752
FXUS63 KFSD 182309
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
609 PM CDT Thu Jul 18 2024

.KEY MESSAGES...

- Showers and thunderstorms return to the area on Friday. Some
  could be strong to severe with large hail up to the size of a
  quarter (1 inch) and damaging winds to 60 mph. Isolated
  pockets of heavier rainfall are also possible.

- Cooler conditions return for the weekend with funnels possible
  on Saturday.

- Cooler temperatures and daily chances for rain will continue
  through the majority of the work week next week.

&&

.DISCUSSION...
Issued at 225 PM CDT Thu Jul 18 2024

A beautiful rest of the afternoon is in store as high pressure
continues to slide east of the area. Winds will remain light out of
the south/southeast at 5 to 10 mph. While quiet conditions will
persist into the night, a weak ridge riding shortwave trough will
bring the chance for showers to weak thunderstorms to parts of south
central South Dakota late tonight. Soundings show a weak moist layer
around 750 mb along with steeper lapse rates around this layer, thus
small instability on the order of a few hundred J/kg of CAPE is
expected. The weak instability will coincide with weak wind shear,
keeping any chance for severe storms at bay. Low temperatures will
be warmer, near seasonable in the upper 50s to mid 60s.

Southerly return flow on the backside of the departing high will
persist into the afternoon hours on Friday. However, moisture return
does not look all that impressive as only low 60 degree dew points
will be advected into the region. Should still see some moistening
of dew points due to evapotranspiration into the mid 60s though.
High temperatures will warm to the upper 70s to low 80s, generating
sufficient instability up to around 1,500 J/kg of CAPE. Another,
slightly stronger shortwave trough will push into the Northern
Plains, setting the stage for strong to severe storms. Wind shear is
also on the lower side with deep layer shear values between 20-30
knots expected. While not a classic environment for severe weather,
there is enough of an overlap between marginal shear and instability
where some storms could be strong to severe. Storms look to develop
along a surface trough during the late morning to early afternoon
hours across parts of central South Dakota and push southeastwards
into the forecast area. Given the convergence within the surface
trough, think that mixed storm modes are possible with multi-cells
and smaller, broken lines. Given the more marginal environment and
mixed storm mode, think large hail to the size of quarters (1 inch)
and damaging winds to 60 mph are the primary hazards. Any chance for
strong to severe storms will come to an end by 10 pm at the latest.
However, non-severe storms look to persist through the night.
Rainfall totals between a tenth or two to up to an inch+. The
highest amounts will be more isolated but the bulk of the rain will
fall across parts of southeastern South Dakota, far northeast Iowa,
and northwest Iowa. Low temperatures look to fall to the 60s
overnight.

Saturday will be a partly cloudy and somewhat dreary kind of day.
The previously mentioned upper level wave will become vertically
stacked and slow down. Latest deterministic guidance is in good
agreement that the wave becomes vertically stacked just south of the
forecast area. Wrap around moisture from the low will provide
another round of showers and thunderstorms. Good news is that
vertical shear will be very weak to negligible so severe storms are
not expected. However, can`t rule out the chance of a funnel cloud
or two with the low hanging around the area. This will also keep
rainfall totals much lower with amounts from a few hundredths to up
to around a quarter of an inch. With some cloud cover and
showers/storms around, high temperatures will be on the cooler side
with highs in the 70s to low 80s expected. Lows will fall to the 60s
overnight.

The upper level low will continue to meander across parts of the
Upper Midwest on Sunday. With similar conditions to Saturday,
afternoon showers and weak storms are possible. Only difference is
that the upper low will wobble a bit further away from the forecast
area which should prevent any funnel clouds from forming. Highs will
again be in the 70s to low 80s and lows in the 60s.

Broad troughing will encompass parts of the Northern Plains and
Upper Midwest for the majority of the work week. This will keep near
to below normal highs in the 70s and 80s along with daily chances
for rain. Ensembles support this as they all show a near 100%
probabilities for exceeding a hundredth of an inch. Without adequate
forcing and shear, daily afternoon shower and non-severe storms are
expected.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 609 PM CDT Thu Jul 18 2024

VFR conditions expected for the duration of this period. Remaining
cumulus will quickly dissipate after sunset. Winds will be
southeasterly 3-8 kts becoming southerly 5-10 kts with gusts 14-
18kts by sunrise and continuing through sunset.

Clouds increase through the day as well as the chances for showers
and thunderstorms. Ceilings will gradually decrease as the clouds
thicken settling around 7000-9000 ft AGL. KHON may see showers as
early as 19.12Z, but the best chances will be after 19.18Z. KFSD and
KSUX could begin to see showers after 19.21Z. Afternoon showers and
thunderstorms could become strong to severe. Reduced ceilings to
2500 ft AGL under thunderstorms.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...AJP