117
FXUS63 KFSD 051121
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
621 AM CDT Fri Sep 5 2025

.KEY MESSAGES...

- Fall-like temperatures in the 50-60s today. Afternoon clouds
  may produce some isolated sprinkles to light showers north of
  I-90.

- Breezy afternoon winds will gust between 25-35 mph with strongest
  winds west of I-29.

- Lows Saturday morning will fall to the mid 30s along and north of
  I-90. Patchy frost may be possible.

- Next week there are some chances for showers and
  thunderstorms, though many details are unknown at this time.

&&

.DISCUSSION...
Issued at 240 AM CDT Fri Sep 5 2025

TODAY: Northwesterly flow from the surface through the upper levels
will bring down strong CAA throughout the day. Temperatures in the
mid-levels will cool through the day, decreasing to 2-6 degrees C.
Despite good mixing through approximately the 800 mb layer, these
cooler temperatures will only allow highs to rise to the upper 50s
to low 60s. We`ll begin the day with partly cloudy skies but as we
enter the afternoon hours clouds will increase as moisture from
Canada is bought south on a shortwave associated with a large upper
low spinning over eastern Canada. Weak instability above the mixed
layer will allow clouds to build into towering cumulus, resulting in
afternoon mostly cloudy skies. While we do not expect much to come
from these clouds, a roughly 5000 ft deep saturated layer may result
in a few isolated sprinkles to light showers north of I-90. In
addition, with winds well aligned through the depth of the column,
we can expect stronger gusts to reach the surface as we reach peak
mixing this afternoon. Northwesterly gusts of of 30-35 mph can be
expected for areas west of I-29. Areas to the east can expect
slightly lower gusts of 20-25 mph. Winds will decrease after sunset,
becoming light and variable overnight. Lows are expected to fall to
the upper 30s to low 40s.

THE WEEKEND: Surface high pressure settles over the region for the
weekend. Though flow aloft remains primarily northwesterly,
some weak subsidence aloft will help warm the mid-levels back
into the 8-12 degree C range for Saturday. Good mixing again
will help us tap into those slightly warmer temperatures and
warm our surface highs into the 60s. Diurnal winds will be
slightly breezy with gusts generally 20 mph or less. As we lose
afternoon heating those winds will become light and variable.
With mostly clear skies, maximum radiational cooling will be
achieved. Lows for Saturday will dip into the mid 30s to low
40s. Isolated pockets of frost are possible along north of I-90.
Tender outdoor plants may need to be taken inside or covered.
Sunday the surface high shifts east, turning our winds
southerly. WAA at the surface and in the mid-levels helps warm
highs into the upper 60s and low 70s. Winds overnight remain a
little more mixy as a surface low pressure begins to move east
out of Wyoming. This will help overnight lows stay out of frost
range, in the mid 40s to low 50s.

NEXT WEEK: By Monday morning the low pressure will be over western
South Dakota and an associated warm front will lift north through
the region. This may act to trigger some isolated showers and
thunderstorms Monday morning. Monday afternoon into Tuesday morning
the main mid to upper wave will pass over the region, bringing
renewed chances for thunderstorms. A moderately unstable
thermodynamic profile may allow for some of these storms to be
on the strong side. Though, there is very low agreement on long
range guidance to speculate on the details at this time.
Periodic waves keep storm chances in the forecast for the second
half of next week. Highs will be warmer, in the upper 70s to
low 80s for Monday through Thursday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 620 AM CDT Fri Sep 5 2025

Clouds associated with an upper low situated over eastern Canada are
streaming into the region from the north-northwest. As the day
continues, expect clouds to thicken and become widespread as a
shortwave brings with it moisture in the mid-levels. Weak
instability just above the mixed layer will allow clouds to grow
into towering cumulus with peak afternoon heating. Ceilings may
briefly drop down to MVFR, but will quickly improve to VFR through
the late afternoon. Some isolated sprinkles to light showers are
possible noth of I-90 this afternoon. Clouds will diminish after
sunset becoming clear overnight.

Winds today will be out of the northwest and breezy. Gusts of 20-26
kts are expected with the highest gusts west of I-29, and especially
over south central South Dakota. Winds will also diminish after
sunset becoming light and variable.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...AJP