521
FXUS63 KFSD 180353
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1053 PM CDT Fri Jul 17 2026

.KEY MESSAGES...

- Hot conditions are expected again Sunday and likely Monday
  where heat indices could climb to around 100. Saturday should
  see a slight break from the heat as winds turn northerly
  behind a weak front.

- Very patchy morning valley fog is possible daily, but
  widespread dense fog remains unlikely. Fog could reduce
  visibility below two miles at times.

- Wildfire smoke is possible this weekend, with the better
  chances over parts of southwest MN. While lower surface
  concentrations are expected, any sensitive groups should begin
  to monitor their local air quality.

- Precipitation is very unlikely (less than 10%) through Sunday.
  Isolated to scattered shower and storm chances return Sunday
  evening and night, but confidence is low on details.

&&

.UPDATE...
Issued at 825 PM CDT Fri Jul 17 2026

As of 8:00 pm CDT a weak cold front is draped from roughly Hendricks
MN southwest to Chamberlain SD. There is little moisture available
to produce much more than clouds. However for areas of east central
South Dakota and into southwest Minnesota there may be enough
moisture return in the 800-700 mb level for isolated showers and
thunderstorms. We`ve already seen a few small showers go up and then
rapidly come down. While there is around 1000-1500 J/kg of MLCAPE
available, there is no appreciable shear. Severe weather is unlikely
with these storms, however a few strikes of lightning and wind gusts
to 35 mph are possible. This front will continue to progress
southeast through Saturday morning. Saturday morning patchy areas of
dense fog may form, mostly along water ways and low areas.

Winds behind the front will be northerly to northeasterly, bringing
cooler air to the region temporarily. Highs for Saturday are
expected to in the mid 80s to the mid-90s, warmest over south
central South Dakota. An upper ridge will build through the day with
a surface high pressure sliding southeast into the region. As it
does so winds gradually become southeasterly Saturday night and
southerly by Sunday morning. Deep mixing and WAA will result in
Sunday being another very hot day with Heat Index values in the mid-
90s to low 100s. A Heat Advisory may be necessary for areas
west of Highway 81, but as it is still two days out have opted
to wait to issue.

Over the next few days more smoke will begin to filter into the
region from the Canadian wildfires. Near surface concentration
should remain low, however sensitive populations may need to
take precautions. Sunday overnight into Monday an upper low over
central Canada will begin to drift southeast. As it does so it
will push the smoke back off to the northeast.

&&

.DISCUSSION...
Issued at 1251 PM CDT Fri Jul 17 2026

A weak cool front will sag south tonight into Saturday. Moisture
and forcing along this boundary are very weak, so showers and storms
are very unlikely. Parts of northwest IA late this afternoon could
see a spotty shower or storm as a few of the models indicate a
weakening cap, but with no shear and about 500 J/kg of skinny CAPE,
brief heavy rain should be the only concern.

Otherwise Saturday should see a bit of a reprieve from the heat for
many with highs expected to range from the mid 80s in southwest MN
to the mid 90s along the Missouri River. One concern on Saturday
will be the potential for some surface based smoke from the fires
across northern MN. With winds turning north and then northeast,
some of this could leak into the area. For now smoke concentration
look to remain fairly low.

Sunday will see a return of southerly flow and hotter conditions as
upper level ridging builds ahead of a strengthening jet along the
Canadian border near MT. Still some hints of elevated moisture and
very weak instability l;ate Saturday night into Sunday morning which
could lead to isolated showers and a very isolated thunderstorm.
However, the latest model runs are drier aloft than previous runs,
so confidence in this is waning. Otherwise, may need a heat advisory
for areas near and west of I-29 Sunday afternoon and evening with
heat indices likely above 100. Sunday night will see fairly strong
southerly flow in place which will lead to very warm lows in the 70s.

Monday still has a few question marks on heat, but for areas near
and south of I-90 there will again be a very good chance for heat
indices of 100 or greater. This is due to that jet max to the
northwest now diving southeast into the area and dragging some
cooler air south. For now coverage of any showers and thunderstorms
looks isolated to scattered with the better chances Sunday night
into Monday evening. Frontal timing and mid level moisture will play
a bog role on coverage.

Once this front sags south Monday evening, stronger northwest flow
aloft will remain in place which will bring temperatures back to
normal or a bit below normal for the remainder of the week. While
there will likely be a couple of weaker waves during this time
confidence on anything more than isolated is low.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1053 PM CDT Fri Jul 17 2026

VFR conditions are expected to prevail for the period. Winds are
light becoming northerly and light behind a cold front as it works
its way through the region tonight. Skies will be clear to scattered
high level clouds.

&&

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

&&

$$

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