447
FXUS63 KFSD 181946
AFDFSD

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

.KEY MESSAGES...

- Mainly dry conditions are expect for the rest of this
  afternoon. Though a highly isolated chance (<10%) remains
  that a storm could develop along parts of highway-14 and west
  of the James River.

- 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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1237 PM CDT Mon Aug 18 2025

Latest satellite imagery shows some low level clouds mainly along
and north of I-90. These clouds are sitting at VFR/MVFR/IFR levels.
Should see gradual lifting and dissipation of these clouds thanks to
diurnal mixing. At the same time, a CU field is beginning to develop
south of I-90, mainly across parts of southeast South Dakota and
northwest Iowa. Could see the CU field mix out as drier air is mixed
to the surface. Light and variable winds are expected throughout the
vast majority of the period. This may lead to fog developing late
tonight into tomorrow morning. Currently thinking that the Buffalo
Ridge in southwest Minnesota is the most likely area to see fog
tonight. Have included BR in KFSDs TAF as of now but may nudge it
down to FG if confidence increases in fog potential. Otherwise,
light east/northeasterly winds will finish out the TAF period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...Meyers