


Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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634 FXUS65 KCYS 151146 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 545 AM MDT Wed Oct 15 2025 .KEY MESSAGES... - Dense Fog Advisory remains in effect for all of the eastern plains of southeast Wyoming and the Nebraska Panhandle this morning. Visibility below one quarter mile can be expected. - A storm system will move through the area today and Thursday, first bringing showers and thunderstorms, followed by mountain snow and strong winds across the wind prone areas of southeast Wyoming. - A few of the thunderstorms this afternoon may become strong to marginally severe, of which they may produce hail and gusty winds along with heavy rainfall. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 345 AM MDT Wed Oct 15 2025 Forecast remains on track today and tonight with models continuing to indicate 99th+ percentile PWATs across most of the eastern high plains. This is evident with the widespread dense fog early this morning with visibility down to one eighth of a mile at times along and east of the I-25 corridor. Expanded the Dense Fog Advisory further west to include most of the Interstate 25 corridor up to Converse county. Current surface observations show dewpoints above 55 degrees across western Nebraska, which is going to set up a potentially active period of weather the next 24 to 36 hours. Fog is forecast to slowly lift by noon today as a warm front slowly lift northeast across the forecast area. IR Satellite loop shows the strong upper level low pressure center starting to track eastward across the Great Basin region early this morning. This feature, along with the stationary front, will be responsible for late season thunderstorm activity over the next 24 to 30 hours. Thunderstorms have already been observed late last night across Carbon and Converse counties well ahead of the upper level low. There remains a conditional risk for strong to severe thunderstorms for areas just east of the Laramie Range eastwards across all of western Nebraska. However, much of the thunderstorm activity isn`t expected to form until the evening hours and especially overnight due to the remaining stratus deck and arrival of dynamic forcing...with model soundings showing conditional instability and increasing lapse rates tonight as the cold pool aloft moves over the area. This is going to lead to a tricky forecast after noon today for this time of the year. With MLCAPE near 1000 j/kg and MUCAPE closer to 1500 j/kg late this evening, worded forecast for strong to severe thunderstorms. The most favorable locations are northeast of a line from Casper Wyoming to Bridgeport Nebraska where forcing should be the strongest north of the developing surface low. However, locations along the I-80 corridor have a decent chance at seeing some activity as well, especially if the forecast location of the surface low is just a little off. High res CAMs have been consistent, so increased POP and prob thunder across the most favorable areas. Multiple lines of convection are expected through midnight tonight with some activity lingering into early Thursday morning. Strong gusty winds, hail, and brief very heavy rainfall are the most likely threats with these storms. Variables that may bust this forecast include mid to upper level clouds moving into the area early, a stubborn stratus deck and/or fog lingering through the afternoon, and the upper level low slowing down today. Pretty confident that mid to upper level cloudiness may not be much of a problem given current trends on IR Satellite early this morning. For Thursday, all models show the upper level low lifting northeast from the Salt Lake City area to central and northeast Wyoming by Thursday afternoon. This position is a little further south and east compared to 24 hours ago. Expect another round of precipitation Thursday with strong jet energy out ahead of the trough axis. Any thunderstorm activity looks to be in the morning, with rain shower activity along the surface cold front, which could stall across the eastern plains in the afternoon and evening. High temperatures will return to slightly below average on Thursday for most areas with highs in the mid 40s to upper 50s across southeast Wyoming, and low to mid 60s across western Nebraska. Given the storm track, winds are also expected to increase with windy conditions looking more likely across southeast Wyoming Thursday afternoon and evening. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Issued at 222 AM MDT Wed Oct 15 2025 Heading into Thursday night, the next round of high winds will arrive. The cold front will cause MSLP gradients to tighten west of the Laramie Range, which will in turn cause 700 mb winds to increase up to 60 kts over the usual southeast Wyoming wind prones. Strong subsidence will easily push these winds down to the surface. 60+ MPH winds will be possible at Arlington, Bordeaux and the South Laramie Range late Thursday night into Friday morning. Winds will gradually decrease throughout the day Friday as the trough pushes away. For the weekend, models are struggling with the shortwave energy digging southeast out of western Canada. All models show a strong cold front, with the potential of some lower elevation rain/snow mix Saturday morning. However, models are out of phase with this trough axis with the GFS the most progressive...showing it clipping the area but mainly moving across the Dakotas. The Canadian and ECMWF show the trough digging further south with possible snow down to near 6000 feet as 700mb temperatures lower to -4c to -8c. Ensemble spreads amplify this disagreement with low confidence with POP and temperature forecasts. Similar pattern unfolds for early next week with large temperature and POP spreads as another progressive shortwave moves east across the area. Decent model agreement with the ECMWF and Canadian, but the GFS shows a ridge axis dominating the weather pattern on Monday. Lowered Max and Min temperatures Saturday through Monday, and kept 15 to 30 percent POP for now. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 545 AM MDT Wed Oct 15 2025 Dense fog will impact the eastern plains terminals this morning with VIS below one half mile at times. Fog should lift by this afternoon as a Pacific storm system tracks eastward across the Great Basin. Several rounds of thunderstorms are possible beginning late this afternoon through tonight. HAZARDS/WEATHER TRENDS: IFR or LIFR conditions will prevail for all western Nebraska terminals and KCYS until 16z to 20z today. KCYS will fluctuate between VFR and IFR in fog, being on the western fringe of the low stratus deck. KCDR may remain in light fog and IFR CIGS through the day, with only brief breaks during shower or thunderstorm activity. Low confidence with timing of thunderstorm activity today and tonight. Models have trended later with convection initiation, holding off until late this evening and tonight. Added PROB30 groups to the sites with higher confidence in timing (KRWL, KBFF, KAIA, and KCDR). && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Dense Fog Advisory until noon MDT today for WYZ102-107-108-118- 119. NE...Dense Fog Advisory until noon MDT today for NEZ002-003-019>021- 054-055-095-096. && $$ SHORT TERM...TJT LONG TERM...TJT/SF AVIATION...TJT