677 
FXUS63 KFSD 070840
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
340 AM CDT Mon Sep 7 2026

.KEY MESSAGES...

- Isolated, non-severe thunderstorms continue across
  northwestern Iowa through daybreak. Severe weather is not
  expected, but locally heavy rain has been occurring and may
  lead to isolated flash flooding.

- Isolated to scattered showers and storms are possible along
  and north of I-90 this morning into early afternoon. Severe 
  risk is low.

- Additional scattered and possibly severe storms expected late
  this afternoon across southeastern and south central South 
  Dakota, moving east through tonight. Ping pong ball sized 
  hail, 60 mph wind gusts, and brief heavy rain are the main 
  threats. A tornado or two possible. 

- Quiet but continued warm conditions are expected for the rest
  of the work week.

&&

.UPDATE...
Issued at 339 AM CDT Mon Sep 7 2026

An area of showers and storms continues over northwestern IA into 
southeastern SD early this morning, tied to a wave and some LL 
convergence. Although severe weather is not expected, am concerned 
with flash flooding  due to  training storms over northeastern 
Woodbury and into northwestern Plymouth county - have seen reports 
of over 3 inches since midnight and issued a Flash Flood Warning 
through 6 AM for this area. May see further development in this area 
into southwestern MN through the morning hours as the 700 mb wave 
lifts north. 

Further west, watching the activity across western SD/NE which is 
tied to the next wave and another segment of the LLJ. This may be 
the catalyst for additional showers/storms, mainly north of I-90, 
mid-late morning into the early afternoon hours. Severe weather risk 
is low with these storms. 

Main focus is with the increasing LLJ later this afternoon and 
tonight, in tandem with main trough ejection from the Rockies. 
Leading wave and LLJ along with a surface boundary and destabilizing 
atmosphere should provide the catalyst for showers and storms to 
develop. Instability All modes of severe weather are possible from 
roughly 5 PM through 1 AM, as initial discrete cells may grow 
upscale and move east. Shear at all levels increases through the 
evening, and increasing mid level lapse rates will also be 
supporting of hail to the size of ping pong balls - possibly larger 
if a storm can maintain discrete status for longer. A tornado or two 
are possible with surface based storms with curved hodographs and 
increasing shear in the lowest levels. 65 mph wind gusts are also 
possible. May see some locally heavy rainfall as well, but more 
progressive storm motion should help limit widespread concerns. 
Localized flash flooding is possible, especially if storms move over 
areas which have seen recent heavy rain.

Still questions for Tuesday regarding where the surface boundary 
ends up and impacts from overnight/early morning convection. Better 
shear looks to be offset from the greatest instability which lies 
ahead of the front. Could see a stronger storm or two across 
northwestern IA and adjacent areas of central MN/eastern NE/far 
southeastern SD in the afternoon and evening. 

&&

.DISCUSSION...
Issued at 1246 PM CDT Sun Sep 6 2026

THIS AFTERNOON: Strong convection continues to develop in areas 
along but mostly east of I-29 this afternoon.  The area continues to 
reside in a moderately unstable environment, but lacks any 
meaningful shear and mid-lvl lapse rates.  However, climatologically 
significant PWATs are in place, with enough DCAPE to suggest an 
increased risk for wet microbursts over the next 1-3 hours in a 
narrow corridor from Madison to Sioux Falls, Sioux Center, Cherokee, 
Storm Lake, Le Mars, and Sioux City. Rainfall may be the most 
impactful hazard this afternoon with 1-2 hr totals of 3-4" already 
in portions of southern Minnesota.  Additional convection is likely 
to continue to produce 2-4" totals in pockets of NW Iowa, though 
cold pool development may help push storms off an area before 
extreme values may be produced.  The stronger MCV will also nudge 
it's way northward later this afternoon, and may work to produce 
additional northward/northeastward convection with it. 

TONIGHT: This shortwave/MCV will drag it's feet eastward this 
evening, with some expected weakening of convection with the lost of 
daytime heating and general stabilization of the environment nearby. 
However, an increased LLJ may begin to develop after 02Z which 
could bring returning elevated showers and isolated 
thunderstorms to the CWA late this evening and continuing into 
the overnight hours. This activity will likely not be severe, 
but any shower could still bring brief heavy rain. 

MONDAY-TUESDAY: Elevated shower activity diminishes towards daybreak 
as shortwave ridging arrives. An ejecting trough out of the Rockies 
will bring additional elevated convection into central and northern 
South Dakota into Monday afternoon, perhaps grazing the western CWA. 
As the EML gradually erodes into south central SD late in the 
afternoon, a few strong to severe storms may develop and track 
east southeast into the early overnight hours. As the LLJ 
increases after dark, elevated convection may expand in coverage
with continued low- end severe weather risks for Tuesday 
morning. 

More uncertainty for Tuesday, which is focused moreso on the 
location of the surface front and impacts of overnight elevated 
convection.  While the primary surface front settles in northwest 
Iowa, a secondary stronger dew point gradient arrives later in the 
afternoon. Should sufficient clearing develop, then a storm or two 
could become stronger by mid-afternoon with activity quickly 
tracking southeast by the evening.

EXTENDED: With ongoing convection, no forecast changes made to the 
extended as a temporarily reprieve from active weather 
develops. Temperatures may still remain near to above normal 
for the rest of the work week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1238 AM CDT Mon Sep 7 2026

Scattered light showers are ongoing over northwest Iowa. These will 
taper off over the next few hours. VFR conditions for the overnight 
except for areas in southwest Minnesota where winds have become 
light enough for patchy fog to form. Fog will dissipate as southeast 
winds increase through 07.12Z. Gusts west of I-29 will be 20-27 kts, 
while gusts to the east will be 20 kts or less. Breezy winds expand 
east through the afternoon with gusts of 20-30 kts with a few gusts 
to 33 kts possible over south central South Dakota. Winds remain 
gusty through the end of the period. 

We'll be watching for two rounds of showers and thunderstorms 
tomorrow. The first round looks to begin around 07.15Z through the 
late morning to early afternoon. This round looks to remain mostly 
north of I-90. Widespread severe weather is not expected, however an 
isolated storm may become strong to severe producing 1 inch hail and 
52 kt winds. The second round looks to begin in the late afternoon 
to early evening. This round brings increased potential for severe 
weather. Initial storm mode over central South Dakota will most 
likely be supercells. These could produce hail up to the size of a 
ping-pong ball, heavy rain, and wind gusts to 60 mph. Though the 
risk is low an isolated tornado is also possible. As storms approach 
the I-29 corridor they may begin to grow upscale into a broken line 
to a QLCS. Hail threats diminish to marginally severe but wind risks 
increase. Isolated brief spin ups and weak tornadoes are also 
possible along bowing sections. Storms will be ongoing east of I-29 
through the end of the period.

&&

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

&&

$$

UPDATE...SG
DISCUSSION...Dux
AVIATION...AJP