880
FXUS63 KFSD 171116
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
616 AM CDT Thu Jul 17 2025

.KEY MESSAGES...

- Decreasing clouds after noon, dry, and cool conditions on
  today with highs in the low to mid 70s.

- Shower and thunderstorm chances return Friday afternoon and
  night. Precipitation probabilities of 30 to 60 percent.

- Precipitation chances of 20-30 percent daily this weekend into
  early next week. Details remain uncertain at this time.

- Temperatures will rise to near or above 90 degrees in many
  locations by next Tuesday.

&&

.UPDATE...
Issued at 615 AM CDT Thu Jul 17 2025

Some patchy dense fog has developed this morning, mostly in
areas north of I-90 and west of I-29. Please use caution as you
make your way this morning. Fog should begin to burn off as the
surface temperatures begin to rise this morning.

&&

.DISCUSSION...
Issued at 327 AM CDT Thu Jul 17 2025

TODAY: Zonal flow aloft as a surface high pressure builds in from
the northwest this morning. This will push the clouds out of the
area and by afternoon we should have mostly sunny skies. As the high
moves off to the east winds will gradually change from northerly to
southerly, remaining light at around 5-10 mph. Weak WAA will warm
temperatures slightly higher than yesterday, but still 10 degrees
below average for mid July (Average is mid 80s). Highs will be in
the 70s with lows in the 50s and 60s.

FRIDAY: Southerly winds increase slightly to around 10-15 mph with
gusts up to 20 mph. The highest winds are expected west of the James
River Valley. A stronger push of WAA comes with the winds as we
begin to warm closer to the average with highs in the upper 70s to
80s. Lows will be in the 60s. In addition, the southerly winds will
bring north higher dew points in the upper 60s to mid 70s. Humid
conditions can be expected for Friday as a result. At the surface, a
weak inverted trough moves in from the west in concert with a subtle
short wave trough embedded in the quasi-zonal mid-levels. This with
the WAA will support showers and thunderstorms. The GFS indicates
showers beginning as early as Friday morning along and north of
Highway 14, then expanding in coverage and intensity Friday
afternoon and evening. The EC and CAN have more broad showers
beginning Friday morning and increasing in intensity for the
afternoon and evening. The NAM doesn`t have much for showers until
Friday afternoon. Due to the inconsistencies, confidence in shower
initiation is low.

With the increasing dew points comes increasing instability. CAPE
values of 2000-3000 J/kg are possible, with good 0-6km shear of 35-
45 kts, mid-level lapse rates of 7-8 C/km, DCAPE of 800-1500 J/kg
and PW values of 1-1.5 inches (90th percentile for climatology).
These numbers lend confidence to the storm environment being
moderately favorable. However, warming above 850 mb will result in a
strong cap on the environment. There is some disagreement on
whether or not the cap can be overcome with the generally weak
forcing. Considering this I think that the most likely scenario
will be elevated showers and thunderstorms. Threats would
include heavy rainfall, large hail (1-1.5 inches), and damaging
wind gusts (60-70 mph). Timing of strong storms is uncertain due
to discrepancies in models, however Friday late afternoon into
early Saturday morning looks to be the most active.

SATURDAY-SUNDAY: For Saturday WAA and another week embedded mid-
level wave keeps light isolated to scattered showers and
thunderstorms going for most of the day. PW water values remain at
1.5-2 inches, and though the storm environment is less favorable for
severe, locally heavy downpours remain possible. Highs for Saturday
will be warm despite the clouds and rain thanks to the warm
southerly winds, in the upper 70s to 80s. Lows will be in the 60s.
Sunday will be very similar; isolated to scattered showers and
thunderstorms that may include locally heavy rainfall. Highs will be
in the upper 70s to 80s with lows in the 60s.

NEXT WEEK: Guidance indicates the active pattern will continue
through at least the middle of next week. Nearly daily a weak wave
works through the shallow ridge pattern bringing chances for showers
and thunderstorms. Highs warm into the 80s and 90s for Monday
and Tuesday. Then, a cooling trend for the middle part of the
week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 615 AM CDT Thu Jul 17 2025

VFR to MVFR ceilings to start this cycle. Expect the low level
stratus to gradually lift over the next few hours. Clouds will then
become few to scattered for most of the day. This evening clouds
will build in to broken as mid-level southerly winds bring north
more moist air.

Winds will be light and variable, becoming easterly then southerly
through the late morning into the afternoon. Slightly breezy
conditions west of the James River with gusts 16-20 kts this
afternoon in to the overnight.

&&

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

&&

$$

UPDATE...AJP
DISCUSSION...AJP
AVIATION...AJP