Yankton, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

472
FXUS63 KFSD 290300
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1000 PM CDT Sun Jun 28 2026

.KEY MESSAGES...

- A Heat Advisory is in effect for some areas into Monday, and
  further adjustments to headlines are possible in the coming
  days.

- Isolated to scattered severe thunderstorms will be possible on
  Monday late afternoon into the evening. The better chances
  will be near and east of I-29.

- Summer heat and humidity is expected periodically through
  next week. Daily heat indices of 95 to 105 degrees will lead
  to Major to locally Extreme Heat Risk at times. Begin planning
  now to reduce the risk of heat illness and impacts.

- An active pattern through the week leads to periodic moderate
  chances for showers and storms. Uncertainty in the timing of
  rain also brings lower confidence in daily excessive heat.

&&

.UPDATE...
Issued at 945 PM CDT Sun Jun 28 2026

Very humid conditions continue across the area this evening,
with little relief heading into tonight as temperatures remain
very warm ranging from the upper 60s west to the middle to upper
70s east for lows tonight. A warm front is lifting northward
into Minnesota this evening, with some showers and isolated
storms developing north of the boundary. This will be occurring
mostly north of the area with the exception of maybe a shower
or two for the next hour or so over the Highway 14 corridor in
southwest Minnesota.

Another area of storms looks to develop off to our west tonight
near the Black Hills and the far western Nebraska panhandle and
then track northeastward heading towards daybreak. With these
storms likely forming farther west of the area than last night,
it is likely that this activity misses us to our north and
west. However, it can`t be entirely ruled out that these storms
clip the far western reaches of our area from Chamberlain to
Huron and points northwest of their late tonight, after about
3-4 am. Model soundings indicate that these areas will have
around 2000-2500 J/kg of elevated instability when lifting from
about 850-700 mb with not too much CIN in place at times. With
large CAPE profiles and mid level lapse rates around 7.5-8 C/km,
hail up to the size of ping pong balls would be the threat if
the core of these storms were to clip the area. Once those
storms out west get more organized, should have a better idea of
where they track. But as of now, chances for early morning
storms north and west of the aforementioned Chamberlain to Huron
line is low (<15%).

Lastly, patchy fog looks to develop in parts of the area tonight
given diminishing winds and wet grounds. The best chance of
this will be north of I-90 where winds will be lightest for the
longest stretch of time overnight; however, high clouds from
storms out to our west could help limit fog impacts overall.

&&

.DISCUSSION...
Issued at 144 PM CDT Sun Jun 28 2026

Thunderstorm Risks:

Very warm and humid conditions in place today in the wake of the
overnight MCS that brought a fairly widespread half an inch to 2
inches, with pockets around 3 inches. Even with the warm and humid
conditions, drier air aloft and a general lack of upper level
support suggest showers and thunderstorms will remain at bay. A very
weak wave moves through parts of western IA tonight but moisture
appears to be fairly scant with this. The more impressive wave is to
the west of the area with storms looking to remain well west of the
area as well.

This stronger wave pushes into central SD on Monday and brings
another hot and humid day to the area. A trough of low pressure
moves into the area at the surface as low pressure lifts northeast
and could spark a few showers and thunderstorms. The better chances
will be near and east of I-29 but once again will be fighting a bit
of a cap. If storms do develop there will likely be close to 300
J/kg CAPE as well as moderate shear to support wind gusts to 70 mph
and hail to the size of golf balls. Heavy rain will be a threat as
well with the freezing level around 14000 feet AGL.

Tuesday night into Wednesday night may be the next period where more
widespread chances for showers and thunderstorms returns. Models are
fairly agreeable lifting a wave northeast into the area and only
slowly exiting. This brings a somewhat extended period of warm
advection in the lower levels. Instability appears to be sufficient
around 2500 J/kg with weak to moderate shear. With the freezing
level around 13000 feet AGL, heavy rain will also be a threat.

Another fairly well agreed upon wave ejects northeast on Thursday
and may continue chances for thunderstorms. Friday into next weekend
less agreed upon but continued pieces of upper level energy should
move through the area bringing a continued threat for showers and
thunderstorms.

Heat Risks:

Long story short, daily excessive heat is no guarantee this week
given the southwest flow aloft and numerous weak waves which will
likely spark showers and storms as well as produce additional cloud
cover.

Monday will prove to be windy and hot with fairly high humidity.
This should bring widespread heat indices of 95 to 105 to areas near
and east of I-29. Heat indices west of I-29 will likely remain in
the lower to mid 90s.

Tuesday will see a little drying in the low level as this Monday
night wave lifts north and induces a little mixing in the low
levels. While highs will again be in the 90s, lower dew points
should bring a break from the higher humidity levels and likely keep
heat indices in the 90s.

Wednesday will bring more question marks in regards to higher heat
indices, more so the temperatures than the dew points. With the
expected wave lingering around during the day, cloud cover, and
possible precipitation, will bring about a lower confidence in
temperatures climbing high enough to push us into more dangerous
heat risk levels.

Thursday continues with a few question marks regarding excessive
heat due to another wave as will Friday. Still likely daytime
temperatures will climb into the upper 80s to mid 90s with some
humidity, but the ability to produce widespread 100 + degree heat
indices every day will be limited.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 655 PM CDT Sun Jun 28 2026

Patchy fog is likely over portions of the area tonight as winds
turn lighter and the grounds remain wet from recent rainfall. The
best chance of fog will be over portions of the Highway 14 corridor
where winds will be the lightest for the longest stretch of time
overnight. One limiting factor to fog development especially in the
portion of Highway 14 near and west of the James River will be the
fact that thunderstorms that develop off to our west may send some
high clouds into these areas and limit cooling. That said, still
enough confidence to at least add a couple of hours of MVFR
conditions at KHON. Speaking of those storms, can`t rule out one of
those moving near the vicinity of KHON closer to sunrise, but
chances for this are low (<15%) at this time.

Any fog will likely lift quickly by sunrise as winds increase area-
wide through the morning hours. Winds could gust to 25-30 kts
(locally to 35 kts) Monday afternoon. A low pressure system
will bring a cool front into the area from west to east
throughout the day Monday and turn winds from out of the
southeast to out of the southwest gradually through the day.
This cool front will also be responsible for isolated to
scattered storm development Monday afternoon, but not enough
coverage is expected at this time to warrant mention in the
TAFs.

&&

.CLIMATE...
Issued at 410 AM CDT Sat Jun 27 2026

Summer heat builds into the area from Sunday through much of
next week. This will lead to a potential for a few temperature
records to be tied, or possibly broken:

Current Record Highs:

Monday (06/29): KFSD(101|2002) KSUX(100|2022)

Current Record Warm Lows:

Monday (06/29): KFSD(77|2020) KSUX(80|1931) KHON(75|2020)

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 9 PM CDT Monday for SDZ062-066-067-069>071.
MN...Heat Advisory from 1 PM to 9 PM CDT Monday for MNZ072-080-081-
     089-090-098.
IA...Heat Advisory until 9 PM CDT Monday for IAZ001>003-012>014-
     020>022-031-032.
NE...Heat Advisory until 9 PM CDT Monday for NEZ013-014.

&&

$$

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