430
FXUS63 KFSD 270326
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1026 PM CDT Wed Jun 26 2024

.KEY MESSAGES...

- River crests have already occurred or will occur within the
  next 24 hours.

- An active pattern aloft will lead to multiple precipitation
  chances from Thursday into Friday and again on Monday. While
  significant precipitation is not expected, a conditional
  severe weather risk is possible by Thursday night.

- Accumulations will vary between 0.25" to 0.50" of an inch for
  most of the area with isolated pockets of up to an inch with
  any developing storms.

&&

.DISCUSSION...
Issued at 255 PM CDT Wed Jun 26 2024

The Short Term (Rest of the Afternoon/Tonight & Thursday):

A slightly cooler and mostly quiet day continues! Taking a look
across the area, much more pleasant conditions continue with most
areas showing observing temperatures in the low to mid 70s and low
80s with dew points in the mid to upper 50s. This combined with
light to marginally breezy northerly to northeasterly surface winds
makes it feel almost spring-like across the area. As we continue
into the evening, a surface high will slide just to our northeast
allowing surface winds to become light and variable overnight as
temperatures fall into the mid to upper 50s and low 60s. Shifting
gears to precipitation chances, upper-level ridging begins to build
to our west shifting our flow to the northwest aloft. By late
evening, a combination of warm air advection (WAA) and a
strengthening LLJ ahead of a quick shortwave will lead to the
development of some scattered showers and isolated thunderstorms
over the western portions of South Dakota initial.

Expect this developing activity to spread eastwards into the day on
Thursday as more isentropic lift makes its way into our area. While
severe weather isn`t expected with this developing activity, PWATs
up to 1.75 inches and warm cloud depths over 10kft could lead to
pockets of moderate to heavy rainfall at times especially west of I-
29. With all this in mind, accumulations between a quarter to half
an inch will be possible through 00z Friday. Otherwise, expect
dreary and mostly breezy conditions on Thursday as increasing
southeasterly surface winds produce gusts up to 35 mph.
Increasing rain chances and shallow mixing will help our cooling
trend continue as highs only peak in the low to upper 70s
across the area.

The Long Term (Thursday night-Tuesday):

By Thursday night, our attention will once again pivot to the
Rockies as a more robust mid-level trough ejects into the northern
and central Plains along with its associated cold front. Increasing
WAA and instability ahead of the trough will lead to scattered
showers and thunderstorms developing across the western portions of
South Dakota initially. As this wave tracks eastwards, the
developing convection will likely follow suit with a few storms
likely becoming severe. Looking at the environment, deterministic
guidance continues to show the better axis of instability (1000-1500
J/kg MUCAPE) setting up across central SD with about 30-40 kts deep
layer shear. With this in mind, the general expectation is for the
stronger storms to gradually weaken as they get further away from
the instability axis and enter our southcentral SD counties. While
this doesn`t completely diminish our severe weather risk, this does
lower our potential enough to keep the risk isolated to areas west
of James River with large hail up to half dollar size and damaging
winds up to 65 mph being the primary threats.

As convection continues to weaken, the primary threat will shift
towards pockets of heavier rainfall by late Thursday night as the
activity approaches the I-29 corridor. Could see a bit more
widespread development east of I-29 as the LLJ strengthens and
better moisture return surges in. While this could lead to a few
more pockets of heavier precipitation, the general expectation is
for additional accumulations between a quarter and half an inch
along and east of I-29 through 12z Friday with a few isolated
pockets of up to a inch. Most of the activity should exiting our
area just after daybreak on Friday as the cold from swings
southeastwards. Otherwise, lingering WAA will keep most of the cloud
cover over our area through the early afternoon. With this in mind,
expect temperatures closer to seasonal on Friday with highs expected
to peak in the upper 70s to low 80s for the day. Looking aloft, a
weak mid-level shortwave will swing through the region by the
evening hours on Friday. While there is still a slight chance that
the atmosphere can recover by this time, model derived soundings
show a cap in place around the 850 mb level. Nonetheless, if an air
parcel can overcome the cap, there`s about 2000-3000 J/kg of MLCAPE
and 30-40 kts of deep layer shear to work with for additional
development. If not, things should stay quiet heading into the rest
of the weekend.

From Saturday onwards, a strong cold front will swing throughout the
region during the day. Strong CAA aloft will help keep our overall
temperatures below normal with highs expected to dip into the 70s to
low 80s through Monday as the upper-level ridge begins to build.
More rain chances will be possible from Monday night into Tuesday.
However, timing and intensity differences among guidance continue to
keep things a bit uncertain at this time. Lastly, temperatures will
begin to trend near to above normal from Tuesday onwards.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1019 PM CDT Wed Jun 26 2024

Cloud cover will be on the increase through the overnight hours
with scattered showers developing in central South Dakota by
3am. This rain will gradually move east and northeast through
the morning, continuing into Minnesota/Iowa by mid-day. MVFR to
locally IFR ceilings may move into the area after the rain
arrives. Visibility drops will be associated with any stronger
showers.

Rain may move east in the evening, but lower MVFR ceilings may
continue. Winds will remain light for most of the 24 hour period
outside of a brief afternoon window where 20 mph gusts may be
possible.


&&

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

&&

$$

DISCUSSION...Gumbs
AVIATION...Dux