135
FXUS63 KFSD 141140
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
640 AM CDT Mon Sep 14 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms will continue to develop
  this morning. While locally heavy rainfall be the main hazard,
  marginally large hail up to half dollar size will also be
  possible as this activity continues to lift northeastwards.

- A very conditional risk for severe storms could develop by
  late 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.

&&

.UPDATE...
Issued at 400 AM CDT Mon Sep 14 2026

Taking a look across the area, we`re continuing to see showers and
thunderstorms develop this morning along the 850mb warm front
stretching roughly from a Chamberlain to Norfolk, NE to Lincoln NE
line. As this front continues to lift to the northeast and interact
with a strengthening LLJ, should see coverage gradually expand
across our area as we head towards daybreak. While locally heavy
rainfall will be the primary threat given the lower LCLs and higher
PWATs (1.25"-1.75" inches), there will also be a marginally large
hail risk with some of this developing activity as increasing shear
helps steepen mid-level lapse rates. With this in mind, can`t rule
out a few quarter to half dollar sized hail stones. From here,
intermittent development will continue through the evening hours
with the LLJ overhead.

Depending on if things can clear out by early afternoon, there could
be a narrow window for additional strong storms across our far
southeastern zones near the U.S. Highway-20 corridor. The 06z HRRR
is by far the most aggressive of the CAMs. However, given the
potential for 1500-2000 J/kg MLCAPE and 40-50 kts of shear; all
hazards will be possible. IF this occurs, the best time frame would
be between 5 pm and 10 pm as the cold front progresses through the
region. Again, this potential will be conditionally dependent on if
those areas can sufficiently recover in time. Lastly, should
see most of this activity move out of our area by early evening.

&&

.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 /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 634 AM CDT Mon Sep 14 2026

Mainly VFR conditions will transition to a mix of MVFR to IFR
conditions this morning with developing thunderstorms and lower
stratus. A line of convection continues to lift northeastwards
this morning promoting occasional MVFR to IFR cigs and vsbys.
With trailing stratus behind it, MVFR to IFR cigs could hang
around through the early afternoon before mainly VFR conditions
return. Otherwise, added in TEMPO groups to all TAF sites as the
line moves through. Lastly, southeasterly winds will strengthen
throughout the day with gusts between 30-40 mph expected
through this evening.

&&

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

&&

$$

UPDATE...05
DISCUSSION...Dux
AVIATION...05