175 FXUS63 KFSD 170908 AFDFSDArea Forecast Discussion National Weather Service Sioux Falls SD 408 AM CDT Wed Sep 17 2025
.KEY MESSAGES...
- Periodic showers and storms are expected today, with locally heavy rainfall the main threat though some weak funnels can`t be ruled out.
- Rainfall totals today into tonight will be around a half an inch for most of us, though locally higher amounts up to an inch or more are possible mainly north of I-90 (20-40% chance).
- Continued rain chances and cloudy skies will keep temperatures mainly cooler than normal through the start of the weekend, though another warm-up is possible heading into next week.
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.DISCUSSION... Issued at 355 AM CDT Wed Sep 17 2025
A steady light to moderate rain continues along the Missouri River Valley early this morning, with widely scattered showers and pulse storms elsewhere. Expect a re-invigoration of showers and storms as a shortwave from the main upper-low just off to our west pivots through the area this morning. After this morning push, some drier air may try to enter into the system and create another lull in at least some of the heavier rain/storm activity for the early afternoon. Guidance currently indicates the surface low lifting north into central South Dakota through the day today, leaving most of the area east of the circulation and so we`ll have to watch developing confluence bands later today as the focus for additional showers and storms late this afternoon into the evening. The tricky part of the forecast today is nailing the location of where these bands set up, but tall, skinny CAPE profiles are likely and so the threat for severe weather is low, but storms will likely produce locally heavy downpours. Some minor urban and small stream flooding will be possible in these storms and so a broad Marginal Risk is in place for excessive rainfall. The best chance for this thunderstorm activity will be east of I-29 where some breaks in the cloud cover may lead to more destabilization. Can`t rule out a few weak funnels with this activity, but tornadoes are not expected. Highs today will be running from the upper-60s west where cloud cover will be greatest, to the low-80s east where more cloud breaks are likely and where we`ll be squarely in the warm sector.
For tonight, the low pressure system will meander around the area, centered over south-central South Dakota. We`ll continue to see waves of showers develop east of the low`s center, but coverage will likely be more widely scattered as instability wanes. Still enough CAPE for some rumbles of thunder overnight, but torrential downpours appear less likely compared to what we`ll see this afternoon. Temperatures tonight will drop to the upper-50s to low-60s. In terms of rainfall for today into tonight, we`ll see around a half an inch of rain for most of the area, but locally up to an inch to an inch and a quarter will be possible, with GEFS and ECMWF ensemble probabilities of an inch plus of rain highest (20-40%) north of I-90.
The upper-low will begin to lift north on Thursday, but as another shortwave pivots into the area, more showers and storms are expected through the day. A second upper low coming out of southern Canada on Friday will finally provide the kick to start gradually getting the rain and storms out of the area from west to east. With that said, rain and storms are still likely on Friday, especially east of I-29 (50-70% chance). Small shower chances (
NWS FSD Office Area Forecast Discussion