Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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096 FXUS65 KCYS 122054 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 254 PM MDT Sun May 12 2024 .KEY MESSAGES... - Trending warmer through Monday, but remaining unsettled with daily chances for showers and storms through mid-week. Severe weather is not expected. - A cold frontal passage is expected on Wednesday, with much of the region returning to below-normal temperatures and increased chances for rain and high-elevation snow. && .SHORT TERM /THROUGH TUESDAY/... Issued at 249 PM MDT Sun May 12 2024 Regional radar currently shows widely scattered high-based showers and storms across the the CWA. There is enough instability, especially east of the Laramie Range, to possibly get pea to dime sized hail out of some thunderstorms this afternoon. The dry low- levels and inverted-V soundings could also lead to a few stronger wind gusts with storms as well. Storms will continue throughout the afternoon hours before finally dissipating this evening, per Hi-Res guidance. Clouds will likely clear out by later this evening, which will lead to unobstructed views of the auroras across most of the CWA. The CWA will sit sandwiched between two shortwaves on Monday. This will lead to shallow ridging over the Rockies and a warmer, above average day across the area. Unfortunately, the ridging won`t be enough to keep unsettled weather away. Weak disturbances within the ridge will spark another round of scattered convection across the CWA later in the afternoon. Severe storms look unlikely based on model soundings, however, small hail and strong wind gusts could be possible yet again. Potentially looking at a better chance for storms on Tuesday as the western shortwave makes it into Wyoming. Both the GFS and ECMWF do differ a bit, with the ECMWF showing more numerous and widely scattered storms as the shortwave directly impacts the CWA. GFS soundings do show CAPE values below 1000 J/kg, but continue to show inverted-V soundings. Therefore, smaller hail and gusty winds will be the primary threats. However, higher dewpoints across the Nebraska panhandle and northern tier of the CWA could lead to some marginally severe storms. Aside from storms, the incoming shortwave will lead to cooler temperatures and windy conditions for the usual wind prones and for areas west of the Laramie Range. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Issued at 249 PM MDT Sun May 12 2024 The long term forecast will start off active as numerous showers and thunderstorms look possible mid-week. The weather will quiet down towards the end of the week as a ridging pattern takes hold of western CONUS. A shortwave digging down from the Pacific Northwest on Tuesday will likely spark widely scattered showers and thunderstorms during the afternoon and into the overnight hours. A vorticity max over the CWA, as well as a weaker 250 mb 85 kt jet streak just north of the CWA will provide some of the ingredients needed to get thunderstorms. Location of the jet streak puts the CWA in the right entrance region, which is favorable for lift and the development of potentially stronger storms. GFS soundings from Tuesday afternoon into Tuesday evening do show areas of instability, with over 1000 J/kg of MUCAPE in parts of the CWA. There are even some impressive effective shear values over the northern tier of the CWA, with both Douglas and Chadron showing 35 kts EBWD. Because of this, cannot rule a few marginally severe to severe thunderstorms. Based on current sounding profiles, the main concern would likely be the potential for severe hail. This would mainly be in the northern tier of the CWA, as well as the Nebraska panhandle. Showers will likely become more numerous Tuesday night as the shortwave pushes into Wyoming, bringing with it more mid-level moisture. Showers will continue into the day Wednesday with the shortwave passing over the CWA. Cooler temperatures are expected with this shortwave which will lead to a more stable environment with less of a chance of thunderstorms developing. Could still hear a rumble of thunder or two, but it will predominately be rain showers across the area. With the shortwave pushing off to the east Wednesday night, expect a warmer and drier end to the week as an upper-level ridge builds over western CONUS. Temperatures will warm up above average across the CWA on Thursday and Friday, with minimal chances for precipitation both days. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1140 AM MDT Sun May 12 2024 An upper level disturbance over eastern Colorado will continue to track eastward into the Great Plains today. Showers and thunderstorms are forecast to redevelop over most of southeast Wyoming and western Nebraska this afternoon. HAZARDS/WEATHER TRENDS: Overall, VFR conditions are expected through tonight with very low probabilities for IFR or lower conditions associated with fog or heavy rainfall. Showers and thunderstorms will continue to develop between now (18z) and 23z, with some heavy showers expected and brief MVFR to near IFR conditions possible. The most favorable location to see these conditions in the near future is KSNY, so kept the tempo group going. Otherwise, kept VCSH for most other terminals. Probability for fog tonight is very low...below 5 percent. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...SF LONG TERM...TJT AVIATION...TJT