335
FXUS63 KFSD 210507
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1207 AM CDT Tue Jul 21 2026

.KEY MESSAGES...

- Cooler temperatures and lower humidity are expected for the
  rest of the work week, with temperatures climbing back to the
  90s next weekend.

- The majority of this week will be dry. Possible exceptions may
  bring light showers to portions of the Missouri River Valley
  Tuesday night-Wednesday, with a broader 30-50% chance of showers
  or a few non-severe storms late this week.

&&

.UPDATE...
Issued at 851 PM CDT Mon Jul 20 2026

Less hot and significantly drier air mass has pushed across the
vast majority of the CWA, with just Sioux City to Storm Lake
still seeing dew points at/above 70F as of 8:00 PM, and 5-minute
observations from KSUX show even that location has seen the dew
point drop into the lower 60s as of 8:30 PM. As such, the heat
headlines were allowed to expire as scheduled at 8 PM.

This is the lead-in to multiple more comfortable days ahead with
highs in the upper 70s to mid 80s through Friday. Nighttime lows
will similarly be more comfortable, potentially allowing for some
open-window nights as readings dip into the 50s for a couple of
nights mid-week. Enjoy it while it lasts (if you like that kind of
weather) as heat/humidity are on tap to return just in time for
the upcoming final weekend of July.

&&

.DISCUSSION...
Issued at 125 PM CDT Mon Jul 20 2026

THIS AFTERNOON: A cool front continues to push southeast through
the forecast area early this afternoon. Behind the front, elevated
moisture may continue to produce isolated showers or thunderstorms
driven by a narrow corridor of vorticity sinking through central
Minnesota. This activity is likely to remain elevated as it moves
into south central Minnesota. Eventually it may become more surface
based as it moves into northern Iowa. Secondary ACCAS or isolated
thunderstorms further west into Central South Dakota are expected
to continue to struggle southeast. Elsewhere, moisture pooling
ahead of the boundary along with thermal compression ahead of the
front will push heat index values into the 100s along and south of
I-90 this afternoon. Drier air advecting behind the passage of
the front should lead to dropping heat index values after 3pm from
north to south, with all headlines on schedule to end by 7-8pm.

The southward progression of the boundary will continue into the
evening reaching a line from Norfolk to Sioux City To Estherville by
4-5pm. Soundings along the boundary continue to look very capped,
with much less forcing generally expected over the front. It`s the
ACCAS over central SD that we`ll need to keep an eye on early this
evening, as it does have some potential to intensify slightly as it
reaches Highway 20 and could become surface based.  IF upscale
growth could happen, the combination of shear and instability
could signal some golf ball sized hail and 60 mph winds. Again
though, this looks like a VERY limited area in time and space
this evening.

TONIGHT:  Dew points will crash overnight, signaling a return of
cooler and drier air.  Overnight lows may fall well into the 60s by
daybreak Tuesday.

TUESDAY: A beautiful day is anticipated on Tuesday with Canadian
high pressure sinking southward. High temperatures only in the
upper 70s to lower 80s with dew points in the 50s will signal a
great.

WEDNESDAY-FRIDAY:  The semi-northwest flow through the second half
of the week will keep cooler temperatures in the region through the
rest of the week.  Highs are expected to reach the lower 80s each
day.  A weak perturbation in this flow pattern leaves the Central
Rockies early Wednesday.  Most guidance tracks this wave through
Nebraska, but a few solutions could bring light rain risks into mid-
day Wednesday along and west of the James River valley.  A second
wave arrives by Thursday night into Friday, but again, uncertainty
in track keeps the risks for any precipitation less than 30% in most
locations along or west of I-29.

SATURDAY-SUNDAY:  We`ll again see rising temperatures by next
weekend, as confidence is high in an expanding mid-lvl ridge through
the Plains. This ridge however will be more suppressed than the
one that has just left the region, signaling a shorter surge in
temperatures to the 90s/100s, but also allowing a ridge rider
or two to move through the Plains by the end of the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1207 AM CDT Tue Jul 21 2026

VFR conditions are expected through this TAF period with a broad
area of wildfire smoke remaining mostly aloft.

North-northwest wind gusts 20-25kt develop shortly after sunrise
Tuesday, with gusts quickly diminishing by sunset Tuesday evening.

&&

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

&&

$$

UPDATE...JH
DISCUSSION...Dux
AVIATION...JH