Sioux City, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

524
FXUS63 KFSD 191917
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
217 PM CDT Sat Jul 19 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms are possible into this
  evening with the best chances south of I-90. While the risk is
  low (level 1 out of 5) there is some potential a couple of
  these storms could be strong to severe along the Missouri
  River Valley into Northwest Iowa. Locally heavy rainfall is
  also possible.

- Another risk of severe thunderstorms exists Sunday night into
  Monday morning, mainly north of I-90. Finer details remain
  uncertain at this time.

- An active pattern persists aloft Monday through Friday next
  week which looks to bring daily chances for showers and
  storms. A few of the days could see isolated severe storms.

- Seasonally warm conditions are expected next week with
  afternoon heat indices into the 90s each day. Tuesday could
  see heat indices in a few locations push 100 degrees.

&&

.DISCUSSION...
Issued at 204 PM CDT Sat Jul 19 2025

Afternoon/Evening: A fairly muddied space in terms of forcing across
the immediate region as of mid afternoon with subtle lift from the
right entrance region of the departing jet streak, weak vort lobes
riding through the westerly flow, and the northern fringes of
the better mid level lapse rates all in play. This has resulted
in a couple of different areas of showers (Hwy 14) and
weak thunderstorms (MO River).

A bit more cohesive wave begins to lift toward south central South
Dakota by early evening and would be the next feature to watch for
additional thunderstorm development. Any storms that do develop
west river should quickly dive southeast along the instability
gradient but may perhaps clip our MO River counties. MLCAPE
values as high as 1500 J/kg and sufficient deep layer shear
could provide for a marginal (level 1 out of 5) severe weather
risk across our far south but feel that the current activity
along the NE/SD border may be doing a good job of delineating a
northern boundary to this risk.

Overnight: Previously mentioned activity could move toward the Hwy
20 corridor overnight but again, the better severe weather risk
appears south. Even north of the severe threat, general thunderstorms
are possible (30-60% chance) with HREF max QPF guidance
indicating the potential for very isolated 2+ inch rainfall
totals. This would align with the slight (level 2 out of 4) for
excessive rainfall toward the Hwy 20 corridor in NW IA.

Sunday: Could start the day with isolated elevated convection but
this should fade through the morning hours with a mix of sun and
clouds by afternoon. A wave passing to our north should be enough
for some thunderstorm development near the ND/SD boarder Sunday
night that would then have a tendency to dive southeastward
toward the Hwy 14 corridor into early Monday. SPC currently
covers this risk with a Slight (level 2 out of 5 risk).

Next Week: More pronounced ridging develops by Tuesday with
expanding heat back into the upper 80s and 90s. This ridging is
shunted by Thursday leaving our region closer to its periphery.
Likely will see sporadic convection chances buried within this
period with currently the better wave passages looking to be Tuesday
and again late Wednesday. AI and machine learning probabilities
would also suggest some potential for severe weather and excessive
rainfall although details with this sort of pattern are notoriously
tricky until the previous day`s weather is clarified. Much of
the same could be said in terms of temperatures with likely
some potential for boundaries, convective contamination, and
cloud cover. Nonetheless, with crop evaporation season well
underway, dewpoints will drive heat indices toward headline
values at times, namely south of I-90 on Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1154 AM CDT Sat Jul 19 2025

A somewhat messy aviation period with IFR/MVFR conditions
intermixed across the region currently along with SHRA/TSRA
chances. Lingering sub-VFR ceilings still stretch either side of
a KVTN to KFSD to KMML line. Should see these lower ceilings
continue to mix higher or scatter out with mid/upper clouds
hanging on. HREF probabilities suggest these MVFR ceilings may
return later tonight.

We`ll also see TSRA chances focus mainly near and especially
south of the MO River Valley but could at times impact KSUX.
Further north, a period of -SHRA around KHON early this
afternoon and perhaps even grazing KFSD by mid to late
afternoon.

&&

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

&&

$$

DISCUSSION...Kalin
AVIATION...Kalin