623
FXUS63 KFSD 102007
AFDFSD

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

.KEY MESSAGES...

- Scattered strong to severe storms are possible this evening,
  capable of damaging wind gusts and large hail, and potentially
  a tornado. Greatest threat locally is along and south of
  Highway-20.

- A marginal (level 1 of 5) risk of severe storms continues
  Friday afternoon and evening, as a front brings scattered
  thunderstorms southward into the evening and early overnight
  hours. Marginal risks of 1" hail, brief strong winds, and
  brief heavy downpours possible.

- Temperatures cool Saturday, but return back to above normal
  levels Sunday and Monday. Humidity is expected to build each
  day.

- Thunderstorm risks return late Monday through Tuesday, with
  signals for severe weather potential 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 /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1251 PM CDT Thu Jul 10 2025

Scattered showers and storms are set to develop near and along the
Missouri River Valley this afternoon, bringing a risk of severe
weather and heavy rainfall. With that, the best chances of
thunderstorm impacts will be from KYKN to KSUX through the evening
hours, and thus have a TEMPO group in KSUX from 00Z to 03Z to
account for this. The strongest storms will bring IFR visibilities
and the potential for severe wind gusts in excess of 50 kts. After
the storms, showers may continue for areas mainly south of
I-90, but guidance varies largely regarding any activity through
the early morning hours. We`ll dry out heading into Friday
morning, with additional thunderstorm development possible on
KHON`s doorstep just after this period.

Winds will be mainly out of the southeast through this evening,
before turning lighter and more variable Friday morning. With
lessening winds and moisture left behind from these last rounds
of rain, can`t entirely rule out some patchy light fog, but not
enough confidence to include in the TAFs at this time. Winds
will pick up again later Friday morning as a cold front
approaches and turns winds to the west-northwest for areas west
of the James River at the end of the period.

&&

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

Thunderstorm are expected to track eastward through portions of
northeastern Nebraska and northwestern and western Iowa this
evening. PWAT values approaching 2.0" along with storm motion
along an elevated boundary will lead to an increased potential
for excessive rainfall later this evening and overnight. HREF
PMM indicate potential for localized 2 to 5" of rain along, but
especially south of Highway 20 during this event. While
probabilistic models suggest lower river flooding in southern
CWA basins the greatest risks may rise from urban and small
stream flooding given potential for 1 to 3" per hour rainfall
rates. Thus have issued a narrow flood watch for the Highway 20
corridor this evening into early overnight.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...Flood Watch from 7 PM CDT this evening through Friday morning
     for IAZ031-032.
NE...Flood Watch from 7 PM CDT this evening through Friday morning
     for NEZ013-014.

&&

$$

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