614
FXUS63 KFSD 131820
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
120 PM CDT Thu Aug 13 2026

.KEY MESSAGES...

- Areas of low stratus and patchy fog may form again late
  tonight into Friday morning, though confidence in coverage is
  low. This may be a recurring theme through the weekend.

- Showers and isolated thunderstorms will be possible later
  tonight into Friday morning. The better chances will be in
  northeast NE and northwest IA. The main threat will be locally
  heavy rain.

- Near to below normal temperatures through most of next week.
  Periodic showers and storms expected. Humidity lingers.

&&

.DISCUSSION...
Issued at 118 PM CDT Thu Aug 13 2026

Upper level flow becomes a bit more southwesterly tonight into
Friday, which will allow a weak wave to drift north into the area.
With an elevated 1000-1500 J/kg CAPE, a freezing level around 14 kft
and weak shear, locally heavy rain with slow moving storms will be
the main concern. This weak mid to upper level support lingers
into the afternoon and early evening, especially across parts of
northwest IA, and may allow for additional showers and isolated
thunderstorms. One note, the LLJ and 850 mb boundary looks to
remain just south of the area so the pockets of heavier rain may
stay just south as well. To the northwest of northwest IA weak
capping may keep the activity more limited. For now severe
weather very unlikely and flash flooding threats also look low.

Additional weak mid and upper level support moves through the area
later Friday night into Saturday and may bring additional showers
and isolated thunderstorms. Severe weather and flash flooding appear
very unlikely.

One common theme for Friday into the weekend will be persistent and
potentially difficult to dissipate stratus and patchy fog. Weak low
level flow and some residual boundary layer moisture from the latest
rainfall may help keep this stratus potential in place until a bit
stronger push of drier air can move into the area. Sunday does look
like the day with the lowest threat for any showers and storms.

Monday will see a west northwest jet max sag south into the area
which should allow for heating ahead with a weak cool front
trailing Monday night. This cool front could spark a few
thunderstorms Monday night with isolated severe storms possible. The
EC and Canadian are slower with this front than the GFS, so will
need to watch trends and for now low confidence on any storms.

West northwest flow aloft remains in place Tuesday through Thursday
with periodic weak waves expected to move through. This should keep
shower and thunderstorm chances in place during this time with near
to below normal temperatures.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1203 PM CDT Thu Aug 13 2026

Patchy MVFR ceilings will be possible through the afternoon into
the early evening. IFR to possibly LIFR ceilings are expected
late tonight into Friday morning. The better chances for these
lower conditions will be near and south of I-90. Also expected
later tonight into Friday morning will be scattered showers and
thunderstorms, with the best chance across northeast NE into
northwest IA from about 8z through 15z. The main threats from
the thunderstorms will be locally heavy rainfall and wind gusts
to 45 mph.

&&

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

&&

$$

DISCUSSION...08
AVIATION...08