Flandreau, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

776
FXUS63 KFSD 261010
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
510 AM CDT Sun Jul 26 2026

.KEY MESSAGES...

- Extreme Heat Warning through 9 PM this evening. Heat index
  values as high as 115 degrees.

- While details are uncertain and confidence remains low, if
  storms develop in the late afternoon to evening today, some
  may be strong to severe with damaging winds, isolated large
  hail and locally heavy rain possible.

- Still a good chance for highs in the 90s through mid-week in
  most locations. Additional heat headlines are possible.

&&

.UPDATE...
Issued at 508 AM CDT Sun Jul 26 2026

Scattered high-based showers or perhaps an isolated thunderstorm
will linger into the morning. This activity is expected to wane
by midday, which should still allow ample heating within a very
moist boundary layer. Dew points well over-performed most guidance
on Saturday and see no reason why similar conditions will not be
seen today. As a result, nudged NBM dew points upward slightly by
blending in some ECMWF/Canadian Regional data to counteract the
significant hot/dry bias seen in the GFS. This data continues to
support the Extreme Heat Warning through this afternoon, and have
pushed the expiration out to 9 PM as forecast heat indices remain
above 100F a bit later than previously expected.

While the heat/humidity is a high confidence forecast, confidence
in convective potential later today is at the opposite end of the
spectrum. The main question is whether storms will form, and if
so, where. Some weak consensus in development toward the Missouri
River Valley in the very late afternoon (5-7 PM), with isolated to
perhaps scattered activity drifting east toward northwest Iowa
through the evening.

With lingering uncertainty, will keep PoPs on the low side. That
said, a deep dry sub-cloud layer yields plenty of DCAPE, so any
storm that forms will bring a potential for locally severe wind
gusts. The warm atmosphere should limit hail growth, but isolated
marginally severe hail could occur with the strongest updrafts.

The boundary which could potential trigger storms late today will
drop southeast of the area on Monday, allowing less humid air to
filter into the area. Temperatures will remain warm with highs in
the 90s, and locations south of Highway 18 may still be humid
enough in the afternoon to support heat indices above 100F.
However, with the Extreme Heat Warning in place for today and some
uncertainty regarding influx of less humid air on Monday, opted to
hold off issuance of any further heat headlines at this time.

&&

.DISCUSSION...
Issued at 117 PM CDT Sat Jul 25 2026

Heat:

Not much change as dew points in the upper 60s to mid 70s provide
the area with an oppressive environment. As temperatures rise into
the 90s today and Sunday, heat indices will jump to between 100-110
degrees in most locations. The hottest conditions continue to look
to be along the James and Missouri River valleys.

For now Monday through Wednesday should see highs generally in the
90s but with a bit less humidity. This will keep the heat index in
the 90s as well. Will have to keep an eye on the dew points trends
as a few more degrees of moisture will push heat indices above 100.

A wave moving through on Wednesday will likely bring slightly cooler
air into the area so the second half of the week may not be quite as
hot.

Thunderstorms:

Overall a capping inversion will be in place for the area through
the afternoon, so development is not expected. One exception may be
in and around Gregory/Charles Mix counties where model soundings
hint at possibly breaking the cap. If this can happen, an isolated
storm with the potential for wind gusts around 70 mph are possible.
CAPE values only running about 500-1500 J/kg with fairly weak shear,
but with a very dry subcloud layer. Otherwise, development should
take place west of the area and move in after about 6-8 pm. This
cluster of storms will likely be a bit pulsy, but with better
instability and still a fairly significant sub cloud dry layer wind
gusts to 75 mph will be likely with the potential for a cold pool to
develop. Hail to the size of quarters will also be possible, but
wind will be the main threat. Many of the latest 12z models are
jumping on this wind threat and the HRRR has been very consistent
bringing this wind threat right down I-90 this evening.

Some lingering showers are possible from midnight into early Sunday
morning, but are not expected to be severe and may even have trouble
reaching the ground with a significant dry layer below. Still a lot
of question marks regarding the severe threat tomorrow afternoon and
tomorrow night. For now a significant amount of dry air in the low
to mid levels should provide enough capping to avoid afternoon
thunderstorm development. If a storm could develop, 2000 J/kg CAPE,
30-40 knots of deep layer shear and a significant dry layer in the
lower levels would support wind gusts to 75 mph and hail to the size
of half dollars. Otherwise during the later evening and overnight
hours the models are really backing off on any potential for the
area and keeping the isolated to scattered activity to the northeast.

A wave will move through the area Wednesday into Thursday morning
and be the next chance for showers and thunderstorms. This will be
the next threat for possible severe storms. The main threat for
showers and thunderstorms should come on Thursday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1244 AM CDT Sun Jul 26 2026

Scattered showers will continue to push through the area
into the early morning hours today, with additional showers
possibly redeveloping after sunrise through the late morning.
Thunder threat with all this activity will generally remain
quite isolated. Stronger thunderstorms may develop late this
afternoon over northern Nebraska and perhaps as far north as
southern South Dakota and push eastward into tonight. Trends
will be monitored, but chances of this impacting our area are
low at this time, generally less than a 25% chance of occurring.

Winds could gust up to 20 kts at times this morning through the
early evening. Winds will be generally out of the south through
the period, though the wind direction may become a bit erratic
in central South Dakota late this afternoon/early this evening
as a weak boundary impinges on this area.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Extreme Heat Warning until 9 PM CDT this evening for
     SDZ038>040-050-052>071.
MN...Extreme Heat Warning until 9 PM CDT this evening for MNZ071-
     072-080-081-089-090-097-098.
IA...Extreme Heat Warning until 9 PM CDT this evening for
     IAZ001>003-012>014-020>022-031-032.
NE...Extreme Heat Warning until 9 PM CDT this evening for NEZ013-
     014.

&&

$$

UPDATE...JH
DISCUSSION...08
AVIATION...Samet