073
FXUS63 KFSD 230809
AFDFSD

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

.KEY MESSAGES...

- Breezy conditions prevail through the end of the work week,
  with increasing south winds Thursday, and west-northwest winds
  Friday, gusting to 30-35 mph.

- Clusters of strong to severe thunderstorms are possible from
  late Thursday afternoon into early Friday morning. Level 2 of
  5 risk for severe storms through the Missouri and James River
  Valleys, with a Level 1 of 5 risk to the northeast. Large hail
  and damaging wind gusts would be the primary threats.

- Periods of unsettled conditions continue into early next week,
  though confidence in timing/location of favored precip chances
  is low. Higher confidence that temperatures will be on the
  cool side of normal for much of the Memorial Day holiday
  weekend, coldest on Friday.

&&

.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 /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1042 PM CDT Wed May 22 2024

VFR conditions begin the TAF period. Winds are currently beginning
to turn southerly this evening and will remain southerly through the
overnight hours with light speeds of only 5-10 knots. The low level
jet (LLJ) remains on track to strengthen during the overnight hours,
bringing low level wind shear (LLWS) to locations along and west of
the James River. As such, have included LLWS in KHON`s TAF.

Southerly winds strengthen tomorrow as mixing increases with gusts
up to 20-30 knots expected. Latest hi-res guidance has convection
developing across south central South Dakota tomorrow afternoon and
moving into locations east river during the evening hours.
Confidence has increased enough to to include mention of VCTS in
KHKON`s TAF. Storms may reach KFSD and KSUX by the end of the TAF
period but confidence is not high enough to include in their TAFs as
of now. The storms will finish out the TAF period.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...Meyers