Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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066 FXUS65 KCYS 091742 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1140 AM MDT Sun Jun 9 2024 .KEY MESSAGES... - Areas of (locally dense) fog will persist through mid-morning across the high plains of southeast Wyoming and the western Nebraska Panhandle. There will be a risk for a couple of strong thunderstorms in the vicinity of the central and northern Laramie Range later this afternoon. - A more widespread threat for showers and thunderstorms will occur with a cold frontal passage on Monday afternoon and evening. A few storms may be severe. - Mainly dry and rather warm conditions will prevail for Tuesday through Thursday, with increasing chances for showers and thunderstorms for Friday and Saturday, along with slightly cooler temperatures. && .SHORT TERM /THROUGH MONDAY/... Issued at 352 AM MDT Sun Jun 9 2024 Widespread fog & low-level stratus has developed across the high plains of southeast Wyoming & the western Nebraska Panhandle, in response to southeasterly low-level upslope & residual low-level moisture from earlier convection. Surface observations & webcams indicate fog has become quite dense over mainly southern Kimball County w/ visibilities being reduced to one quarter of a mile or less. The lowest visibilities have been fairly localized so far, but would not be surprised to see this expand in coverage across the area over the next few hours. This could require a Dense Fog Advisory prior to sunrise, but decided to hold off for now until the area of fog becomes a bit more widespread. Visibilities will most likely improve by mid-morning, but would expect to see low- level stratus persist through at least early afternoon given the favorable wind/moisture profiles. The westward extent and temporal residency of the fog/stratus is expected to significantly impact convective coverage today, with high-res models generally keeping showers and storms confined to the higher terrain. A few ripples in the mid & upper-level flow, along with deep/moist southeasterly low-level upslope & enhanced low-level convergence along the central & northern Laramie Range should support convective initiation near Laramie Peak by mid to late afternoon. This activity will most likely follow the narrow instability axis just west of I-25, courtesy of the differential heating resulting from earlier clouds. The overall severe threat is fairly low with only around 1000 J/kg of CAPE and very modest vertical shear, but any storm in this environment would have the potential to become strong to marginally severe hail. There is a MRGL Risk for this area, per SPC. A more widespread convective threat is expected Monday, with the passage of another cold front. Pre-frontal air mass will be very warm and unstable w/ dew points in the lower to middle 50s along with widespread surface temperatures in the 80s supporting steep mid-level lapse rates & resultant CAPEs up to 1500 J/kg. Overall shear profiles appear fairly modest, but decent veering profiles should support 30+ knots of effective bulk shear & the resulting potential for organized strong to severe storms. The DY2 outlook from SPC has much of extreme eastern Wyoming and the western Neb Panhandle in a SLGT Risk for Monday. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Issued at 352 AM MDT Sun Jun 9 2024 Monday night/Tuesday...Scattered showers and thunderstorms will end from west to east Monday evening, mainly east of I-25. Northwest flow aloft remains, though with increasing heights aloft along with warmer temperatures, and a decrease in low and mid level moisture, we should see less coverage of late day showers and thunderstorms. Wednesday...Even warmer as the flow aloft turns westerly, and with 700 mb temperatures near 17 Celsius, maximum temperatures will be in the mid 80s to mid 90s. Warmer temperatures aloft will increase the convective inhibition, and with less low and mid level moisture around, it looks like it will be dry. Thursday...Similar synoptic pattern as on Wednesday, though low level winds will become northeast, and with an increase in low and mid level moisture, we expect to see isolated late day showers and thunderstorms. Perhaps a few degrees cooler than Wednesday with upslope winds and more cloud cover. Friday...Ridging aloft, over our forecast area, begins to break down as the next shortwave trough aloft approaches, and with surface lee trough convergence and an increase in atmospheric moisture, we expect scattered late day showers and thunderstorms. Slightly cooler with an increase in cloud cover and precipitation coverage. Saturday...Looks like we will likely see a shortwave trough aloft passage around peak heating, helping to spark scattered late day showers and thunderstorms. Maximum temperatures look similar to those of Friday. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 1140 AM MDT Sun Jun 9 2024 Low clouds and patchy fog will slowly lift and dissipate early this afternoon for the western Nebraska terminals and KCYS through 20z. A quick moving upper level ridge axis will be overhead today, and combined with the low stratus, may greatly limit shower and thunderstorm potential today and this evening. HAZARDS/WEATHER TRENDS: Expect KCYS to hold onto IFR CIGS for the next hour (19z) before low clouds lift and dissipate. VFR expected after 20z for the rest of the afternoon and into the evening hours. Some patchy fog or low clouds may reform tonight, but should primary impact KCYS and KSNY with brief IFR possible towards sunrise Monday. && .HYDROLOGY... Issued at 254 PM MDT Sat Jun 7 2024 Above normal temperatures have resulted in accelerated mountain snowmelt across the Rocky Mountains. Temperatures in the Snowy and Sierra Madre Ranges are expected to remain elevated this weekend. Flood warnings for snowmelt continue for the Little Laramie River west of Laramie, and the Encampment River south of Saratoga, mainly due to minor flooding concerns. Emergency Managers have reported some flooding in these areas over the last 48 hours. Flood Watches continue for the upper North Platte River valley and Medicine Bow River near Elk Mountain for potential impacts this weekend. Current forecasts suggests river levels will peak later this weekend and remain elevated into early next wee. Will continue to monitor the potential for locally heavy rainfall due to thunderstorms in and around the mountains this weekend. However, the last round of thunderstorms generally produced less than a quarter inch of rain Saturday afternoon. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...CLH LONG TERM...RUBIN AVIATION...TJT HYDROLOGY...WFOCYS