Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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405 FXUS63 KUNR 220828 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 228 AM MDT Wed May 22 2024 .KEY MESSAGES... - Compact upper low brings storms, wind, bit of snow later Thursday into Friday - Relatively active pattern expected through Memorial Day weekend - Upper level ridge brings milder and drier weather mid-week next week && .DISCUSSION...(Today Through Tuesday) Issued at 223 AM MDT Wed May 22 2024 08z surface analysis had deep low over the MN arrowhead with weak high over WY. Water vapour had shortwave over KVTN with leftover deformation zone showers finishing up from KIEN-KICR. Drier air filtering into the CWA per westerly low level flow. Next weather maker over southwest BC per water vapour loop. Today, weak shortwave ridge drifts through bringing drier/milder air to the CWA. Residual moisture may allow isolated shra/TS over the Black Hills during peak insolation. Temperatures will be near guidance. Tonight, BC upper low moves into northwest WY spinning up surface low over eastern WY. Low level jet develops over the western SD plains with modest theta-e advection and low/unmentionable pops on the plains. Low will be near guidance. Thursday into Friday, compact upper low strengthens as it moves across the CWA. Surface low elongates and deepens as it splits along surging dry-line. Narrow tongue of 1-1.5KJ/kg SBCAPE pools ahead of dry-line over central SD with 25-35kt 0-6km bulk shear. TSRA should develop east of the Black Hills later afternoon and exit the CWA by early evening. Isolated severe thunderstorms possible, with CAMS targeting south-central SD. On back side of upper-low deformation zone forcing robust with moisture wrapping back into northeastern WY/northwestern SD where there is a 50-75% chance of >0.25" QPF. Forecast soundings cold enough for some snow over the highest Black Hills (10-30% chance 1-2"). As colder air surges into CWA Thursday night, 3-5mb/3hr pressure rises possible which would support headline winds(40-70% chance 40kt+ wind gusts on western SD plains), particularly just east of the Black Hills (50%+ chance 48kt+ wind gusts). EFI guidance supports. Have trended forecast toward NBM50/90th percentile to account. Drier air will end precipitation Friday afternoon. Temperatures will be near guidance. Saturday, weak disturbance supports low PoPs. Another upper low drops in for Sunday with increased chances for thunderstorms, lingering into Memorial Day. Upper ridge looks to bring milder/drier weather into the middle of next week. && .AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night) Issued At 915 PM MDT Tue May 21 2024 MVFR conditions in low clouds/showers across parts of northeastern WY, BH, and southwestern SD will improve to VFR overnight as showers dissipate and skies clear. VFR conditions will then continue through the rest of the TAF period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Helgeson AVIATION...Pojorlie