742
FXUS63 KFSD 040348
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1048 PM CDT Thu Jul 3 2025

.KEY MESSAGES...

- This afternoon will be dry, but hot and humid. Heat index
  values in the upper 90s to near 100 today. Hot and humid
  Independence Day with heat index values in the mid 90s to near
  100.

- Chances for showers and storms continue Independence Day
  through the holiday weekend. Highest chances (45-70%) begin
  Friday afternoon and continue into Saturday evening. Periodic
  shower and storm chances continue into next week.

- Severe weather risk remains low but not zero for Independence
  Day and Saturday. Locally heavy rain is also possible. Keep
  an eye on the forecast if you have outdoor or travel plans.

- Temperatures generally near to above normal through mid next
  week.

&&

.DISCUSSION...
Issued at 225 PM CDT Thu Jul 3 2025

TODAY: Upper ridging and surface high pressure will keep us hot and
dry today. Southerly winds will bring north dew points in the mid
60s to mid 70s. This combined with high temperatures in the upper
90s will result in heat index values approaching critical. Some
uncertainty in dew points keeps confidence in actually meeting heat
headline criteria low. However, we will monitor this trend through
the rest of the afternoon. Warm temperatures remain for the
overnight with lows falling only to the 70s.

FRIDAY: Friday will be another hot and humid day, though not quite
as hot as Thursday. Highs Friday will reach the upper 80s to mid
90s. Dew points will still be high in the upper 60s to low 70s.
However, the coverage of low 70s will not be as widespread. Heat
index values will still be high, peaking in the upper 90s, but they
do not currently appear to be reaching any headline criteria.

Through the day Friday, we will watch as a mid-level shortwave works
its way east from western Wyoming. At the surface a low pressure
will build in over north central South Dakota. By Friday afternoon
this system will begin to move north-northeast, dragging a cold
front through the region as it does so. Along this front showers and
thunderstorms are expected to form in central South Dakota between
roughly 2-5 pm. Initially storms will be surface based and
discrete thanks to a very weakly capped environment. However,
the best shear will be slightly behind the front(~30-35 kts),
while the best instability (~1500-2000 J/kg) will be in front.
Mid-level lapse rates are weak, only around 6 deg C/km. However,
should environmental factors line up sufficiently, strong to
severe thunderstorms are possible. The most likely threats upon
storm initiation will be large hail up to an inch in diameter,
and damaging wind gusts of 60 mph. Storms are expected to
quickly grow upscale as the shear vectors are mostly parallel to
the boundary. As they continue to progress east they will
likely become elevated as surface stability increases after
sunset. DCAPE values of 1000-1200 J/kg indicate that after this
transition the most likely threat will be damaging wind gusts of
60-70 mph. In addition, precipitable water values in the 99th
percentile for climatology indicate that localized, heavy rain
may also be a threat.

THE WEEKEND: Early Saturday morning the showers and
thunderstorms may reintensify as a vorticity band sweeps
through an area of more unstable air along and east of I-29.
Shear and lapse rates remain low, while DCAPE values remain
moderate, around 700 J/kg. Still think the most likely threat is
wind gusts to 60 mph and heavy rain. As the day continues, a
secondary wave and weak WAA will keep light, isolated to
scattered showers in the forecast. Severe risk for Saturday day
time into the afternoon is low, and the the area most likely to
see additional rain will be east of the James River Valley.
Rainfall totals from Friday to Saturday will range from around a
quarter of an inch up to a half an inch. Locally heavier
amounts under stronger thunderstorms is possible. Highs for
Saturday will be slightly cooler thanks to northerly winds on
the backside of the front, in the low to mid 80s. Lows will fall
to the 50s and 60s.

By late Saturday night to early Sunday morning showers should have
moved east of the area. Highs Sunday will climb into the low to mid
80s. Another mid-level compact short wave will sweep through the
region Sunday afternoon and evening. This round will have a slightly
better thermodynamic profile with the factors lining up a little bit
better. MUCAPE of 1000-1500 J/kg, lapse rates of 6.5-7 C/km, 0-6 km
bulk shear 25-35 kts, and DCAPE greater than 1000 J/kg all indicate
that conditions will be favorable for strong to severe thunderstorms
capable of producing large hail and damaging wind gusts. Guidance is
in low agreement on timing of these storms, but the general
consensus has them move through the area beginning in the late
afternoon, and clear of the region by early Monday morning.

NEXT WEEK: The active pattern looks to continue through at least the
early part of next week. Mostly zonal flow aloft will have several
short waves move through bringing chances for rain approximately
every other day. Details are lacking, so stay tuned for updates as
they become available.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1046 PM CDT Thu Jul 3 2025

VFR conditions expected tonight through much of the day Friday.
Uncertainty arises in storm development and timing going into Friday
evening into the night. Enough confidence to put PROB30 groups at
each TAF site during the last quarter of the period, but these
details will be refined as guidance hopefully comes into better
agreement as we get closer to Friday night. Occasional drops to
MVFR visibilities will be possible in the heavier storms,
especially around KHON.


LLWS wind shear will be a concern at KHON at the start of the
period, but will fade as we approach sunrise Friday. Southerly wind
gusts will pick up again Friday afternoon, with gusts as high as 25-
30 kts expected across much of the area.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...Samet