499
FXUS63 KFSD 301740
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1240 PM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Rivers across the area have crested, with a slow downward
  trend in river levels this weekend as dry conditions are
  expected to prevail.

- Well below normal temperatures (~10 deg F) continue through Monday,
  and remain a touch below normal (0-5 deg C) Tuesday through
  Saturday as well.

- Monday and especially Monday night will be the next better
  chance for severe weather and heavy rain. Higher confidence
  in showers and storms (70-90%) with decent chances for more
  than an inch of rain in northwest IA and southwest MN
  (30-50%). Certainly a time frame to keep an eye on.

- Stronger westerly flow aloft continues through the end of the
  week, resulting in a busy pattern.

&&

.DISCUSSION...
Issued at 312 AM CDT Sun Jun 30 2024

High pressure at the surface will slide eastward today allowing a
southerly flow to develop, with gusts around 25 mph west of I-29
this afternoon. While today should be mostly quiet, some elevated
instability within roughly the 700-500 mb layer along with some
moisture increase from 800-700 mb may allow some isolated shower and
thunderstorm development. The more aggressive Nam is indicating
about 300 J/kg of available energy while the GFS is even lower. With
a weak mid level wave moving into the area some weak forcing will
also aid potential development. Right now the moisture in the mid
levels is a bit skiddish and not very well agreed upon so will keep
chances from about 10-20 percent.

The chances for showers and storms continues tonight as upper level
troughing spreads across the area and increases low to mid level
flow, thus bringing an increase in moisture and instability aloft.
Model soundings suggest that late tonight enough moisture will advect
northward to break the weak mid level cap and allow showers and
storms to develop. Currently not enough instability to support any
severe storms.

Through the day Monday, showers and thunderstorms will gradually
lift northeast as deeper instability, especially that about 900 mb
or lower, builds to the south of the area. The main focus for our
area will be the mid level wave moving through from late morning
into the afternoon and then waiting to see the response from the low
level jet Monday evening into the overnight. Not surprisingly the
Nam indicates way more elevated instability than the GFS, roughly
3500 J/kg vs 1000 J/kg lifting from about 800 mb. Overall right now
this is not a big concern as we will need to get through the day on
Monday to figure out how much the morning and daytime showers and
thunderstorms play a role in the low to mid level flow and
instability in the evening and overnight hours into Tuesday morning.
Right now this activity does not appear to be too widespread to
suppress at least some aggressive elevated activity, likely in the
form of hail to golf ball and wind gusts to 60 mph. The other
concern, and likely more important, is the threat for heavy
rainfall. Plenty of moisture in the environment as well as very
strong forcing with the developing low level jet to support some
higher rainfall rates. While upper level flow is not perfectly
parallel to the low to mid level boundary with new updrafts likely
to develop on the southwest flank there could be some short term
training that would support some locally heavy rainfall amounts.
Really tough to determine at this time, but a few locations could
reach 3-4" on MOnday night, and unfortunately that focus could be
across far southeast SD and northwest IA.

Continued weak warm advection and a weak mid level wave will keep
the chances for showers and thunderstorms in the area, but
instability will likely be diminished as the earlier activity pushes
east. By late in the day most of the activity should be out of the
area. If this activity does diminish quickly enough Tuesday should
be a nice day with highs in the 70s and northerly winds about 10 to
15 mph.

This drier more stable air should bring quieter conditions Tuesday
night into Wednesday with lows in the 60s and highs in the upper 70s
to mid 80s.

The next system of interest will be Wednesday night into Thursday as
upper level low pressure deepens to the north and swings through
some mid level warm advection then a front at the surface. Right
now it looks like the better chances for showers and storms will be
Wednesday night into Thursday morning, as the cold front will likely
be east of the area by late afternoon.

Some spotty chances remain for Friday then another possible wave
will move into the area Saturday. Temperatures remain below
normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1240 PM CDT Sun Jun 30 2024

Southeasterly winds will become somewhat breezy west of I-29 this
afternoon, sustained in the teens with gusts into the upper 20s and
lower 30s, while areas along and east of I-29 will see the light
winds continuing. Overnight, winds will be increasing aloft and
changing direction, resulting in a couple hours of LLWS across
central South Dakota affecting the KHON terminal. Monday will
feature breezy south-southeasterly winds gusting into the upper 20s
and mid 30s, with a couple chances for scattered showers and
thunderstorms throughout the day, bringing MVFR/IFR conditions along
with them.

&&

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

&&

$$

DISCUSSION...08
AVIATION...APT