260
FXUS63 KFSD 091745
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1245 PM CDT Wed Jul 9 2025

.KEY MESSAGES...

- A Mesoscale Convective System (MCS) will likely develop over
  western SD this afternoon and progress through our area this
  evening. The primary hazards with this activity will be
  damaging winds up to 75 mph and up to half dollar size hail.

- Additional chances for showers and storms will continue into
  the late week with the focus being between Thursday and
  Friday. Mixed storm modes could bring a variety of severe
  weather risk, but slower storm motions may also bring a
  locally heavy rain risk.

&&

.DISCUSSION...
Issued at 350 AM CDT Wed Jul 9 2025

TODAY & TONIGHT: Taking a look across the area, mostly quiet
conditions continue as of 4 am this morning. The forecast still
remains on track for a few isolated thunderstorms to develop
across southcentral SD through daybreak as pieces of vorticity
interact with a 20-30 kt LLJ. However, the severe risk with this
activity will likely stay on the lower side with only around
500-750 J/kg of instability to work with. As the LLJ weakens,
should see this activity weaken and diminish by mid-morning.
Shifting gears here, another warm day is ahead as increasing
southeasterly winds and increasing mid-level warm air advection
(WAA) lead to temperatures in the 80s to low 90s with the
warmest conditions closest to the warm/stationary front situated
along and west of the Missouri River Valley. From here, the
focus turns to our next precipitation chances this evening and
overnight.

Taking a look aloft, a quick mid-level wave will push across the
state and intersects the previously mentioned surface front
triggering semi-discrete clusters of showers and thunderstorms
across western and central SD. While this developing activity
will have access to an unstable environment characterized by
2000-3000 J/kg of instability and 25-35 kts of bulk shear, model
soundings continues show a stabilizing boundary layer as this
developing activity moves into our CWA. As a result, most high-
resolution guidance has this developing Mesoscale Convective
System (MCS) weakening as it progresses eastwards towards the
I-29 corridor. With this in mind, the majority of the severe
risk (if any) will likely be isolated to areas west of U.S.
Highway-281 where remnant thunderstorms could produce damaging
winds up to 65 mph and half dollar sized hail. Lastly, as the
LLJ strengthens across areas east of I-29 overnight; some
potential redevelopment will be possible mainly in northwestern
IA. While this activity will likely be sub-severe due to waning
instability, can`t completely rule out the potential for a few
additional thunderstorms with some smaller hail.

THURSDAY-FRIDAY: Looking into the latter parts of the week, could
see the previously mentioned activity lingering across areas east of
I-29 through the mid-morning hours on Thursday before things
progress out of our area. From here, quieter conditions temporarily
return through the late afternoon as temperatures peak in the 80s to
low 90s for the day. More shower and thunderstorm chances will
return during the evening to overnight hours on Thursday as a
strengthening shortwave lifts through our area and intersects a few
lingering surface boundaries left behind from the previously
mentioned MCS. While there is still some uncertainty regarding where
things will set up, the high CAPE/low shear environment associated
with this system; will likely support an isolated to scattered
severe risk with stronger storms potentially develop up to 2 inch
hail (Hen Egg) and damaging winds up to 70 mph with strong cold
pools. As instability wanes overnight, slower storm motions along
with PWATs between 1.50 to 1.75 inches (90th percentile) will
promote a locally heavy rainfall risk into Friday morning.
Nonetheless, with the variety of convective scenarios its still a
bit difficult to pin point an area of focus for the overall severe
risk and subsequent heavy rainfall threats at this time. Lastly,
there will be additional chances for showers and thunderstorms by
Friday afternoon as a cold front swings progresses through the area.
However, the severity of those storms is still uncertain at this
time.

SATURDAY ONWARDS: Heading into the extended period, quieter
conditions return to the area as surface ridging moves in by
Saturday to replace the departing system. With backing surface wind
profiles and increasing warm air advection (WAA) in the mid-levels,
expect temperatures to trend near to above normal over the next few
days with highs increase from the upper 70s to mid 80s by Saturday
to the mid 80s to low 90s by Monday. From here, our next shower and
thunderstorm chances likely return by Tuesday as a cold front swings
through the region. While the severity of this activity is still
uncertain, some of the machine learning guidance has started to show
some weak signals for stronger activity so this period will likely
be one to watch moving forwards.

&&

.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...05
AVIATION...Samet