Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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017 FXUS65 KCYS 091038 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 438 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 /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1149 PM MDT Sat Jun 8 2024 Ridging aloft will develop and move over the area today, with moist southeast low level winds aiding in keeping in areas of low clouds much of the day. Wyoming TAFS...For Rawlins and Laramie, expect scattered clouds from 10000 to 12000 feet, otherwise skies will be clear. Winds will gust to 24 knots at Laramie after 02Z. For Cheyenne, expect ceilings near 11000 feet until 10Z, then ceilings will range from 100 to 1200 feet until 20Z, with areas of fog reducing visibilities to one mile or less from 10Z to 15Z. Thunderstorms will be in the vicinity from 20Z to 02Z with ceilings near 3500 feet, then scattered clouds around 10000 feet will occur after 02Z. Winds will gust to 18 knots after 20Z. Nebraska TAFS...For Chadron, ceilings will range from 4000 to 10000 feet until 02Z, then skies will be clear. Thunderstorms will be in the vicinity from 21Z to 02Z, with winds gusting to 24 knots after 02Z. For Alliance, Scottsbluff and Sidney, scattered clouds near 10000 feet will occur until 08Z, then ceilings will lower to 700 to 2500 feet until 18Z, then improve to 3500 feet until 02Z, then scattered to broken clouds near 15000 feet will occur. Thunderstorms will be in the vicinity from 18Z to 02Z. Winds will gust to 25 knots after 15Z. && .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...RUBIN HYDROLOGY...WFOCYS