Allendorf, Iowa Weather Forecast Discussion

369
FXUS63 KFSD 091957
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
257 PM CDT Tue Sep 9 2025
.KEY MESSAGES...
- Additional scattered showers and isolated thunderstorms are
  possible into the early evening hours east of Interstate 29.
  Severe weather is not expected.
- There is 30-50 percent chance for fog late tonight into early
  Wednesday morning for areas mainly east of the James River
  Valley. Pockets of reduced visibility below 1 mile are
  possible.
- Canadian wildfire smoke will linger aloft through Wednesday
  and begin to move east Wednesday night. Any surface impact
  will be minimal.
- Temperatures warm to well above mid-September normals Thursday
  through Saturday.
- The next best chance for showers and thunderstorms (30-50
  percent) will be Saturday night through Sunday.
&&
.DISCUSSION...
Issued at 257 PM CDT Tue Sep 9 2025
09.1930Z water vapor shows a compact short-wave moving east
into central MN/IA. Scattered showers/isolated thunderstorms
with this wave have moved east of the forecast area and expect a
dry forecast for most this evening and overnight. The exception
being areas east of I-29 where some additional development is
possible as another weak area of positive vorticity advection
moves through the eastward advancing trough aloft. Severe
weather is not expected with any additional storms that develop.
Also monitoring areas of stubborn low stratus from the James
River Valley east and along and south of Interstate 90. These
clouds should continue to slowly dissipate and lift with peak
afternoon heating. However, recent guidance suggests this cloud
cover could expand again overnight given moist, weak low-level
flow. This could also manifest itself as some areas of fog as
well. 12Z HREF shows a 30-50 percent chance visibility drops
below 1 mile by daybreak Wednesday. For now, added patchy fog to
the forecast, but something to watch. Any cloud cover/fog
tonight would help keep overnight lows elevated into the upper
50s to low 60s.
Wednesday will be warmer and dry given building heights aloft.
However, Canadian wildfire smoke is expected to remain,
resulting in milky skies. At this time, smoke is not expected to
reach the surface. Temperatures will top out in the upper 70s
to low 80s with light southeast surface wind.
Thursday through Saturday, the main story will be summer-like
temperatures with an amplified ridge across the nation`s mid-
section. Afternoon highs will rise a bit each day with some
areas along and south of I-90 pushing the 90 degree mark.
Aforementioned ridge begins to slide east Saturday, allowing
flow aloft to turn to the southwest in response to a large
Pacific northwest trough. Elevated instability/shear may lend
itself to some stronger to severe storms, as hinted at by
machine learning models. However, many details still need to be
worked out, so broad brush 30-50 NBM POPs Saturday night through
Sunday seem reasonable at this time.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1242 PM CDT Tue Sep 9 2025
Scattered showers/isolated thunder have now moved east of TAF
airfields as of 09.1730Z. While some additional isolated
activity is possible late afternoon/evening at KFSD/KSUX, not
enough confidence in spatial coverage to include in 18Z
forecast.
Bigger concern will be timing of low stratus at KFSD/KSUX that
has been stubborn to lift/dissipate this morning. Most recent
guidance suggests improving conditions to VFR by mid-afternoon,
but will need to monitor trends and update as necessary. Once
these lower clouds move out, expect VFR through the remainder
of the evening.
Some hints at fog potential overnight at KFSD/KSUX. Will
introduce 3SM/BR at 10.13Z. Any fog that does develop is expected
to dissipate by mid-Wednesday morning.
Winds through the period will be light, generally from the
south-southeast during daylight hours and light/variable
overnight.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
DISCUSSION...Rogers
AVIATION...Rogers

NWS FSD Office Area Forecast Discussion