FXUS63 KFSD 040832
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
332 AM 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 /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...JM
AVIATION...Dux