194
FXUS63 KFSD 181128
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
628 AM CDT Fri Oct 18 2024

.KEY MESSAGES...

- Although to a lesser extent than the past two days, today will
  again feature gusty southerly winds and dry air east of a cool
  front, especially along/east of US Highway 81, which will lead
  to elevated (Very High) fire danger.

- Low to moderate (30-70%) probabilities of 0.10" rain or greater
  remain west of I-29 this afternoon to early Saturday. Ensemble
  probabilities of 0.25" or more are generally low (20-30%) and
  focused in south central South Dakota, though HREF shows pockets
  of moderate (40-60%) probabilities.

- Temperatures through the 7 day forecast will remain 10 to 20+
  degrees above normal through much of the next week, briefly
  cooling around Wednesday-Thursday time frame.

&&

.DISCUSSION...
Issued at 333 AM CDT Fri Oct 18 2024

TODAY-SATURDAY: STrong upper ridge continues to dominate much of the
eastern CONUS while an elongated trough slowly digs through the
Rockies. Our forecast area will be in somewhat more active southwest
flow in the mid-upper levels, with a cool front slowly working east
into our South Dakota counties, only reaching roughly a Lake Andes
to De Smet to Watertown line by sunset. More abundant cloud cover
along with low (20-30%) chances for late afternoon post-frontal
showers will allow for slightly cooler air along/west of the front
today while locations east of the front climb back into at least the
lower-mid 70s. More notable east of the front will be another day of
gusty southerly winds, though to a lesser extent than the past
couple of days with gusts generally 30-35 mph through mid-afternoon.
The southerly flow will draw slightly higher dew points northward,
but still looking at relative humidity levels falling to around 30%
minimums in the areas with these stronger gusts, generally near and
east of US Highway 81. This will result in Elevated (Very High) fire
danger, so caution is still advised for those working in the very
dry fields/grasslands.

Farther west, subtle waves sliding northeastward along/west of the
front will attempt to produce some light rain showers this afternoon
through tonight. Main challenge will be overcoming a rather deep dry
sub-cloud layer. Models focus the greatest possibility for rain in
south central South Dakota, where both the global ensembles and HREF
show low-moderate (30-70%) probabilities of rainfall exceeding 0.10"
to 0.25" this afternoon through Saturday morning.

Rainfall probabilities drop off quickly as you move east, where
saturation below 8-10kft is limited. However, cannot rule out a few
sprinkles from thickening mid-clouds as they expand east toward the
I-29 corridor later this afternoon/evening. The front will continue
to nudge eastward toward I-29 and southwest Minnesota overnight, and
with it we could see spotty showers work into these areas. However,
with the aforementioned dry low levels, rainfall will be limited to
a few hundredths at best.

Saturday will be a slightly cooler but much less windy day as the
front washes out and we transition back to a modest west-southwest
flow. Could still be a little breezy in our east with decent mixing
during the afternoon, but higher dew points/cooler temperatures will
allow for higher RH values of 40-60% in most areas, so fire danger
will be held in check for one day.

SUNDAY-TUESDAY: Cutoff upper low lingers over the southern Rockies
and Four Corners region as we head into next week, allowing for
modest ridging to build back over our forecast area on Sunday. This
low then swings northeastward through the first part of the work
week, but limited moisture return will lead to only low (10-30%)
chances for 0.10" rainfall or more Monday-Monday night.

A weaker pressure gradient will keep wind speeds more in the 15-25
mph range during the day through this period, while NBM holds onto
dew points from the mid 40s east to lower-mid 50s in our west. Tough
to argue with potential for these higher dew points to stick around
when even the dry-bias GFS shows readings only a few degrees lower.
So while we will likely see areas of elevated (High) fire danger, we
should remain far shy of the extreme conditions of the past couple
of days.

MIDWEEK ONWARD: Northern stream trough and associated cold front
push through the region Tuesday night-Wednesday, bringing a brief
cool-down for Wednesday-Thursday. Though these mid-week highs are
still near to above normal with forecast highs in the 50s and 60s.
Rainfall chances with the front look quite limited, with a return to
warmer temperatures favored by the end of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 628 AM CDT Fri Oct 18 2024

A frontal boundary from south central to northeast South Dakota to
start this TAF period will move very slowly east through tonight.
Mid-level clouds will become more abundant at times, and locations
near and west of the boundary may see isolated to scattered light
rain, though limited low level moisture should keep ceiling and
visibility in VFR range.

East of the boundary, gusty south winds will be the dominant story
once again today. Though lighter than recent days, frequent gusts
of 25-30kt are expected during the daylight hours. Unlike the past
couple of nights, gusts are expected to diminish with sunset this
evening. Late night/early morning hours will still have a potential
for low level wind shear east of the boundary as well, impacting
KFSD/KSUX early this morning, and KSUX after 19/06Z tonight.

VFR conditions will prevail through much of the period, though
locations west of the frontal boundary including KHON may see MVFR
ceilings develop late tonight after 19/09Z.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...JH