885
FXUS63 KFSD 202340
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
640 PM CDT Mon Jul 20 2026

.KEY MESSAGES...

- A cool front brings an isolated risk for strong thunderstorms
  along Highway 20 into north central Iowa early this evening.
  Large hail and 60 mph winds will be risks.

- 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, outside of a 30% risk
  of showers and non-severe thunderstorms Wednesday into
  Thursday.

&&

.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 /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 632 PM CDT Mon Jul 20 2026

VFR conditions are expected through this TAF period with a broad
area of wildfire smoke remaining mostly aloft. Some hint at minor
smoke concentrations near the surface this evening, but visibility
impacts are not expected.

Lingering north-northwest wind gusts at the start of the period
will quickly diminish by sunset, but gusts 20-25kt will develop
again shortly after sunrise Tuesday and persist through the end of
this TAF period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 8 PM CDT this evening for SDZ050-063>069.
     Extreme Heat Warning until 8 PM CDT this evening for SDZ070-
     071.
MN...None.
IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003-
     012>014.
     Extreme Heat Warning until 8 PM CDT this evening for
     IAZ020>022-031-032.
NE...Extreme Heat Warning until 8 PM CDT this evening for NEZ013-
     014.

&&

$$

DISCUSSION...Dux
AVIATION...JH