Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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527 FXUS65 KCYS 282341 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 540 PM MDT Tue May 28 2024 .KEY MESSAGES... - Strong to severe thunderstorms mainly along and east of I-25 into the Nebraska Panhandle Wednesday afternoon with large hail and strong winds. - Active weather pattern will continue through the weekend with daily chances for showers and thunderstorms. - Summertime temperatures will be on the horizon next week. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 155 PM MDT Tue May 28 2024 Visible satellite imagery shows clouds developing over the high terrain early this afternoon. From this, a few isolated showers and thunderstorms are likely to develop later this afternoon. Per Hi-Res guidance, any storms that develop will stay confined to the Interstate 80 corridor in southeast Wyoming. Both surface observations and model soundings show dry low-levels across the area, so expect high-based storms with little to no rain and strong, erratic winds. Could also see a few dry lightning strikes with these storms as well. Showers and storms will dissipate later this evening. Overnight, a LLJ will develop over the Nebraska panhandle. Besides being a bit breezy in the panhandle overnight, south to southeasterly flow will advect warm moist air into the eastern half of the CWA. This will steadily increase dewpoints, leading to the potential for some patchy fog, but will also help set the stage for severe weather on Wednesday. A few different dynamics at play will help spark potentially severe convection across our eastern plains Wednesday afternoon. A strong shortwave will move into the northern Rockies, increasing PVA across the the CWA. At the surface, a trough across eastern Wyoming will keep southerly winds and moisture advection into the panhandle. This moisture will keep dewpoints in the upper 40s to potentially low 50s across western Nebraska, favorable for the development of storms. Most Hi-Res guidance has storms developing off the high terrain during the early afternoon and pushing eastward into the plains throughout the afternoon and evening. Early on, storms will most likely be discrete, leading to more of a hail threat. Still some model discrepancies regarding how much MUCAPE will be present, which will likely affect hail size and how many storms could contain large hail. But a safe bet, based on the HRRR and GEFS will be roughly 1200 to 2000 J/kg of MUCAPE. This could lead to hail up to ping pong ball size. As storms push further east, they will become clusters, and lead to more of a wind and strong outflow threat, with possibly a few embedded hailers. By the evening, most of the storms will have pushed out of the CWA. && .LONG TERM /THURSDAY THROUGH MONDAY/... Issued at 155 PM MDT Tue May 28 2024 The main concern with this portion of the forecast is when the best chances of convection will be through the remainder of the week into the weekend. After an active day on Wednesday, we are looking at a frontal boundary moving through the forecast area late Wednesday night into Thursday morning. This front will bring breezy and drier conditions to the area on Thursday which will limit our convection chances compared to Wednesday. Some locations such as Arlington and I-80 summit may even see some 45 to 50 mph wind gusts Thursday morning into the early afternoon after the front passes through due to some decent winds aloft combined with downward vertical motion. Still cannot rule out a few isolated showers and thunderstorms developing along the southern Laramie Range on Thursday afternoon, and affect parts of the I-25 corridor during the late afternoon. However, we are not confident that this convection will hold on past sunset especially if anything that does develop closer to the I-80 corridor may peel off to the southeast in response to the steering flow turning northwest and weak instability. Although, still cannot rule some potential for strong wind gust due to inverted V soundings. The GFS/ECMWF and NBM are showing some signs of isentropic lift around 300k early Friday morning across Nebraska panhandle in response to the low level jet and moisture advection. Therefore, we are keeping some small precipitation chances in that region. On Friday, the deterministic solutions are still showing a subtle shortwave moving through the eastern half of Wyoming. As this shortwave moves across Laramie Range, we may see more convection initiate and shift east of the I-25 corridor during the late afternoon and evening. Cannot rule the potential for more strong to severe storms especially in the southern Nebraska panhandle where the shear and instability will be the greatest. Saturday-Tuesday: Quasi-linear upper level flow will be the main theme this weekend. This will set the stage for daily afternoon showers and thunderstorms especially along and east of the I-25 corridor. Not confident about the severe potential at this point, but the GFS/ECMWF are showing some signs of subtle shortwaves moving through, but the exact timing of these shortwaves is uncertain at this time. WPC clusters are still showing signs of the upper level ridge building over the area next week. If this continues to pan out, we will mostly likely see a switch to summertime temperatures. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 540 PM MDT Tue May 28 2024 Broad upper level ridge axis will remain over the area tonight ahead of the next cold front. A weak disturbance aloft will result in a few showers and thunderstorms over southeast Wyoming this evening, mainly impacting KCYS and KLAR through 03z. Higher coverage of thunderstorms expected for Wednesday afternoon across most of the region. HAZARDS/WEATHER TRENDS: Generally VFR conditions expected this evening and tonight with increasing winds across western Nebraska due to the low-level jet between 03z and 11z Wednesday. For KLAR and KCYS, gusty winds over 30 knots and brief MVFR conditions with locally heavy rainfall possible, but coverage will be less than 20 percent, so will keep VCTS in the TAF for now. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...SF LONG TERM...REC AVIATION...TJT