024
FXUS63 KFSD 301128
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
628 AM CDT Thu Jul 30 2026

.KEY MESSAGES...

- Thunderstorms should increase in coverage this afternoon into
  tonight. Locally heavy rain, possibly as high as 4-5 inches,
  will be the main concern. A secondary concern will be hail to
  the size of quarters and wind gusts to 65 mph.

- While many locations will receive a beneficial half an inch
  to inch and a half of rainfall, the higher amounts could lead
  to localized flash flooding in urban and flood prone areas.

- Dry conditions and seasonable temperatures return for the
  weekend.

&&

.UPDATE...
Issued at 327 AM CDT Thu Jul 30 2026

An MCS in central SD will continue to weaken through the morning as
it encounters more stable air in eastern SD. Deep layer shear is
also fairly weak and not supportive of a continuing MCS. However,
some weak elevated instability could produce isolated to scattered
showers and thunderstorms throughout the morning. There is pretty
low confidence in the location and development however.

The somewhat higher confidence showers and thunderstorms will come
this afternoon into the evening as low pressure deepens over the
area. Initially storms should develop closer to central SD where the
deeper instability and incoming upper level low pressure come
together. Some of the latest model runs suggest that some of this
development could take place as early as noon-2pm, with the activity
progressing southeast through the afternoon into the evening.
Overall shear and instability are very marginal so only isolated
severe weather will be possible. Taller skinny CAPE with values
around 1500 J/kg are expected while deep layer shear likely only
climbs to around 30 knots. This scenario should support hail to the
size of quarters and wind gusts to 65 mph.

The more likely concern with this set up is heavy rainfall. With the
freezing level around 14000 feet, PWAT values likely around 1.75"
and, barring an outflow dominant MCS developing, fairly slow storm
motion is expected. This will likely lead to very efficient rainfall
with amounts around 2" per hour. If everything come together, some
locations could receive 4-5" of rain, which could cause some
localized flash flooding, especially if this rain falls over
populated locations.

Luckily ground water concerns are minor so it will take some of
these higher amounts to bring flood and flash flood concerns, so for
now believe this will remain fairly localized.

&&

.DISCUSSION...
Issued at 241 PM CDT Wed Jul 29 2026

Lines of cumulus clouds have developed near and south of the
Missouri River Valley this afternoon. Without much upper level
support to get storms going, we will need to rely on spots
reaching convective temperatures to get storms to initiate.
According to soundings, this will be around 95 degrees or so.
Chances for storm development with this is low, but either way
severe weather is unlikely given weak mid level lapse rates and
weak shear. However, can`t rule out a wind gust up to 55 mph in
any collapsing thunderstorm if they even develop in our area in
the first place. Otherwise another very warm and humid
afternoon continues, with heat indices pushing 100 degrees at
times especially west of I-29 into the Sioux City metro.
Doesn`t look like these 100 degree heat indices will be too
widespread and dew points do look to drop off a bit more through
the afternoon, so did continue to hold off on any heat
headlines. However, it`s still important to be hydrated and take
some breaks when working or playing outdoors this afternoon!

Showers and storms over western South Dakota will be knocking on
south-central South Dakota`s door by daybreak Thursday;
however, this activity will likely be weakening as it moves into
the area. Additional showers and storms will likely develop as
an upper level wave moves across the area and will likely have
enough with it to break the cap in the fairly weakly capped
environment. This morning activity is unlikely to be severe and
should help limit full destabilization from occurring before
any afternoon/evening activity develops. However, we will still
likely see a line of stronger thunderstorms develop in the
afternoon over central South Dakota and move southeastward
across the area through the evening hours associated with a cool
front. 65 mph winds and quarter sized hail will be the main
threat with this afternoon/evening activity.

There is an alternate, but less likely scenario where we don`t
get much if any rainfall during the Thursday morning time frame
due to a stronger than expected cap, allowing for more
destabilization to occur. In this scenario, like shown in the
29.12z HRRR, a stronger line/MCS would develop in the afternoon
and evening and bring wind gusts potentially up to around 65
mph. Trends will be monitored, so keep up to date with the
latest forecast. A secondary wave and an upper level low will
close off near the area Thursday night into early Friday
morning, likely keeping general showers and thunderstorms
continuing into the night. This will also lead to some flash
flooding concerns Thursday afternoon into the night. Wet grounds
from morning showers/storms will combine with the stronger
afternoon storms and overnight storms to lead to some flash
flooding concerns mainly in urban areas that see multiple
thunderstorms. Rainfall totals through Thursday night/early
Friday morning will be around a half an inch to 1.5", but
localized amounts exceeding 4+ inches will be possible. Make
sure to stay weather aware and keep up to date with the latest
forecast!

After this next storm system passes, an upper level ridge will build
into the area and help to keep us dry. And with northerly flow in
place, high temperatures for Friday and Saturday will be a lot more
pleasant with some areas especially on Friday having highs staying
only in the 70s! Southerly flow returns again by Sunday, so we
should start to see another warm up, though we should stay below
heat advisory criteria even as highs warm back up to the middle 80s
to lower 90s. The next appreciable rain chances will return Monday
night into Tuesday as cold front moves into the area. It looks like
there may be enough instability and shear for at least some severe
threat, but uncertainty remains high at this time.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 625 AM CDT Thu Jul 30 2026

Spotty showers and thunderstorms will be possible this morning,
with the better chances west of I-29. This afternoon
thunderstorm coverage should increase and gradually shift
southeast throughout the late afternoon and evening. A few of
the storms will contain heavy rain and potentially produce hail
as large as quarters and 65 mph winds. Most of today, outside of
any thunderstorms, VFR conditions are expected. Tonight
ceilings will lower to MVFR and potentially IFR as low pressure
settle south. The more widespread thunderstorm activity should
become more scattered in nature after about midnight.

&&

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

&&

$$

UPDATE...08
DISCUSSION...Samet
AVIATION...08