave passage to our northeast. This upper level trough will continue to dig into the MS River valley, while 500mb height rises climb across the central Rockies today. As clouds continue to clear through this morning, dry conditions will prevail with seasonable weather today. Afternoon highs will be in the 70s for most. Wednesday and Thursday will be quite warm across southeast WY and western NE as the thermal ridge of 700mb temps 14-16C move overhead. Latest NAEFS guidance places these 700mb temps over the climatological 99th percentile value for late September. Afternoon highs Wednesday will be in the 80s for most while Thursday will temperatures climb into the upper 80s and 90s, especially east of the Laramie Range. Latest NBM probability of afternoon highs exceeding 90F degrees is 50-80% for much of the NE panhandle. Would not be surprised to see observed afternoon temperatures rival record highs for a few sites. The current forecast high for Thursday in Chadron is 96F degrees which would be the 4th latest 95+ degree day in their climatological record. In addition to Thursday`s warmth, near-critical fire weather conditions are possible with the above normal temperatures and westerly downsloping winds across the Laramie Range dropping afternoon RHs below 15 percent. An upper level system passing well to the north will lead to a weak frontal passage Thursday afternoon supporting winds gusting 25-35 mph. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Issued at 230 AM MDT Tue Sep 24 2024 No major changes to the long term forecast, with the broad upper level ridge pushing further southward as an upper level shortwave passes to the north. Under this setup, zonal flow is expected to take hold keeping the upper level high to the south across the Four Corners and an upper level cutoff low cycling off across the southeast CONUS. A decent warmup is expected to continue during this time period, with 700mb temperatures hovering around +14c to +16c, leading to prolonged warmer temperatures for late September. As a result, will begin to see daytime highs in the low to mid 80s through at least Sunday. Decided to keep temperatures close to the NBM, with any model guidance still a bit too far out to make any significant changes. However, will need to start considering blending in higher NBM percentiles to the current blends for this weekend, with the NAEFS mean 700mb temperatures in the climatological 90th percentile for the majority of our areas in southeast Wyoming and the Nebraska Panhandle. In addition to the increased temperatures, dry forecast associated with dry downsloping flow will inevitably raise fire weather concerns as the minimum RH values drop to the mid to low-teens for much of southeast Wyoming and the Nebraska Panhandle. Winds do not appear to reach fire weather critical thresholds during the times of critical level humidity values through Weekend. However, will need to monitor the development of an upper level closed low that will retrograde towards eastern Colorado by late weekend, which could induce some stronger gradients for the CWA and some possible shortwave disturbances to pulse across the zone on the back end of the low. Otherwise, the upper level pattern begins to break down by the beginning of the work week, with the upper level low finally pushing towards the Eastern Seaboard, making way for shortwave to dig across the zone and bringing colder temperatures both Monday and Tuesday. Little moisture advection associated with this front, keeping the region dry and on the colder side. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1017 PM MDT Mon Sep 23 2024 Expect mostly cloudy skies overnight east of the Laramie Range. Ceilings will remain above MVFR range. An isolated sprinkle can not be ruled out at AIA before sunrise. Expect VFR at all terminals on Tuesday with mostly sunny skies and light northwest winds. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MB LONG TERM...MRD AVIATION...MAC