Yankton, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

668
FXUS63 KFSD 121742
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1242 PM CDT Tue Aug 12 2025

.KEY MESSAGES...

- Confidence is increasing (>60%) in chances for thunderstorms
  on Wednesday night. A few storms may become severe, producing
  hail up to half dollar size, wind gusts up to 70 mph, and/or
  locally heavy downpours.

- High heat and humidity return Thursday through the weekend.
  Afternoon heat index values could approach 100 degrees,
  especially south of I-90 on Friday.

- An active weather pattern brings low to moderate chances
  (20-40 percent) for showers and thunderstorms Thursday night
  through the weekend. Severe weather cannot be ruled out, but
  confidence in any details is low.

&&

.DISCUSSION...
Issued at 301 AM CDT Tue Aug 12 2025

TODAY: Early this morning, a few sprinkles linger north of I-90 near
the passing sfc front. Canadian wildfire smoke at the surface
continues to reduce visibility to as low as a half mile at times.
Fortunately the passing weak front is also helping to clear out near
surface smoke, advecting it eastward out of the region.

Could see patchy fog develop in low lying areas such as river
valleys again early this morning. Otherwise mostly sunny, pleasant
weather prevails today as dry sfc high pressure slides east into the
region. Cold air advection behind the departed front and a northern
stream upper trough will bring a cooler day with a slight northwest
breeze. Expect high temperatures to only reach the mid 70s to around
80 degrees across the region, mild for this time of year.

TONIGHT: Expect a cooler night with a near calm wind and mostly
clear skies prompting strong nocturnal radiative cooling.
Temperatures will drop into the 50s early Wednesday morning. With
dew points in the upper 50s in northwest Iowa, light winds, and
clear skies, could see patchy fog develop in portions of northwest
Iowa early Wednesday morning, especially in river valleys.

WEDNESDAY: Warmer with increasing humidity on Wednesday as heights
rise with warm air advection ahead of a broad ridge over the
Southwest. High confidence in highs in the 80s to lower 90s, hottest
in south central SD, and a south breeze.

By Wednesday evening, attention turns to potential for incoming
storms and severe weather threat. A stout shortwave trough coming
onshore in the Pacific Northwest this morning will reach the High
Plains by Wednesday afternoon, sparking thunderstorms in western
and/or central SD. Confidence has increased considerably in the last
24 hours that storms will merge into a complex/cluster tracking into
eastern SD on Wednesday evening. 0-6km deep layer shear of 35-45 kts
amidst an unstable warm sector nosing into the eastern Dakotas
suggests potential for organized embedded supercells and isolated
(or perhaps scattered) severe storms. However decreasing mid level
lapse rates and stabilization as the complex progresses east will
favor threat transitioning from large hail (up to half dollar size)
to more wind (up to 70 mph) and locally heavy downpours. Low
confidence in how far east severe weather threat can maintain
strength, especially after sunset.

THURSDAY THROUGH SATURDAY: Southern stream upper ridging shifts east
over the Central and Southern Plains, bringing hotter, more humid
weather to end the week. The best chance for heat index readings
exceeding 100 F comes Friday afternoon, near and south of the I-90
corridor as dew points peak in the mid 70s and the warmest air aloft
builds in. Will be monitoring these three days for potential heat
headlines, especially Friday.

Stout mid level capping should prohibit daytime storm development as
we reside in the warm sector, but confidence in storm timing/chances
is quite low late week through the weekend. A low chance for storms
(<30%) continues each night as we remain in southwesterly flow aloft
with potential for weak shortwaves to trigger storms somewhere in
the Northern to Central Plains.

SUNDAY INTO EARLY NEXT WEEK: Above normal temperatures are favored
heading into next week as the northern jet lifts further into Canada
and strong upper ridging develops over the Rockies. Lower confidence
in rain chances during this period, which are dependent on how far
east upper ridging builds and the track of any ridge-riding
disturbances, as well as the track of now-Tropical Storm Erin.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1242 PM CDT Tue Aug 12 2025

With patchy fog and smoke from earlier this morning finally to
the east of TAF airfields, expect VFR conditions through the
period. Outside of some afternoon thermal cumulus around 5000 ft
agl, skies should be mostly sunny/clear. The one potential
caveat is at KSUX, where some guidance suggests the redevelopment
of fog Wednesday morning along the Missouri River (20-50 percent
chance). Confidence not high enough at this time to include in
the 18Z TAFs, but something to monitor with future forecasts/
updates.

Winds will be light from the northwest this afternoon with some
gusts up to 20 kts at KHON/KFSD. Winds will then become light
and variable tonight, before turning to the southeast toward the
end of the forecast period.

&&

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

&&

$$

DISCUSSION...BP
AVIATION...Rogers