633
FXUS63 KFSD 300346
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1046 PM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Rivers across the area have crested, with a slow downward
  trend in river levels this weekend as dry conditions are
  expected to prevail.

- Well below normal temperatures (~10 deg F) continue through
  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 better
  chance for severe weather and heavy rain. Higher confidence in
  showers and storms (70-90%) with decent chances for more than
  an inch of rain in northwest IA and southwest MN (20-30%).
  Certainly a time frame to keep an eye on.

- Stronger westerly flow aloft continues through the end of the
  week, resulting in a busier pattern.

&&

.DISCUSSION...
Issued at 258 PM CDT Sat Jun 29 2024

In the post-frontal environment, temperatures have rebounded back up
into the upper 60s to mid 70s, with a touch of lingering instability
and moisture resulting in partly cloudy skies. As we head into the
evening hours, the southern tip of a surface high pressure will
traverse the region from west to east. This will continue our calm
conditions, while swinging the winds around to become out of the
southeast throughout the morning hours on Sunday.

Having transitioned towards southerly flow throughout the mixed
layer, warm air advection (WAA) in addition to weak moisture
advection builds across the area during the day. However, it will
likely be too late in the afternoon before we see more substantial
WAA for our area, so expect another day with temperatures around 10
degrees below normal in the lower to upper 70s. As the previous
discussion mentioned, moisture levels under the 700mb layer remain
fairly dry. In addition, the WAA in the same layer is leading to
increased CIN, so if anything were able to get going it likely won`t
be able to sustain itself for long. So, while there are some very
low chances for light showers/storms in the afternoon, the lack of
forcing and moisture in the mid-levels makes me think we`ll remain
dry into the evening hours.

Overnight into Monday, a shortwave ejects onto the central plains,
with a surface low pressure expected to develop over the western
Dakotas, along a surface trough. Out ahead of the main wave, WAA in
tandem with weaker shortwaves is expected to develop scattered
showers and thunderstorms throughout the morning hours in Nebraska,
lifting into our area shortly after daybreak. Probabilities for half
an inch with this round of rain straddles the I-29 corridor south of
I-90, with probabilities from 25 to 35%. We`ll need to see how this
earlier round of convection influences the environment for when the
warm front and main wave aloft reach the area. This looks to enter
our south-central South Dakota counties by mid-day, though some
models keep it from entering our area until the evening hours. If a
storms were able to form in the narrow corridor behind the warm-
front and ahead of the cold front, 2-3kJ/kg of CAPE would be
available along with 40 to 50 knots of mostly speed shear, which
would allow for a thunderstorm to be capable of golf-ball sized hail
and gusts to 60 mph. However, this would also require the cap to be
considerably weaker. The more likely scenario is for us to see the
remaining convection that goes off in western South Dakota or
western Nebraska, though by the time it gets to our area storms will
likely not be surface-based anymore, resulting largely in non-severe
thunderstorms, though can`t rule out quarter sized hail. Chances for
showers and thunderstorms continue overnight into Tuesday morning,
with chances for 24 hour rainfall totals exceeding 1 inch highest
across SW MN and NW IA at 20 to 30%.

May see another round of showers and thunderstorms as the cold front
finishes tracking across the region on Tuesday, though with the
progressive mid/upper level flow rainfall amounts look to remain on
the lighter side, with a 25% chance for a half inch of rain along
and east of highway 71. After a dry and warm day with temperatures
near normal on Wednesday, chances for light rain return overnight
into Thursday, with another chance Thursday night into Friday. Upper
level ridging builds along the southwest throughout the weekend,
which may bring quieter weather back to the region.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1046 PM CDT Sat Jun 29 2024

Light/variable winds will prevail overnight. Southeasterly
winds increase again late morning-afternoon Sunday, with areas
along and west of the James River Valley seeing occasional gusts
of 20-25kt develop after 18Z, continuing through the end of this
TAF period.

VFR conditions are expected through the period, with mid-level
clouds at times Sunday into Sunday evening.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...JH