024
FXUS63 KFSD 291141
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
641 AM CDT Wed Jul 29 2026

.KEY MESSAGES...

- Warm and mostly dry conditions are expected today. Increasing
  humidity may push heat indices near 100F in a few areas west
  of I-29 this afternoon. Trends will be monitored to see if
  heat headlines are needed.

- Chances for showers and storms increases late tonight through
  Thursday, continuing Thursday night into early Friday. Some
  storms may be strong to severe late Thursday into Thursday
  night with strong wind gusts and heavy rain the main threats.

- Beneficial rainfall is expected Thursday through Friday
  morning, with a 50-90% probability of at least 0.50 inches
  across most of the region.

&&

.UPDATE...
Issued at 340 AM CDT Wed Jul 29 2026

Seeing some generally shallow fog develop in parts of the area
as of 3 AM. Some signal that it may become a bit deeper in our
east during the next 2-3 hours before sunrise with some fog
becoming apparent on satellite, so have added mention of fog to
the grids through 7-8 AM, mainly over portions of northwest IA
and southwest MN.

Pre-sunset satellite also depicted a broad area of smoke aloft
across the region so have bumped up sky cover from the mostly
clear NBM forecast to account for potential of smoke limiting
view of the stars overnight and filtering sunshine into the day
Wednesday.

Unsure whether smoke will hamper warming significantly, but NBM
continues to show a general warm bias with influence from the
GEFS members, so conservatively nudged highs Wednesday down a
degree or two. This combined with dew points in the upper 70s to
mid 70s does yield heat indices marginal for Heat Advisory in
some areas west of I-29, but given uncertainty in smoke impacts
on warming, opted to hold off issuing any heat headlines at this
time. Day shift will want to monitor for potential headlines
generally along/west of the James River Valley (Huron-Yankton)
and potentially as far east as Sioux City).

Evening shift thoroughly covered convective potential over the
next couple of days, and not seeing any significant changes to
that thinking in the latest data. That discussion in included
below.

Issued at 907 PM CDT Tue Jul 28 2026

Wednesday looks to be somewhat of a rinse and repeat of what we
saw today. A mid level ridge axis will be sitting right over
the forecast area, contributing to weaker vertical shear values
over the area. Instability looks to still be sufficient to allow
for the potential of some afternoon showers and storms to
develop. Tough to say where specifically storms may develop as
no boundary will be in play. Should showers and storms develop,
they look to be diurnally driven and will dissipate during the
evening timeframe. Severe storms are not expected. The potential
for overnight convection remains but it looks to be sub severe
and won`t make it into the forecast area until near daybreak
early Thursday morning.

The overnight storms may have an affect on the potential for storms
later on Thursday. With a surface high pushing further off to the
east, allowing for moist southerly return flow to take over. This
will allow dew points to moisten into the upper 60s and 70s. If the
morning showers and dissipate fast enough to allow for sufficient
destabilization to take place during the afternoon, then additional
showers and storms will be possible. A mid level wave will be
pushing through the forecast area with both deterministic and
ensemble guidance suggesting that this mid level wave could close
off as it moves over the forecast area. These models also show the
surface front residing beneath the center of this mid level wave.
This looks to potentially limit the strength of the deep layer
shear. At the same time, mid level lapse rates also look to be near
moist neutral. Precipitable water (PWAT) values look to climb to
nearly 2.0 inches, placing them at about the 99th percentile of
climatology. Thus, a heavy rain threat remains possible. Latest
ensembles continue to show a broad 50-90% chance for rainfall
amounts to exceed a half an inch. These probabilities decrease to a
30-60% chance for exceeding an inch. Tough to say exactly how
convection will evolve, but with a generally uncapped atmosphere in
play and the mid level wave providing at least wave forcing for
ascent, think that more widespread convection could develop across
the area. With the mid level wave residing right over the forecast
area, storm motions do not look to be fast, suggesting that slow
moving to potentially some training storms will be possible. Severe
storms could be possible with this potential heavy rain threat if
storms could develop on the previously mentioned front and possibly
congeal into some kind of MCS. This potential remains uncertain so
continue to check the latest forecast for the most up to date
information.

&&

.DISCUSSION...
Issued at 135 PM CDT Tue Jul 28 2026

A very subtle wave continues to move to the southeast. As it does so
clouds will dissipate, gradually becoming scattered to clear.
Similar to yesterday, smoke from wildfires will result in an overall
milky appearance to the sky. Highs today will warm into the upper
80s to low 90s. Dew points will be lower than the past couple of
days but still in the mid 60s to low 70s, highest over northwest
Iowa. Localized higher values are possible in areas with large corn
fields, as the plants add moisture through evapotranspiration. Heat
Index values remain below critical today. However, it is still
important to take care of yourself while working in hot conditions.
Winds today will be southerly and light. Overnight they become light
and variable. Patchy areas of fog are possible as overnight lows
fall to the mid 60s and low 70s, which is right around the dew point
temperature. Most of the fog should be contained to water ways and
low areas, and will burn off by mid-morning Wednesday.

Northwest flow aloft continues for Wednesday, keeping the smokey
skies in place. Wednesday during the day will be very similar to
today with highs in the upper 80s and low 90s. Southerly winds
increase in the afternoon as a shortwave approaches from the west.
Gusts of 15-25 mph are expected with gusts increasing as you move
toward central South Dakota. Showers and thunderstorms form in the
late afternoon and evening over western South Dakota and progress
east. Storms will reach central South Dakota and our western CWA
border around midnight. There remains some variance in mid-
range guidance on how this wave and resulting storms will
evolve, therefore uncertainty in severity remains high. Model
soundings show a dry subcloud layer and tall skinny CAPE. This
indicates the most likely threats will be strong to marginally
severe wind gusts and periodic heavy rainfall. A weak LLJ helps
to maintain convection through much of the day Thursday.

Meanwhile, an upper level trough develops over the Pacific Northwest
and speeds east. The mid-level and upper troughs deepen and a
surface low forms over eastern Wyoming and western South Dakota.
Similar to Wednesday night`s storms, uncertainty in storm evolution
is high due to wide variance in guidance. In addition, the
activity and outflows from storms earlier in the day will likely
play a role in evening development. The most likely scenario is
a few isolated strong to severe supercells form over central
South Dakota and quickly grow upscale into an MCS with damaging
wind gusts and periodic heavy rain the primary threat. This
tracks east through the overnight and early Friday morning,
bringing beneficial rainfall to much of the area. LREF
probabilities of 0.50 inches of rain or more are 55-75% region
wide. This probability is for total rainfall from Wednesday
night through Friday morning.

Thursday will be cooler due to clouds and rain with highs in the low
to mid 80s. Friday continued CAA will result in highs slightly
cooler in the upper 70s to low 80s. A beautiful weekend is in store
with mostly sunny skies and highs right around average for this time
year in the mid 80s.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 641 AM CDT Wed Jul 29 2026

Areas of MVFR-IFR and locally VLIFR visibility in fog to start
this period, but conditions should improve quickly by 13-14Z.
Remainder of the day should see VFR conditions with southeast to
south winds sustained around 10kt or less. Locations west of
I-29 and toward the Buffalo Ridge in southwest Minnesota may see
occasional higher gusts, but generally remaining less than 20kt.

Low chances of showers/storms moving into areas west of the
James River Valley toward south-central SD late in this period,
but this activity is not expected to impact TAF locations prior
to 30/12Z.

&&

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

&&

$$

UPDATE...JH
DISCUSSION...AJP
AVIATION...JH