708
FXUS63 KFSD 190339
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1039 PM CDT Mon Aug 18 2025

.KEY MESSAGES...

- Patchy fog, with some visibility below one half of a mile,
  develops tonight into Tuesday morning. Although fog may
  stretch to the James River Valley, lowest visibility is
  expected across southwestern Minnesota.

- The next chance for rain will come Thursday evening and night.
  There is the potential for strong to severe storms but
  details are uncertain as of now.

- Dry conditions look to return on Friday through the weekend
  along with near to below average temperatures. This looks to
  be the first taste of Fall for the area.

&&

.DISCUSSION...
Issued at 245 PM CDT Mon Aug 18 2025

Quiet conditions have returned for this afternoon after this
mornings storms have pushed east of the area. Capping persists
across the bulk of the area and with only weak forcing in place, dry
conditions look to prevail. Can`t rule out a highly isolated chance
(<10%) that a storm or two develops across parts of highway-14 and
west of the James River though where capping is weaker. Should
convection develop, it is expected to be mainly across central and
southern Nebraska where a weak shortwave trough will track through.
Aside from rain chances, highs have warmed to upper 70s and 80s
while dew points have moistened to the upper 60s and 70s. This is
yielding heat indices up to the 80s and low 90s, making for another
humid afternoon. Low temperatures will remain warm overnight, with
lows only falling to the 60s due to dew points remaining in the 60s
as well. Given the moist environment, fog is again possible late
tonight into tomorrow morning. Think that locations along the
Buffalo Ridge in southwest Minnesota have the highest chances (40-
50%) for seeing fog tonight.

Tuesday and Wednesday will be much quieter days as large scale
descent parks itself over the Northern Plains. High temperatures
will remain near to above average in the in the 80s to low 90s. The
warmest temperatures look to occur west of the James River. Dew
points will remain in the 60s and 70s, continuing humid conditions
across the area. Heat indices will push into the upper 80s and 90s
in response to the hot and humid environment. Low temperatures will
also remain near to above average in the 60s.

The next chance for rain returns to the area on Thursday as a
stronger shortwave trough rounds the top of an upper level ridge
sitting over the four corners area. High temperatures will remain in
the 80s and 90s while dew points again remain in the 60s and 70s. A
cold front tied to this wave will push through the area during the
evening and overnight hours on Thursday, sparking showers and
thunderstorms along it. Instability looks to be more than sufficient
with CAPE values having a 50-90% chance for exceeding 2,000 J/kg
along and west of the James River. With an upper level jet
associated with the wave, vertical shear will be sufficient as well.
However, the cold front could potentially push out ahead of the jet
just enough to prevent meaningful overlap between the shear and
instability. Will continue to monitor this potential but do think
that model blended PoPs are sufficient in the 30-60% range.

Friday through the weekend looks to be mainly quiet as broad
northwest flow takes over. At the surface, surface ridging will be
spilling into the Northern Plains. This will finally bring relief
from the heat and humidity as dew points slowly fall to the 60s on
Friday, 50s on Saturday, and 40s and 50s on Sunday. High
temperatures will fall to the 70s and 80s, coldest on Sunday. Low
temperatures will also fall to near to below average to the 40s and
50s, coldest again on Sunday. With such cool conditions on the
table, this cooler airmass will deliver the first taste of fall to
the area.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1033 PM CDT Mon Aug 18 2025

Area of showers and isolated storms moving southeast near the
ND/SD/MN border should stay northeast of our area. Focus for the
next 12 hours or so is on the fog and stratus, which is already
developing near KFSD to KMML to KSPW. Expect this to continue to
expand overnight and through the daybreak hours Tuesday, with
MVFR/IFR conditions. May see some visibility below 1/2 SM,
mainly across southwestern MN.

VFR conditions return mid/late Tuesday morning with continued
light winds. Fog may begin to develop once again at the end of
this TAF period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...SG