593
FXUS63 KFSD 090339
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1039 PM CDT Tue Oct 8 2024

.KEY MESSAGES...

- Temperatures will be warm and above average through Thursday,
  then cooling off into next week. Dry conditions expected to
  continue.

- Skies will continue to appear milky as thick wildfire smoke flows
  over the area over the next few days.

- Marginally breezy periods may result in periods of elevated
  fire danger, with Thursday looking to be at highest risk.

&&

.DISCUSSION...
Issued at 252 PM CDT Tue Oct 8 2024

Under northwesterly flow aloft, a weak shortwave is observed in the
water vapor satellite images slowly drifting into southwestern SD,
with surface observations showing generally southwesterly winds and
temperatures in the mid 70s to lower 80s. Areas in south-central SD
have a more variable wind direction as the the aforementioned
shortwave is creating a weak surface disturbance, but as the
inversion strengthens this evening the surface disturbance weakens
further as it drifts eastwards overnight. For tonight, winds become
calm and variable as the disturbance weakens, leading to another
night of radiational cooling dropping us back into the 40s.

The slow moving shortwave continues to slide east-southeastwards
throughout Wednesday, with high-res convection allowing models
(CAMs) continuing to suggest light rainfall may be possible with the
provided lift out in south-central SD. However, soundings show
mostly dry air aside from a shallow moisture layer 10kft above the
ground, with fairly capped instability. Have thus only increased
cloud coverage slightly for areas west of the James River Valley,
with the rest of the area seeing increased cloud coverage due to the
continued thick wildfire smoke aloft. As the ridge expands
eastwards, the area sees 850mb temperatures exceeding the 90th
percentile of climatology (per latest Ensemble Situational Awareness
Tables) of 16-18 deg C by the afternoon hours. Afternoon highs in
the mid 80s are expected, with the daily max temperature record of
87 for Sioux City in jeopardy as the current forecast has them
reaching 86. After an uneventful overnight period with lows in the
mid 40s to lower 50s, Thursday will see a slightly warmer repeat of
Wednesday as a cold front approaches from the northwest. 850mb
temperatures remain above the 90th percentile at 17-19 deg C,
resulting in max temperatures in the mid to upper 80s, possibly even
90 degrees. NBM shows a 10% chance for reaching 90 degrees F for
areas along the Missouri River Valley, starting in south-central SD
and continuing along the SD/NE border. Fire danger looks to remain
in the elevated category on both days given low relative humidity
values below 30 percent, but wind gusts look to remain at or below
20 mph.

The ridge axis gets flattened overnight into Friday, with the
aforementioned cold front moving through the area from northwest to
southeast. Deterministic and ensemble models now expect the front to
clear our area around 18Z (1 PM), which has taken a few degrees off
the daytime highs. NBM has shifted the 50%+ probabilities for
reaching 80 degrees southeastward, now reaching from a Sioux
City, IA to Storm Lake, IA and southwards. Areas north of that
line will see highs in the upper 60s (north of I-90) to upper
70s south of I-90. Zonal flow transitions towards northwesterly
flow throughout the weekend, and behind two passing shortwaves
to our north cooler temperatures get brought down into the
region. Latest model runs have drastically cooled temperatures
for Sunday and Monday, as stronger high pressures are expected.
Highs on Saturday fall into the mid 60s to mid 70s, with Sunday
in the upper 50s to mid 60s, and Monday looking to see highs in
the 50s. There are indications that cooler weather may continue
into the week, with clustering solutions starting to suggest
that as well.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1039 PM CDT Tue Oct 8 2024

VFR conditions are expected to prevail this TAF cycle. Should see
light and variable winds persist for much of the overnight period,
with direction becoming southerly by late morning. Otherwise, look
for quiet conditions and mostly sunny skies to continue.

&&

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

&&

$$

DISCUSSION...APT
AVIATION...SST