509
FXUS63 KFSD 150354
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1054 PM CDT Fri Jun 14 2024

.KEY MESSAGES...

- While a few showers and isolated thunderstorms will be
  possible near and west of the James this evening, a high
  chance for showers and storms comes overnight and through
  Saturday morning. There is a low chance for an isolated severe
  storm or two in south central SD.

- A few strong to severe storms are possible near and east of a
  Marshall to Sioux Falls to Yankton line Saturday evening.

- Sunday night into Monday brings a moderate to high (50-80%)
  chance for more organized rain and thunderstorms. Scattered
  severe storms and locally heavy downpours are possible
  overnight. The highest risk for heavy rain and/or severe
  weather is for locations near and north of a Yankton SD to
  Spencer IA line.

- Summer heat brings highs in the 80s and 90s through Monday
  with a high chance of heat index readings of 90 to 100
  degrees. The pattern remains active with periodic rain chances
  through the remainder of next week.

&&

.DISCUSSION...
Issued at 233 PM CDT Fri Jun 14 2024

Mid to upper level moisture will increase through the afternoon and
into the evening ahead of an upper level wave moving out of the
Rockies. Initially, most of the area will see only the increase in
clouds and the fairly deep 10-12 kft dry layer below this moisture
provides no instability and makes and weak precipitation development
aloft difficult to reach the ground. After about 03z moisture from
the south begins to deepen as the wave moves onto the Plains. The
instability remains fairly weak and elevated thus limiting any
severe potential, but the strength of the wave and the availability
of increasing mid level moisture should allow showers and
thunderstorms to overspread the area. GEFS and EC ensemble support a
very good (40-70% chance) for a half an inch or more of rain, with
higher chances near and south of I-90.

The wave that will bring the overnight activity slowly moves through
the area Saturday, which could leave a small corridor of instability
across mainly northwest IA and southwest MN late Saturday afternoon
and evening. Not a lot of model agreement on dissipating clouds and
allowing heating in this area, so instability values are all over
the place. A worst case scenario looks like maybe 1500-2000 J/kg
CAPE and 20-30 knots of shear. So would be enough to support a hail
and wind threat but likely remain isolated to scattered. With the
wave in place Saturday eastern SD and northeast NE will likely see
some scattered shower and isolated thunderstorm activity but it
should not be severe.

Saturday night into Sunday weak mid and upper level ridging spreads
across the area which should keep mainly quiet conditions in place.
Low pressure aloft deepens to the north with a front expected to
slowly sag southward through the day. The environment ahead of this
front becomes very unstable, but with a prominent cap in place not
expecting any development. But with the strong cap in place and
nearby boundary we may see some areas with dew points exceed 70
degrees, so starting to feel pretty humid. Better chances for this
oppressive humidity will be northwest IA, southwest MN and far
southeast SD.

Sunday night into Monday becomes very interesting as a boundary
should be in place near the Missouri River in the low levels and a
little farther north and west in the mid levels. As a right entrance
region of the jet races into ND, a mid level wave is expected to
eject into western NE and central SD. This should force some
stronger southerly flow in the low levels and bring some strong
forcing across the low and mid level front. The question then
becomes just where along this front will activity try to develop.
Barring breaking the cap, the timing of the mid level wave suggests
that development will be more likely after 3z, and if capping can
hold from about 900 mb to the surface, capping looks much weaker in
the 800-850mb layer. Even lifting from this level yields about 2000-
3000 J/kg CAPE with about 30 knots of shear so severe weather would
become fairly likely in this environment. Likely not tornadoes but
hail and wind. However if storms get going around 925 mb then a bit
more shear and instability could support a more organized linear
system. One other concern will be heavy rain. Mid and upper level
flow will likely run normal to the low level boundary which would
support training and with such deep instability and a warm cloud
depth around 14000 feet some high rainfall rates will be likely.
Still a lot of unknowns right now, but later Sunday night into
Monday definitely shows potential.

Tuesday through Friday remains active with southwest flow aloft and
occasional mid level waves to trigger some activity. A lot to happen
between now and then but for now Tuesday night into Wednesday and
Friday appear to be the best chances.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1052 PM CDT Fri Jun 14 2024

VFR conditions may deteriorate to MVFR overnight as an area of
showers and scattered thunderstorms spread in from
central/eastern Nebraska. Southeast winds remain fairly light,
near or below 15 kts with occasional gusts, but may see gusts in
the 20s mix down overnight with rain. MVFR and occasionally IFR
ceilings are expected with scattered showers and storms
continuing through Saturday morning. Southeast winds will
weaken Saturday afternoon as ceilings lift and rain clears out.
May see some storms redevelop and/or move back in during the
afternoon and evening, especially east of I-29, but confidence
was too low to include in the TAF at this time.


&&

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

&&

$$

DISCUSSION...08
AVIATION...BP