942
FXUS63 KFSD 160824
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
324 AM CDT Sun Aug 16 2026

.KEY MESSAGES...

- Patchy fog continues, mixing out by mid morning. Pleasant
  Sunday expected.

- A front will bring a risk for isolated to scattered storms,
  including severe thunderstorms, Monday afternoon and evening.
  Stronger storms could produce 2" hail and 65 mph winds along
  with brief heavy rain.

- An active weather pattern keeps intermittent thunderstorm
  chances in the forecast from Tuesday through Thursday.
  Conditional risk for severe storms Tuesday afternoon and
  evening.

&&

.UPDATE...
Issued at 322 AM CDT Sun Aug 16 2026

Some very patchy and briefly dense fog developed earlier this
morning, but increasing high clouds has been limiting coverage.
Still would not be surprised to see additional patchy and locally
dense fog into the early morning. Fog mixes out mid morning.
Pleasant today with occasional wind gusts to 20 mph. We`ll see some
high clouds and wildfire smoke aloft, but expect plenty of sun. A
weak wave grazing the MO River this evening and tonight could lead
to some isolated showers/storms in south central SD. Made some small
changes to pops to reflect more isolated coverage through Monday
morning.

Active pattern early this week although guidance still shows quite a
bit of variance in the details. Southeasterly flow brings warmer and
more humid air and a mid level wave tracks through during the
evening. Strong to severe storms are possible as isolated to
scattered storms develop along a cold front moving east, with the
main threats large hail and damaging wind in the afternoon and
evening. May also see brief heavy rain. More conditional severe
threat remains on Tuesday as another wave dives through the
northwesterly flow aloft. However, timing and location differences
in the models lead to lower confidence.

&&

.DISCUSSION...
Issued at 124 PM CDT Sat Aug 15 2026

THIS AFTERNOON: Mid-lvl vorticity continues to lift northeast
through the Tri-state area early this afternoon. Scattered showers
and thunderstorms tied to this wave will continue to slide east
northeast into the afternoon hours.  Most of the strongest activity
has been tied to the NW quadrant of the wave, aligned with an
approaching cool front  moving in from the northwest. Some of the
convection has produced rainfall rates greater than 3-4" per hour,
with radar estimates suggesting 2-4" of rain has fallen in isolated
pockets in Miner county. Convection risks will remain focused mostly
on heavy rain this afternoon, though if sufficient clearing can
develop in SW Minnesota and NW Iowa, then a small risk of 50 mph
winds, small hail, and also brief funnels could be possible given
the weak and chaotic surface flow. The heavy rain risk will persist
in any thunderstorm given deep warm cloud layer, and PWATs above the
90th percentile of climatology.

TONIGHT: The front clears the CWA by late evening, with skies
briefly clearing.  Those skies may only stay clear for a short
duration of time as increasing mid-uper forcing could bring high lvl
clouds back into the region.  If these clouds don`t develop, then
overnight lows could fall into the upper 50s to lower 60s, inducing
some fog potential.

SUNDAY: A dry day is anticipated for Sunday as winds remain
northerly.  Temperatures rise into the lower 80s in most locations,
with a bit of mid-high lvl cloud cover in the region through the day
and diurnal CU in the afternoon.

MONDAY: Northwesterly flow will persist into the new work week
and is expected to bring a frontal boundary into the Dakotas on
Monday. An initial surge of warm advection Sunday night into
Monday could bring scattered showers and thunderstorms eastward
out of central South Dakota/Nebraska by daybreak. This activity
may slowly fade through the morning allowing stronger diurnal
heating to occur. The frontal boundary arriving in the afternoon
will then be watched for convection risks. Should convergence
along this boundary be strong enough to overcome lingering
inhibition, isolated to scattered storms may develop by 3-5pm as
soundings show a relatively uncapped environment through
eastern SODAK. Upwards of 2000-2500 J/KG MLCAPE ahead of the
boundary, may combine with modest effective shear approaching 35
knots to help produce a few severe storms with 2" hail and 60
mph wind potential. The overall coverage of storms remain most
uncertain given unknown impacts of morning clouds.

TUESDAY: Monday`s convection may dictate the placement of the
frontal boundary by Tuesday. Some guidance pushes the front and
boundary layer moisture south of the CWA, with other models holding
the effective boundary closer to I-90. The NW flow will likely bring
another wave into the Plains in the afternoon, which could trigger
isolated to scattered strong late afternoon and evening storms once
again.

WEDNESDAY-FRIDAY: With the mid-lvl ridge centered back over the Four
Corners region we`ll continue to see northwesterly flow aloft
through the Plains for the second half of the week. This problematic
flow pattern will keep a rain risk into the region Wednesday and
potentially Thursday, before the ridge sharpens and pushes more
stable air into the Plains into next weekend. Expect lower than
typical confidence in specific forecast details during the middle of
the week.  Temperatures through the second half of the week will run
near to slightly below their seasonal normals which are now in the
lower 80s.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1234 AM CDT Sun Aug 16 2026

A mix of VFR to MVFR for the first portion of the period. Lingering
low stratus along a weak cold front over northwest Iowa and
southwest Minnesota will continue to push east and lift through the
next few hours. In addition patchy fog has begun to form in this
area. Mostly clear skies behind the front will allow surface
temperatures to cool to near dew point temperature. This may allow
patchy fog to develop as far west as the James River Valley.
Visibility may be reduced to less than 5 miles at times. Fog
should burn off by mid-morning Sunday.

Additional mid-level clouds will flow in from the west overnight due
to a weak mid-level wave passage. These will progress east followed
by mostly clear skies by late morning. Overnight winds will be light
and variable, becoming northerly with light gusts of 15 kts after
daybreak.

&&

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

&&

$$

UPDATE...SG
DISCUSSION...Dux
AVIATION...AJP