920
FXUS63 KFSD 261122
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
622 AM CDT Thu Jun 26 2025

.KEY MESSAGES...

- Rainfall will continue through Thursday afternoon. Additional
  rainfall of a quarter to 1.5 inches is possible by the time
  rain finally ends. Pockets of observed totals of more than 3
  inches are already present in some areas.

- A risk of strong to severe storms is possible late this
  morning and afternoon. Low confidence on where stronger storms
  may initiate, but most likely southeast of a rough line from
  Sioux City to Spencer.

- Additional rain may pose some flood risk. Primarily focused
  towards urban and small stream flooding as opposed to
  widespread river flooding.

- Temperatures rise into the weekend. Periodic chances of
  showers and thunderstorms persist Sunday through the upcoming
  week. Some indication that storms could become strong to
  severe. Begin monitoring this time period if you have outdoor
  plans.

&&

.DISCUSSION...
Issued at 351 AM CDT Thu Jun 26 2025

TODAY: Elevated showers and weak thunderstorms continue this
morning, triggering along an area of convergence supported by the
nose of the LLJ and a mid to upper level shortwave. These are
expected to remain sub-severe due to low instability (only a couple
hundred J/kg CAPE) and shallow upper lapse rates (< 6 Deg C). As the
surface front makes its final push through northwestern Iowa late
this morning into the early afternoon there is a chance of renewed
convection. CAMS show a line of stronger thunderstorms forming along
this boundary as it moves off, but there is disagreement in the
location of initiation. Some have storms initiating as far west
as a rough line from Sioux City to Spencer. Others don`t have
the stronger convection initializing until it`s east of our
area. Looking at the dynamics, 0-6 bulk shear of 30-40 kts could
support a few isolated stronger cells. However, the instability
is looking less favorable, only a few hundred J/kg, with the
better thermal profile just east of our area. In either case,
PWAT values are at or near the maximum for climatology.
Considering this, the deep, warm cloud layer of 12,000+ feet,
and long skinny sounding profiles, these will likely still be
efficient rain producers. An additional quarter to an 1.5
inches of rain is possible by the time rain ends this afternoon.
Higher pockets are possible for areas in northwestern Iowa. As
such, will leave the Flood Watch that is already in place.

In addition, as the low passes over the region, an area of enhanced
stretching potential and vorticity advection sets up over
northwestern Iowa and southwestern Minnesota. Here a few brief
funnels are possible this afternoon through this evening. Threat of
funnels should wane as the sun sets and afternoon heating
dissipates.

Storms will gradually cease by late this afternoon. Clouds will
gradually decrease from west to east this afternoon. As the sun
comes out we can expect temperatures to begin to rise into the upper
70s to 80s for areas along and west of the James River. Slightly
cooler east of there where clouds last longer, in the 70s. Overnight
lows will be in the upper 50s to low 60s.

FRIDAY-SATURDAY: Surface high pressure moves in for Friday, keeping
us dry. Through the day, winds will turn to the south-southeast.
Areas to the west of James River will see winds increase in response
to a tightening SPG as a shortwave approaches from western South
Dakota. Gusts in the afternoon will be 15-25 mph in this area, less
than 10 mph to the east. As the wave continues to progress east, a
warm front will push into the region from the west. This will help
our highs for Friday warm into the 80s to low 90s over central South
Dakota.

As the wave continues its progress, a quick shot of rain is possible
early Saturday morning. The best shear remains north of the area,
but instability and steep mid-level lapse rates could support a
storm or two becoming stronger. The threat is short lived as the
wave clears the area quickly. Location of activity is uncertain, as
there is low consensus in the model guidance. The rest of the
afternoon a very strong push of WAA on southwesterly winds will help
our highs for Saturday reach into the 90s. Dew points will be in the
upper 60s to mid 70s. These combine to create heat index values in
the upper 90s to low 100s. We will need to continue to monitor this
trend as it may become necessary to issue a heat headline in
the future.

SUNDAY-NEXT WEEK: The hot weather will be short lived this time as
another short wave and cold front move through the region. Highs
will be in the mid 80s to low 90s, with the warmest temperatures
along and south of the HWY 20 corridor. Showers and thunderstorms
are expected to trigger off this system late Saturday night into
Sunday. Guidance is in low agreement on track of this system. The
GFS keeps the track to the north, just clipping out Minnesota
counties. The EC, CAN, and NAM vary on coverage, but all have the
system traversing from northwest to southeast through the day
Sunday. The best shear will lag behind the best instability.
Soundings are well capped, but do indicate some elevated storms
are possible. Plentiful instability will be present with steep
lapse rates, however shear will be marginal. It is possible a
few isolated to scattered severe thunderstorms may develop. If
they do, the primary threats will be large hail and damaging
wind gusts.

Next week the active pattern aloft looks to continue. Periodic rain
chances will be in the forecast through the end of the week. That
includes the 4th of July. If you have outdoor plans for that day,
keep an eye on the forecast, you may need to make adjustments.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 622 AM CDT Thu Jun 26 2025

A mix of MVFR to LIFR ceilings and visibilities this morning as rain
showers continue to move northeast through the region. Some showers
could produce moderate to heavy downpours, reducing visibility to
less than 4 miles at times. Showers are expected to gradually
decrease from west to east beginning late this morning through this
afternoon. Ceilings should improve as clouds begin to break up
shortly after.

Wind direction varies greatly from one point to another through the
region. This is due to the surface low sitting over southeastern
South Dakota. As the low continues to move off to the east winds
will become northerly by the mid afternoon at 5-10 kts. Winds become
light and variable overnight.

&&

.HYDROLOGY...
Issued at 351 AM CDT Thu Jun 26 2025

As mentioned above, an additional quarter to 1.5 inches of rain
is possible through the end of the precipitation this afternoon.
The highest amounts are expected over portions of northwestern
Iowa and southwestern Minnesota. Pockets of heavier rain are
also possible.

There is risk of an increase in thunderstorm activity late this
morning into the afternoon for portions of northwestern Iowa.
There is low agreement in CAMS where stronger storms initiate.
Some have them as far west as a rough line from Sioux City to
Spencer, others have them east of the area before intensifying.
Stronger convection that develops could potentially produce 0.5
to 1.5 inch per hour rain rates, resulting in isolated flash
flooding of small creeks and streams, as well as urban streets.
Considering this, have left the current Flood Watch as it is.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...Flood Watch until 1 PM CDT this afternoon for IAZ013-014-
     020>022-031-032.
NE...Flood Watch until 1 PM CDT this afternoon for NEZ013-014.

&&

$$

DISCUSSION...AJP
AVIATION...AJP
HYDROLOGY...AJP