813
FXUS63 KFSD 211940
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
240 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Rainfall amounts remain low for the remainder of the weekend,
  with low chances (20-30%) for a few hundredths to a tenth of
  an inch of rain, mainly for southern Woodbury and Ida counties
  in Iowa.

- With the passage of a cold front today, temperatures trend
  downward to below normal levels tomorrow and Monday.

- Temperatures trend back to normal and above normal levels for
  next week, with limited chances for precipitation through the
  period.

&&

.DISCUSSION...
Issued at 239 PM CDT Sat Sep 21 2024

Surface observations show the cold front moving out of our far
eastern counties, with temperature observations showing cold air
advection starting to overcome radiational heating out in central
South Dakota as temperatures are now beginning to fall. Breezy north-
northwest winds continue to gust into the 20s east of I-29 and into
the 30s west of I-29. Satellite and radar show an area of scattered
showers trying to move into far SE South Dakota and NE Nebraska
along some weak frontogenesis in the mid-levels, though dry air in
the lower levels have prevented the vast majority from reaching the
surface. A secondary band of frontogenesis is lagging behind
slightly along a line from Armour to Madison to Marshall, which has
been able to develop an isolated thunderstorm sporadically.
Instability has waned significantly behind the front, especially for
non-surface based thunderstorms, and with the cold front now off to
our east and south, not expecting any additional severe
thunderstorms in our area today, though a few scattered
thunderstorms are possible.

For tonight a surface high pressure will begin to slide into the
area, continuing to overspread the area with cold air advection
resulting in overnight lows in the mid 40s to mid 50, with coldest
readings north of I-90. This will keep winds on the semi-breezy
side, though much weaker than they have been today already. As a cut-
off upper level low begins to interact with the trough axis already
sliding across the area, we remain north of the fronts that will be
the focus for rainfall. So, outside of our far southern area which
may see sporadic light rain overnight into the morning hours on
Sunday, most of the area will remain dry with mostly cloudy skies
for the start of Sunday. The rest of the day will be largely
uneventful weather wise as the surface high pressure remains parked
over the area, with daytime highs largely in the mid to upper 60s.
Not impossible for some areas to reach 70 degrees, with ensembles
keeping the probabilities for 70 or greater temperatures remaining
below 10%, largely driven by the warm-biased GFS. Overnight
temperatures into Monday dip down into the upper 30s to mid 40s.

Southerly return flow sets up again on Monday as the surface high
slides off to our east, and a front begins to move towards the area
from the west as the parent low pressure slides eastwards in
southern Canada. This will begin our upward trend for temperatures,
though we`ll only be marginally warmer with highs in the upper 60s
to lower/mid 70s. Behind an upper level trough and dry surface front
moving through on Tuesday, upper level heights rise into Thursday as
a ridge of high pressure aloft builds back into the central/northern
plains. Ensemble situational awareness tables show that this ridge
will bring temperatures and geopotential heights at or above the
99th percentile of climatology for this time of year for layers
above 700mb, while 850mb temperatures don`t quite reach the 90th
percentile. So, expect warmer than normal temperatures up into the
upper 70s to lower 80s for Wednesday into Friday. Dry conditions are
expected, with chances for a tenth of an inch of rain remaining
below 10% each day.
&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1235 PM CDT Sat Sep 21 2024

VFR throughout the period. Strongest north-northwesterly winds have
subsided back down into the mid 20s to mid 30s, further
weakening/remaining in the lower to mid 20s throughout the rest of
the afternoon hours. Can`t rule out an isolated shower/storm along
and east/south of a line from Yankton to Sioux Falls to Marshall
into the late afternoon hours, but given the isolated nature have
left mention out of the FSD & SUX TAF. Winds remain semi-breezy
gusting into the 20s for the same aforementioned area overnight,
with minimal chances for rain on Sunday.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...APT