Vermillion, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

774
FXUS63 KFSD 130819
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
319 AM CDT Wed Aug 13 2025

.KEY MESSAGES...

- There is a Level 2 of 5 risk for severe thunderstorms tonight
  for areas west of Highway 281 and a Level 1 of 5 risk
  extending to the east near the I-29 corridor. The greatest
  risk for severe weather will be from 8pm through midnight,
  with potential for wind gusts to 70 mph, half dollar size
  hail, and locally heavy rain.

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

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

&&

.DISCUSSION...
Issued at 312 AM CDT Wed Aug 13 2025

TODAY: As of 3 AM, patchy fog has begun to develop in portions
of northwest Iowa, especially near river valleys. Expect fog to
persist until we start to warm and mix around 8-9 AM. Upstream,
an area of elevated showers and isolated thunderstorms tracks
east into the Black Hills. Hi-res models struggle to recognize
this activity, but those that do suggest high-based showers and
perhaps some rumbles of thunder should reach Huron/Chamberlain
around 9-11 AM and track east into southwest MN into the early
afternoon. Any severe weather threat is unlikely with this as
storms remain high-based and track into a weakly unstable and
capped regime further east.

Warmer with increasing humidity today with warm air advection ahead
of a developing northern stream shortwave trekking through the
Rockies and a broad ridge over the Southwest. High confidence in
highs in the 80s to lower 90s and a south breeze. A weaker low level
jet brings gusts in the 20s to near 30 mph to south central SD this
afternoon.

TONIGHT: The main short-term story is a stout 500mb shortwave likely
to spark scattered thunderstorms near the Black Hills 4-7 PM.
Storms should merge into clusters tracking southeast or east
through the evening, not reaching the MO River in central SD
until 8-10 PM. Expect the greatest severe weather threat to be
confined west of the I-29 corridor, from 8 PM to 12 AM. 30-40
kts of 0-6 km shear favors embedded supercells within storms
merging into a cluster. Initial cells will be fueled by LLJ
feeding into central SD, but weakening mid level lapse rates and
destabilization as storms track east should weaken severe
weather threat as they approach I-29 and beyond. The strongest
storms will be capable of producing large hail up to half dollar
size, wind gusts up to 70 mph, and locally heavy rainfall.
Can`t entirely rule out a brief tornado in south central SD with
slight backing of low level winds. 00z/06z CAMs suggest
damaging winds will be the main threat heading later in the
evening, with a nonzero potential for gusty wake low winds
behind the departing storms.

THURSDAY: Scattered showers and thunderstorms may persist near and
east of I-29 early Thursday morning, exiting eastward. By Thursday
afternoon, a northern stream elongated sfc trough sets up in the
western Dakotas to eastern CO with strong WAA ramping up gusty south
winds and dew points into the 70s. Heat index readings will approach
100 degrees along the MO River Valley as well.

Thursday looks primarily dry, but weak mid level "ridge-riding
waves" give a low (<30%) chance of showers and storms both in south
central SD and east of I-29 late Thursday night. Although severe
weather cannot be entirely ruled out, threat is notably lower than
the surrounding days.

FRIDAY 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 and Saturday afternoons, near and south
of the I-90 corridor as dew points peak in the mid 70s. Will be
monitoring these two days for potential heat headlines.

Stout mid level capping keeps most storm threat confined to the
nighttime hours, but confidence in storm timing/chances is
quite low this weekend. A low chance for storms (<40%) continues
as we remain in southwesterly flow aloft with potential for weak
shortwaves to trigger storms somewhere in the Northern 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. Rain chances are
slightly higher Sunday night during a brief period of more zonal
flow aloft, but storms are continually dependent on the low-
confidence track of any ridge-riding disturbances and the track of
now-Tropical Storm Erin.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1049 PM CDT Tue Aug 12 2025

Patchy fog is expected to develop tonight under clear skies and
light winds. The best chance of seeing fog will be in areas near and
in river valleys in northwest Iowa, where there was enough
confidence to include an IFR TEMPO group for KSUX between 12 and 14Z
Wednesday morning. Fog should dissipate quickly after 14Z. VFR
conditions are expected otherwise through the period. There is a low-
end of chance of showers and isolated thunder Wednesday morning in
areas west of the James River, but should miss KHON.

A second, more organized round of showers and storms is set to move
in from western South Dakota late Wednesday evening. Added a PROB30
group to KHON starting at 14.03Z for -SHRA to account for this.
Decided against including thunder in the PROB30 for now as there is
too much uncertainty regarding strength and location of this round
of showers and storms. Light and variable winds tonight turn
southeasterly Wednesday morning, with gusts picking up to around 25
kts west of the James River Wednesday afternoon.

&&

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

&&

$$

DISCUSSION...BP
AVIATION...Samet