813
FXUS63 KFSD 221116
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
616 AM CDT Fri Aug 22 2025

.KEY MESSAGES...

- Lingering severe weather risks through the daytime hours of
  Friday, though will be mostly focused from the pre-dawn hours
  through mid-day. Very low chance of afternoon redevelopment.
  Golf ball size hail and 60 mph winds will be the primary
  risks.

- A Flood Watch is in effect until 10 AM today for localized
  flash flooding. Areas with the greatest potential for flash
  flooding will be along the Highway 14 corridor.

- A cooler trend this weekend into next week will give us a
  brief taste of fall. Lower humidity with highs generally in
  the upper 60s to mid 70s with generally dry conditions.

&&

.DISCUSSION...
Issued at 124 AM CDT Fri Aug 22 2025

CURRENT CONDITIONS: Weak dPVA combined with low-lvl convergence
continues to spur the development of scattered thunderstorms in
areas north of I-90 in eastern SODAK early this morning.  Given
lingering MUCAPE AOA 2000-2500 J/KG, along with effective bulk shear
AOA 40 knots, an isolated elevated supercell will be possible.
Activity has shown some preference to build southward into both
the low-lvl jet axis but also along the edge of deeper
instability west of I-29. A stronger secondary shortwave is
beginning to eject into the western Dakotas and Nebraska as of
1am and will likely being to develop additional convection over
central SD through the sunrise hours. Given the supercell
potential, golf ball size hail will be possible. IF storms can
break through a stabilized boundary layer, DCAPE remains
moderate suggesting some severe downdraft potential in storms
as they move into the western CWA after 4-7am.

TODAY: Around sunrise, the cold front that is draped from
northwestern Minnesota through central South Dakota and into east
central Wyoming will begin to drift southeast. Ongoing
convection in central South Dakota will continue to slide
eastward this morning.  0-6 km bulk shear generally increases
through the morning, however, most models project that MUCAPE
begins lessens after 12Z as mid- lvl lapse rates also weaken.
That said, would not be surprised to see an isolated severe
storm risk continue through the mid- day hours as the associated
wave and convection moves into NW Iowa and SW MN by early
afternoon. Slow storm motion and high PWATs continue to product
the potential for locally heavy rainfall. As such a Flood Watch
has been issued until 10 AM today. More on this in the Hydrology
section.

The true cold front arrives later in the afternoon, through some
uncertainty remain on both the atmospheric recovery, but also the
remaining forcing in place.  If an isolated storm could develop,
with deep shear 35 to 45 kts, a strong to severe storm could develop
in this area. Dry mid-levels may enhance downdraft potential.
Considering this, the main threats look to be hail to the size of a
half dollar, and wind gusts to 70 mph. Given the speed-up of the
true cold front in the afternoon, the greatest redevelopment risk
may end up just along the eastern and southern portions of the CWA.

THE WEEKEND INTO NEXT WEEK:  We`ll get a little taste of fall
temperatures beginning this weekend into mid next week. Aloft a
northwesterly flow pattern will set up over the central to Western
Plains. Behind Friday`s cold front we will see temperatures in the
850 mb level decreasing to between roughly 8 and 12 deg C. At the
surface this will translate to cooler temperatures. Saturday Highs
will in the 70s with lows in the 40s and 50s. Sunday and Monday
highs will be in the upper 60s to mid 70s with lows in the 40s.
Tuesday through Thursday look for a little bit of variance in
highs, but in general upper 60s to low 70s with a few 80s over
central South Dakota on Wednesday. Lows will continue to be in
the 40s, and warming slightly to the 50s by the end of the week.


Conditions are expected to remain dry until at least Tuesday. Within
the northwesterly mid-level flow a couple of weak waves move through
the region bringing low chances (<20%) of rain Tuesday and
Wednesday. A potentially stronger wave on Wednesday night into
Thursday morning could bring chances for showers and thunderstorms.
However, at this time model guidance is in very low agreement, and
so confidence in storm formation is low. Keep and eye on the
forecast for updates as they become available.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 613 AM CDT Fri Aug 22 2025

An areas of thunderstorms will continue to move east this
morning bringing brief periods of MVFR visibility and gusty
winds to around 35 mph.

This rain moves into MN and northern IA later this morning, with
a cold front passing through by mid-day. VFR ceilings linger
into the afternoon and evening hours, with some very low
probabilities for isolated showers or thunderstorms along a line
from Vermillion to Spencer late in the afternoon.

VFR conditions with a northerly wind are expected areawide
Friday night into Saturday morning.


&&

.HYDROLOGY...
Issued at 124 AM CDT Fri Aug 22 2025

A flood Watch for portions of east central South Dakota through
10 AM Friday. Convection will again take an eastward track over
some areas that have had 1-3" of rainfall through the overnight
hours. Convection moving in from the west after daybreak will
likely track along a west to east low-lvl convergent zone. HRRR
max QPF guidance suggests potential for an additional 1 to 3" in
isolated pockets.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Flood Watch until 10 AM CDT this morning for SDZ038>040.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...Dux/AJP
AVIATION...Dux
HYDROLOGY...AJP