644
FXUS63 KFSD 042058
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
358 PM CDT Thu Jul 4 2024

.KEY MESSAGES...

- Intermittent periods of scattered showers with an occasional
  rumble of thunder will continue into the overnight hours with
  additional accumulations of up to a tenth or two possible.

- Multiple rain chances will continue through the weekend
  before mostly dry conditions return to start the new week.

- Slightly cooler temperatures will continue into the new week
  with highs expected to be between 5-10 degrees below normal.

&&

.DISCUSSION...
Issued at 354 PM CDT Thu Jul 4 2024

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

A cool and wet day continues! Taking a look aloft, an upper level
low (ULL) continues to rotate across areas north of I-90 bringing
completely clear conditions to one part of our area and scattered
showers and thunderstorms to the other parts of our area. As of 19z,
the focus continues to be east of Hwy-59 as scattered showers
and thunderstorms continue to push eastwards ahead of slow
moving cold front. Looking at the environment, long-skinny CAPE
values between 500-1500 J/kg and 35-45 kts of deep layer shear
should be sufficient enough to continue the isolated severe
weather threat through 21z with the primary threat being large
hail up to quarter size. While widespread heavy rainfall isn`t
expected with this activity, PWATs closer to 1.50 inches along
with the back building nature of developing cells could lead to
quick accumulations of up to a quarter inch with heavier cells.

From here, the focus will turn to the backside of the low as
increased isentropic lift and a strengthening LLJ help develop
additional showers and thunderstorms across the northern and
northwestern portion of South Dakota. Expect this developing
activity to rotate into our area this evening and overnight as the
mid-level low slowly drifts to our southeast. While the severe
weather risk will be low for this time period, lingering instability
overnight could lead to a few rumbles of thunder with developing
cells. Lastly, an increasing warm sector on the backside of the
mid-level low could lead to mostly cloudy conditions to start
the day on Friday.

The Long Term (Friday-Wednesday):

Heading into the start of the weekend, an active pattern continues
aloft as the base of the mid-level low pushes eastwards into
southeastern Minnesota and western Wisconsin. With our area now on
the backside of this system, could see some scattered showers with
an occasional rumble of thunder redevelop on Friday mostly due to a
combination of lingering isentropic lift and wrap around moisture.
While most of this activity should be focused in areas east of I-29,
accumulations are expected to be fairly limited with accumulations
up to a tenth of two possible especially underneath heavier cells.
Otherwise. lingering cloud cover and northwesterly surface winds
will keep temperatures below our seasonal normals with highs only
expected to peak in the low to upper 70s for the day. By Friday
night, a quick mid-level ridge will slide southeastwards bringing
increasing mid-level WAA to the area setting the stage for our next
precipitation chances.

By Saturday and Sunday, an amplified pattern will continue aloft as
an upper-level ridge builds over the western coastline. Continued
westerly to northwesterly mid-level flow will lead to a particularly
wet pattern through Sunday as multiple shortwaves rotate through our
area bringing intermittent periods of scattered showers with
isolated thunderstorms. A few developing thunderstorms could become
severe by Saturday afternoon as a cold front sides through the area.
While the exact timing and location of our severe risk chances is
still uncertain, long-skinny CAPE values between 1000-1500 J/kg
along with 30-40 kts of deep layer shear could make for a decent
environment for large hail and damaging winds to develop with any
isolated activity. With this risk in mind, SPC has issued a Day 3
marginal risk (Level 1 of 5) for most of southeastern SD and portion
of northwestern IA/southwestern MN. Looking aloft, the base of the
main upper-level wave begins to drift southeastwards with its
associated cold front during the day on Sunday. Increasing
isentropic lift along with upper-level support from the left exit
region of a jet could lead to the development of scattered showers
with isolated thunderstorms during the day. Otherwise, expect the
cooler conditions to continue into Monday as highs peak in mid to
upper 70s and low 80s.

Looking into the new week, mostly quieter conditions should return
by Monday as the building upper-level ridge over the western CONUS
pushes eastwards. While a brief period of showers will be possibly
by Monday afternoon, most ensemble guidance shows only shows low to
medium confidence in up to a tenth of an inch of QPF. Otherwise,
mostly quiet conditions will continue into the midweek. Lastly, the
cooler conditions will continue through Monday with slight warmer
conditions building from Tuesday onwards as highs climb towards the
upper 70s to mid 80s.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1239 PM CDT Thu Jul 4 2024

VFR conditions with occasional MVFR/IFR ceilings are expected
this TAF period mostly due to developing showers and
thunderstorms. Taking a look across the area, scattered showers
and thunderstorms continue to push across areas east of I-29
with more scattered showers developing north of the Hwy-14
corridor. Expect the intermittent periods of showers to continue
into the overnight hours mostly north of I-90 before things
begin to clear across the area. Otherwise, northwesterly surface
winds will continue for the duration of the period with gusts up
to 20-30 mph possible at times.

&&

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

&&

$$

DISCUSSION...Gumbs
AVIATION...Gumbs