889
FXUS63 KFSD 221130
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
530 AM CST Fri Nov 22 2024

.KEY MESSAGES...

- Dry conditions are expected through the weekend, with high
  temperatures moderating back into the 30s and 40s.

- A colder holiday week is expected with high (>80%) probability
  for sub-freezing highs, especially near/north of I-90 Monday.
  Tuesday-Wednesday may bring a slight reprieve followed by a
  stronger push of cold air for Thanksgiving into Friday.

- While still non-zero, the chance for light precipitation
  (snow) for Wednesday-Thursday has trended lower (30-50%
  probability of measurable precip over the 2 days). This will
  still be a period to monitor, however, given it is peak
  holiday travel and higher chances are still in place to our
  south and northeast.

&&

.DISCUSSION...
Issued at 355 AM CST Fri Nov 22 2024

TODAY-TONIGHT: Immediate concern is potential for fog/low stratus
development during the late night/morning hours today. Our forecast
area remains clear as of 09Z save for some cirrus streaming into
south central SD. However, seeing some patches of low stratus (per
Watertown observation) or perhaps fog developing near the eastern
edge of the snow field north of Highway 14. Have maintained patchy
fog mention here as well as in our eastern CWA where Thursday`s
stratus was slow to clear and will monitor trends over the coming
hours. If fog does develop, some model guidance suggests it could
persist well into the morning, which is not unreasonable given the
light boundary layer flow within a surface ridge drifting east
across the area today.

Otherwise today should be a pleasant late autumn day with light
winds and seasonable temperatures, topping out in the 30s and 40s.
Coldest readings (lower 30s) will be over the lingering snow on the
Coteau, while the warmest (mid-upper 40s) will build into south
central SD.

The ridge axis slides east tonight followed by broad warm advection
above the surface. This should lead to areas of mid-level cloud
development and steady, if not slightly non-diurnal, temperature
trends overnight. Cannot rule out patchy fog development if we see
sufficient cooling beneath clear skies, but confidence is not high
enough to include in the forecast at this time.

SATURDAY-SUNDAY: Broad warm advection continues Saturday into
Saturday night as weak mid-upper level ridge builds over the
northern Plains. This is followed by a cold front which will push
east across the forecast area on Sunday, though exact timing of the
front is uncertain due to model differences. Most prevalent solution
has the front entering our western CWA late Saturday night, reaching
the James River Valley/Highway 81 by daybreak Sunday, then exiting
our eastern counties by mid-late afternoon. If the faster solutions
are correct, we could end up with some non-diurnal temperatures in
this period as well, however this is a low confidence and will be
refined in later forecasts. Post-frontal winds will become more
gusty as the cold advection pushes east, though not near the levels
of this last Wednesday with the 90th percentile of the NBM still
holding below advisory levels.

HOLIDAY WEEK: Dry weather looks to prevail early in the week, with
the post-frontal air mass briefly settling in on Monday and holding
high temperatures below freezing in most areas. Temperatures look to
rebound slightly for Tuesday-Wednesday in quasi-zonal flow, though
seeing increasing spreads between the 10th and 90th percentiles,
reflecting diverging model solutions and lower confidence in the
temperature forecast for this mid-week period. Still some consensus
in a weak upper trough/surface cold front swinging southeast through
the northern Plains on Wednesday, followed by a reinforcing shot of
even colder air which will bring sub-freezing high temperatures to
the region for Thanksgiving and into the weekend.

Seeing varying projections on available moisture with these features
mid-week, leading to similar low confidence precipitation chances.
However, it should be noted that the latest deterministic solutions
are largely dry for our forecast area. Those with longer-distance
travel plans will want to monitor forecasts, though, as we are still
seeing higher precipitation chances to our south on Wednesday, and
to our northeast Wednesday into Thursday. These trends are also seen
in the broader ensembles, with peak 24-hour probabilities for more
than 0.01" liquid equivalent are decreasing (now roughly 30-50%),
while higher probabilities remain in place to our south/northeast.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 530 AM CST Fri Nov 22 2024

VFR conditions and light winds will prevail at TAF sites through
this period. Could see patchy MVFR fog near lingering snow field
between the James River and I-29 this morning, but this is not
expected to impact KHON or KFSD.

Some models hinting at additional fog development across portions
of southwest Minnesota/northwest Iowa this evening-tonight, but
at this time confidence is too low to introduce given expected
increase in mid-high level clouds which should inhibit strong
radiational cooling.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...JH