005
FXUS63 KFSD 302340
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
640 PM CDT Thu May 30 2024

.KEY MESSAGES...

- Multiple chances for showers and thunderstorms through the
weekend. Locally heavy rainfall may result in isolated flooding
concerns and small river rises if training occurs.

- A Marginal Risk (Level 1 of 5) for severe storms remains in place
for much this afternoon, with damaging winds to 60 MPH and quarter
size hail being the primary hazards. Additional strong to severe
storms may occur over the weekend, especially Sunday afternoon and
evening.

- Near normal temperatures and periodic breezy conditions continue
through the weekend, with above normal temperatures forecast to
prevail heading into the new week.

&&

.DISCUSSION...
Issued at 311 PM CDT Thu May 30 2024

CURRENT THROUGH FRIDAY NIGHT: Latest radar imagery shows a line of
showers and storms developing ahead of an advancing cold front just
west of the James River. Will see this line push eastward through
the afternoon and evening before it stalls out near/east of I-29.
Though cloud cover has plagued much of our area this morning, have
seen a bit of clearing ahead of the front, which may provide enough
destabilization to see a few strong to severe storms. In regard to
dynamics, do have CAPE values ranging between 500 to 1500 J/kg,
depending on which model you look at. Dewpoints have also risen a
bit in the last few hours, with most locations in the upper 50s to
lower 60s. While there is a decent amount of moisture to work with,
effective shear remains rather lacking, and mid-level lapse rates
still hover in the 6-6.5 degC/km range. That being said, there is a
decent amount of sfc vorticity along the aforementioned front, which
could support the development of perhaps a few funnel clouds or
landspouts. SPC`s latest Day 1 Outlook has maintained a Marginal
(Level 1 of 5) risk for severe weather - so don`t want to entirely
rule things out, especially if we can destabilize enough. As such,
think the primary hazards with any storm that does become severe
will be damaging gusts up to 60 MPH and quarter size hail. In
regard to timing, believe the best window for seeing severe weather
will be between 3 to 9 PM.

Instability quickly diminishes as we approach midnight, which should
limit the overall severe threat. Given that the front is expected to
stall/slowly meander eastward, have scattered showers and storms
lingering for the remainder of the overnight period. Similar to the
last forecast package, PWATs still look to approach 1.5 inches,
suggesting that locally heavy rainfall will be possible. While
widespread flooding is not expected at this time, any heavy rain
that occurs over urban or already saturated areas may result in
ponding of water and perhaps isolated flash flooding. In an effort
to mitigate impacts around your home, ensure that your sump pump is
turned on and that your downspouts are attached. And remember, Turn
Around, Don`t Drown, if you encounter a flooded roadway.

Trough axis swings north of the area on Friday, with another weak
short wave ahead of it. This keeps at least scattered activity
around through the end of the week, especially along and east of I-
29. In regard to rainfall totals, currently have amounts through
Friday evening ranging between a tenth of an inch to near/just above
half an inch along and west of I-29. Areas east could see upwards of
half an inch to 2 inches, with the highest totals likely across SW
Minnesota.

SATURDAY: Should see a brief reprieve from showers and storms
throughout much of Saturday morning and afternoon as sfc high
pressure slides overhead. Winds look to be light and variable with
afternoon highs in the mid to upper 70s under partly cloudy skies.

SATURDAY NIGHT THROUGH TUESDAY: Upper level wave near the Rockies
ejects northeastward toward the region Saturday evening, causing
precipitation chances to return to forecast. Could see showers and
storms develop as early as sunset with the initial surge of WAA,
though the better chances look to occur Sunday afternoon and
evening. As noted in days past, CIPS analogs continue to show a 15%
chance for severe weather, with CSU Machine Learning probabilities
now ranging between 15-30%. SPC`s latest Day 4 Outlook has also
highlighted a 15% chances of seeing severe weather for much of our
area. In regard to dynamics, still seeing a decent amount of support
from both deterministic and ensemble guidance that CAPE values will
near/exceed 1500 J/kg. Shear and low level moisture will also be on
the rise ahead of an advancing cold front, with a few models
forecasting dewpoints to rise into the 60s to lower 70s. Certainly
something to keep an eye on in the coming days. In addition to this,
will need to monitor today`s and Friday`s rainfall amounts, as
periods of heavy rain will also be possible with this system.
Certainly more moisture in the soils of late, which may result in
localized flooding and river rises - especially if training storms
were to develop. Nonetheless, there are still a bit of moving parts
in place to put too much confidence behind any one solution just
yet, as timing, amounts, and hazards will largely depend on how sfc
and upper level boundaries evolve. For now, encourage folks with
outdoor plans to keep an eye on the forecast and have a way to
receive warnings.

Outside of a few lingering showers on the far eastern fringes of our
CWA Monday morning, should see largely dry conditions prevail across
the region. Models vary in timing and strength of the next
wave/trough Tuesday, but expect more shower and storm chances.
Depending on the track and evolution of this system, additional
strong to severe storms may be possible, but very low confidence at
this time. Otherwise, look for afternoon highs to rise into the
upper 70s to lower 80s. Overnight lows will also remain quite mild,
as temperatures only fall into the 50s to lower 60s.

WEDNESDAY AND BEYOND: Upper level ridging builds across the western
CONUS mid-week, keeping us in NW flow aloft. As a result, should see
dry conditions prevail for the remainder of the extended period.
Winds will be fairly breezy, with gusts between 20 to 30 MPH
possible during the afternoons.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 635 PM CDT Thu May 30 2024

Scattered showers and thunderstorms are ongoing across the region
this afternoon and are expected to continue through the overnight. A
few storms may become strong to severe with the greatest threats
being wind gusts of 60 mph and hail up to the size of quarters.
Ceilings are currently VFR, but expect these to bounce around a bit
between VFR and MVFR, especially under any stronger storms that
develop. Visibility may also be reduced under stronger storms. Winds
will drop off quickly after sunset, becoming light and variable
through sunrise. Then they become east-northeasterly at 5-10 kts.
Daybreak sees another round of showers develop along and east of I-
29. These will linger through most of the day Friday.

&&

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

&&

$$

DISCUSSION...SST
AVIATION...AJP