059
FXUS63 KFSD 140902
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
402 AM CDT Sat Sep 14 2024

.KEY MESSAGES...

- Wildfire smoke aloft is projected to linger over the region
  today, but trends pointing to improvement through the latter
  half of the weekend.

- Isolated to scattered showers/storms impact mainly central to
  northeast South Dakota again later today-tonight, with a low
  (20%) chance mainly west of a Huron to Wagner line this evening.
  Gusty winds are possible with storms, but severe weather is not
  expected.

- Temperatures remain above mid-September normals through much of
  next week, with nighttime lows showing greater departures above
  normal due to anomalously high low level moisture/dew points.

- Greater chances for rain (40-70+%)return mid-late week next
  week, though details in exact timing/rainfall amounts are
  uncertain.

&&

.DISCUSSION...
Issued at 358 AM CDT Sat Sep 14 2024

TODAY-TONIGHT: Somewhat a repeat of yesterday/last evening expected
over the next 24 hours with a couple of notable exceptions. First, a
weaker surface gradient will allow for less gusty winds today, with
south-southeast winds generally 10-20 mph (a few higher gusts west
of the James River Valley). Second, some areas along and east of US
Highway 81 will see more cloud cover, at least into this morning.
This is a result of either scattered-broken ACCAS in response to
subtle mid-level waves converging on our eastern counties. and/or
stratus in Iowa attempting to expand a bit farther west across
northwest Iowa. Either of these could work to hold temperatures
slightly cooler in our eastern counties today, but still expecting a
seasonably warm day with highs near 80 east to the mid 80s west.
Locations free of clouds may still notice a hazy sky due to smoke
aloft, though this is expected to slowly diminish as we move through
the weekend.

Late afternoon-evening will bring another low chance (<30%) for
storms to areas mainly west of the James River Valley, as another
subtle wave slides northeast through central South Dakota. While
this area could see CAPE values pushing 1000 J/kg, shear is on the
weak side generally less than 30kt, so not expecting severe storms
in our forecast area. However, could see locally stronger gusts near
any storms due to a continued dry sub-cloud layer. Like tonight,
precipitation will struggle to make much progress farther east into
the CWA as it encounters even drier air.

SUNDAY-MONDAY: A large blocking high from the Great Lakes into New
England will persist into early next week while a mid-upper level
trough deepens over the Intermountain West. This will leave our
forecast area with relatively quiet weather to begin the new week,
though a gradually tightening surface gradient will lead to an
upward trend in southerly wind speeds by Monday. Various model
solutions show periodic very light QPF amounts so cannot completely
rule out isolated showers or storms at times during this period, but
confidence in timing/location is far too low to include anything
more than a 10-20% chance of rain in any one period. Temperatures
remain similar to recent days with highs in the 80s, while an influx
of higher dew points will keep lows a bit higher, mostly in the 60s.

MONDAY NIGHT-WEDNESDAY: Low level jet of 40-50kt becomes focused
across central Nebraska into the central-eastern Dakotas Monday
night as a weak wave ejects northeast out of the western trough.
This will bring low chances (20-30%) for nocturnal showers/storms to
areas mainly west of I-29 Monday night, with activity waning after
sunrise Tuesday as the wave exits. While mostly dry, the daytime
hours Tuesday will be on the windier side, especially west of I-29
where occasional gusts 35-40 mph are expected.

Tuesday night will see the low level jet slide farther east as the
southwest upper low swings northeast through the Rockies and High
Plains of the Dakotas. This will bring increasing rain chances to
areas along and west of I-29 Tuesday night, with moderate to high
(60-80+%) chances for measurable rain. While exact rainfall amounts
are uncertain, the broad ensemble probabilities indicate a moderate
(40-70%) chance of exceeding 0.25" Tuesday night and Wednesday, but
generally low (20-30%) chance of exceeding 0.50", both highest in
areas west of I-29. Severe weather risk during this time appears low
given weak deep layer shear <20kt and mid-level lapse rates near to
below 7C/km.

THURSDAY-SATURDAY: The latter part of next week looks to remain a
bit more active than the relative dry pattern we`ve seen in recent
weeks. However, model consistency is lacking, so confidence in the
day to day details of timing/location of favored rain chances is on
the low side. Above normal temperatures are still favored at least
through Friday, but trends are currently pointing to a least a brief
cool down beyond the end of this forecast period.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1035 PM CDT Fri Sep 13 2024

Any shower chances look to be dwindling this evening as very
light rain lifts into northeastern SD. Latest ensembles would
suggest a little better probability (50-60%) of MVFR stratus
lifting into northwestern IA later tonight, and this may affect
KSUX after 10Z. This stratus then looks to lift/break up by mid
to late morning on Saturday. Southeasterly winds will be light
overnight, then increase slightly by late morning on Saturday.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...JM