River Flood Warning 4, NWS Sioux Falls, SD

Area Forecast Discussion
National Weather Service Sioux Falls SD
639 AM CDT Thu May 2 2024

.KEY MESSAGES...

- With up to 1-1.5" of rainfall fallen across portions of
  northwestern Iowa overnight by sunrise, there may be ponding
  of water on roadways and low-lying area, with some rises on
  the local rivers/streams.

- Main area of showers and thunderstorms will move east this
  morning, with additional pop-up showers possible throughout
  the day.

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

&&

.DISCUSSION...
Issued at 406 AM CDT Thu May 2 2024

Early morning radar shows showers and thunderstorms shifting
eastwards across the region, and as of 3 AM majority of the rainfall
is occurring east of the James River Valley. This activity is
occurring as an inverted trough is extending northwards into the
region, further aided by shortwaves moving around the cut-off upper
level low parked on the International Border. As the inverted trough
continues to shift eastwards, majority of the currently observed
rainfall will be pushing east of US 71 across SW Minnesota and NW
Iowa by the mid-morning hours. Soundings from across the region show
that the low-levels remain saturated throughout the day, and as
additional, albeit weaker, shortwaves move across the region,
another round or two of showers are possible throughout the day.
Given the saturated low-levels, not impossible to see some drizzle
falling out of the stratus deck during the morning hours.

Otherwise, a surface high pressure will be developing on the
backside of the exiting surface low pressure, which result in a
tightened surface pressure gradient leading to breezy winds
developing throughout the afternoon hours. Highest wind gusts are
expected along the central NE/SD border, where gusts into the mid
30s are possible, whereas elsewhere wind gusts into the mid 20s are
expected. Afternoon temperatures are expected to rebound up into the
mid 50s to lower 60s, possible mid 60s near the SD/IA/NE border.

We'll be watching a new surface low pressure develop under the
aforementioned cut-off upper level low, sending a cold front towards
the region. After early morning lows in the mid 30s to lower 40s,
with some patchy frost in central South Dakota, southwesterly winds
will advect warm air into the region out. Areas west of I-29 will be
the first to see the cold frontal passage, thus will see the coolest
high temperatures in the upper 50s to lower 60s. Areas well ahead of
the front are expected to reach back up into the mid 60s to lower
70s. The trough axis moves in quickly behind the cold front as it
pushes eastwards across the area throughout the afternoon hours, and
will lead to additional chances for scattered showers and
thunderstorms overnight into Saturday. Instability looks to remain
quite limited, with models showing a modest 200-500 J/kg of CAPE
available, so no severe weather is expected. Given little time for
moisture return since the last event, rainfall amounts are expected
to remain light, resulting in a 20 to 40% chance for a quarter inch,
lowest north of I-90 and highest south of I-90.

As a strong cut-off upper level low moves ashore onto the west
coast, upper level ridging will lead to dry conditions expected for
the rest of Saturday and throughout Sunday. Highs on Saturday will
fall into the lower to mid 60s, increasing on Sunday into the mid
60s to lower 70s.

The upper level ridging breaks down into Monday as the big trough
slides eastwards. The similarly strong surface low pressure will
continue warm air advection as we remain in the developing warm
sector, which will bring surface temperatures into the lower to mid
70s. Chances for showers and thunderstorms return Monday afternoon
as the surface low continues to move eastwards, with a strong cold
front moving across the region overnight into Tuesday. SPC has added
a 15% chance for severe thunderstorms south of the area, with
uncertainties on how north the instability is able to reach. Model
solutions continue to show that the cut-off upper level low will
stall out somewhere over the northern plains, which would result in
continued chances for scattered showers and thunderstorms.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 639 AM CDT Thu May 2 2024

Overnight showers are continuing to shift eastwards east of I-29,
with MVFR/IFR cigs building into the region. Lowered cigs will stick
around for most of the morning hours, begining to lift and clear for
areas west of I-29 by the late morning. For areas along and east of
I-29, lifting and clearing will occur from west to east throughout
the afternoon hours. Breezy easterly winds will weaken throughout
the morning hours, with winds strengthening again during the
afternoon hours with winds out of the west. Highest wind gusts are
expected along the central NE/SD border, where gusts into the mid
30s are possible, whereas elsewhere wind gusts into the mid 20s are
expected.

&&

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

&&

DISCUSSION...APT
AVIATION...APT

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
451 AM CDT Thu May 2 2024

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-031000-
Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson-
Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-Brookings-Gregory-
Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-
McCook-Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-
Yankton-Union-
451 AM CDT Thu May 2 2024

This Hazardous Weather Outlook is for portions of northwest Iowa,
west central Iowa, southwest Minnesota, northeast Nebraska,
central South Dakota, east central South Dakota, south central
South Dakota, and southeast South Dakota.

.DAY ONE...Today and Tonight

Early morning showers and thunderstorms exit the region
throughout the morning hours. With up to 1-1.5" of rainfall fallen
across portions of northwestern Iowa overnight, there may be
ponding of water on roadways and low-lying area, with some rises
on the local rivers/streams.

Additional pop-up showers are possible throughout the day, though
only light accumulations are expected.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

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

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.