Alcester, South Dakota Weather Forecast Discussion

309
FXUS63 KFSD 201921
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
221 PM CDT Sat Sep 20 2025
.KEY MESSAGES...
- Sprinkles and a few showers continue this afternoon into early
  evening, mainly across southwestern Minnesota and adjacent
  areas of Iowa and South Dakota. Can`t rule out a very isolated
  thunderstorm.
- Temperatures warm Sunday and Monday, bringing a risk for a
  few thunderstorms. Severe weather risks remain low, but not
  zero.
- Latest guidance continues to trend towards a drier and
  relatively cooler middle and end of next week. Temperatures
  will be near seasonal normals in most areas.
&&
.DISCUSSION...
Issued at 219 PM CDT Sat Sep 20 2025
NOW THROUGH TONIGHT: Scattered sprinkles and showers continue to
move southeast this afternoon, mainly across southwestern MN and
adjacent areas of SD (through the US Hwy 14 corridor) and into
northwestern IA. This is tied to the mid/upper trough axis off to
the northeast and a vorticity lobe moving through the area. Not
expecting much in the way of accumulations, with a tenth of an inch
or less. Could see a very isolated lightning strike, but risk is
very low given meager instability. Mix of lower and mid clouds which
have been slower to clear thus far today. Highs in the lower 70s for
most.
Aforementioned mid/upper trough lifts off to the northeast through
tonight, followed by the next mid/upper trough moving south out of
ND. Some question how much we see mid level clouds clear out
(impacting how low temperatures drop and if fog redevelops). That
said, since we`ll either have clouds or a mix of clouds and fog
around the area, warmed lows a couple of degrees from previous
forecast. Still expect lows to fall into the 50s. Light and variable
winds prevail.
SUNDAY-SUNDAY NIGHT: Next mid/upper low spins off to the north and
east of the area across MN during the day Sunday and Sunday night.
This brings a few vort maxes through the area, which could lead to
some showers earlier in the day. Surface warm front stretches across
the CWA, tied to a subtle low over northern NE/south central SD.
Guidance varies on the location of the warm front and whether or not
it will be a catalyst for storms later in the afternoon and the
evening - although CAMs are beginning to trend more in the direction
of yes. Better synoptic forcing should remain to the east with the
main mid/upper low with a couple of very subtle waves over our area
through the afternoon and into Sunday night. However, tall/skinny
CAPE around 1000-1300 J/kg and bulk shear around 25-30 kts may be
enough for a couple of stronger storms. Half dollar sized hail is
the main threat with mid level lapse rates 6.5-7 deg C/km. Greatest
risk for a stronger storm is along/south of a line from Yankton to
Minneota during the late afternoon/evening and possibly into the
early overnight hours due to enhancement of the LLJ.
Regardless, temperatures north of the front should warm to the mid
70s, with upper 70s to lower 80s south of the front. Light winds
early in the day increase and shift southerly. Lows again in the 50s.
MONDAY-MONDAY NIGHT: Another weak short wave moves through the area
during the day Monday, but most of the area should be dry through
the first part of the day. Sunday`s warm front remains over the
forecast area, although again, some uncertainty where exactly this
lies south of I-90. Surface low and next wave move out of NE through
the afternoon and evening, bringing the return of shower and storm
chances. Severe weather risk remains low with the better shear and
instability more offset in time and space. Highest probability of
rainfall amounts exceeding a tenth of an inch will be along the MO
River toward US Hwy 20 (60%+). Slightly warmer on Monday with highs
in the mid/upper 70s to lower 80s. Lows Monday night remain in the
50s.
TUESDAY-FRIDAY: Mid/upper low swings through the Plains early in the
week, with the surface low across the central Plains into the
Ozarks. Mid to late week, this positively tilted trough deepens and
guidance indicates a stronger low will develop over the midwestern
US with another weaker low/waves rotating around the main low. This
pattern should keep temperatures near seasonal normals. Low end
chances for rain early in this period mainly along and south of I-
90, with largely dry weather expected through the rest of the week
thanks to the building ridge. Predominantly light winds
expected.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1219 PM CDT Sat Sep 20 2025
Mix of predominantly MVFR stratus and VFR stratus/developing
cumulus should continue through the early afternoon, with VFR
conditions over most of the area this afternoon and evening.
Most of the morning fog/drizzle has dissipated, and have now
seen some showers/sprinkles being to develop - mainly along the
US Hwy 14 corridor. This should continue to move southeast with
additional development east of I-29 this afternoon and evening.
Will keep mention out of KHON and KFSD at this time.
Some uncertainty with how much cloud cover clears out during the
day. If we see more clearing, expect fog to redevelop late
tonight into Sunday morning with continued light and variable
winds. For now, kept the fog mention out of any of the TAF
sites, but did add some IFR SCT ceilings to KHON and KFSD. Will
definitely be watching trends.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
DISCUSSION...SG
AVIATION...SG

NWS FSD Office Area Forecast Discussion