731
FXUS63 KFSD 110344
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1044 PM CDT Thu Jul 10 2025

.KEY MESSAGES...

- Scattered showers and storms will persist overnight, mainly
  south of the I-90 corridor. The main hazards with the
  strongest storms will be locally heavy downpours, small hail,
  and gusty winds.

- A marginal (level 1 of 5) risk of severe storms develops
  Friday evening, as a front brings scattered thunderstorms
  southward into the region. The main threats with the strongest
  storms will be up to quarter sized hail, strong winds up to 60
  mph, and heavy downpours.

- Temperatures cool Saturday, but heat and humidity build in
  Sunday and Monday.

- Thunderstorm risks return late Monday through Tuesday, with
  signals for severe weather threat present in most data.

&&

.DISCUSSION...
Issued at 258 PM CDT Thu Jul 10 2025

A line of elevated thunderstorms is crossing the Missouri River in
South Dakota this afternoon in an environment characterized by
around 3000 J/kg of MUCAPE and mid-level lapse rates of 7.5-8 C/km.
Hail would be the main threat with this activity if an updraft along
the line is able to sustain itself long enough. These storms also
have around 1000-1500 J/kg of DCAPE to work with; however, the
elevated nature of the storms may make it difficult for strong winds
to make it to the surface. So overall, this activity looks mostly
like a heavy rain and lightning threat over the next few hours as it
lifts slowly east-northeastwards and fades as it closes in towards I-
90.

The bigger question going into late this afternoon will be storm
development that is expected to occur somewhere in north-central
Nebraska. The aforementioned storms crossing the Missouri may act to
suppress the greater thermodynamics south of the area through
this evening, keeping the greatest threat of severe weather
closer to the I-80 corridor. Still, the greater severe weather
threat locally will be mainly along and south of Highway-20.
These storms will be capable of all modes of severe weather,
mainly large hail and damaging winds, though a brief tornado
cannot be ruled out. Heavy rain and urban flooding may also be
possible, more on that below.

FRIDAY: Lingering showers are likely to continue moving east or
southeast in the morning as rapid subsidence develops behind
departing upper trough.  A light and variable wind could lead to a
bit of patchy valley fog into mid-morning.  Recent CAMS and lower
resolution guidance have backed off PoPs through mid-day, holding
off on any diurnally based convection until mid-afternoon in most
locations.  Better focus for convection is expected to develop along
a slowly advancing cold front sinking through central and northern
South Dakota in the morning along with a weak pre-frontal trough
bisecting the CWA. Soundings within the warm sector ahead and near
these features continue to indicate modest MLCAPE of 1500-2000 J/KG,
but unidirectional shear remains very limited.  This would suggest
any activity that develops will be pulsy in nature, but also capable
of smaller hail and brief downburst winds.

FRIDAY NIGHT: The front and accompanying convection will slowly
drift through the CWA overnight, with isentropic downglide
clearing out precipitation quickly by daybreak. Temperatures
Saturday morning expected to fall into the middle 50s to lower
60s.

SATURDAY-SUNDAY: A perfect Saturday will be in store for the region
as high pressure drifts across the area.  Combined with light winds
and temperatures only in the upper 70s to lower 80s, the afternoon
may feel quite comfortable.  Some isolated high based showers and
thunderstorms may develop west of the James River early Sunday
morning, signaling the return of warmer air aloft.   Temperatures
Sunday are expected to climb back into the mid 80s to lower 90s.

MONDAY-WEDNESDAY: As we`ve been discussing the past days, we`ll keep
our eyes on a frontal boundary dragging across the Dakotas Monday
into Tuesday. Dew points will likely surge higher Monday afternoon
given the southerly flow but also increasing evapotranspiration of
the season.  Will likely continue to need to bump dew points upwards
from NBM values.  A mid-lvl wave moving through early Tuesday will
bring our next risk of convection, possibly strong to severe, to the
region.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1035 PM CDT Thu Jul 10 2025

Showers and occasional thunderstorms will continue to train east
near Yankton and Sioux City overnight. The strongest storms will
bring MVFR visibility, heavy downpours, and small hail. Isolated
showers and storms are possible further north at Huron and Sioux
Falls, but confidence was too low to include in the TAF at this
time. We`ll dry out heading into Friday morning before another
round of scattered showers and storms develops Friday afternoon
into evening. Light southerly winds persist overnight, gusting
up to 20 kts during the day Friday. A passing front will shift
winds to the north late Friday afternoon and evening.

&&

.HYDROLOGY...
Issued at 1035 PM CDT Thu Jul 10 2025

Scattered thunderstorms persist south of the I-90 corridor
overnight, bringing locally heavy downpours especially near and
south of the Highway 20 corridor. PWAT values approaching 2.0"
along with storm motion along an elevated boundary will lead to
an increased potential for water ponding and flash flooding
overnight. The latest HREF PMM still favors a swath of 2"
overnight with localized up to 4" near and south of the Highway
20 corridor. Pockets of 1 to 2 inches of rain have already
fallen so will continue to monitor rain rates overnight. While
probabilistic models suggest lower river flooding in southern
CWA basins, the greatest risks rise from urban and small stream
flooding given potential for 1 to 2" per hour rainfall rates.
Thus have maintained a narrow flood watch for the Highway 20
corridor overnight.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...Flood Watch until 7 AM CDT Friday for IAZ031-032.
NE...Flood Watch until 7 AM CDT Friday for NEZ013-014.

&&

$$

DISCUSSION...Dux/Samet
AVIATION...BP
HYDROLOGY...BP