459
FXUS63 KFSD 041722
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1222 PM CDT Sat May 4 2024

.KEY MESSAGES...

- Rain will exit the CWA by mid morning, with total rainfall
  amounts of up to 0.50-0.75" over northwestern IA, and lesser
  amounts back to the north and west. Dry weather expected for
  the remainder of the day.

- Cooler temperatures today (low 60s), with middle and upper 60s
  on Sunday. Dry conditions also expected on Sunday.

- 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 330 AM CDT Sat May 4 2024

A frontal boundary/inverted surface trough resides east of
Interstate 29 very early this morning. Current radar and
observations indicate showers - with a few isolated lightning
strikes - pushing eastward across the CWA. This in conjunction with
midlevel frontogenesis and theta e advection pushing through the
region. This area of showers will continue to push eastward through
the morning hours, exiting the CWA sometime around 14Z. Additional
rainfall amounts during the late night/early morning hours will
range from a few hundredths in the western CWA, to a half to three
quarters of an inch over northwestern IA. For the remainder of the
day, surface high pressure begins to build into the region, with
skies clearing from west to east through the day. With cold air
advection on the backside of the system, afternoon temperatures will
remain in the upper 50s to lower 60s. With the surface ridge axis
sliding over the area tonight, light winds and clear skies will
allow temperatures to fall into the upper 30s to lower 40s.

The high pressure slides into the Mississippi Valley on Sunday. With
that, winds will become southerly, increasing to 15 to 25 mph west
of Interstate 29 in the afternoon as the surface pressure gradient
tightens up - this the result of a deepening surface trough over
eastern MT and WY. With weak warm air advection during the day,
temperatures will bump up just a bit - into the mid and upper 60s.

A well advertised upper level low over the Rockies lifts into the
Northern Plains on Monday, as a surface low deepens over the western
Dakotas on Monday into Monday night - pulling a warm front northward
across the region during the day. Models still vary in the amount of
instability over our area - generally ranging around 500-1000 J/KG
in our southern CWA on Monday afternoon - depending on model of
choice. Latest ensembles indicate only a 30-40% probability of CAPE
greater than 1000 J/KG through the lower MO River Valley into
northwest IA on Monday afternoon, while CIPS analogs and machine
learning probs do give us at least some potential for severe storms
on that day. So in summary, uncertainty still does exist, though
cannot rule out a few strong to severe storms on Monday afternoon
and evening - as supported by the SPC Day 3 outlook. Even so, the
much better chance looks to be to the south of our CWA. In addition
to the storm potential on Monday, it will also be quite windy - and
there will be at least some potential for a Wind Advisory at some
point. Any storms that develop will move eastward on Monday night,
exiting the area sometime on Tuesday morning. We could receive
another round of moderate to heavy rain with the system, and
ensembles indicate around a 70% probability of portions of our area
receiving a half an inch or greater of rainfall during this time
frame.

The upper level low meanders over the Northern Plains through at
least midweek, before shifting to the east by the end of the week.
This will keep at least small chances (20-30%) of showers for much
of the week as various shortwaves rotate around the upper level
trough. Highs through the period will mostly be in the 60s to lower
70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1214 PM CDT Sat May 4 2024

Mostly VFR conditions with occasional MVFR ceilings are
expected for this TAF period. Taking a look at satellite
imagery, a cumulus field has developed across most of the area
in response to some elevated instability with parts of
northwestern IA dealing with lingering stratus from this
morning`s cold front. As the surface high continues to move into
the area this evening, expect conditions to begin to clear from
west to east. Otherwise, breezy northwesterly winds will
continue through the late afternoon before diminishing as the
surface high moves overhead tonight. Lastly, some high
resolution guidance has started to hint at some patchy fog
developing across northwestern IA overnight. However, confidence
is still low in occurrence so far.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Gumbs