219
FXUS63 KFSD 231126
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
626 AM CDT Thu May 23 2024

.KEY MESSAGES...

- Breezy conditions as south winds increase for Thursday. Look
  for mid-afternoon gusts around 25-30 mph. Gusty winds
  continue for Friday as winds become northwesterly gusting to
  30-35 mph.

- Strong to severe storms are possible Thursday afternoon
  through the overnight. Risk level for severe storms is 2 of 5
  from the James River Valley and west. Risk level 1 of 5 for
  areas to the east. The greatest threat with these storms is
  large hail and damaging wind gusts.

- Periodic showers and thunderstorms for Memorial Day weekend.
  While we are not currently expecting strong storms, lightning
  is still possible. When thunder roars, go indoors!

&&

.DISCUSSION...
Issued at 308 AM CDT Thu May 23 2024

THURSDAY: Southerly winds will increase throughout the morning
as a low pressure system approaches from the west, tightening
the SPG. Look for sustained winds to peak around 15-20 mph with
gusts 25-30 mph by mid-afternoon, highest through the James
River Valley. Plentiful WAA will warm our highs into the upper
70s and 80s for today. Our southerly winds will also transport
modest moisture northward, helping dewpoints to climb into the
mid-upper 50s west of the James River Valley and low 50s east.
These will support some moderate instability of around 1500-2000
J/kg MUCAPE over central South Dakota. Model soundings continue
to indicate a capping inversion today, that will erode quickly
once we reach peak afternoon heating. At the same time the cold
front will be approaching from the west, forcing convection
initiation. Strong vorticity from the top of the boundary layer
through the mid-levels, coupled with 35-45 kts deep layer shear,
is enough to support a few strong updrafts. This set of model
runs also indicates similar steep mid-level lapse rates
mentioned in the previous discussion which will support large
hail up to 1.5-2 inches in diameter. Dry mid- levels at
convection start and high DCAPE values around 1000 J/kg support
strong down drafts, and so damaging wind gusts up to 70 mph are
also possible.

As the storms progress eastward, 700 mb steering winds are nearly
parallel with the forcing, indicating quick upscale growth into a
line. From here, the better instability is along and south of the
Missouri River along the South Dakota and Nebraska border. This
should focus the stronger storms along our southern counties for the
evening/overnight hours. As the storms move into northwestern Iowa
around 05-06Z, they look to become more elevated and hail will
become the more dominant threat. However, at the same time the low
level jet kicks into gear, which increases the chance that a few
strong to severe gusts could make it to the ground. Storms should
move east of the region by early Friday morning.

FRIDAY AND BEYOND: Things dry out for Friday with breezy
northwesterly winds gusting up to 30-35 mph. Strong CAA limits highs
to the 60s. Saturday warms a little more into the upper 60s and low
70s. Meanwhile, another upper trough is digging south along the
Pacific Northwest. Saturday night into Sunday there is another
chance for showers and thunderstorms. Currently, we do not expect
these storms to be strong, as the better dynamics are over southern
Nebraska and Kansas. Light scattered showers continue for most of
Memorial Day and highs remain on the cool side of normal, in the low
70s.

An upper ridge begins to build in for Tuesday, finally allowing us
to dry out and warm up a bit through the end of the week. Look for
highs to warm from the mid 70s Tuesday into the upper 70s and mid
80s by Thursday.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 626 AM CDT Thu May 23 2024

VFR conditions expected for the first half of the period. Clouds
will build in after noon as a low pressure system approaches from
the west. Winds are southerly around 20 kts sustained, with gusts 25-
29 kts.

Expect thunderstorms to develop from west to east beginning around
23.22Z. Some of these storms could be strong to severe with the
greatest threats being hail up to 2 inches in diameter and damaging
wind gusts up to 70 mph. These storms will impact KHON around 24.00Z
and progress eastward impacting KFSD around 24.04Z and KSUX around
24.05Z. Storms will then move east into central Iowa.

Behind this system, winds will become northwesterly and increase to
around 20 kts by the end of the period. Gusts will be stronger at 27-
32 kts.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...AJP