593
FXUS63 KFSD 162359
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
659 PM CDT Fri May 16 2025

.KEY MESSAGES...

- Strong winds and patchy rain showers diminish this evening.

- Patchy frost possible on Sunday morning.

- Elevated instability Sunday night into Monday morning could
  lead to isolated severe storms, with hail the main threat.

- Widespread rain and isolated thunderstorms are expected
  Monday into Tuesday. EC ensemble and GEFS still pretty bullish
  for 1" or more rainfall amounts (40-70% chance).

&&

.DISCUSSION...
Issued at 155 PM CDT Fri May 16 2025

Low pressure will shift east of the area tonight into Saturday,
slackening the pressure gradient and taking the lift with it. So
winds will diminish tonight, although they remain breezy into
Saturday, and showers should mainly be out of the area by mid
evening.

Saturday night into Sunday morning a surface ridge of high pressure
noses into the area which will allow winds to drop further, likely
less than 5 mph in many locations. This will then allow temperatures
to drop with lows likely sneaking into the mid 30s in some
locations. This may lead to some frost across the area and will need
to be watched as the chance for lows below 35 are running about 30-
50% north of I-90.

Sunday will see increasing easterly flow and increasing cloud cover
as low pressure deepens over the Northern and Central Rockies. A
fairly weak mid level wave will swing north into central SD with
some moisture return in the mid levels as well. This should result
in some spotty showers during the day, mainly west of I-29.
Otherwise highs will likely top out in the 60s.

Sunday night will see a much better surge of elevated warm and moist
advection. Models are indicating about 500-1500 J/kg CAPE with 20-30
knots of elevated speed shear which could result in some isolated,
elevated hailers. Currently timing for this would be in the evening
to overnight hours. Fairly deep easterly flow in the lower levels
should help preclude any wind threat.

As this wave of lift moves through Sunday night into Monday morning
some question marks arise for Monday and just how much and how
widespread rain and thunderstorm chances will be. If enough warm air
aloft moves in, the dendritic layer is well elevated and fairly dry,
so instability will be needed to get showers and thunderstorms
going. Most models do indicate decent instability (1000 J/kg CAPE)
through the day, but are less agreeable on this warm layer aloft
potentially cutting off development.

On thing that continues to work in favor of additional development
is a persistent inflow from the southeast of moisture and a bit
more unstable air which should help produce enough lift for further
development. One big thing to watch will be the upper level low and
how this wobbles eastward with the potential for another low to
develop in roughly IA Monday evening as a jet races into the Central
Plains. This could bring a more distinct northern edge to the
heavier rain and thunderstorms Monday afternoon into Tuesday morning
and keep the bulk of this activity across NE and IA.

Tuesday will likely see rain diminish from northwest to southeast as
the low pressure wraps up and moves southeast. Still a lot of
question marks regarding just where and when this low will end up,
but for the most part unless some major changes occur, rainfall will
be much diminished by Tuesday night.

Flow becomes more westerly aloft Wednesday into Friday which should
allow for milder temperatures and more sporadic chances for showers
and thunderstorms.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 655 PM CDT Fri May 16 2025

Scattered showers will continue to fade through the evening as its
parent low pressure system slides east of the area. MVFR clouds will
linger; however, through the rest of the night and into Saturday
morning. Biggest forecast challenge of the period was ceiling
heights from KHON to KFSD in regards to the 2 kft level.
Guidance indicates constant fluctuation on either side of 2 kft
through much of the night into tomorrow morning in those
locations. Based on downstream observations and which guidance
has the best handle on the situation, opted to stay at 2 kft for
KHON and mostly just below 2 kft for KFSD.

All the clouds associated with this low pressure system will move
away from southwest to northeast through the day Saturday, starting
along the Missouri River Valley by mid-morning Saturday. These
clouds will clear the entire area by Saturday afternoon, leaving
mainly clear skies in place to end the period.

Gusty 30-35 kt northwest winds will continue through this evening.
Winds will gradually diminish through tonight and into Saturday
morning. Gusts will be in the 15-20 kt range to end the period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 7 PM CDT this evening for SDZ038>040-050-
     052>071.
MN...Wind Advisory until 7 PM CDT this evening for MNZ071-072-080-
     081-089-090-097-098.
IA...Wind Advisory until 7 PM CDT this evening for IAZ001>003-
     012>014-020>022-031-032.
NE...Wind Advisory until 7 PM CDT this evening for NEZ013-014.

&&

$$

DISCUSSION...08
AVIATION...Samet