Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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356 FXUS63 KUNR 150840 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 240 AM MDT Sun Sep 15 2024 .KEY MESSAGES... - Very warm through Tuesday with near critical fire weather conditions - Strong/severe thunderstorms possible late today/this evening - Pattern change end of next week with cooler and wetter weather likely && .DISCUSSION...(Today Through Saturday) Issued at 233 AM MDT Sun Sep 15 2024 08z surface analysis had trough from central ND into western NE. Dry line from MT/ND border through southwest SD. Water vapour loop had upper trough dropping into the western CONUS with southwest flow over the northern Plains. Next upstream shortwave of interest over southern NV. Today/tonight, NV shortwave moves into the CWA tonight. Weak low develops along dry line with southeasterly boundary layer flow promoting influx of richer moisture into western SD. Steep mid- level lapse rates will contribute to 2KJ/kg MLCAPE by late afternoon ahead of dry line. 0-6km bulk shear around 35kts. If MLCIN erodes, should see convection in/near Black Hills by mid- afternoon, expanding regardless as shortwave approaches this evening. PWATs surge to 150-200% of normal tonight as moderate MUCAPE persists. Most CAMS depict isolated strong/severe storms late this afternoon/early this evening where marginal risk is painted and then a blob of welcome precipitation overnight over western SD on nose of low level jet. Even though the probability of >0.25" QPF (HRRR) is low, suspect some folks will hit the jackpot under the stronger thunderstorms. Temperatures will be near guidance. Monday, subsidence behind shortwave promotes mostly dry weather as upper trough moves into the Rockies. Tight pressure gradient creates southerly wind gusts in excess of 40 MPH over south- central SD. Temperatures will be near guidance. Tuesday, upper trough lifts into the region with Fall-like synoptic forcing Tuesday night. Widespread showers/thunderstorms will occur with a 50% chance of >0.10" QPF for much of the CWA. Temperatures will be near guidance. Wednesday through next weekend, high probability that upper trough/moist cyclonic flow slowly settles into the northern Plains. A welcome pattern change. Thermal profiles cool with highs struggling to exceed the 60s next weekend. && .AVIATION...(For the 06Z TAFS Through 06Z Sunday Night) Issued At 930 PM MDT Sat Sep 14 2024 Some patchy fog with MVFR/IFR conditions may form across north central SD early Sunday morning. Thunderstorms are expected over SW SD late Sunday afternoon and evening with gusty winds and small hail possible. Otherwise, VFR conditions are expected through the TAF period. && .FIRE WEATHER... Issued At 233 AM MDT Sun Sep 15 2024 Elevated to near critical fire weather conditions expected through Monday (possibly stretching into Tuesday), especially over northeastern WY and far southwest SD where minimum relative humidities will dip to 10-20%. The strongest winds today and Monday look to be east of the Black Hills, so probabilities for widespread critical fire weather conditions over northeast WY and far southwest SD is low (joint probability of <15% RH and wind gusts >25 MPH is less than 25% this afternoon). A wetter and cooler pattern will develop mid to late next week. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Helgeson AVIATION...JC FIRE WEATHER...Helgeson