438
FXUS63 KFSD 201750
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1250 PM CDT Fri Sep 20 2024

.KEY MESSAGES...

- Although there will be moderate precipitation chances south
  of Interstate 90 for the weekend, precipitation amounts
  continue to trend downward.

- With the passage of a cold front, temperatures trend downward
  to below normal levels for Saturday through Monday.

- Temperatures trend back to near normal levels for next week,
  with a limited chance of precipitation through the period.

&&

.DISCUSSION...
Issued at 350 AM CDT Fri Sep 20 2024

Weak surface high pressure continues to drift across the region very
early this morning, and it is pleasant across the area with current
temperatures in the mid 50s to lower 60s. Temperatures are expected
to bottom out in the lower to mid 50s as we head toward 12Z. With
high pressure overhead, winds have become light, and as temperatures
continue to cool through the early morning - nearing dew point
temperatures - we may see patchy fog develop in some areas.

Otherwise, the surface ridge will drift into the Mississippi Valley
by this evening. Related to that, will see increasing warm air
advection as the low to mid level flow takes on a southerly
component, and this will result in slightly warmer temperatures for
some areas today. Highs will range from the upper 80s through the MO
River corridor to the lower to mid 80s to the north and east. It
will become breezy through south central SD by afternoon - this in a
tightening surface pressure gradient and higher winds at the top of
the mixed layer. It will not be overly windy, but could see gusts up
to 25 to 30 mph at times. This in combination with the warm
temperatures will result in an enhanced fire danger over that area
as fuels dry out and afternoon RH values fall to around 25 percent.

Tonight should remain dry, though with the warm air advection and
slightly higher winds overnight, lows will only drop into the upper
50s to lower 60s.

For Saturday, an upper level trough swings through the Dakotas into
MN during the day, while at the surface a relatively strong cold
front plows through our area during the morning and afternoon hours.
Models are in good agreement on this front being through our entire
area by 21Z.  Rainfall chances look low for much of the area with
the system (20% or less), with a lack of moisture and capping,
though some hi-res guidance would suggest the possibility of some
post frontal elevated convection over northwestern IA during the
afternoon (mainly 30-50%) as a weak midlevel shortwave lifts into
the area. With the cold front tracking through the area, highs will
range from the lower 70s west of the James River Valley to the lower
80s over northwestern IA.

For Saturday night through Sunday night, an upper level low lifts
from CO into Central Plains through the period. While this will keep
low to moderate rain chances (30-50%) mainly south of Interstate 90
through the period, models and ensembles continue to trend farther
southward with the higher QPF. Latest ensembles indicate only a 20-
30% probability of our far southeastern NW IA zones receiving 1 inch
of precipitation through the period, and a 30-50% of that area
receiving 0.50 inch. It will be much cooler on Sunday with 850 mb
temperatures around 7-9 degrees C. It will feel much more fall-like
with highs only in the mid to upper 60s.

For next week, while models are in fairly decent agreement on our
area remaining under the influence of upper level troughing through
midweek - yielding toward upper level ridging for the end of the
week - there is a good bit of spread with regard to the specifics of
how this pattern evolves. Even so, both deterministic models and
ensembles suggest our area remaining mostly dry through the week -
with ensembles showing a 10% or less of our receiving 0.25" of
precipitation in any one 24 hour period for Monday through Friday of
next week. Because of the model differences, NBM given temperatures
remain appropriate with highs just either side of normal (70s)
through the period.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1250 PM CDT Fri Sep 20 2024

VFR throughout the period. Southerly winds are expanding eastwards
throughout the rest of the afternoon hours, becoming marginally
breezy for areas west of I-29 with gusts into the lower 20s. Expect
a few hours of LLWS across the area as south-southwesterly winds
aloft strengthen above our south-southeasterly surface winds. A cold
front will be moving through the area tomorrow, abruptly swinging
winds around out of the north-northwest. A few hours of stronger
wind gusts into the 30s are possible behind the front, especially
along and west of I-29, with wind gusts into the 20s continuing
throughout the day. Will likely see scattered thunderstorms form
tomorrow morning into the afternoon hours along and east/south of a
line from Tyndall to Sioux Falls to Windom, though given the
scattered nature have omitted TS mention in this round of TAFs.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...APT