423
FXUS63 KFSD 071138 CCA
AFDFSD

Area Forecast Discussion...CORRECTED
National Weather Service Sioux Falls SD
638 AM CDT Sat Jun 7 2025

.KEY MESSAGES...

- Areas of showers and/or thunderstorms today into Sunday
  morning. Severe weather is not expected, but a few stronger
  storms north of I-90 this evening could produce isolated gusts
  in excess of 40 mph.

- Gusty west-northwest winds will become prevalent Sunday into
  Monday, with afternoon gusts 30-40 mph (strongest Sunday west
  of I-29). The northwest flow may bring areas of wildfire smoke
  back into the region, with surface impacts possible by Sunday
  morning.

- Near to below normal temperatures continue through Monday,
  then warmer air with highs in the 80s to lower 90s builds in
  by mid-late week. Sporadic rain/thunderstorm chances return
  late next week, but low confidence in timing/location.

&&

.UPDATE...
Issued at 555 AM CDT Sat Jun 7 2025

Patchy light fog (2-5SM visibility) has developed in our clear
areas along/north of I-90 early this morning. Do not expect the
fog to persist more than another hour or two, but did add patchy
fog into the grids.

Additionally, latest HRRR/RAP Smoke model output shows potential
for at least low concentrations of surface-based wildfire smoke
to return to the area behind the cold front tonight, so have
added that to the grids late tonight into Sunday morning as
well.

&&

.DISCUSSION...
Issued at 425 AM CDT Sat Jun 7 2025

TODAY-SUNDAY: Multiple waves sliding across the forecast area
will maintain varying areas of showers/thunderstorms today into
tonight, and possibly lingering along the Missouri River Valley
into Sunday morning. Main question will be how much rainfall we
will see as lower levels of the atmosphere remain on the drier
side. First things first, a compact wave moving east through
Nebraska early this morning could produce some light showers or
sprinkles in our southern counties, though the better chances
for measurable rain look to be in areas south of Highway 20.

An elongated trailing wave moves into the area this afternoon,
and this could bring a better chance for showers and storms to
eastern parts of the forecast area this afternoon. Minimal deep
layer shear for storms to work with and instability is also on
the weaker side, so severe storms are not expected. However,
similar to Friday, steep low level lapse rates combined with
weak instability and weak winds within the lowest 2-3km could
lead to weak funnels as showers/storms develop this afternoon.
These showers/storms/clouds will hold temperatures in the lower
to mid 70s in our east this afternoon, but locations along and
west of I-29 should see more sunshine help warm afternoon highs
to around 80F.

This wave moves east of the area by 00Z as attention turns to a
stronger wave and associated cold front dropping into the area
from the northwest. A line of storms along the cold front will
slide across areas mainly along/north of I-90 tonight. Could
see isolated stronger storms with this activity this evening,
as they should have stronger shear but still meager instability
with long/skinny CAPE profiles. Main concern with these storms
will be a potential for isolated stronger wind gusts in excess
of 40 mph given a dry sub-cloud layer. That said, DCAPE values
are generally less than 500 J/kg, so not expecting wind gusts to
reach severe levels in our forecast area. Latest SPC outlook
reflects this as well, with the southern edge of the Marginal
Risk lifted slightly northward from previous outlooks.

By later tonight into Sunday morning, focus will shift back to
the south as an extension of the mid level front lingers back to
the west across far northern Nebraska. Could see some light
showers along the Missouri River Valley/Highway 20 corridor in
response to this feature, but again dry low levels will likely
limit potential for measurable rainfall in our forecast area.
Post-frontal mixing will bring stronger winds to the region on
Sunday than we have seen in recent days. Forecast soundings
show winds atop the deep mixed layer could support gusts to
around 40 mph west of I-29 Sunday afternoon, with a low (20%)
probability for isolated gusts reaching advisory criteria of
45 mph. This will combine with a return to below normal highs
in the lower-mid 70s. Unfortunately, this deeper northwest flow
may bring areas of smoke back into the region for the latter
half of the weekend. Latest HRRR/RAP Smoke model output shows
potential for at least low concentrations of surface-based
wildfire smoke to return to the area behind the cold front
tonight, so have added that to the grids late tonight into
Sunday morning.

SUNDAY NIGHT-MONDAY: Closed upper low lingers over northeast
Minnesota/western Great Lakes into Monday with a secondary cold
front dropping through Minnesota and the eastern Dakotas Sunday
night. An associated wave rotating around the back side of the
upper low will bring a chance of showers or a few thunderstorms
to northeast South Dakota/southwest Minnesota late Sunday night
and Monday. Another breezy and cooler day with west-northwest
winds gusting to around 30 mph and highs in the upper 60s to
lower 70s.

TUESDAY-WEDNESDAY: Building upper ridge will allow warmer, more
summer-like air to finally build into the northern Plains by
midweek. Wednesday looks to be the warmest day of the week as
the low level thermal ridge lays over across our forecast area.
NBM/Ensembles currently showing moderate (50-70%) probabilities
for highs topping 90F over much of the forecast area Wednesday,
highest through the Missouri River Valley. An approaching wave
could bring a few showers/storms to our northern counties in the
afternoon, though timing of this trough varies, so confidence
in precipitation/clouds limiting potential warming is low.

THURSDAY-FRIDAY: Upper ridge is projected to break down late
next week, though solutions showing little agreement on timing
and strength of various waves which may move across the region.
Ensembles still showing moderate (40-60%) probability for highs
topping 90F on Thursday with these numbers decreasing further
by Friday. As for precipitation, NBM shows low-moderate rain
chances from Wednesday night onward, focused largely in the
afternoon and nighttime hours. With little model agreement, it
is difficult to pinpoint any favored period at this range.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 610 AM CDT Sat Jun 7 2025

Areas of MVFR-locally IFR visibility in BR (light fog/mist) to
start off this TAF period. This fog should quickly erode within
the first hour or two of the TAF period. Thereafter focus will
be on scattered rain/thunderstorm chances. Better chance during
the afternoon will be east of I-29 in southwest MN/northwest IA,
with no impact to TAF sites expected.

After 00Z, an approaching cold front will shift the potential
for scattered storms to the Highway 14 corridor and perhaps as
far south as I-90. Will target a small window for potential TS
at KHON in the early evening (01Z-03Z). With lower confidence in
storms impacting KFSD, will maintain -SHRA in the later evening
(03Z-06Z) with no mention of TS for now. Storms may produce
brief erratic wind gusts of 35+kt, especially in areas closer to
Highway 14.

By the end of this TAF period, may begin to see surface-based FU
return to the region with northwest flow behind the cold front.
Opted to not include FU in this TAF issuance given uncertainty in
exact timing/location of surface impacts.

&&

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

&&

$$

UPDATE...
DISCUSSION...JH
AVIATION...JH