Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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672 FXUS63 KUNR 181051 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 451 AM MDT Wed Sep 18 2024 .KEY MESSAGES... - Upper low over southeast MT will create dry gusty winds today resulting in critical fire weather conditions over portions of the SD plains - Elevated fire weather conditions Friday - Low confidence long term forecast with cooler weather for the weekend && .DISCUSSION...(Today Through Tuesday) Issued at 230 AM MDT Wed Sep 18 2024 08z surface analysis had low over KJDN with upper low stacked on top. Surface trough extended into central NE with cold front into northeastern WY. Waning band of showers/TS ahead of surface trough slowly moving north/northeast over central SD per regional radar loop. Main short term concern revolves around disposition of upper low. Today/tonight, upper/surface low spins into southwest SK pushing a cold front into the CWA this afternoon. Tight pressure gradient as well as well-mixed boundary layer will promote gusty west/southwest winds ahead of the cold front and gusty northwest winds behind the front. Bufkit momentum transfer suggests gusts to 50mph over northwest SD this afternoon/tonight and 45mph over southern SD today/this evening. HREF supports with >50% chance of 45+ mph for these locations. Will hoist Wind Advisory to account over northwest SD, but leave out where fire weather headlines are hoisted on the western SD plains. Backwash moisture will slide into the WY/MT/SD/ND border areas with showers this afternoon/tonight. Temperatures will be near guidance. Thursday, gradient slowly decreases as stacked low pulls away with slightly cooler temperatures. Friday, warm air advection will support summery MaxTs with a few spots approaching 90F. Over the weekend into early next week, progressive west/northwest flow supports a series of waves and fronts. First front moves through Friday night with noticeably cooler temperatures for the weekend. Moisture chances low with main moisture-laden upper low passing south of the CWA. Confidence is low with substantial ensemble guidance uncertainty. Chance of >0.25" QPF over the weekend <40% over southeast half of the CWA and <20% over the northwest half. Thus, lowish PoPs scattered about for the long term forecast. && .AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning) Issued At 447 AM MDT Wed Sep 18 2024 VFR conditions are expected through the day with gusty southwest winds late this morning through this evening. A few showers are possible this afternoon into tonight across northeastern Wyoming and northwestern South Dakota. MVFR/IFR ceilings could spread into far northeastern Wyoming/northwestern South Dakota tonight. && .FIRE WEATHER... Issued At 230 AM MDT Wed Sep 18 2024 Upper low over eastern MT will promote subsidence, deep boundary layer mixing, and a tongue of very dry air (HREF >70% chance <20% RH) over southwest into central SD this afternoon. Gusty west/southwest winds foreseen, sufficient to hoist a Red Flag Warning this afternoon and early evening. Northeastern WY/northwestern SD will see elevated fire weather conditions per gusty winds and MinRH dipping to 20-30%. Some relief expected Thursday, but elevated fire weather conditions return Friday with MinRH 15-30%. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Wind Advisory from noon today to noon MDT Thursday for SDZ001- 002-012-078. Red Flag Warning from noon MDT /1 PM CDT/ today to 8 PM MDT /9 PM CDT/ this evening for SDZ322-324>326-329>335. WY...None. && $$ DISCUSSION/KEY MESSAGES...Helgeson AVIATION...7 FIRE WEATHER...Helgeson