225
FXUS63 KFSD 021826
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
126 PM CDT Sun Jun 2 2024

.KEY MESSAGES...

- Monitoring potential for severe weather late this afternoon
  into tonight. Still not a cut and dry forecast with multiple
  scenarios possible. Favored scenario produces multiple rounds
  of mostly sub-severe showers/storms, first moving east this
  morning and another possible midday-mid afternoon. This is
  followed by a final round of scattered to numerous storms very
  late afternoon-evening, some of which may be strong-severe,
  though greater severe threat largely splits the forecast area
  to the north and south.

- Tuesday may be the next chance for severe weather, but will
  be dependent on recovery from scattered morning convection and
  timing of a cold front pushing through the region. Favored
  area for an isolated severe threat is along and east of the
  MN/IA Highway 60 corridor.

- Quiet weather and seasonable temperatures are expected to
  prevail mid to late week.

&&

.UPDATE...
Issued at 1150 AM CDT Sun Jun 2 2024

No major changes to the afternoon and evening forecast for
thunderstorms. Still some decent agreement on how organized the
initial development will become this evening. While far from a
great set up for tornadoes, the latest models are indicating
some decent low level shear/turning along with CAPE values of
2000-2500 J/kg as well as a fairly low LFC. If any isolated
supercells can develop from about the James Valley towards I-29
they should at least have the ability to attain some low level
rotation and potentially produce isolated tornadoes. The main
threats will be hail to golf ball size and wind gusts to 70
mph. There is still some concern on how much we will recover
behind the exiting morning showers and storms but right now
clouds are clearing pretty quickly.

&&

.DISCUSSION...
Issued at 358 AM CDT Sun Jun 2 2024

TODAY-TONIGHT: Starting off early this morning with an area of
elevated showers and storms moving through the James River Valley,
associated with a subtle mid-level wave and warm advection. This
area of storms should push east through the I-29 corridor into
portions of southwest MN/northwest IA through mid-late morning.
Instability is still somewhat limited, so expect most of this
activity to remain sub-severe, though occasional lightning and
perhaps small hail will be possible.

Behind this initial activity, we are still seeing diverging
solutions among the various CAMs regarding exactly how things will
evolve through tonight.

Favored Scenario: We are already seeing additional showers/storms
developing over western portions of South Dakota/Nebraska, likely in
response to a slightly stronger wave moving out of the Rockies. This
trailing activity advances eastward and reaches our western counties
by around 12Z, and likewise tracks east through mid-late morning.
Continued low level moisture advection and modest heating provide a
bit more instability, which could result in some stronger storms
capable of producing marginal hail up to quarter size. Focus then
turns to the approaching cold front, with still some questions on
where along the boundary storms will initiate. Given disruption from
the earlier rounds, anticipate initial storms will develop across
central Nebraska and farther north toward north central/northeast
South Dakota into North Dakota. These discrete cells quickly grow
upscale into linear segments which tend to track east-southeast
through the evening to early overnight hours. Believe the southern
line will be far enough south that it will not impact our forecast
area. The northern line is more questionable, with some solutions
keeping it well north of our area, while others slide it farther
south into portions of the Highway 14 corridor and southwest MN.
Despite the aforementioned delay in building instability, this round
of storms should bring the primary threat for severe weather,
perhaps with large hail up to ping pong ball size with initial storm
development, but quickly transitioning to a more dominant strong to
damaging wind threat.

Alternate scenario: The alternative has minimal showers/storms
across the forecast area through the late morning-early afternoon
period (behind the ongoing early morning activity), which allows for
greater heating and destabilization ahead of the cold front. This
could lead to more robust storm development during the evening, with
a broader potential for strong to severe storms capable of damaging
winds and isolated large hail. However, given the ongoing convection
in southwest SD which is on track to slide into our forecast area
shortly after daybreak, believe this is a less likely scenario.

Given deeper moisture advecting northward through the day, we are
still seeing projections for precipitable water values of 1.25-1.50"
building north ahead of the cold front. This could lead to pockets
of heavier rainfall, and given antecedent conditions across our
central and eastern areas which have seen pockets of very heavy rain
in recent days, cannot rule out areas of ponding water or isolated
flash flooding. Confidence in where this will occur is low, though,
especially given the variance in storm evolution as described above.
As such, will forgo a Flood Watch for Flash Flooding at this time.
However, it may be something for later shifts to consider if the
threat for heavy rainfall across our most saturated areas becomes
more apparent.

MONDAY-TUESDAY: Storms are expected to exit our eastern counties
by daybreak Monday, leading to a quiet day with relatively light
winds and seasonably warm temperatures topping out in the 80s.
Expect to again see some scattered showers/storms develop in the
broad warm advection Monday night, in advance of a sharper mid
to upper level trough which swings into the northern Plains
through the day Tuesday. Broad consensus has the cold front near
to just east of the I-29 corridor by peak heating, with modest
instability (perhaps as high as 1000-1500J/kg MUCAPE) along with
marginal deep layer shear across our east. As a result, could
see a few strong to severe storms along/ahead of the cold front
during the late afternoon-early evening, before the front pushes
east of the forecast area.

WEDNESDAY-SATURDAY: Deep northwest flow will prevail across the
region mid-late week between a stalled upper low over the Great
Lakes and a building ridge across the Rockies. This will suppress
deeper moisture/instability to our south, leading to mainly dry
conditions with gusty northwest winds during the later morning
to afternoon hours. Temperatures will be near seasonal normals
with lows in the 50s and highs in the 70s to lower 80s.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 122 PM CDT Sun Jun 2 2024

The main concerns will be showers and thunderstorms, a few
severe. Strong storms and likely a few supercells will develop
in central SD, towards the James Valley from about 21z through
2z. This activity should then form into a cluster of storms and
move east through the evening and overnight hours with scatterd
strong storms towards I-29 from about 1z through 4z then into
southwest MN and northwest IA from about 3z through 9z. Outside
of the thunderstorms some patchy MVFR ceilings will be possible
and some MVFR and IFR fog will be possible late tonight into
Monday morning.

&&

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

&&

$$

UPDATE...08
DISCUSSION...JH
AVIATION...08