844
FXUS63 KFSD 040331
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1031 PM CDT Fri May 3 2024

.KEY MESSAGES...

- Rain is expected to move through after dark and into Saturday
  morning. Rainfall amounts from 0.25" to 1" may be possible.
  Highest amounts in Northwest Iowa could lead to minor
  increases in already ongoing flooding.

- Cooler temperatures on Saturday (low 60s), with middle and
  upper 60s on Sunday. Dry conditions expected both days.

- Winds approaching advisory criteria may arrive Monday, prior
  to the arrival of late afternoon and overnight thunderstorms.

- The greatest severe weather risks continue to remain focused
  south of the Missouri River and Highway 20 corridor, however
  continue monitoring of the forecast is recommended.

&&

.DISCUSSION...
Issued at 623 PM CDT Fri May 3 2024

Surface obs indicate the location of the cold front to be in a line
roughly from Mission South Dakota northeast through Redfield South
Dakota. This front will continue to advance southeastward through
the afternoon and evening. Strong frontogenesis in concert with
the front will trigger showers and maybe even some thunder.
Current radar indicates light rain showers over central South
Dakota. These showers will advance along with the front. There
is little in the way of instability tonight, so we do not expect
these showers to become severe. However, some of the
rain showers could produce significant rainfall, especially
over northwestern Iowa, where a half to an inch is possible.
Elsewhere, totals are expected to be around a quarter to a half
inch. Rain showers will be well east of our area by mid Saturday
morning. Lows for tonight will be cool, in the upper 30s to
40s.

Clouds thin as high pressure builds in Saturday, revealing sunny
skies for the afternoon. Winds will be northwesterly bringing a
healthy dose of CAA southward, limiting our highs to the upper 50s
and 60s. The overnight lows will again be cool, in the upper 30s and
40s. As the high moves to the east, winds will swing around to the
southeast Sunday. WAA in the 850 mb level warms temperatures there
into the 6-10 deg C range. This indicates that highs at the surface
will warm into the mid 60s to low 70s. Sunday night, a low pressure
system begins to push through the Rockies, tightening the SPG in
front of it. Winds will increase overnight and through the day
Monday. I felt that the NBM winds were too strong after considering
the model soundings. After collaboration with neighboring offices,
went with a 50/50 blend of the NBM and CONSALL. Even after knocking
winds back a bit, we are still looking at strong winds for Monday.
Sustained at 30-35 mph with gusts 40-45 mph. It may be necessary
as we get more information to include a headline for winds, but
at this time confidence is too low.

Monday morning the surface low ejects out of the Rockies into the
north-central Plains, bringing the next round of showers and
thunderstorms. Models this round have come into better agreement on
the low exiting Colorado and taking a sharp northeasterly track
through western Nebraska and South Dakota. As it does so, it will
drag a warm front across eastern Nebraska and South Dakota.
Instability in the warm sector increases to 500-1000 J/kg of CAPE.
Enough to support some thunderstorms. The more favorable environment
for severe weather remains over the central Plains, however, a few
strong to severe thunderstorms are still possible over southeastern
South Dakota and northwestern Iowa Monday night into early Tuesday.
Rain totals are still a question mark, with ensembles indicate 80-
100% probability of exceeding 0.1 inches, and 30-60% probability of
exceeding 0.5 inches. Rain is expected to be east of the area by
Tuesday afternoon. Highs will be 70s for Monday and 60s for Tuesday.

The low pressure system then hangs out over the northern plains for
the rest of the week, gradually occluding and then moving off to the
southeast. Multiple shortwaves form and pass through the area off of
that main system, bringing multiple chances for showers through the
week. Temperatures will be in the 60s.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1029 PM CDT Fri May 3 2024

Frontal band of rain continues to make slow progress eastward
late this evening. Meanwhile, convection over central Nebraska
will continue to move east and northeast into the overnight
hours. These two areas will merge after 1am over the Tri-State
area, with potential for MVFR ceilings and visibility through
the pre-dawn hours. In Sioux City,will not rule out some
stronger 35 knot winds at times as convection passes through the
area.

Rain moves east of the CWA by 12Z, with MVFR ceilings hanging on
through the morning. Eventually ceilings will scattered with
some limited low-lvl instability shower/sprinkle potential in
the afternoon.


&&

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

&&

$$

DISCUSSION...AJP
AVIATION...Dux