Sioux City, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

560
FXUS63 KFSD 280652
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
152 AM CDT Sat Jun 28 2025

.KEY MESSAGES...

- Hot and humid day expected throughout the region. Heat index
  values may reach the 100 degree mark, and anyone spending time
  outdoors should take extra caution to prevent heat illness.

- Isolated to scattered strong to severe thunderstorms again
  possible late Saturday afternoon into early Sunday morning.
  Storm risks begin after 4-5pm, bringing brief 2.0" hail risks,
  but larger potential for 70 mph downburst winds.

- Storm risks continue into Sunday, though potential remains
  highly murky and depends on storm development Saturday
  evening/night.

- Near to above normal temperatures for much of the upcoming
  week, with storm risks returning by the middle of the week.

&&

.DISCUSSION...
Issued at 150 AM CDT Sat Jun 28 2025

THIS MORNING: Cluster of strong thunderstorms persist across areas
east of I-29 as of 2am. These storms remained tied to a weak lobe of
vorticity moving through the region, and will continue to move east
through daybreak. With the increase in the LLJ some isolated
stronger cells remain possible in the southwestern periphery of this
weakening MCS. Additional scattered thunderstorms may develop
over the northern half of South Dakota on the nose of the low
lvl jet through daybreak. Well to the north over eastern North
Dakota and western Minnesota, a second developing MCS may track
east southeast into Saturday morning. While this convection
won`t impact the Tri- State area, it will lay out an outflow
boundary over central MN into Northern South Dakota.

TODAY: Lingering morning scattered showers and thunderstorms north
of Highway 14 will gradually dissipate by mid-morning. By mid-day
we`ll have a better idea where two primary features will fall.  One
being an west to east running outflow boundary over central MN into
northeastern South Dakota, and second area will be a trailing cold
front potentially stretching from Valentine to Huron and Watertown
by early afternoon.  South and east of these features, a very warm
and humid day is likely.  Given increase in moisture have lowered
highs slightly and bumped dew points up a bit.  This results in heat
index values approaching the 100 degree mark by mid-afternoon. At
this time, will hold off on a heat advisory, but if morning
trends show higher temperatures/dew points an advisory could be
issued.

Instability is expected to grow substantially through the day,
with MLCAPE approaching 3000-4000 J/KG through most of the warm
sector. The biggest question that models continue to struggle
with is the degree of inhibition and resolving the weak and
subtle shortwaves that could help spur development along the
residual outflow and fronts after 4-5pm. The most favored area
for development will be through central Minnesota and
northeastern South Dakota where synoptic forcing and mid-lvl
winds will be stronger. Development southeast on the cold front
into central SD is more conditional. Given the pool of
instability, any storm that develops will become strong to
severe quickly. However we`ll remain on the southern periphery
of stronger mid-lvl winds, leaving effective shear on the lower
end. Most of the area on the cold front could see multi-
cellular development, with better supercell chances (and
accompanying very large hail/wind/tornado potential) form along
the outflow to our north into Minnesota. Much like Friday
evening, initial storms may have 1.5-2" hail, before shifting
towards 70+ mph downburst winds. Cold pool development could
push a cluster or two of storms southeast into the evening and
early overnight hours.

SATURDAY NIGHT:  Models remain largely split on a secondary wave
crossing the Rockies overnight and developing some sort of MCS over
the Dakotas.  Should this develop an attendant wind risk could
persist through daybreak Sunday.

SUNDAY:  Confidence remains lower than normal into Sunday given all
the scattered convection risks up to this point.  A belt of stronger
mid-lvl winds enters the Northern Plains early Sunday, with
increasing troughing pushing the cold front southeast during the
day.  It`s not impossible to have some convection remaining through
Sunday morning and any MCS that crosses the state could push the
effective front further southeast through the CWA.  However if no
overnight convection forms, then areas along and east of the passing
front remain in a good position for scattered development early in
the afternoon Sunday. This activity may again produce hail/wind
risks.

MONDAY-FRIDAY:  High pressure moves into the Plains early next week,
pulling temperatures down slightly, but keeping conditions dry
through Tuesday.  Some signals for modest mid-lvl moisture return
and warm advection into Wednesday morning, owing to an increase in
PoPs.  Mid-lvl heights try to build for the second half of the week,
and that would likely push high temperatures back towards the 90s
for the 4th of July holiday.  Convection chances remain highly
uncertain for the holiday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1213 AM CDT Sat Jun 28 2025

Scattered convection continues to move through eastern South
Dakota early this morning. Within thunderstorms, drops to
MVFR/IFR visibility is possible, with CIGs near 3k ft AGL.

Into mid-morning, the greatest convection risks will continue
near or north of Highway 14, with skies clearing further south.

A frontal boundary sets up over eastern South Dakota, with
isolated to scattered convection forming along this boundary
after 4-5pm. Highly uncertain on the eventual track of this
convection into the evening, so will continue to remain with
PROB30 groups at all TAF locations.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...Dux