Sioux City, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

437
FXUS63 KFSD 271121
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
621 AM CDT Sun Jul 27 2025

.KEY MESSAGES...

- An Extreme Heat Warning remains in effect for the entire area
  this afternoon and evening with heat index values near and
  above 105 degrees. Use caution to prevent heat illness today.

- Dangerous heat continues Monday given a combination of air
  temperatures in the 90s to near 100 degrees and dew points
  predominantly in the 70s. Heat index values are forecast to
  rise above 104 degrees for most areas.

- There is a 20 to 40 percent chance for showers and thunderstorms
  tonight into Monday. Storms could be strong to severe with
  the primary hazards wind gusts to 70 mph and quarter sized
  hail.

- Shower/storm chances continue Monday night into Wednesday.
  Additional strong to severe storms are possible Monday night
  into Tuesday and again Tuesday evening into Wednesday.

- Temperatures cool significantly by the middle of next week,
  peaking in the 70s to near 80 Wednesday onward.

&&

.DISCUSSION...
Issued at 339 AM CDT Sun Jul 27 2025

NOW THROUGH TONIGHT: Patchy fog has developed this morning in areas
with clear skies. Not expecting dense fog, but could see isolated
reduced visibilities to one mile or less through mid morning. Be
prepared for quickly changing conditions if traveling.

Mid and upper level ridge meanders westward through today. Continued
southerly surface low aids in continued ample moisture transport,
with dew points in the 70s again today. Temperatures aloft continue
to warm today, with 925 mb temps in the mid 20s to mid 30s degrees
C. Highs today warm into the 90s to lower 100s, highest in south
central SD (which is also offset from the highest dew points).
Although some of the higher res guidance is coming in a couple of
degrees cooler (likely due to the influence of wildfire smoke aloft
and possibly from some lingering cloud cover/convective debris), the
combination of these temps and dew points keeps heat index values
for most of the area near to above 105. No changes to the Extreme
Heat Warning for the afternoon and evening hours. Limit time
outdoors during the peak heating of the day if you can. If you have
to spend time outside, take precautions to avoid heat illness - stay
hydrated and take frequent breaks.

Increased sky cover again today to account for wildfire smoke
concentration aloft. Surface impacts are not expected.

Shower and storm chances increase late this evening and tonight as a
mid level wave moves from ND/MN, likely the catalyst for storm
development in the early afternoon. Timing and coverage remain in
question for our area for a couple of reasons: where/when does the
inverted surface trough track southeast and where are any remnant
outflows end up from last night and this morning. Convection still
looks to build southwest from the main 500 mb wave, and given the
strong cap in our area, confidence is low in how far southwest
storms fire. However, guidance seems to agree on the greatest risk
for southwestern MN. If storms are able to break the cap, main
threats are wind gusts to 70 mph with DCAPE at or above 1000 J/kg
and quarter sized hail (ample instability and steep mid level lapse
rates). Can`t rule out some larger hail to ping pong ball sized in
any more discrete cells with the up to 70 mph gusts. Locally heavy
rainfall is possible as well.

MONDAY-TUESDAY NIGHT: Ridge axis meanders west through the early
part of the week. One more hot day expected Monday as we still have
the potential for heat index values above 100 degrees, especially
near and south of I-90. However, continued to hold off on any heat
headlines at this time. Uncertainty in where boundaries from Sunday
night`s convection as well as cloud cover and increased smoke aloft
lead to lower confidence on temperatures (thus where might need a
headline and what type). Regardless, it looks like another day to
take it easy and limit time outdoors if you can.

Another mid level short wave rides the ridge east Monday evening
into Tuesday, with upper level jet streak across northern SD and
surface low pressure ejecting out of the Panhandle. Expect showers
and storms to develop in the warm sector. Storms could be strong to
severe with robust instability and shear as well as steep mid level
lapse rates. Main threats with any stronger storms are large hail
and damaging wind gusts. Exact timing and location remain uncertain,
due to the influence of previous round(s) of showers and storms the
previous day(s). Locally heavy rainfall is possible.

Storms may continue into the day on Tuesday, with additional waves
moving through into Tuesday night. Although models disagree on
timing/location, more defined surface front swings through Tuesday
night as well, likely forcing additional showers and storms to
develop in the warm sector once again. Confidence is low, but may
have enough lingering instability and shear with steep mid level
lapse rates for a stronger storm or two. Again, stronger storms may
produce locally heavy downpours.

With clouds and convection around, Tuesday should be a cooler day
with highs in the 80s to lower 90s.

WEDNESDAY-SUNDAY: Pattern changes mid week as troughing aloft
deepens over both coasts of the US and we return to a northwesterly
flow regime. Cooler surface high pressure sneaks down from Canada
into central MN, and with the northwesterly flow, brings much cooler
temperatures to the region with highs in the 70s to near 80 and lows
in the 50s. Since we`ll be on the periphery of the high, a couple
short waves could bring shower chances to the region, but details
are uncertain. Expect periodically breezy conditions with a
compressed surface pressure gradient. By next weekend, surface high
pressure slides east and the pattern aloft flattens as a stronger
wave treks through the Plains.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 614 AM CDT Sun Jul 27 2025

Patchy MVFR and lower VFR fog has developed this morning, and
should mix out through 14z. Have seen very brief and isolated
visibility below two miles, but given how isolated/brief this
is, did not include mention at any site. Otherwise, VFR
conditions for most of the area through the period. Showers and
thunderstorms are possible this evening through tonight, with
the greatest chances in southwestern MN. With uncertainty in
location of storm development, may need to add mention to KFSD
or KSUX at some point.

Winds generally southerly through the day today with gusts
around 20 knots. Direction is expected to shift tonight with
boundaries moving through the region. NAM guidance hints at some
LLWS for the southern MO Valley into northwestern IA; kept
mention out of KSUX for now with marginal conditions and lack
of agreement in guidance.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Extreme Heat Warning from noon today to 8 PM CDT this evening
     for SDZ038>040-050-052>071.
MN...Extreme Heat Warning from noon today to 8 PM CDT this evening
     for MNZ071-072-080-081-089-090-097-098.
IA...Extreme Heat Warning from noon today to 8 PM CDT this evening
     for IAZ001>003-012>014-020>022-031-032.
NE...Extreme Heat Warning from noon today to 8 PM CDT this evening
     for NEZ013-014.

&&

$$

DISCUSSION...SG
AVIATION...SG