355
FXUS63 KFSD 011750
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1250 PM CDT Wed May 1 2024

.KEY MESSAGES...

- Near normal temperatures are favored for today, with chances
  for light scattered showers increasing throughout the day.

- Wednesday night into Thursday will see a round of scattered
  showers and thunderstorms, with highest rainfall amounts
  across portions of northwestern IA where up to an inch is
  possible. While severe weather is not expected, minor flooding
  issues are possible.

- Continue to have a couple periods where overnight lows dip
  into the upper 30s through Saturday night, but widespread
  frost/freeze conditions not expected.

- Additional chances for scattered showers and thunderstorms
  Friday night into Saturday, and again Monday night into
  Tuesday.

&&

.DISCUSSION...
Issued at 400 AM CDT Wed May 1 2024

On the northern edge of a weak surface high pressure, early morning
satellite imagery shows cloud coverage increasing up into the I-90
corridor, with some light returns seen on radar across portions of
northeastern Nebraska. These showers/storms are occurring as
isentropic lift from the northwest quadrant of the surface high
pressure moves across the region, aided by some very scattered
shortwave moving through the mid-levels. Soundings and surface
observations show cloud bases are currently at 7.5-12.5 kft, so as
this activity continues into the mornings hours as the surface high
drifts northwards, expect low chances for showers/storms into the
morning hours for areas south of I-90.

Warmer air is brought into the region by the surface high during the
morning hours, which looks to bring the region into the mid to upper
60s by the afternoon hours. Winds will remain on the lighter side,
but will be varying in direction throughout the day. Attention turns
to a developing surface low pressure forming down in the southern
plains, with the inverted trough working on extending itself up into
the region during the afternoon and evening hours. Further aided by
shortwaves from an upper level low over the International Border,
chances for rainfall will be increasing into the overnight period.
Confidence in exact timing is medium, as some of the higher
resolution guidance suggests we won`t see much rainfall activity
until shortly before midnight, so have kept pops on the lower end
before increasing them during the late evening hours.

Rainfall amounts will be highest for areas southeast of a line from
Jackson, MN to Canton, SD to Vermillion, SD, where over an inch of
rainfall is possible. NBM and HREF both show roughly a 30 to 50%
chance for an inch of rain for that area, with probabilities for
half an inch in the 70 to 90% range. Areas northwest of the
aforementioned line will see chances for half an inch dwindle fairly
quickly the further away from the line one travels, with areas from
Huron to Burke looking to see between a tenth to a quarter inch of
rain. Given the recent rainfall across northwestern Iowa and
adjacent area, there are some minor flooding concerns as the soil
moisture content remains high. Thankfully rainfall rates are not
looking to impressive in the 0.25-0.5 inch per hour range, so mostly
expecting ponding of water in low-lying areas and additional rises
on local streams/rivers.

The main mid-level wave pushes the inverted trough axis off to the
east, which brings an end to that round of rainfall throughout the
daytime hours. With clouds clearing throughout they day, slightly
below normal temperatures are expected, in the mid to upper 50s
north of I-90, and upper 50s to mid 60s south of I-90.

After a mostly dry day on Friday with highs in the lower to upper
60s, a weak cold front moves through the area. The trough axis moves
in quickly behind it, and will lead to additional chances for
scattered showers and thunderstorms overnight into Saturday.
Ensemble clustering analysis shows there remains good agreement
amongst the various ensemble members, so have left NBM pops as is,
which increase rainfall chances during the evening hours on Friday
and continuing into Saturday. Upper level ridging on Sunday leads to
warming temperatures across the region, though some models are
hinting that some shortwaves may move across the region giving us
more rainfall. Most hold off on the rain chances until the main wave
from the cut-off upper level low moves onto the central plains on
Monday, leading to rain chances Monday night into Tuesday. Some
model solutions show the cut-off upper level low stalling out
somewhere over the northern plains, but we`ll have to see if that
solution continues over the coming days.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1248 PM CDT Wed May 1 2024

VFR conditions begin the TAF period. Mid level clouds based around
10,000 ft blanket most of the area this afternoon. These mid level
clouds are expected to persist through the rest of the daylight
hours. With a dry sub-cloud layer in place, virga to perhaps some
sprinkles is also possible. A surface high is moving through the
area this afternoon, contributing to light/marginally breezy winds.
Wind direction will swing easterly this evening as chances for rain
increase across the region. Ceilings will slowly lower to MVFR/IFR
levels as rain overspreads the area. While all TAF sites will see
rain, the bulk of the rain looks to fall south of I-90. The low
level jet (LLJ) will strengthen during the overnight hours and
contribute to low level wind shear for a few hours across parts of
northwest Iowa, including KSUX. Rain will push east of the area to
end the TAF period.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...Meyers