Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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645 FXUS65 KCYS 181727 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1127 AM MDT Wed Sep 18 2024 .KEY MESSAGES... - Strong gusty winds continue in the wind prone areas through midday Wednesday. A High Wind Warning is in effect. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 350 AM MDT Wed Sep 18 2024 Current IR Satellite loop shows the strong storm system from yesterday pushing northeast and stalling across Montana early this morning with a textbook comma cloud pattern noted on Satellite. This storm is producing heavy rainfall across the lower elevations with heavy mountain snowfall over 9500 feet. For southeast Wyoming and western Nebraska, mainly a wind forecast today with some very dry air advecting eastward on the backside of the storm. Current High Wind Warnings look good at this time with a few locations reaching gusts of 45 to 50 MPH. Winds are expected to strengthen around sunrise. Will keep the High Wind Watch going for eastern Platte county due to lower confidence and a conditional risk for strong gusty winds associated with mountain wave activity and low level mixing. Otherwise, cooler temperatures expected today but it will remain near normal for this time of the year. Observations near Alliance Nebraska do show some patchy fog early this morning, but expect this fog to dissipate by sunrise with increasing cold air advection and northwest winds at the surface. All models show a shortwave ridge axis building into the Front Range and Rocky Mountain region Through late Thursday. Expect a gradual warming trend on Thursday with dry conditions continuing through early Friday morning. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Issued at 355 AM MDT Wed Sep 18 2024 An active weather pattern remains well advertised for the extended forecast due to multiple weather disturbances impacting our cwa. A large dome of high pressure will be spread across the Mexican Plateau into Texas. The associated upper level ridge at H5 will amplify northward on Friday, bringing WAA and southerly flow to the high plains. Further upstream, a pronounced upper level longwave trough will be carving its way out of the Southern CA and Four Corners region. This will assist with a 75-85 knot jet streak max propagating toward the Intermountain West by Friday afternoon. Model soundings depict a dry air mass being present for most of our forecast zones, and a well-mixed lower boundary layer should provide breezy winds during the afternoon hours. 700mb temperatures are progged to have a spread of +10C to +14C by 0Z Saturday. The dry air mass and breezy winds will create elevated fire weather concerns for our cwa, especially east of the I-25 corridor. Daytime highs are progged to be approximately 5-12 degrees F above average for SE WY and western NE. Highs in the 80s for areas east of the I-25 corridor, and 70s west of that line for the lower elevations. Slightly cooler temperatures for the mountain zones of mid 50s to low 60s. Our primary focus then turns to this weekend as deterministic and ensemble model data are coming into better agreement for an impactful weather system to arrive. The autumnal equinox will occur this coming Sunday, and based off the current weather data, it will certainly feel like it outdoors. At this time of inspection, lee cyclogenesis is advertised via a mid-latitude cyclone/Colorado Low scenario. The aforementioned longwave trough is anticipated to become cut off from the mean steering flow at 500mb between Saturday afternoon and late Sunday. The timing and location of the surface low still needs some work to have a higher confidence, but have taken the initial steps of bumping up PoPs and lowering MaxT for Sunday. The first measurable snowfall of the season is possible for elevations above 10,000 feet in the Snowy Range Mountains on Sunday. For lower elevations, temperatures will be chilly, especially on the eastern foothills and lower elevations of southeast WY. An upslope regime is anticipated to set up, translating to daytime highs in the upper 40s to low 60s from cloud cover and rain showers. Depending on that surface low track, several drought-stricken areas could see beneficial rainfall between 0.5 and 1.5 inches. The GFS is the most aggressive, with the Euro and Canadian model hugging the I-80 corridor and areas south into CO with the highest potential rainfall accumulation. The high plains will continue to see below normal temperatures early next week. The cut-off Upper level low (ULL) will slowly become absorbed into the mean steering flow again by Monday, with another weak cool front on its way towards our cwa. The cool air will spill down the spine of the Colorado Rockies via northwest flow aloft by Tuesday, keeping the region below normal for daytime highs. By the middle of next week however, upper level ridging will begin to amplify over the western CONUS. The upper level ridge will begin its trek towards the High Plains, and bring another opportunity for slightly warmer temperatures and dry conditions. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1125 AM MDT Wed Sep 18 2024 VFR conditions expected across area terminals through the forecast period with gusty west to southwest winds continuing into this afternoon. Most terminals can expected gusts 25-35 kt before winds begin to calm headed into this evening with SKC prevailing. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...High Wind Warning until 3 PM MDT this afternoon for WYZ101- 103>105-107-110. NE...None. && $$ SHORT TERM...TJT LONG TERM...BW AVIATION...MB