617
FXUS63 KFSD 131749
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1249 PM CDT Sun Sep 13 2026

.KEY MESSAGES...

- Showers and thunderstorms develop after 3am Monday morning. A
  low chance for a marginally severe storm with hail could be
  possible through 9am as activity moves northeast.

- A very conditional risk for severe storms forms late Monday
  afternoon along Highway 20. All hazards could be possible,
  though cloud cover may play a significant role in potential.

- We`ll remain near to slightly below normal for temperatures
  during the upcoming week.

- Scattered non-severe rain chances will focus in three
  timeframes, with the highest probabilities of rainfall focused
  Wednesday and again late Thursday night and Friday.

&&

.DISCUSSION...
Issued at 1240 PM CDT Sun Sep 13 2026

THIS AFTERNOON: Another cool, but pleasant early Fall day in
the region as continued mid-lvl clouds cross the CWA. With a
light east southeast wind, we`ll continue to see temperatures
rise towards the upper 60s.

TONIGHT: Two thirds of the overnight hours are expected to remain
quiet.  However as we move past midnight, a steady increase in a
broad LLJ through the Plains, along with the approach of mid-lvl
vorticity will begin to develop showers and thunderstorms. Two
areas of focus for convection will develop through the morning.
One area will be across central and north central South Dakota,
with a second band of elevated convection forming from south
central South Dakota into eastern Nebraska where strong theta-e
advection begins to move northeast. While widespread severe
weather isn`t anticipated, soundings show elevated CAPE around
1500 J/KG through the CWA. Mid- lvl lapse rates are marginal,
but shear could be strong enough for a few storms briefly
capable of quarter size hail.

MONDAY: Ongoing convection at daybreak Monday will continue to
move northeast during the morning hours. HREF/NBM mean QPF
suggests fairly widespread 0.25-0.50" totals by mid-day, but the
ceiling is also quite high with outside potential for an inch
of rain in very isolated locations. While the initial band of
moderate rain will move away from the CWA by early afternoon,
model consensus keeps the orientation of the LLJ favorable to
allow persistent showers or even isolated thunderstorms well
into the afternoon. Depending on cloud cover, a very narrow
window for surface based convection will still be possible by
mid/late afternoon as a surface warm front attempts to lift
northward. While most guidance has backed off on the northward
extent of destabilization and kept this south of Highway 20, a
few models remain steadfast that upwards of 2000+ J/KG MLCAPE
could develop from Sioux City to Storm Lake by 23Z. A quick
upscale growth situation would then develop as lift is maximized
with an approaching mid-lvl vort. IF storms could develop, all
hazards would be possible initially, with activity rapidly
shifting SE early in the evening.

The persistent cloud cover and development of widespread low stratus
will leave cooler temperatures over the CWA. I have again attempted
to lower highs towards the cooler side of NBM guidance. Barring a
late afternoon jump if clouds scatter, most locations especially
east of I-29 may struggle to reach 70 degrees and those in Southwest
Minnesota could still be too warm with their forecast highs.

One final item of note for Monday will be winds.  A sharpening of
the SPG through the morning will promote sustained winds as high as
20 mph at times.  Gusts, especially behind departing rain, may rise
into the 30 to 40 mph range into early afternoon.

TUESDAY-WEDNESDAY:  High pressure arrives for Tuesday, signaling dry
conditions in most locations with continued slightly cooler than
normal high temperatures.  A slight shift of mid-lvl flow back to
the southwest by Wednesday could bring enough moisture return for
scattered showers in most areas during the day Wednesday. The focus
of the strongest moisture return, and resultant risk for heavier
precipitation continue to stay focused south of Highway 20.

THURSDAY-SUNDAY: Shortwave ridging moves back through the Plains for
Thursday and early Friday, spelling a return of dry conditions and
some potential for temperatures to return to normal levels to
finish the week. As alluded to in yesterday`s discussion,
signals remain favorable for rain by Friday as a stronger wave
ejects out of the Southern Rockies and into the Plains. Still
lots of details to work out with this system, but as expected,
the 24 hr probabilities for >0.25" ending Saturday morning have
jumped over 50% in all three major ensembles. Quite a bit of
uncertainty for next weekend in regards to the eventual shift
of mid-lvl flow. Ensembles showing low percentage PoPs over a
large area suggesting a significant spread in guidance. While
severe weather risks are expected to remain low, temperatures
stay near seasonal normals with an 8 degree spread in the
25/75th percentile data split either side of normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1214 PM CDT Sun Sep 13 2026

VFR conditions will persist into the evening and overnight
hours. After midnight, we`ll see an increase in lift and drop in
ceilings with the eventual development of scattered showers and
thunderstorms. This activity lifts northeast Monday morning,
producing brief MVFR conditions as it move through. Widespread
MVFR to perhaps pockets of IFR ceilings may develop through
Monday morning with occasional showers lingering. Also watch for
the intensification of southeasterly winds behind the rain,
which may gust over 30 mph at times.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...Dux