862
FXUS63 KFSD 140833
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
333 AM CDT Mon Jul 14 2025

.KEY MESSAGES...

- Heat and humidity continues for today and Tuesday, with
  increasing storm chances on Tuesday and Tuesday night. With
  that comes a chance for severe storms along with heavy
  rainfall.

- Cooler temperatures expected for mid to late week, with
  periodic low confidence precipitation chances continuing
  through next weekend.

&&

.DISCUSSION...
Issued at 330 AM CDT Mon Jul 14 2025

Continued warming across the area today as an 850 mb thermal ridge
over the western CONUS expands to the east. This places 850 mb
temperatures of 20-26 C across our area by this afternoon, and this
will mix down to highs in the upper 80s east of Interstate 29 to
upper 90s over the James River Valley and westward. These
temperatures combined with dew points mostly in the 60s to lower 70s
will result in a fairly uncomfortable day across the area. Even so,
lowest dew points (~60 degrees) will reside with the hottest
temperatures, so heat indices will remain below headline criteria.

For tonight into late Tuesday morning, an upper level trough begins
to shift out of the of the Northern Rockies as a surface trough
deepens over the western portions of SD and NE. Although this will
bring increasing thunderstorm chances to those areas, latest
guidance continues to indicate this will stay out of our CWA for the
most part - being focused to the north and west along a frontal
boundary draped through northern SD into central MN. Tonight will be
a warmish night with lows in the upper 60s to lower 70s.

Increasingly unsettled weather by Tuesday afternoon and Tuesday
night as the aforementioned frontal boundary shifts southward across
our area as an upper level shortwave tracks overhead. With that,
thunderstorms are expected to develop over central SD in the late
afternoon, pushing to the east across our area on Tuesday
evening/Tuesday night. These storms will develop in the presence of
strong instability with MLCAPE of 2000-3000 J/KG and mid level lapse
rates of 7-8 C/KM. Even so, 0-6 km bulk shear will not be especially
strong in the absence of an significant mid/upper level flow -
running mainly in the range of 25 to 30 kts. In spite of that,
cannot rule out a few severe storms into Tuesday evening with large
hail and damaging winds (with DCAPE along the leading edge of the
convection initially running around 1000-1500 J/KG). This aligns well
with the SPC Day 2 Slight risk (level 2 of 5) for portions of our
area. In addition to these threats there will be a risk for pockets
of heavy rainfall on Tuesday night. PWAT values (1.5" to just over
2") will be in the 90th percentile with respect to climatology, with
current ensembles indicating a 50-70% of areawide averages of at
least 0.50" of rainfall (lower probabilities of 1.00" at 10-30%) -
though localized higher amounts will be possible. This scenario is
outlined in the WPC Day 2 ERO with a Slight risk (level 2 of 4) in
place for our area.

By Wednesday the frontal boundary settles into southern IA and NE,
with some threat of showers/isolated thunderstorms remaining even
into Wednesday night as another shortwave tracks across the region
and an upper level jet streak develops over eastern SD into MN. It
will be cooler on Wednesday with cold air advection behind the
departing front. Highs will be in the 70s to near 80.

In a persistent zonal upper level flow, below normal temperatures
(70s/lower 80s) will linger for Thursday and Friday with our next
best chance of showers and storms perhaps coming on Friday night -
this as a frontal boundary lifts northward into the MO River Valley.
Temperatures then begin to warm back closer to seasonal averages as
we head into next weekend. Confidence in precipitation chances for
that period are low with the usual model differences that far
out.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1032 PM CDT Sun Jul 13 2025

Expect VFR conditions for most of the area through the period.
However, seeing some MVFR conditions (likely lingering smoke)
for some locations in northwestern IA. This should improve
through the early overnight hours. Guidance this evening is
showing some potential of fog and stratus developing (about a
35% chance or less from the HREF). Think that some of this is
due to where guidance thought there would be precip this
evening/earlier tonight, and we did not see any precip. This
keeps confidence in development very low, but will continue to
watch trends.

Winds become light and variable tonight, turning southerly and
gusting 15-20 knots Monday. NAM guidance shows some potential
for marginal LLWS at KHON toward the end of the period, but
confidence remains low enough to preclude inclusion.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...SG