Area Forecast Discussion

KEY MESSAGES

- Strong northwesterly winds remain in place early this morning over north central South Dakota, gusting up to 40 to 50 miles per hour at times. A Wind Advisory remains in effect through 7 AM CDT / 6 AM MDT this morning.

- Dry conditions expected today before a weak disturbance tracks over the region Wednesday through the weekend bringing the opportunity for isolated to scattered showers and weak thunderstorms.

- Another round of rainfall is expected late Thursday through Friday. The highest accumulations are expected over eastern South Dakota, where probability to see an inch of rain or more ranges from 40-60%.

DISCUSSION

Issued at 239 AM CDT Tue Sep 15 2026

Satellite and webcam observations indicate a couple of patches of lingering fog this morning over eastern South Dakota (and along I-29 in Deuel County in particular) as of roughly 07Z. As winds increase over that area, the expectation is that the remaining fog will clear out over the next couple of hours. Gusty winds have arrived over north central South Dakota this morning, up to 45 to 50 miles per hour at times. Given the delayed onset of the winds and the persistence of 40+ mile per hour gusts, have extended the Wind Advisory through 12Z this morning for all counties previously under the Advisory. No additional counties have been added at this time. Winds are expected to die down through the day today as a high pressure center builds in. With this high pressure overhead, light winds, and nearly full humidity recovery overnight, another round of fog will be possible early Wednesday morning, mainly over northeast South Dakota and western Minnesota.

Over the next few days, a negatively tilted ridge will build over the Northern Plains, while and upper-level low develops over the western CONUS. This setup will allow for a warmer airmass to build into the region, increasing high temperatures by the end of the week. Latest NBM median values sit in the mid to upper 70s over nearly the entire forecast area Thursday and beyond, which is near- normal to slightly above normal.

The upper-level setup will allow for stronger winds aloft to develop a weak low pressure center with some rain out ahead. No severe weather is expected with these rain showers, and neither is much significant precipitation. Latest NBM probability of seeing a tenth of an inch through 06Z Thursday is generally less than 20 percent across the forecast area, with some pockets of 20 to 30 percent over central South Dakota.

More robust chances for rain come into the forecast area Friday into Saturday as the upper-level low mentioned in the above paragraph moves eastward into the Northern Plains. There is some disagreement on the timing within model guidance, but there seems to be strong agreement amongst the ensembles (NBM, GFS, Euro, and Canadian specifically) in the track of the highest precipitation totals. At the moment, it appears that the axis of heaviest precipitation will remain to the south, running through or just north of Sioux Falls. This means that eastern South Dakota will be the area within the Aberdeen CWA that is set to receive the most rainfall, with totals decreasing moving to the northwest. Still a fairly large degree of spread exists over eastern South Dakota, with the NBM 25th/75th percentile rainfall totals ending Saturday morning ranges from 1"-3" in total. Euro and Canadian ensembles are generally in agreement with that spread, although are perhaps a bit lower on the 75th percentiles. The GEFS is a bit of an outlier in that it is much lower, having a spread around 0.5"-1.5". Given how it verified with recent rainfall, confidence would lean against trusting those lower values. All this to say that these QPF totals raise somewhat of a red flag with regards to the flooding potential. Will dive more in- depth on the flooding risk in future discussions, but to give a brief overview: Storm motion, warm cloud layer, and high PWATs all give additional credence to the flooding threat over eastern South Dakota during this event. Through 12Z Friday, a Slight Risk Excessive Rainfall Outlook is in place for portions of eastern and central South Dakota, with a Marginal through 12Z Saturday.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1227 AM CDT Tue Sep 15 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast throughout the TAF valid period. Low-level wind shear (LLWS) potential may exist, mainly at KATY during the first few hours of the TAF valid period.

ABR WATCHES / WARNINGS / ADVISORIES

SD...Wind Advisory until 7 AM CDT /6 AM MDT/ this morning for SDZ003>005-009-010-015. MN...None.