220 FXUS63 KUNR 191117 AFDUNRArea Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 517 AM MDT Fri Sep 19 2025
.KEY MESSAGES...
-Dry and warmer this weekend
-Rain chances return early next week
-Growing uncertainty in forecast details much of next week given tendencies for a blocking pattern with a wandering upper low
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.DISCUSSION...(Today Through Thursday) Issued at 115 AM MDT Fri Sep 19 2025
Mean trough over the Northern Plains will continue to slowly shift east today, allowing for warmer and dry weather for the weekend. Backside impulse and associated potent jet streak continues to graze the southwest third of the FA with scattered showers and isolated thunderstorms there. This activity will quickly shift southeast out of the FA this morning. Low clouds and fog expected to develop this morning across much of western SD, with patchy dense fog possible along the eastern slopes of the Black Hills into NW SD. Skies are expected to clear west to east later today, with portions of the SD Plains toward central SD expected to see clouds most of the day. This will allow for a gradient of temps across the FA, with 70s for highs in the west to around 60 far east. Dry air will advect into the region tonight aloft. However, light winds, clear skies, and lingering low level moisture will support fog on the SD Plains. Added a mention to the forecast. Much warmer this weekend with highs in the 70s and 80s under mostly sunny skies. Deep upper trough in the northeast Pac will split this weekend with a frontside impulse traversing the northern Rockies. This system will support a cold front into the region Monday, with breezy northwest winds expected. Forecast models close this low off while offering a blocking ridge over the western CONUS. This sets the stage for poor model performance. Hence, low confidence in forecast details beyond Monday, particularly precip chances. The latest runs suggest keeping the low over/near the region through Tues, with rain chances in that period, the solution the NBM has offered. However, this will likely change as the pattern evolves. The Rockies ridge will eventually shift east later in the week, supporting warmer temps into the region when it does.
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.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning) Issued At 514 AM MDT Fri Sep 19 2025
MFR to IFR conds can be expected on the SD Plains this morning, with local LIFR in fog on the Plains north of the Black Hills. Conds will improve to VFR later this morning and afternoon west to east. Patchy fog will be possible once again on the SD Plains late tonight.
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.UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. &&
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DISCUSSION/KEY MESSAGES...JC AVIATION...JC
NWS UNR Office Area Forecast Discussion