277
FXUS63 KFSD 122338
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
638 PM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Scattered light rain and sprinkles move in around daybreak
  tomorrow and gradually dissipate by mid-day. Precipitation
  amounts will be light with a slow temperature recovery towards
  70 degrees in the afternoon.

- Scattered rain and non-severe thunderstorms arrive by daybreak
  Monday. A brief, localized, and conditional risk for severe
  storms develops Monday afternoon in NW Iowa and NE Nebraska.

- Near normal temperatures for the rest of the week with
  increasing rain chances during the second half of the week.

&&

.DISCUSSION...
Issued at 106 PM CDT Sat Sep 12 2026

THIS AFTERNOON: A perfect early fall Saturday across the region as
any lingering sprinkles to showers have move away from the area.
Quiet conditions will continue into the evening with winds
eventually turning light and variable after 00Z.

TONIGHT:  Temperatures will fall quickly this evening towards the
40s before upper and then mid-lvl clouds increase after midnight.
The settling of a mid-lvl trough into the Dakotas will increase mid-
lvl dPVA but also layered frontogenesis focused at the 850 mb level
near and south of the Missouri River and 700:600 mb frontogenesis
near or north of Highway 14.  CAMs and some lower resolution
guidance struggling on the placement of this lift, leading to a
higher than typical spread in PoPs by time lift is maximized near or
after daybreak. High cloud bases will keep QPF light.

SUNDAY: Morning light sprinkles/rain will persist at times through
the morning focused in or or two narrowing bands.  As the vorticity
passes east late in the morning, we should see this activity
dissipate, but leave a lingering mid-lvl cloud field in the area.
Temperatures will recover slowly in the afternoon, but may struggle
to reach the 70 degree mark.

SUNDAY NIGHT-MONDAY: Shortwave ridging moving through the Plains
early Sunday evening and early in the overnight hours will keep
skies clear allowing for another quick temperature fall.  After
midnight hours, models remain in good agreement that troughing
arriving into the Western High Plains will induce a 40 knot LLJ
through central South Dakota and Nebraska. Convergence on this LLJ
will spark scattered convection that may arrive into the Missouri
River valley communities by 12Z. This non-severe convection
continues to lift northeast Monday morning with most of the focus
before 18Z. Given the orientation of the LLJ lingering and
persistent showers may continue in the afternoon. My big concern on
Monday may be with temperatures given ongoing cloud debris into
the afternoon. Latest NBM 25/75th percentile spread suggests
7-12 degree temperature variance, with the 10/90th spread as
high as 17 degrees. While we certainly could see highs in the
middle to upper 70s, clouds could also hold us considerably
lower.

Severe weather risks Monday afternoon remain focused in only the
very far portions of the CWA where there may be potential for a warm
front to lift northward.  Greatest potential remains focused across
northeast Nebraska and northwest Iowa from 3pm to 7pm. It`s also
very possible that continued convective debris really prevents any
meaning warming to arrive and limits the risk further south.

TUESDAY-SATURDAY: We`ll remain on the cool side of the baroclinic
zone for the remainder of the work week. With mid-lvl flow remaining
westerly, this will present fewer opportunities for any large scale
surge of warm air northward.  Both limiting high temperatures to the
upper 60s to lower 70s (near seasonal normals), but also keeping
severe weather risks minimal. Medium range ensembles hint at two
timeframes of focus for rainfall focused around Wednesday (lighter
amounts), and then late Thursday and Friday where stronger synoptic
lift enters the Plains and forces more abundant low-lvl moisture
northward. Ensembles have been trending the probabilities for >0.25"
higher each model run and this trend may continue based on the 12Z
data.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 635 PM CDT Sat Sep 12 2026

Light rain showers look to develop tonight and linger through
the morning Sunday for areas north of Highway-20 and through
the early afternoon near and south of there. Some brief pockets
of MVFR visibilities may accompany the heaviest showers, but
confidence was not high enough to include any category changes
at the TAF sites at this time. Winds will turn light and
variable this evening and overnight, picking up out of the east
through the day Sunday to around 5-10 kts, slightly higher in
south-central South Dakota by the end of the period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...Dux
AVIATION...Samet