299
FXUS63 KFSD 042357
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
657 PM CDT Fri Jul 4 2025

.KEY MESSAGES...

- Slightly less hot but still humid for this 4th of July with
  peak heat index values in the 90s. Temperatures more typical
  of early-mid July (highs mostly in the 80s) settle in for the
  rest of the holiday weekend through much of next week.

- Marginal (Level 1 of 5) risk for severe storms today/tonight.
  Main concern is isolated damaging wind gusts in the late
  afternoon and evening west of the I-29 corridor. Lower but
  non-zero risk that a stronger storm could develop during the
  overnight hours.

- Pockets of heavy rain could accompany storms this afternoon
  into Saturday morning. The risk for widespread flash flooding
  is low, but localized urban flooding is possible.

- Additional chances for showers/storms focused on Saturday and
  next Monday night-Tuesday. Some stronger storms are possible
  early next week, but details are uncertain.

&&

.DISCUSSION...
Issued at 205 PM CDT Fri Jul 4 2025

This Evening and Overnight: Mid afternoon WV imagery shows
short wave lifting northeastward with a trough axis draped
through the central Dakotas down into western Nebraska. These
two features have already been the focus of thunderstorm
development today and should continue to be so with eastward
extent through the evening hours, perhaps aided further late
this evening by the arrival of the primary front.

Deep layer shear is weak, denoted by both 0-6km shear and EBWD of
<20 kts and thus any organization to thunderstorms will be minimal
and likely more of a multicell variety. While a lack of shear and
rather warm mid levels should limit the hail risk, enough
instability exists for a storm to briefly pulse to marginally severe
hail levels during initial development. Thereafter, damaging wind
gusts to around 60 mph will be the primary risk through the evening
with DCAPE values hovering around 1000 J/kg. This is all obviously
in addition to lightning which should be of an equal concern for
those with outdoor celebrations/activities.

A secondary threat to consider that was well discussed in the
previous forecast discussion is for locally heavy rain. PWAT sit AOA
the 90th percentile of climatology via recent observed RAOBs at OAX
and ABR. Additionally, a deep warm cloud layer in excess of 4000m
should allow for efficient rain rates in any more persistent storm
clusters. While any heavier rain amounts should be highly localized,
PMM/LPMM from the HREF show potential for an isolated amount
exceeding 2 inches.

In terms of timing of thunderstorms, storms will continue through
central South Dakota through the afternoon, into the James River
Valley by early to mid evening (6 to 9pm) and then into the 1-29
corridor by late evening (9pm to midnight). A secondary wave pivots
through the base of the shortwave trough late tonight and very well
could keep shower and storm activity lingering across SW MN and NW
IA into Saturday morning.

Saturday: This previously mentioned strung out vorticity ribbon
through the base of the trough lingers east of I-29 through much of
Saturday and could keep precipitation chances around, especially by
midday through the afternoon/early evening as daytime heating again
pushes MLCAPE values as high as 1000-1500 J/kg. Deep layer shear
again not supportive of organized severe weather although a storm or
two may pulse near the strong category. Temperatures largely in the
80s with apparent temperatures approaching 90 across the Hwy 20
corridor of NW IA where a better overlap of warmer temperatures and
moist dewpoints remains.

Sunday: A wave pushing into eastern MT/WY Saturday is expected to
result in an eastward moving MCS that may approach our western
coverage area by the daybreak hours Sunday morning. While an
unfavorable diurnal period will likely result in its demise by the
time it reaches the James River Valley we`ll wait to see what, if
any, convective contamination it leaves behind for the remainder of
the day.

Monday through Thursday: Fairly zonal flow to start the next work
week, eventually transitioning to ridging through the Central US by
midweek. A quick moving wave late Monday could bring additional
thunderstorm chances with overall pattern recognition and ML
probabilities highlighting at least some severe weather risk.
Another chance of storms may arrive late Thursday as aforementioned
ridging begins to break down. Temperatures in the 80s to lower 90s
are currently expected for this period.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 655 PM CDT Fri Jul 4 2025

Scattered showers and storms will impact the area through tonight as
a cold front moves in, bringing the potential for some drops to IFR
visibilities as the heaviest storms move through. Storms will
become more isolated to scattered in nature after midnight
tonight, with the better chances for storms shifting east of
I-29 around daybreak. Additional showers and storms will develop
Saturday afternoon, mainly east of I-29.

Outside of any thunderstorms, VFR conditions are expected through
the evening, but CIGS will likely drop after midnight tonight. With
that, MVFR conditions are expected into Saturday morning. Clouds
will scatter out heading into the afternoon, marking a return to VFR
conditions during the last quarter of the period.

The cold front will arrive in the western part of the area just
after midnight tonight and will continue moving eastward through
Saturday morning. With the frontal passage, winds will turn from the
south to the northwest through the period.


&&

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

&&

$$

DISCUSSION...Kalin
AVIATION...Samet