246
FXUS63 KFSD 112343
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
643 PM CDT Fri Jul 11 2025

.KEY MESSAGES...

- Wildfire smoke moving in behind a cold front this evening is
  reducing visibility below 3 miles at times. Additional
  wildfire smoke moves into the region tomorrow afternoon and
  evening, reducing visibility and air quality.

- A low end (level 1 of 5) risk of severe storms develops by
  late this afternoon, as a cold front brings scattered
  thunderstorms southward into the region. The main threats with
  the strongest storms will be up to quarter sized hail, strong
  winds up to 60 mph, and heavy downpours. An isolated funnel
  cloud or landspout is possible, mainly along the cold front
  itself.

- Temperatures cool Saturday, but heat and humidity build back in
  for Sunday through Tuesday. Cooler temperatures return for
  the middle and end of next week.

- Thunderstorm risks return for Sunday through Tuesday, with
  some threat of severe storms possible.

&&

.DISCUSSION...
Issued at 309 PM CDT Fri Jul 11 2025

A few showers and weak thunderstorm persist east of I-29 this
afternoon. Should see these showers and storms drift
east/southeastward over the next couple of hours. At the same time,
a cold front has pushed into the area from the northwest. This front
will serve as the focal point for new showers and thunderstorms to
develop on with convective initiation expected over the next 2 to 3
hours or so. Storms look to be initially discrete before some
upscale growth leads to a broken line/cluster of storms. CAPE value
will be sufficient at around 1,500 J/kg of instability but shear
will be quite weak on the order of 25 knots or less. That said,
still think an isolated chance for quarter size hail and damaging
winds to 60 mph is possible. The other aspect to the storms is the
potential for funnels or even a landspout. This potential is being
driven from the vorticity along the front itself. Despite the
fronts vorticity, LCL`s are decently high at around 4,000 to 5,000ft
so it may be a bit more difficult to any funnel to touch the ground.
Any chance for storms will come to an end by midnight as the showers
and storms push east of the area. Low temperatures will fall to the
upper 50s to low 60s.

High pressure will push into the Northern Plains on Saturday,
delivering dry and quiet conditions for the area. 850 mb
temperatures will warm to the teens aloft. Mixing these temperatures
to the surface will result in high temperatures in the upper 70s and
80s. Dew points will lower to the 60s to low 60s, which will keep
humidity values down to 30-60%, lowest west of the James River.
Thus, Saturday will be a nice day though there could be some
wildfire smoke both aloft and at the surface. Low temperatures will
fall to the upper 50s to low 60s overnight.

Sunday will be a hotter day as highs warm to the 80s to 90s, warmest
west of the James River. Southerly return flow on the backside of
the previously mentioned departing surface high. Dew points will
moisten to the 60s to even up to about 70F. This will increase
humidity values and also result in CAPE values up to 1,500 to 2,000
J/kg. Effective shear value will be sufficient on the order of about
30 knots but lift is questionable. A shortwave trough will reside
east of the forecast area, providing upper level subsidence across
the Northern Plains. However, a weak shortwave trough at 700 mb will
push into the area. A weak surface trough will push through the area
which could result in another chance for showers and thunderstorms.
This potential is quite uncertain though given the weak forcing that
is in place. As of now, the ensembles only show a low 10-30% chance
for rainfall amounts to exceed a tenth of an inch throughout the
day. Have left model blended PoPs at this time but trends will be
monitored.

Zonal flow sets up for the beginning of next week. This will promote
broad southerly flow into the Northern Plains, promoting humid
conditions across the area. High temperatures will remain near to
above average in the 80s and 90s. With weak shortwave troughs
passing through the upper level flow, chances for showers and
thunderstorms are possible. As of now, it looks like storm chances
will increase heading into Monday evening as forcing for ascent
strengthens. This chance for storms will persist through Tuesday as
a cold front passes through the forecast area throughout the day.
Given sufficient instability and enough shear in place, this could
lead to additional chances for showers and storms, some of which
could be strong to severe. Machine learning guidance also supports
this possibility as these models show about a 5-15% chance for
strong to severe storms. Will keep an eye on this potential over the
weekend.

Rain chances look to continue for Wednesday and Friday next week as
shortwave trough continue to track through the upper level flow.
Details of these waves is uncertain at this time so have left model
blended PoPs. In terms of temperatures, highs look to cool to near
to below average in the 70s to up to about 80F. Lows will fall to
the 50s and 60s overnight.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 630 PM CDT Fri Jul 11 2025

Watching showers/storms develop over northwestern IA into far
southeastern SD and into northeastern NE. Not expecting impacts
to the KFSD terminal, but if this developing line holds
together, showers/storms are expected to move into the KSUX
airspace after 01z. Showers/storms move southeast through
tonight. An additional area of showers and very isolated
lightning continue to move east through central SD. Given the
weakening trend of this area as it moves toward the James
Valley, will keep any -SHRA mention out of KHON. Have seen some
wind gusts around 30 knots with the CAA this evening and these
may continue into tonight.

Otherwise, wildfire smoke is reaching the surface this evening
behind the front, with a couple of hours of MVFR to upper end
IFR visibility. Additional wildfire smoke aloft and at the
surface moves in through the day Saturday, leading to reduced
visibility and air quality.


&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...SG