Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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924 FXUS63 KUNR 021708 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1108 AM MDT Tue Jul 2 2024 .KEY MESSAGES... - Organized severe thunderstorms possible Wednesday - Coolish 4th of July - Warming (and probably drier) pattern starts Friday && .DISCUSSION...(Today Through Monday) Issued at 147 AM MDT Tue Jul 2 2024 07z surface analysis had cool front from the eastern Dakotas into southern WY, which then wrapped northwest into lee trough from central MT into central WY. Water vapour loop had mean upper trough from AB/SK into western WY with embedded shortwave emerging from southern ID. Regional radar loop depicted increasing returns ahead of wave as it interacts with surface features. This will be the main weather feature for today. Today, shortwave moves through southern WY into northern NE. Most guidance depicts cluster of showers/TS scooting across southern half of CWA with PoPs quickly decreasing northward. Weak buoyancy expected with decent 0-6km bulk shear. Probabilities of organized strong/severe thunderstorms is low today. Temperatures will be tricky with cloud cover/precipitation modulating morning temperatures downward, but afternoon solar insolation may be sufficient for most places to reach guidance. Tonight, subsidence behind shortwave will promote mostly dry and seasonally cool temperatures. Wednesday, shortwave drops out of Canada into the northern Plains pushing lee trough/frontal boundary into the Black Hills. Return flow ahead of it brings tongue of 1KJ/kg+ SBCAPE from the Black Hills into far southern SD. 0-6km bulk shear around 45kts. Joint probabilities (SBCAPE > 500J/kg, SBCIN < 25J/kg, 0-6km bulk shear >30kts) 50%+ for these locations, reflected in SPC Day 2 outlook. CAMS suggest early start to strong/severe convection, perhaps by 19z with supercells initially. Large (very large) hail, damaging winds main threat, but a tornado cannot be ruled out near the dry line/surface boundary in far southwestern SD. Temperatures will be near guidance. Wednesday night/Independence Day looks unsettled and cool as upper trough spins through the northern Plains bringing cold pool aloft and showers/TS. How wet/cool is not clear given ensemble guidance, but the weather should improve later in the day/evening for planned outdoor activities. Looking ahead, upper ridge over the western CONUS whisks thermal ridge into the area. However, proximity to northwest flow from central Canada into the Midwest could promote the intrusion of a couple of fronts/waves and convective chances. Odds are overall, it will be warmer/drier for Friday through early next week. && .AVIATION...(For the 18Z TAFS Through 18Z Wednesday) Issued At 1106 AM MDT Tue Jul 2 2024 Isolated to scattered thunderstorms will continue this afternoon and evening, diminishing by midnight. Outside of thunderstorms, VFR conditions will prevail through the forecast period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Helgeson AVIATION...Pojorlie