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Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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979 FXUS65 KCYS 110935 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 335 AM MDT Sun Aug 11 2024 .KEY MESSAGES... - Near critical fire weather conditions return to Carbon county today along with areas of smoke and haze due to distant wildfires. - Much lower thunderstorm coverage is expected this afternoon, but storms that manage to form may quickly become strong to severe. - An active pattern continues through the week ahead with near normal temperatures and daily chances for afternoon and evening showers and thunderstorms. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 330 AM MDT Sun Aug 11 2024 Another round of nocturnal showers is moving across the area this morning, fueled by modest synoptic lift ahead of the next upper level shortwave trough. That features is moving across western Wyoming at this hour, with its axis expected to cross through the forecast area late this morning or early this afternoon. Once the axis passes through, we`ll see synoptic scale subsidence take over which will significantly limit today`s thunderstorm coverage. Meanwhile, plentiful moisture remains in place in the lower atmosphere with weak upslope flow supporting another round of low clouds and fog over the High Plains. This is less thick and widespread than the last few mornings, but travelers should still prepare for patchy low visibility in fog this morning. Any lingering fog will clear by midday. Today will be a dry outlier in the middle of a cool and wet weather pattern. A developing surface low pressure system over northeast Colorado by this afternoon is expected to pull in much drier air along the I-80 corridor. This dry region is visible on GOES satellite water vapor channels moving across southern Idaho at this hour. Breezy westerly winds and low RH will return near critical fire weather conditions to Carbon County, while forming a sharp dryline in the vicinity of I-25. The progressive dryline and a convergence zone along the WY/CO border will provide the best potential to produce thunderstorms this afternoon, but coverage will be much lower than Saturday. However, any isolated storms that manage to develop over the High Plains in the rich moisture environment will exist in a fairly potent environment with decent vertical wind shear, lapse rates, and instability. Thus, we are looking at a conditional threat for severe thunderstorms today, contingent on thunderstorm updrafts overcoming the synoptic subsidence in the wake of the shortwave trough aloft. Large hail, strong winds, and locally heavy rainfall will also be possible. Directional shear in the lowest 1-2km also means that an isolated landspout or tornado can`t be totally ruled out. On the bright side, the window for storms will be fairly short today with synoptic subsidence and dry air winning out by around 6PM. In addition to the drier air making intrusions today, this trough may bring another round of smoke and haze from distant wildfires. The dry air break of Sunday will be short lived though as the ridge axis shifts back to eastern Wyoming during the day Monday. Southwest flow across the Great Basin will allow for monsoon moisture to rapidly fill back into the area for Monday. With a continuous train of vorticity maximums also returning, we`ll kick off another round of scattered to numerous afternoon and evening showers and thunderstorms Monday afternoon, which may carry well into the evening hours once again. Monday`s storms will once again bring the chance for heavy rainfall and isolated strong winds and large hail. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Issued at 330 AM MDT Sun Aug 11 2024 An active extended forecast period for southeast Wyoming and the western Nebraska Panhandle w/ numerous mid and upper-level short wave disturbances embedded within quasi-zonal flow aloft. Expect daily chances for showers and thunderstorms as several pieces of energy continue to emanate from the slow moving parent trough in the Pacific Northwest. Multiple rounds of strong/severe thunder- storms appear possible given substantial low-level moisture with dew points in the 50s and 60s and occasional mid-level jet maxes contributing to adequate deep layer vertical shear for organized storms. Still too early to determine any specifics of which days may feature a more organized severe risk as this will be heavily dependent on the eventual timing of individual waves. Otherwise, expect temperatures to be near seasonal norms with daytime highs mainly in the 80s. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 1059 PM MDT Sat Aug 10 2024 Scattered showers and thunderstorms will continue overnight across the area. Light to moderate rain is expected, which could briefly drop visibility down to MVFR criteria. Low stratus is also likely with southeasterly flow overnight. IFR CIGs will be possible, mainly at KSNY and KAIA. MVFR CIGs will be possible around KCYS and potentially KBFF and KCDR. Expect an isolated storm or two, mainly in the Nebraska panhandle during the afternoon. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MN LONG TERM...CLH AVIATION...SF