756
FXUS63 KFSD 150833
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
333 AM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Hot, humid weather continues today with highs in the upper 80s
  to mid 90s. A cooldown comes for Wednesday through Friday
  with highs only in the 70s to lower 80s.

- Scattered strong to severe thunderstorms are expected to
  develop in central South Dakota and Nebraska Tuesday
  afternoon, tracking east Tuesday evening. Threats include
  heavy rainfall, hail up to the size of a ping-pong ball, wind
  gusts up to 70 mph, and perhaps a tornado or two. The
  greatest threat comes 4 PM to 11 PM.

- Periodic (<50%) rain chances continue through Wednesday night and
  again through the upcoming weekend and early next week.

&&

.DISCUSSION...
Issued at 329 AM CDT Tue Jul 15 2025

TODAY: Hot and humid conditions continue today as dewpoints climb
once again in to the upper 60s to low 70s. Highs will climb into the
upper 80s to mid 90s. Lingering cloud cover may slightly inhibit
highs, but not by much. Lows tonight will fall into the low to upper
60s behind a cold front, with the warmest low temperatures expected
east of I-29.

Speaking of the cold front, Tuesday morning it will be draped from
southern Ontario southwest through northern Minnesota, through
northern South Dakota and into Wyoming. This front will
gradually make its way southeast through central South Dakota
where it will act as a source of lift for thunderstorms late
this afternoon, into the evening and overnight. Initially
isolated to scattered thunderstorms will intensify as the LLJ
kicks in, becoming strong to severe. A moderately unstable
environment will be in place with 1500-2000 J/kg of CAPE and
6.5-7.5 C/km mid level lapse rates. However, 0-6 km Bulk shear
will be marginal at 25-35 kts. Another thing to monitor will be
wind gusts, as the environment will hold DCAPE values of
1000-1400 J/kg. Despite the marginal shear this environment
should be sufficient to support large hail formation of 1 to 1.5
inches (quarter to ping-pong) and damaging wind gusts of 70
mph. In addition, high vorticity and enhanced stretching
potential combine with a focused area of 0-1 km shear (35-45 kts
courtesy of the LLJ) near the surface low create an area where
isolated tornadoes are possible. This area of potential should
remain confined along to just south of the Missouri River
Valley.

Storms are then expected to grow upscale into a line due to deep
layer shear being parallel to the front. There remain a few
questions about the track and coverage of the storms. Some guidance
has a more organized line that stretches along the cold front
from south central South Dakota northeast into southwestern
Minnesota that will track across the entire region. Others have
more of a broken line with severity decreasing with time. The
majority of the guidance indicates the highest intensity storms
will track along the nose of the LLJ along and south of the
Missouri River Valley. How far northeast the stronger jet
extends will likely play a role in how far northeast strong to
severe storms extend. This scenario seems to be the most likely
as of this forecast issuance. As storms continue east they will
weaken in intensity overnight into early Wednesday morning.
Intermittent, light post frontal showers are possible through
Wednesday afternoon. By Wednesday evening showers should be
clear of the region.

As far as totals are concerned, there is some disagreement in
guidance, with a general trend down in this set of runs.
However, they all indicate these storms could be capable of
producing isolated, heavy rainfall. Most areas look to see 0.25
- 0.75 inches in total. The HREF LPMM continues to indicate
pockets of 1.5-2.5 inches are possible over south central South
Dakota and north central Nebraska, with isolated pockets of 3
inches or more. There is also indication that areas along and
north of Highway 14 may also see pockets of 1.5-2 inches.
However, deterministic guidance is much more pessimistic,
showing the highest totals at around 1-2 inches with isolated
pockets of 2+.

WEDNESDAY-FRIDAY: As mentioned, Wednesday may have lingering post
frontal showers through the afternoon. Highs will be cool thanks to
breezy northerly winds, in the upper 60s to mid 70s. Warmest
temperatures are expected over northwestern Iowa. Lows will fall to
the 50s. Dry and cooler conditions prevail Thursday with highs in
the 70s and lows in the 50s. Winds turn southerly Thursday
afternoon, ushering in warmer air for Friday. Highs will climb to
the upper 70s and mid 80s with lows in the 60s. Friday night brings
our next chance for widespread thunderstorms as a swift moving mid-
level waves passes through. Details are uncertain at this point,
please continue to check back for updates.

THE WEEKEND: Showers remain in the forecast for the weekend as a
series of short waves move through mostly zonal upper flow. Highs
for both days will be in the upper 70s to mid 80s and lows will be
in the 60s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1045 PM CDT Mon Jul 14 2025

VFR conditions begin the TAF period. Showers and a few thunderstorms
persist just west of the forecast area late this evening. They could
drift near KHON so have added a PROD30 group for the first few hours
of the period. Otherwise light southerly winds will persist through
the night along with some low level wind shear (LLWS) thanks to the
strengthening low level jet (LLJ). A cold front will push into the
area tomorrow afternoon, sparking new thunderstorm development along
the boundary. Showers and storms will push southeastwards through
the reset of the afternoon and evening hours, brining chances for
rain to all TAF sites. At the same time, ceilings will be lowering
to MVFR/IFR levels behind the front. The lowered ceilings and
showers/storms will finish out the TAF period.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...Meyers