099
FXUS63 KFSD 091956
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
256 PM CDT Wed Jul 9 2025

.KEY MESSAGES...

- Severe storms this evening into tonight will be capable of
  damaging winds up to 75 mph and half dollar-sized hail.
  Greatest threat is west of the James River, with storms
  weakening with eastern extent.

- Additional storm chances into the weekend focus around
  Thursday into Friday. Mixed storm modes could bring a variety
  of severe weather risks, but slow storm motion may also bring
  locally heavy rain risks especially late Thursday through
  Friday.

- A dry weekend is expected, with cooler temperatures Saturday
  warming above normal by Sunday and Monday.

- The next risk for thunderstorms returns to the region late
  Monday into Tuesday.

&&

.DISCUSSION...
Issued at 252 PM CDT Wed Jul 9 2025

THIS AFTERNOON THROUGH TONIGHT: The main story in the short-
term will be a developing Mesoscale Convective System in western
South Dakota that will cross the Missouri River this evening,
but first a quick mention on storm potential this afternoon: A
few areas of ACCAS over southwest Minnesota and northwest Iowa
could develop into a very isolated storm or two in an unstable
environment characterized by 2000-3000 J/kg of MLCAPE. Effective
bulk shear will be less than 20 kts in these areas, thus pulse
storms are expected with any development. Otherwise, expect a
hot and humid afternoon on our Wednesday with highs in the
upper-80s to mid-90s and dew points into the 70s.

For this evening into tonight`s severe weather threat, look for
storms to form rapidly into a line segment in western South Dakota
and surge eastward. Look for this MCS to cross the Missouri River
around the 9-10 pm and slowly weaken as it moves eastward towards I-
29. Damaging winds will be the main concern, especially west of the
James River where storms look to be the strongest. DCAPE values of
1500+ J/kg combined with quick storm motion will favor the potential
for damaging wind gusts as high as 75 mph. Mid-level lapse rates
around 8-9 C/km will support some large hail (up to half dollar in
size) especially west of the James River where storm updrafts will
be at their strongest. Storms will likely weaken as they progress
towards I-29 as instability wanes. Even these dying thunderstorms
will be capable of at least 60 mph wind gusts as far east as the US
Highway-75 corridor late tonight.

THURSDAY: Shortwave energy is expected to be moving away from the
CWA after daybreak Thursday, with temporary subsidence residing over
the forecast area into the afternoon. A slightly cooler,  but still
very humid day is expected across the area, with focus turning
towards the placement of residual boundaries left over by departing
MCS and formation of a surface warm front over central and eastern
Nebraska in the afternoon.  By mid-late afternoon, increasing DPVA
and convergence of increasing low-lvl flow will provide enough lift
to aid in the development of convection south of the CWA along the
aforementioned surface trough. While extremely uncertain, some of
this convection may drift northward in the evening, producing some
severe weather risks locally. However the greatest potential is
likely to stay south of the MO river and Highway 20 where the
majority of HREF 2-5KM  updraft helicity is focused.

THURSDAY NIGHT: Again, extreme uncertainty continues Thursday night
into Friday, with models suggesting a stronger mid-lvl area of
vorticity tracks out of the western High Plains and into the Central
Plains overnight.  The track of this energy remains highly in doubt,
with EC/CMC pushing the wave over the Dakotas, with the NAM/GFS
further south and focusing overall convective risks well south
of I- 90 into Friday morning. The further north EC/CMC would
instead allow for more development along a N-S frontal boundary
through the Dakotas and increase the potential of MCS activity
throughout the CWA Friday morning bringing isolated convective
wind risks and low end hail risks. The southern solutions have
the potential to lead to lower PoPs through most of the CWA,
with heavier rains focused more over Nebraska and western Iowa
into daybreak.

FRIDAY:  A larger upper trough begins to cross Central Canada early
Friday, with the trough axis moving into the central Dakotas mid-day
Friday. With the CWA sitting in-between these features and a slow
moving cold front drifting south in the middle of the day,
precipitation chances may begin to increase rapidly by mid-day
through the afternoon.  Pooling moisture and temperatures warming
into the 80s will again serve to push moderate instability into the
area.  Shear however will be quite weak, owing to more possibility
of brief microbursts winds and marginal hail into the evening
as the front progresses southeast. The slow storm movement will
lead to localized heavy rain potential.

SATURDAY-TUESDAY: Cooler and dry weather is likely Saturday as
northwest flow spreads throughout the northern US.  By Sunday, mid-
lvl heights begin to rise quickly, with southerly winds bringing a
return of upper 80s to 90s to the region. A bit better agreement in
medium range deterministic models into Monday, keeping deeper
southerly flow in place and pushing temperatures a bit warmer.
Convection risks begin to increase quickly again late Monday night
into Tuesday as a frontal boundary moves into the Plains.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1241 PM CDT Wed Jul 9 2025

Very isolated showers/storms are possible over northwest Iowa and
southwest Minnesota this afternoon, but chances of impacts to KSUX
are less than 15% and thus no need to mention in the TAFs. A better
chance of storms arrives this evening as a linear complex of storms
develops over western South Dakota and crosses the Missouri River
around 02-03Z. These storms will be capable of 50+ kt gusts as they
move through the K9V9, KHON, and KMHE areas. Storms will bring MVFR
visibilities, potentially briefly IFR west of the James River where
storms are at their strongest. The storm complex looks to weaken a
bit as it approaches the I-29 corridor, and this adds a bit of
uncertainty to the storm threat for KFSD and KSUX. Left the PROB30
groups for both sites for now, though slightly adjusted the timing
for both sites and added a 45kt wind gust potential for KFSD. Storms
will continue weakening as they move west of I-29 through
daybreak Thursday.

Outside of thunderstorms reducing visibilities, VFR conditions
are expected through the period. Winds will be mainly out of the
southeast, gusting as high as around 20 kts this afternoon
before weakening overnight (except in storms), and then gusting
back up to around 20 kts Thursday afternoon.

&&

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

&&

$$

DISCUSSION...Dux/Samet
AVIATION...Samet