789
FXUS63 KFSD 120755
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
255 AM CDT Wed Aug 12 2026

.KEY MESSAGES...

- Cluster of severe storms with damaging winds up to or locally
  exceeding 75 mph will move through portions of the Missouri
  River Valley early this morning.

- Areas of dense fog and low stratus may form again late tonight
  into Wednesday morning, though confidence in coverage is low.

- Following a warm and dry Wednesday, an influx of moisture will
  bring a chance of thunderstorms into Thursday. Very uncertain,
  but a highly localized heavy rain risk could develop.

- Cloud cover and cooler temperatures move in for Thursday and
  Friday, along with another risk of rain Thursday night.

&&

.UPDATE...
Issued at 245 AM CDT Wed Aug 12 2026

With ongoing severe weather across northern Nebraska, this
update will be short and sweet. An ongoing MCS continues to
propogate to the southeast this morning just south of the SD/NE
state stateline. While gradual weakening has occurred, this
system is starting to take an eastward turn towards the U.S.
Highway 20 corridor as of 3 am. As a result, a downstream
severe thunderstorm watch has been issued for portions of
eastwestern NE and western IA through 10 am with Dakota and
Dixon Counties being the main focus for our area. The main
hazard would be wind gusts between 60-70 mph with a secondary
threat being margially large hail up to quarter size.

&&

.DISCUSSION...
Issued at 115 PM CDT Tue Aug 11 2026

THIS AFTERNOON: VERY humid conditions continue early this afternoon,
but a wide array of temperatures in the region. Early morning
stratus and fog has kept a lid on temperatures north of I-90, but
south of the Interstate we`ve seen highs climb towards the 90s. Heat
index in a few areas may reach the 100 degree mark. A couple
patches of ACCAS based AOA 600 mb continue to move along I-90
this afternoon, but development potential remains low as this
moves into NW Iowa. Will continue to monitor.

THIS EVENING/TONIGHT: CAMS continue to struggle resolving the myriad
of weak forcing waves moving through the Plains, and these trends
continue today.  The result is sporadic convection developing over
the western High Plains in the late afternoon and evening and then
gradual tracks southeast overnight.  Despite the high level of
instability across the Dakotas, very few strong focusing
mechanisms for convection remain apparent this afternoon. What
may happen is gradual upslope flow over the western Dakotas
combined with increasing SE 850mb flow could induce a cluster or
two of storms. This activity will tend to follow the mean flow
and push east southeast into the overnight hours. However, a
closer look at soundings continues to show fairly strong
inhibition both to surface based parcels but also to elevated
parcels. So with that in mind, planning on keeping PoPs low,
with some focus along I-90 and areas moreso over the Missouri
River valley. Continue to monitor trends this evening, as strong
storms could bring some higher wind gusts if they survive.

Higher confidence again in the development of stratus and fog given
the continued light northeast wind and trapped boundary layer
moisture.  Much like this morning, areas of locally dense fog may
form with widespread stratus potential possible.

WEDNESDAY-WENDESDAY NIGHT: Assuming stratus/fog does not hinder the
warmup tomorrow significantly, we`ll continue to see another warm
afternoon on Wednesday with dry conditions. Dew points will remain
in the 70s, which should cap high temperatures in to the middle
80s. A slight shift in the mid-lvl flow begins Wednesday, with
persistent ridging over the Four Corners translating eastward
into the Southern Plains through the day. This will result in
pulling a sub-tropical moisture plume with embedded vorticity
northward through the Rockies and into the Plains late in the
day and overnight. Slightly better signals for convection tied
to this wave will begin to focus over western SD/NE late in the
afternoon, with rain gradually shifting eastward into Thursday
morning. The severe weather risks remain on the lower side but
not non-zero as some lingering wind threat could present itself
along the MO river valley. Mid-lvl lapse rates quickly worsen as
you move into the overnight hours however. One noticeable thing
to watch is the increasing PWAT values which approach 1.75" by
Thursday morning. This could signal at least the potential for
highly localized heavier rain amounts, which the HREF PMM
signals in the 2-4" range. The key to watch will be where the
residual surface boundary falls by late Wednesday, as this could
pull better convection risks south of the CWA.

THURSDAY-FRIDAY: Quite a bit of cloud cover may be in the area for
Thursday as cooler northeasterly flow returns and we`ll be on the
edge of the baroclinic zone to our south.  At this point, highs in
the 70s are likely, with a gradually increasing rain chance into
Friday as mid-lvl flow shifts back to the southwest, mid-lvl
vorticity slides through the Central Plains, and the baroclinic zone
lifts northward. The highest PoPs will be focused Thursday night
into Friday.

SATURDAY-MONDAY: A flattened mid-lvl ridge remains over the central
CONUS into the upcoming weekend, bringing another risk for rain by
Saturday as energy tracks back northward into the Upper Midwest.
Confidence is rising that we`ll see a dry Sunday and Monday as high
pressure arrives, mid-lvl ridging shifts back westward, and quasi-
northwest flow moves back in.  Temperatures may begin to rise back
into the 80s by Sunday and Monday.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1255 AM CDT Wed Aug 12 2026

Monitoring a severe wind-producing cluster of storms in south
central SD at the start of this period. Trajectory most likely
takes the greater risk of severe winds just south of KSUX, but
will closely monitor for a northward shift in the trajectory as
it moves east near the Missouri River Valley. Projected timing
would bring a potential for storms near KSUX by 09Z-10Z if
storms track that far north.

Otherwise areas of MVFR to locally IFR visibility in fog is the
greatest concern into mid-morning Wednesday, though probability
of sub-VFR conditions at KHON/KFSD is too low to include in the
TAF at this time.

Chances for additional showers/storms increase late in this
period, but confidence is too low to include in the TAFs at this
time.

&&

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

&&

$$

UPDATE...05
DISCUSSION...Dux
AVIATION...JH