437 
FXUS63 KFSD 110222
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
922 PM CDT Thu Sep 10 2026

.KEY MESSAGES...

- Storms may develop Friday late afternoon and evening. If
  storms develop, they may quickly become strong to severe.
  Confidence in development and coverage remains low due to 
  strong capping potential.

- Additional chances for showers and thunderstorms return Sunday
  morning and continue into the middle of next week. Some storms
  may become strong to severe. 

- Cooler conditions arrive this weekend into much of next week.  
  Occasional shower and storm chances linger mid next week.

&&

.UPDATE...
Issued at 913 PM CDT Thu Sep 10 2026

Models continue to be very agreeable that surface based
convection will be hard to come by on Friday afternoon with 
fairly strong capping and only weak convergence along the 
surface front. So for now, thunderstorm chances before about 7 
pm look slim. There is some agreement on increasing the LLJ from
about 925mb to 850mb early tomorrow evening with convergence 
focusing mainly east of I-29. If the elevated cap lifting from 
this level can weaken enough we would likely see 1500-2000 J/kg
CAPE with about 30 knots of deep layer shear. This would be 
enough to produce hail to ping ping ball and wind gusts to 65 
mph. One other area to watch will be over parts of southwest MN.
Capping may weaken enough early in the evening to allow storms 
to either develop or build southward into the area. Shear is a 
little stronger in this area with similar instability so a 
couple of stronger updrafts will be possible. Overall continues 
to look like an isolated to scattered at best scenario.

&&

.DISCUSSION...
Issued at 145 PM CDT Thu Sep 10 2026

This afternoon will be dry and breezy with gusts 25-35 mph, mostly 
clear skies, and highs in the upper 70s to 80s. Dew points will be 
lower this afternoon at around 60 or less. Overall a pleasant day is 
in store. Overnight lows will be in the mid to upper 60s with the 
breezy winds continuing into Friday.

Friday will be another warm day with highs in the 80s for most of 
the CWA, and the low 90s west of the James River Valley. Throughout 
the day a narrow plume of Theta-E air will advect in from the south, 
along and east of Highway 81. Instability will increase along and 
east of the plume with MUCAPE values climbing to 1500-2000 J/kg. 
Modest mid-level lapse rates around 7+ deg C/km will align well with 
the plume of instability. Bulk shear will be 35-40 kts. With 
clockwise curved hodographs this set up is marginal to slightly 
favorable for all modes of severe weather. This is also outlined in 
the SPC Day 2 outlook with a Slight Risk (level 2 of 5) for severe 
weather. However, a few items of uncertainty keep confidence in 
convection initiation and coverage low. Probably the most important 
factor is despite the moisture advection model soundings remain
dry through most of the column for areas west of I-29. Forcing 
is on the strong side in the form of the upper trough and 
surface low/cold front, but without moisture not much is going 
to happen besides some cumulus clouds. East of I-29 moisture 
return flow is better, however the environment will be strongly 
capped. As the whole system progresses east through the evening
and into the overnight the airmass slowly saturates. But by 
this point the forcing should be along our eastern CWA border 
if not into central Iowa. In this scenario we will get very 
little if any convection. This is the most likely scenario at
this time.

The other scenario is the better moisture return drifts farther 
west. Then as the system passes through we could see saturation 
occur sooner, and thus convection begin earlier east of Highway 81 
between 4 and 7 pm, and along and east of the I-29 corridor 
roughly between 7 pm and 10 pm. Storms would track east and be 
out of the CWA roughly between midnight and 3 am Saturday. The 
final scenario is we are able to lift off the 850-700 mb layer 
and scattered strong to severe storms could develop. All this to
say a very conditional environment will be in place with risks 
for large hail and damaging wind gusts. Though the risk is low, a
tornado cannot be ruled out.

Behind the cold front overnight lows will cool into the 50s and low 
60s over northwest Iowa. Through the morning hours a few
isolated elevated showers are possible. Winds will become 
northerly and light during the day. Mid-level temperatures will 
fall into the teens C and at the surface highs will be slightly 
below average for this time of year, in the low 70s north of 
I-90 and the mid to upper 70s to the south. Much drier air will 
advect in from the north bringing dew points down to the 40s to 
mid 50s. Saturday will be a pleasant taste of fall. 

Early Sunday morning the flow aloft becomes mostly zonal and high 
pressure builds in at the surface. Modest moisture return on 
southeast winds and WAA ahead of an approaching low amplitude wave 
may be enough to trigger light scattered showers and thunderstorms 
by the late morning to early afternoon. These are not expected to be 
severe but could bring rain to a larger portion of the region. 
Sunday evening into the overnight a strong upper trough swings 
through northwest of the region. An associated surface low ejects 
out of Colorado onto the central Plains and accelerates northeast 
into our CWA. Though many details are unclear at this time, some 
storms could be strong to severe Sunday night into Monday morning. 
Storms may linger into the afternoon.

Northwest flow aloft is expected for the first half of next week. At 
the surface highs will be closer to seasonal averages, in the 70s. 
Another round of storms is possible mid-week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 608 PM CDT Thu Sep 10 2026

VFR through the period. Breezy southerly winds through the
period with some gusts of 35 to 40 mph likely during the day
Friday. A few early morning ACCAS showers will be possible
Friday morning, but confidence is low. A strong to sever storm
will be possible after about 22z Friday, but confidence is low
and any storms that may develop should remain very isolated.

&&

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

&&

$$

UPDATE...08
DISCUSSION...AJP
AVIATION...08