Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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033 FXUS63 KUNR 031123 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 523 AM MDT Wed Jul 3 2024 .KEY MESSAGES... - Organized severe thunderstorms possible this afternoon/evening - Coolish 4th of July - Warmer and progressively drier pattern starts Friday - Hot/dry weather develops next week && .DISCUSSION...(Today Through Tuesday) Issued at 156 AM MDT Wed Jul 3 2024 07z surface analysis had lee trough from central MT into northeast CO. Weak shortwave ridge passing through CWA with quiet weather in place. Upstream wave of interest over southern BC/AB, the main weather maker for the short term. Today/tonight, BC/AB shortwave drops southeast into the northern plains. Surface low develops over central WY along strengthening lee trough and developing weak warm front extending from low into northern NE. Southeasterly upslope flow will promote 1KJ/kg mean SBCAPE (per HREF) from the Black Hills into southern SD by mid- afternoon. Some guidance significant higher, but some lower, so confidence in moisture return a bit shaky. Afternoon buoyancy values most uncertain over northeastern WY as afternoon mixing modulates boundary layer. Forecast hodographs depict significant lengthening with 45-60kts 0-6km bulk shear by evening over much of the CWA. Hodograph shapes initially suggest splitting supercell potential with right movers dominant by evening near surface boundaries. CAMS suggest convective initiation around 19z over northeastern WY, spreading into the Black Hills/southern SD by mid-afternoon. Large/very large hail and damaging winds possible with an isolated tornado near surface boundaries. Some guidance suggests a secondary round of strong/severe convection as main synoptic forcing arrives later this evening, but atmosphere will be worked over. Beneficial rains welcome, however. Temperatures should be near guidance. Coolish/unsettled Independence Day foreseen as shortwave spins across the eastern Dakotas leaving moist/cyclonic flow over the area. Popcorn showers/thunderstorms likely, but not necessarily an all-day rain with subsidence/drying ramping up Thursday evening. Temperatures will be near/slightly below guidance given expected clouds/precipitation. Friday through Sunday, western CONUS upper ridge promotes slowly amplifying thermal ridge over the northern plains. Northwest flow aloft portends small pops as a couple of inevitable waves wiggle through the northern Plains per northwest flow. Next week, confidence is increasing that large scale upper/thermal ridge will dominate with increasingly dry/hot weather developing. Probability of MaxT >= 90F 25-50% in the west Wednesday increasing to 50-75% most areas by Friday. && .AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning) Issued At 520 AM MDT Wed Jul 3 2024 Scattered showers and thunderstorms will develop after 17-18z across NE WY and western SD. Gusty, erratic winds and large hail can be expected near any stronger cores. Expect transient MVFR conditions near any stronger convective cores. Otherwise, VFR conditions will prevail outside of showers and storms through the forecast period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Helgeson AVIATION...SE