530
FXUS63 KFSD 271723
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1223 PM CDT Mon Jul 27 2026

.KEY MESSAGES...

- Showers and thunderstorms are possible this evening into the
  overnight. Severe weather is possible over central South
  Dakota with the primary risk 65 mph wind gusts. Storms are
  expected to weaken as they move east.

- Heat indices climb to 95 to 105 today, mainly south of I-90.
  Locally higher heat indices are possible along and south of
  the Highway 20 corridor. A Heat Advisory remains in effect
  until 8 pm for areas south of I-90 into portions of southern
  Minnesota.

- Next threat for showers and thunderstorms will be on
  Thursday. An isolated storm could be severe.

&&

.UPDATE...
Issued at 440 AM CDT Mon Jul 27 2026

Northern parts of the forecast area have seen areas of fog
develop in response to light winds/clear skies allowing for
optimal cooling in an abundantly moist boundary layer. Have seen
occasional reports of 1/4SM visibility, mostly over the Prairies
des Coteau in east central SD. Initially opted for a Special
Weather Statement (SPS) due to more sparse coverage. However,
webcams and satellite support more widespread coverage of the
lowest visibility over the past hour, so have issued a small
Dense Fog Advisory through 8 AM. Will continue to monitor and
expand the advisory if needed.

Farther south, still monitoring a low potential for a few storms
to develop through these early morning hours. Such activity did
develop in northeast Nebraska, but has thus far remained just
shy of our forecast area. This does support a low potential,
though, and will maintain some low pops in our far south for the
next 2-3 hours.

Otherwise the existing Heat Advisory looks good, though may have
to monitor the Highway 20 corridor for a few hours above 105F
heat indices midday-early afternoon before the drier air works
that far south.

&&

.DISCUSSION...
Issued at 118 PM CDT Sun Jul 26 2026

The thunderstorm threat is still very low confidence for late this
afternoon into tonight. Quite a bit of cloud cover has lingered into
the early afternoon which is slowing heating. And, as opposed to
yesterday, the mid to upper level wave today is a bit weaker and may
not help to organize activity as efficiently, so will need to find a
way to break the cap. For now these chances look best south of I-90
into northwest IA where the deeper moisture resides. South central
SD shows the weakest cap late afternoon while parts of northeast NE,
far southeast SD and northwest IA see a moderately increasing LLJ
during the evening hours, which could focus some thunderstorm
development.

Winds turn more northerly tonight into Monday which should allow dew
points to settle into the 60s and lower 70s. This will likely keep
heat indices in the 90s and thus heat headlines will not be
necessary. One exception may be across parts of northeast NE and
northwest IA where heat indices should creep above 100 again with
the higher dew points. Will have a heat advisory for these locations.

Monday and Monday night should be quiet as more stable air settles
in. One exception may be later Monday night in central SD as some
upper level support spreads from western SD into that area. Just
some small chances west of the James for now.

Tuesday and Wednesday will be on the northern edge of the upper
level ridging which will keep some westerly flow aloft in place.
This should allow for a couple of weaker waves to move through.
While precipitation is unlikely, some occasional cloud cover and
slightly suppressed temperatures will likely keep the more extreme
heat and humidity at bay, so heat headlines for both of these days
looks unlikely.

A stronger wave moves into the area Thursday and should be the next
better chance for showers and thunderstorms. Should see some
isolated severe storms with this activity.

Temperatures settle back to near normal Friday into next weekend as
northwest flow aloft should bring much more comfortable air into the
region with little chance for showers and thunderstorms.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1221 PM CDT Mon Jul 27 2026

VFR conditions are expected to prevail this period. Smoke from
wildfires in the western US and Canada will flow in on
northwest winds aloft. Skies will be partially obscured and
visibility may fall to 6sm at times due to smoke.

Winds are northeast with gusts to 17 kts. Winds will become light
and variable after sunset. Tuesday winds will remain light and
gradually become southerly.

Chances for rain this evening over central South Dakota. Some storms
could be strong to severe with wind gusts of 65 mph the primary
threat. Storms are expected to weaken and become scattered and light
as they progress east overnight. Some showers may linger into
Tuesday morning. Confidence in storms impacting any TAF sites was
too low to include at this time.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 8 PM CDT this evening for SDZ050-063>071.
MN...Heat Advisory until 8 PM CDT this evening for MNZ081-090.
IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003-
     012>014-020>022-031-032.
NE...Heat Advisory until 8 PM CDT this evening for NEZ013-014.

&&

$$

UPDATE...JH
DISCUSSION...08
AVIATION...AJP