Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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413 FXUS63 KUNR 240442 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1042 PM MDT Thu May 23 2024 .KEY MESSAGES... - Compact upper low brings active thunderstorms, wind, and a bit of snow later this afternoon through early Friday - Relatively active pattern expected through Memorial Day weekend - Upper level ridge brings milder and drier weather mid-week next week && .DISCUSSION...(Today Through Wednesday) Issued at 213 AM MDT Thu May 23 2024 08z surface analysis had low over central WY, which is in response to upper low per water vapour spinning over far southwest MT. 35-45kt low level jet (per KUDX VAD/RAP forecast) east of Black Hills producing modest theta-e advection over ND/eastern SD and ACCAS/sprinkles. Effect of upper low main forecast concern in the short term. Today through Friday, upper low rolls through the CWA into tonight and then lifts northeast as it opens up into the eastern Dakotas Friday. WY surface low strengthens/moves northeast as it pushes dryline/trough into the CWA today and then wraps a cold front through the CWA late this afternoon/tonight. A narrow tongue of buoyancy surges into far northern through eastern reaches of the CWA. HREF forecasts 1-2KJ/kg SBCAPE over south-central SD by 21z with 500J/kg over far northwest SD. 25-35kt 0-6km bulk shear increases to 30-40kt as jet streak ahead of upper low elongates hodographs. Should see a narrow line of active convection along dryline/trough late this afternoon with isolated severe thunderstorms (damaging wind/large hail), especially over south- central SD. If discrete supercells develop over south-central SD, very large hail is possible. Strong/severe storms will quickly move out of CWA this evening. Well-defined deformation zone precipitation shield expected over northeast WY/northwest SD (30-50% chance >0.25" QPF) and little precipitation over southwest SD per dry slot. Wet bulb zero heights low enough for 1-2" of snow (25-75th percentile) over the highest Black Hills. 3-7mb/3hr pressure rises expected behind cold front tonight, peaking late this evening. Good setup for strong/gusty northwest winds for the squeeze areas of the Black Hills, so have hoisted high wind watch/wind advisories to account. Probabilistic guidance seems low for 50kt gusts from KRAP-KRCA region given bufkit momentum transfer forecast, but EFI SoT painting strong wind potential over much of western SD. Day shift can hone the wind speeds with likely advisory expansion eastward for late tonight. Drier air ends precipitation Friday afternoon. Temperatures will be near guidance. Saturday, a weak disturbance brings a chance of precipitation, especially over the south. Another upper low/trough moves through Sunday with likely PoPs warranted given synoptic forcing/moisture availability. Lingering precipitation early Memorial Day gives way upper ridge for the middle of next week with drier/milder weather foreseen. && .AVIATION...(For the 06Z TAFS Through 06Z Friday Night) Issued At 1041 PM MDT Thu May 23 2024 A band of rain...and snow over higher elevations...will cross northeast Wyoming, the Black Hills, and northwest South Dakota early this morning. This will bring MVFR and local IFR conditions. After the precip ends late this morning, VFR conditions can be expected areawide through the rest of the forecast period. Gusty winds are expected across much of the plains through the morning hours and will then gradually decrease through the afternoon. The strongest gusts will be over the plains adjacent to the eastern Black Hills, which includes KRAP. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Wind Advisory until 2 PM MDT Friday for SDZ001-002-012-013-026- 078. Wind Advisory from 3 AM to 3 PM MDT Friday for SDZ014-032-043. Wind Advisory until 6 AM MDT Friday for SDZ027-041-075-076. High Wind Warning until 2 PM MDT Friday for SDZ031-072-073. Wind Advisory from 3 AM MDT /4 AM CDT/ to 5 PM MDT /6 PM CDT/ Friday for SDZ044-046-047-049-077. WY...None. && $$ DISCUSSION/KEY MESSAGES...Helgeson AVIATION...13