720
FXUS63 KFSD 271742
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1242 PM CDT Sun Apr 27 2025

.KEY MESSAGES...

- Elevated instability could lead to isolated severe weather
  and locally heavy rain tonight into early Monday morning. The
  best chance for development appears to be from about 10 PM to
  5 AM tonight into Monday morning across western South Dakota,
  possibly moving northeast into our area after midnight.

- Overall mid morning Monday into mid afternoon should be a lull
  in activity. Strong to severe storms may develop along a
  surface front from the Interstate 29 corridor and eastward by
  late afternoon into the evening. Greatest severe risk is 3 to
  8 pm.

- Next better chance for showers and thunderstorms will be
  Wednesday/Thursday of next week.

&&

.DISCUSSION...
Issued at 350 AM CDT Sun Apr 27 2025

Looking around the area very early this morning, scattered showers
which occurred overnight are now exiting to the east of our CWA,
while breezy southeasterly winds have kept temperatures in the upper
40s to lower 50s. Low level moisture continues to surge into the
area out ahead of a surface low situated over the Western High
Plains, and this is reflected in climbing dew points and a broad
area of stratus lifting into our area from the south and west. These
low clouds will continue to overspread the area today, and will
remain in place through at least early tomorrow under a
strengthening capping inversion aloft. These clouds will inhibit any
shower activity today and will put a damper on temperatures with
highs remaining mostly in the 60s.

The aforementioned surface low tracks into central SD by tonight as
an upper level shortwave lifts into western SD. Out ahead of these
features a 40 to 50 kt low level jet will develop across the region
tonight, setting up the possibility for scattered showers and
thunderstorms to the west and north of the nose of the low level
jet. Most of the latest hi-res models keep the majority of this
activity to the north and west of our CWA, though some would have it
scraping areas north of Interstate 90, focused more toward the
Highway 14 corridor. With the strong capping inversion in place
across the area, any convection that may develop would be elevated,
though with MUCAPE around 1500 J/KG and mid level lapse rates of 8-9
C/KM cannot rule out an isolated strong to severe storm with large
hail and damaging winds. That being said, effective shear is not
overly impressive at around 20 kts. Any showers and thunderstorms
should then lift off to the north and east by early to mid morning
on Monday.

Our attention then turns to the next round of severe weather - this
coming on Monday afternoon and evening. The aforementioned low
pressure will pull a cold front across the area during the day. Out
ahead of this feature strong warm air advection will allow
temperatures to soar into the 70s and 80s by afternoon. This as
continuing low level moisture advection into the area results in dew
points in the 50s to lower 60s by afternoon. This will set up a very
unstable atmosphere as CAPE values reach 1500-2500 J/KG during the
afternoon. Although a strong capping inversion will be in place
during the day, this is expected to break by afternoon as the upper
level trough to the west pushes eastward and mid level temperatures
cool. We are still seeing some differences in frontal timing among
the models, though there is enough consensus that it is likely that
thunderstorms will develop along and east of Interstate 29 - perhaps
as early as 3 pm. With mid level lapse rates remaining around 8 C/KM
and strong winds aloft resulting in bulk shear of 50 to 60 kts, any
storms are quickly expected to become severe. All modes of severe
hazards will be possible, with damaging wind gusts of 60 mph+, hail
to the size of golf balls or greater, and even a few tornadoes with
0-1 KM shear of 25-30 kts, LCL heights less than 2000 ft AGL, and
STP (Significant Tornado Parameter) values of 3 to 4. The stronger
storms will then exit to the east by 7 or 8 pm as the
front/instability move out of the area, though post-frontal
showers and isolated weaker thunderstorms will remain possible
even into Monday night.

After Monday`s system exits the area, it will be a quieter period
for mid week into the weekend. Cold air advection will knock
temperatures back into the lower 60s for Tuesday, though a quick
recovery for Wednesday as temperatures climb back to above normal
levels (70s) for the remainder of the week. Models are still
indicating a possibility of showers sometime during the Wednesday
night to Thursday time frame, though ensembles continue to show
light amounts with a 20% probability or less of 0.25" through the
period.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1233 PM CDT Sun Apr 27 2025

MVFR and lower stratus continues through late morning Monday.
Strong southerly winds prevail through the period, with gusts
to 30 knots at times. If gusts diminish overnight, may see some
brief LLWS across the area as the southerly LLJ increases;
however, have omitted mention given the expectation that gusts
will continue.

A couple of periods of showers and thunderstorms are possible
through this forecast period. Hi-res guidance is struggling with
timing and development, but tried to narrow the TSRA periods as
much as possible. Showers look to be more isolated in nature, so
did not mention given low confidence in timing/coverage. An
isolated strong to severe storm is possible, with the greatest
risk after this forecast period.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...SG