134
FXUS63 KFSD 080330
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1030 PM CDT Mon Jul 7 2025

.KEY MESSAGES...

- Lingering showers with isolated lightning strikes over
  portions of northwest IA will end toward midnight.

- With light winds overnight, patchy fog may develop across
  portions of the area late tonight into Tuesday morning.

- Mesoscale storm cluster likely to develop Wednesday night,
  but a high deal of uncertainty on where this cluster of storms
  will track precludes higher heavy rainfall confidence.

- Greatest storm chances into the weekend focus around Thursday
  into Friday. Mixed storm modes could bring a variety of
  severe weather risks, but slow storm motion may also bring
  locally heavy rain risks.

- Trends favor drier and slightly cooler weather into the
  weekend.

&&

.DISCUSSION...
Issued at 212 PM CDT Mon Jul 7 2025

THIS AFTERNOON/EVENING: Mid-lvl vorticity associated with a
minor trough passages continues to move through the Dakotas. At
the surface, satellite and observations show an area of surface
convergence situated along a line from Huron toward Gregory.
Along and ahead of this boundary, we`ve seen gradual warming but
perhaps not to the degree mesoscale models initially indicated.
As we lose inhibition by mid-afternoon, we should begin to see
isolated to scattered convection form along these convergent
boundaries. NSE soundings and areas downstream indicate
1500-2500 J/KG MLCAPE, but only modest 25 to 35 knots of
effective shear initially. Shear will begin to increase late in
the event, but the strongest mid-lvl winds reside behind the
passage of the upper trough. The end result could be a mixed
presentation of scattered multi-cell clusters and very isolated
supercells. Mid-lvl lapse rates remain marginal into the
evening, so while initial updrafts could pose a large hail risk,
the greatest potential may be from locally strong winds. DCAPE
greater than 700 J/KG is focused mostly along or south of I-90,
and greatest towards and south of the Missouri River. While 700
mb winds remain fairly weak (AOA 15 knots), if you can maintain
some adequate updraft/downdraft balance then some linear
organization of multicell clusters could form bringing a larger
risks of stronger winds focused mostly south of I-90 but
especially along the Missouri River into the Highway 20
corridor. The weak low-lvl flow wouldn`t suggest a great
tornadic risk, though a small bit of increased helicity seems to
be present along a subtle Missouri River boundary into the
evening.

TONIGHT: With  most of this convection driven by a mid-lvl
shortwave, the passage of this trough should bring convective risks
lower after 10pm.  It`s not impossible the 850mb LLJ tries to keep
elevated convection percolating over northern Nebraska and the
highway 20 corridor into early Tuesday  morning, but this activity
should be sub-severe. Further north, if skies clear, then some
potential for fog may form into daybreak.

TUESDAY: High pressure moves in for Tuesday keeping winds light and
temperatures in the lower to middle 80s.  Another quiet overnight is
anticipated into Wednesday morning.

WEDNESDAY-FRIDAY:  Southerly winds return early Wednesday as low-lvl
moisture returns to the Dakotas through the day.  By the afternoon,
one or more MCS may begin to form along a north to south frontal
boundary in the Dakotas, with a very uncertain easterly track into
Thursday morning. The greatest severe threat is anticipated to
remain north and west of the CWA.

A large discrepancy in deterministic model guidance builds into
Thursday given uncertainty of MCS activity. Synoptically, the
passage of a stronger mid-lvl trough would favor renewed
afternoon/evening convection over the central Dakotas and
Nebraska areas, with one or more MCS moving east southeast into
the overnight hours. While shear will remain a bit marginal,
instability should drive a severe risk at times, with strong
outflow driven storms suggesting a greater wind risk. Slow storm
movement and high PWAT values also would indicate a localized
heavy rain risk. Confidence on placement of the heavy rain risk
remains VERY uncertain with minimal signal in ensemble guidance
suggesting one targeted area over another. Temperatures through
the end of the week with the return of southerly flow are likely
to climb back into the upper 80s to 90s with increasing
humidity.

SATURDAY-SUNDAY:  A solution towards increased upper troughing over
the Upper Midwest seems to be prevailing in ensemble guidance
for the upcoming weekend. This pattern would signal cooler
temperatures and lower precipitation chances.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1024 PM CDT Mon Jul 7 2025

Light winds overnight could result in patchy fog formation
across the area late tonight into Tuesday morning. Light winds
will continue on Tuesday with VFR conditions expected through
the remainder of the TAF period.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...JM