138
FXUS63 KFSD 010357
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1057 PM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Rivers across the area have crested, with a slow downward
  trend in river levels as dry conditions continue.

- Well below normal temperatures (~10 deg F) continue into
  Monday, and remain a touch below normal (0-5 deg C) Tuesday
  through Thursday as well.

- Monday and especially Monday night will be the next chance
  for severe weather and heavy rain. Higher confidence in
  showers and storms (80-90+%), with chances for more than an
  inch of rain in northwest IA and southwest MN (70-80%), and
  low chances for 2 inches (20-30%) by Tuesday morning.

- Stronger westerly flow aloft continues through the end of the
  week, resulting in a couple chances for rain.

&&

.DISCUSSION...
Issued at 316 PM CDT Sun Jun 30 2024

With the surface high pressure now off to our east, southeasterly
return flow is advecting warmer air back into the region, albeit
temperatures remain firmly below normal. Temperatures as of the
early afternoon hours are in the upper 60s to lower 70s, with only a
couple extra degrees added before the sun starts to go down. Areas
along and west of the James River Valley have been seeing increased
cloud coverage due to some weak isentropic lift, low instability,
and moderate moisture in the mid-levels, but this activity is
expected to remain as ACCAS and not form as measurable
precipitation.

Overnight into Monday, a surface low pressure is expected to develop
over the western Dakotas as a mid-level shortwave ejects onto the
central plains. Out ahead of the main wave, warm-air advection (WAA)
combined with weaker shortwaves are expected to create our first
round of scattered showers and thunderstorms prior to daybreak. High
resolution models show a north to south oriented scattered group of
storms moving up from eastern Nebraska, moving across far eastern
South Dakota and Nebraska throughout the morning hours. That round
of rain will be dissipating as it moves into portions SW Minnesota
and NW Iowa during the early afternoon hours, with amounts looking
to remain on the lighter side as probabilities for half an inch are
in the 20-30% range. Expect a lull in rainfall activity before the
main upper level wave begins to move into the area during the late
afternoon, with rain chances returning during the evening
hours further aided by the warm front moving towards the area.

Severe weather wise, we`ll need to see how the earlier round of
convection influences the environment, as some models keep the big
push of instability behind the warm front from reaching our area.
The western push in south-central South Dakota looks like it has the
highest chance of reaching our area, though again most models keep
the instability away from our area, and if a storm were to form in
that environment golf ball sized hail would be possible out of the 2-
3kJ/kg of CAPE along with gusts to 60mph from 40 to 50 knots of
predominantly speed shear. While severe weather chances are looking
to trend down, the possibility of heavy rainfall returns overnight
into Tuesday as the main wave moves through further aided by the
warm and cold front.

Given 200-1000 J/kg of MUCAPE in addition to precipitable water
values at the maximum of climatology according to the ensemble
situational awareness tables, rainfall rates will likely be fairly
efficient at 1 to 2 inches per hour. Furthermore, the ESATs
highlight integrated water vapor transport towards the NE/IA border,
which is at the 99th percentile of climatology, further raising
concern for efficient rainfall rates. Overall by Tuesday morning,
expecting a widespread swath of half an inch to an inch for areas
southeast of a line from Marshall, MN to Sioux Falls, SD to Tyndall,
SD, with localized totals across portions of NW Iowa and SW
Minnesota of 2-4 inches possible. Probabilities for an inch of rain
are at 50-80% SE of the aforementioned line, dropping to 10-30% for
2 inches, and very isolated chances for 3 inches. Given the wet
antecedent conditions across the flood prone areas, flash flooding
cannot be ruled out, with further rises on local streams and rivers
also possible. WPC has placed the region in a slight risk for
excessive rainfall (level 2 out of 4).

Scattered showers and thunderstorms decrease in coverage Tuesday
morning, though we will likely see another round of rain as the cold
front moves out of the area during the afternoon hours. We`ll have
to see where the cold front ends up being Tuesday morning, but
chances for severe weather return in the afternoon out ahead of the
cold front given 2-3kJ/kg of MUCAPE and 40-50 knots of 0-6km bulk
shear. Again this would lead to chances for golf ball sized hail and
gusts to 60 mph. Can`t rule out additional heavy rain given the
continued climatologically high precipitable water values, but the
integrated water vapor transport has decreased to just above the
90th percentile of climatology.

After a dry and warm start for the day with temperatures near normal
on Wednesday, chances for light rain return during the afternoon
hours continuing into Thursday. Another chance Thursday night into
Friday as a low pressure moves eastwards off to our north, but some
models indicate that we may end up remaining dry as we get dry
slotted. Upper level ridging builds along the southwest throughout
the weekend, but guidance is no longer as convinced as some ensemble
members show the ridging is short lived.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1057 PM CDT Sun Jun 30 2024

Southeast winds increase quickly after sunrise by 12Z, with
frequent gusts 25-35kt through the day. Winds will subside
slightly after sunset Monday evening, though occasional gusts
20-25kt will linger through the end of the TAF period.

MVFR-locally IFR ceilings are expected to expand across the area
Monday morning, accompanied by areas of rain/isolated thunder. A
second round of showers and storms develops in the evening, with
heavier rain favored from northeast Nebraska into northwest Iowa.
May also see localized visibility restrictions at times in areas
with moderate to heavy rain.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...JH