657
FXUS63 KFSD 251138
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
638 AM CDT Tue Jun 25 2024

.KEY MESSAGES...

- River crests have already occurred or will occur within the
  next 24-36 hours. While no significant amounts of rainfall are
  expected, areal flooding caused by the prior excessive
  rainfall continues across portions of the area.

- A conditional severe weather risk this afternoon and evening,
  with the greatest risk along the Missouri River into
  northwestern Iowa from 4 to 11 PM. Storms could quickly
  intensify leading to 2 inch hail and wind gusts to 70 mph.
  Locally heavy rain is also possible.

- Unsettled weather pattern continues through the weekend with
  numerous chances for rain across the area. Next potential for
  more widespread heavy rainfall is Thursday into Friday.

&&

.DISCUSSION...
Issued at 401 AM CDT Tue Jun 25 2024

CURRENTS: With the front still have to our northwest across northern
SD, we`re currently "enjoying" 3 AM temperatures in the 70s to lower
80s with dew points in the 70s as well. Convection tied to
additional WAA and a mid level vorticity maximum continues to decay
as it encounters more stable air. However, a brief shower at
Chamberlain did result in a heat burst, with temps rising 10 degrees
in 40 minutes with a dew point drop from the mid 70s to the mid 50s!
Winds gusted to around 45 mph, with the very dry sounding. With dew
points as high as they are, lows this morning won`t drop more than a
few degrees from our 3 AM temps. Northwest winds may occasionally
gust to around 20 mph.

TODAY: Aforementioned cold front slides south with the vort max
sliding east. This keeps some isolated pops along the Hwy 14
corridor through the morning hours, although dry sub cloud layer
will likely limit most precipitation from reaching the ground.
Meanwhile, attention this afternoon and evening will turn to the
front draped south of I-90, along the MO River toward Hwy 20, with
this morning`s models runs seeming to keep this feature a little
further north. Showers and storms are expected to fire along/near
the front. There is less of a cap in place than yesterday, so do
expect some at least isolated activity in this area. Any storm that
develops could quickly become strong to severe, with CAPE values
over 3500 J/kg, bulk shear values 40 knots or more, and steep mid
level lapse rates again over 7-8 deg C/km. Strong to severe storms
could produce hail to 2" diameter and wind gusts to 70 mph. Locally
heavy rainfall is possible as well, with PWAT values around 1.5
inches - so any thunderstorm could produce an inch to 1.5" of rain.
If a storm can become surface based, there is a very low, but non-
zero tornado chance (greatest risk south of Hwy 20). Overall between
the front and mid level forcing, greatest severe weather risk
stretches from the MO River in south central SD eastward into
northwestern IA north of Hwy 20 between 4 and 11 PM. Highs today
will be a little cooler, in the 80s (did decrease highs by a couple
of degrees due to forecast increase in cloud cover). High humidity
especially across northwestern IA will lead to heat indices in the
90s.

TONIGHT: Cold front barely gets south of our area before the next
short waves dive into our area - a weak wave from the west along the
MO River with a much more defined wave diving south from ND. This
second wave brings isolated showers and storms to the Hwy 14
corridor into southwestern MN near I-90 through the overnight hours,
ending after daybreak Wednesday. Lows tonight in the 60s.

WEDNESDAY: A brief reprieve during the day on Wednesday as a weak
mid level ridge slides overhead and surface high pressure slides
over the eastern portion of the area. A bit cooler with more sun
than clouds with highs in the upper 70s to lower 80s.

WEDNESDAY NIGHT ONWARD: Active pattern continues through the
weekend, with a series of short waves swinging across the synoptic
pattern keeping periodic shower and storm chances in place. More
defined system and trough axis along with a cold front Thursday into
Friday brings the next chance for more widespread, potentially
locally heavy rainfall as PWATs climb again to over 2"; however,
with some location differences in track, this heaviest rain threat
currently lies just outside our areas in IA. This time period could
also bring some severe weather threat, but confidence is low due to
the aforementioned timing issues. With upper low pressure swinging
across the Upper Midwest during the latter part of the weekend,
northwesterly flow aloft prevails with surface high sliding overhead
at some point this weekend and ridging aloft by the end of the
weekend. Another system/wave is poised to move in to start the work
week. Temperatures through this period will be in the 70s and 80s for
highs and 50s and 60s for lows.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 631 AM CDT Tue Jun 25 2024

Isolated showers have moved into portions of southeastern SD,
but dry air below the cloud base is leading to mostly virga.
However, kept VCSH at KHON and added mention at KFSD. Additional
showers and thunderstorms may linger this morning across this
area and into the Hwy 14 corridor. Another area of isolated to
scattered showers and storms may develop along a front later
this afternoon into the evening from the MO River Valley toward
the Hwy 20 in northwestern IA. Have kept mention out of KSUX for
now given uncertainty in coverage. Any storm could quickly
become strong with large hail, strong wind gusts, and locally
heavy rainfall.

Outside of convection, expect VFR conditions. Winds are expected
to vary from easterly to northwesterly, although more variable
direction has been occurring with showers. Gusts around 20 knots
are possible.

&&

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

&&

$$

DISCUSSION...SG
AVIATION...SG