455
FXUS63 KFSD 201151
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
651 AM CDT Wed Aug 20 2025

.KEY MESSAGES...

- Areas of dense fog will cause impacts especially along and
  east of Highway-81 through 9 am. Continue to use extra caution
  on the roads.

- Isolated to scattered strong to severe storms will be possible
  late Thursday into Friday. Some uncertainty remains on the
  overall severe potential, so keep up to date with the latest
  forecast.

- Staying very warm through mid-week, but turning much cooler
  into the weekend and early next week. Highs look to be mainly
  in the 70s starting Saturday, with some spots dropping down to
  the 40s for lows.

&&

.DISCUSSION...
Issued at 421 AM CDT Wed Aug 20 2025

TODAY-TONIGHT: Areas of dense fog will continue to cause issues
on the roadways this morning mainly along and east of the
Highway-81 corridor, though fog should begin lifting by 9 am.
After the fog dissipates, we`ll be left with mostly sunny skies
for the remainder of our Wednesday. It`ll be another warm and
humid day, with highs ranging from the mid-90s in central South
Dakota to the lower-80s in the higher elevations of the Buffalo
Ridge. We are looking to stay dry today and tonight as ridging
aloft dominates the area. Clear skies, plentiful moisture, and
light winds will once again lead to fog development tonight
mainly east of I-29. Some of it could once again be dense as
well.

THURSDAY-FRIDAY: An upper-low will move south across southern
Canada Thursday into Friday, and its attendant trough will move
through the northern Plains will help set off our next round of
showers and storms. At the time, a cold front will be
approaching the area which will also help provide the lift for
storm development. The environment by Thursday evening looks to
be characterized by around 2000-3000 J/kg of MLCAPE and 35-45
kts of bulk shear, sufficient for isolated to scattered strong
to severe storms to become a threat late Thursday into Friday
morning. Questions remain regarding how the higher CAPE and
higher bulk shear will overlap and also regarding the timing of
the cold frontal passage. The best upper-level support will also
be north of the area, so this could be another limiting factor
to severe storm development. Showers and storms may be ongoing
into northwest Iowa during the daytime Friday until the cold
front finally clears the area. Temperatures on Thursday will be
quite warm especially west of I-29 where compressional heating
ahead of the front will coincide with peak daytime heating.
Highs could climb into the upper-90s in parts of central South
Dakota Thursday afternoon. The humidity won`t be too impressive
in these areas, so the heat index will likely stick around the
air temperature through the afternoon.

WEEKEND-EARLY NEXT WEEK: After the front passes, cooler
temperatures are expected by Friday with highs in the upper-70s
to low-80s. With continued pushes of cold air advection due to
northwesterly flow aloft, it will get even cooler with highs in
the 70s and lows in the 40s and 50s through early next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 651 AM CDT Wed Aug 20 2025

Areas of dense fog have developed this morning and should start
lifting entirely around 14Z. Otherwise, VFR conditions are expected
through the rest of the daytime and this evening. Fog is once again
expected to develop tonight, especially east of I-29. With similar
conditions as last night, currently expecting at least MVFR fog at
KSUX. KFSD may have some fog, but the better chances of denser fog
will be east of the terminal so kept out any visibility restrictions
there. Not expecting KHON to see fog due to breezy conditions there
overnight. Winds will be light and variable today, picking up a bit
west of the James River tonight as our next system approaches.

&&

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

&&

$$

DISCUSSION...Samet
AVIATION...Samet