760
FXUS63 KFSD 260339
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1039 PM CDT Fri Jul 25 2025

.KEY MESSAGES...

- Patchy dense fog is possible tonight, especially for areas
  along the I-29 corridor and parts of the Missouri River
  Valley.

- A Heat Advisory remains in effect for areas along and west of
  the James River Valley on Saturday, where heat index values of
  100 to 105 degrees are expected.

- High heat will intensify Sunday/Monday given a combination of
  air temperatures in the 90s and dewpoints in the 70s. Heat
  index values are forecast to rise above 100 degrees for most
  areas.

- There is a 20 to 40 percent chance for showers and
  thunderstorms Sunday night into Monday. Additional
  precipitation chances exist Monday night into Tuesday and
  Wednesday.

- Temperatures will cool significantly by the middle of next
  week, peaking in the 70s Wednesday through Friday.

&&

.DISCUSSION...
Issued at 258 PM CDT Fri Jul 25 2025

Southerly surface flow has allowed dewpoints to rise back into
the upper 60s/lower 70s. This moistened boundary layer, combined
with diurnal heating, has resulted in a widespread cumulus field.
These lower clouds are expected to scatter out later this evening
with areas of cirrus overhead. Elevated winds overnight will
keep temperatures slightly elevated, bottoming out in the mid to
upper 60s. Of greater concern is the possibility of fog. 12Z
HREF is showing a 40-60 percent chance of visibility dropping
below 1-3 miles, primarily along the I-29 corridor and areas
along the Missouri River Valley. Added patchy fog mention to
the forecast, but some spots could see fog become locally dense.

Precipitation-wise, tonight will be dry. Forcing short-waves
necessary for development remain to our north across ND/northern
MN and to our south across southern NE/IA.

Absent large-scale forcing, dry conditions continue into Saturday.
Primary concern will be temperatures given a building 500 hPa
ridge across the Northern Plains. Thermal profiles suggest
highest temperatures will be along and west of the James River
Valley with afternoon highs in the mid to upper 90s. When
combined with dewpoints around 70 degrees, expect the heat index
to top 100 degrees. Previously issued Heat Advisory looks good
with no changes planned at this time.

Synoptic ridge continues to strengthen into Sunday. Air
temperatures west of the James River are likely to reach or
exceed the 100 degree mark. Farther east, highs will be in the
low to mid 90s, but with dewpoints in the 70s and even flirting
with 80 degrees across the corn belt, expect heat index values
well into the 100s. After collaborating with neighboring
offices, will hold off on any headlines, but heat-related
advisories and/or warnings are likely for Sunday.

Precipitation chances of 20 to 40 percent return Sunday night
into Monday as a ridge-riding short wave moves across the
Northern Plains. Given abundant instability and modest shear,
the SPC Day 3 Outlook shows a Level 1 of 5 (marginal) risk
across the eastern two-thirds of the forecast area. However,
predictability is low given the possible development and
evolution of an upstream mesoscale convective system. Something
to watch closely over the next couple days.

High heat remains in place on Monday with little change compared
to Sunday, barring any influence from possible convection
mentioned above. As such, additional heat headlines are possible.

Monday night through Wednesday, the 500 hPa ridge axis retrogrades
westward as a very large Hudson Bay low slowly drops south into
the Great Lakes. Embedded short-waves and a more significant
cold front Tuesday will provide multiple chances for precipitation,
so current forecast POPs of 40-60 percent seem reasonable. On
the backside of the aforementioned cold front, temperatures
Wednesday-Friday will be significantly cooler, topping out only
in the 70s.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1035 PM CDT Fri Jul 25 2025

Winds will be light for most of the area tonight. Latest
ensembles indicate a 40-60% probability of at least patchy MVFR
fog development across much of the area, with pockets of IFR
visibilities possible. This fog could potentially affect KFSD
and KSUX later tonight into Saturday morning. Any fog that
develops would quickly burn off on Saturday morning.
Southeasterly winds pick up later on Saturday morning, gusting
around 20 kts through the afternoon, before becoming light again
on Saturday evening.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM to 8 PM CDT Saturday for SDZ038-039-
     050-052>054-057>061-063>066-068>070.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...Rogers
AVIATION...JM