614
FXUS63 KFSD 151147
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
647 AM CDT Sun Sep 15 2024

.KEY MESSAGES...

- Temperatures remain above normal through at least the middle of
  this week. Nighttime lows show greater departures above normal
  (10-15F) than daytime highs (5-10F) due to anomalously high low
  level moisture/dew points.

- Greater chance for rain (40-70+%) returns mid-week, mainly
  focused near and west of I-29 Tuesday night to early Wednesday.
  Moderate (40- 50%) probability of rainfall exceeding 0.25", but
  low (10-30%) probability of exceeding 0.50".

- Moderate chances (40-60%) for showers/storms late week,
  currently focused Thursday night-Saturday night, though exact
  timing and location details are still uncertain.

&&

.DISCUSSION...
Issued at 355 AM CDT Sun Sep 15 2024

TODAY-TUESDAY: A large blocking high from the Great Lakes into New
England will persist early this week while a mid-upper level trough
deepens over the Intermountain West. This pattern is not conducive
to significant rains for us. However, subtle waves and nighttime low
level jet interaction may trigger isolated activity west of I-29,
mainly nocturnal with low (20-30%) chances late tonight-early Monday
and again Monday night. Any rainfall would be light & severe storms
are not expected.

Daytime hours will feature gusty southerly winds, generally 15-25
mph today, increasing to 20-35 mph on Monday and slightly higher on
Tuesday. Temperatures will remain above normal for mid-September
with highs in the 80s and lows in the 60s. Could still see periods
of wildfire smoke aloft, but expect improving conditions as
southwest flow aloft becomes more established.

TUESDAY NIGHT-WEDNESDAY: Models have been trending slower/farther
west with the energy lifting out of the southwest CONUS trough
during this time. Still seeing a low level jet of 40-50kt across the
eastern Dakotas Tuesday night which along with the tail end of the
wave moving through Montana should bring increasing rain chances to
areas west of I-29 Tuesday night. Still see moderate-high (60-80%)
probabilities for measurable rain west of I-29 through 12Z Tuesday,
with chances decreasing as any showers slide east Wednesday morning.
While exact rainfall amounts are uncertain, the broad ensemble
probabilities indicate a moderate (40-50%) chance of exceeding 0.25"
Tuesday night and Wednesday, but generally low (10-30%) chances of
exceeding 0.50". 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-SUNDAY: The latter part of the week is still looking 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 for next weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 640 AM CDT Sun Sep 15 2024

Near-term concern is a couple of small thunderstorms that have
developed 15-20 miles west of KFSD terminal within the past hour.
These storms are tracking northeast and could brush the northwest
periphery of the terminal area after 13Z if they hold together.
However, trends through the overnight point to gradual weakening
as they move through a weakly unstable air mass, so will lean
toward just a mention of VCSH for now.

Otherwise expect rather quiet VFR conditions through this TAF
period with southerly winds occasionally gusting near 20kt during
the late morning-afternoon. Potential for additional isolated
storms late in the period toward central SD, possibly near KHON,
though confidence is far too low to include in the TAF at this
time.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...JH