717
FXUS63 KFSD 161128
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
528 AM CST Thu Jan 16 2025

.KEY MESSAGES...

- One last day of above average temperatures today with highs in
  the upper 30s to mid 40s. Warmest today along the Missouri
  River Valley.

- Arctic air returns behind a strong cold front Friday,
  remaining in place through early next week. Well below average
  temperatures and dangerously cold wind chills are expected.
  Confidence is high in wind chills colder than -20 F.

- Strong northwesterly winds are expected Friday afternoon into
  Saturday. Gusts of 30 to 40 mph prevail, with gusts 45 mph or
  higher possible.

- Outside of low (< 20%) chances for flurries/sprinkles Friday
  afternoon and evening, dry weather is expected through early
  next week.

&&

.DISCUSSION...
Issued at 335 AM CST Thu Jan 16 2025

TODAY AND TONIGHT: Mild start to the day with temperatures still in
the upper 20s to mid 30s as of 3 AM CST. Raised high temperatures by
a few degrees across the area today in response, despite the
strongest WAA and southerly flow not moving into second half of the
day. Would not be surprised to see us warm more than forecast with
soundings indicating that if we are able to efficiently mix into
warmer 925 mb temperatures, much of the area could warm into the 40s
this afternoon. Regardless of exact highs, we`ll see a warmer than
average January day with surface high pressure sliding overhead.
Breezy winds this morning ease through the day as the surface high
moves east, shifting to the south by the afternoon hours.

High pressure continues to track east this evening, with a strong
surface cold front approaching from the west. Expect winds to
increase tonight as a result, with gusts this evening and tonight 20
to 30 mph, highest along the Buffalo Ridge. As the front moves into
the MO River Valley by early Friday morning, northwesterly winds
return. Lows overnight remain in the 20s with southerly flow and
increasing WAA.

FRIDAY: Our warmer weather comes to an end Friday as the
aforementioned surface front and troughing aloft move through the
area. Although there`s still a bit of uncertainty with high
temperatures, didn`t make any significant changes to highs Friday.
Despite the surface front moving through earlier in the day, 925 mb
temperatures remain in the single digits above zero C with the
stronger CAA behind these temperatures and at 850 mb. So if we are
able to mix during the early part of the day into these warmer
temperatures aloft, highs in the mid/upper 30s to lower 40s are
reasonable with falling temperatures by the evening.

CAMs show light precipitation with the arctic front and the push of
CAA, so have added in some sprinkles/flurries for the afternoon and
evening hours with weak instability. Soundings show a couple of dry
layers, sub cloud and in the DGZ, so some question in coverage. Not
expecting any accumulation at this time.

One other change to the forecast for Friday into Saturday was to
increase winds and gusts. Northwesterly winds remain strong as the
surface pressure gradient compresses and we mix into the stronger
winds aloft associated with the CAA. Gusts Friday afternoon through
Friday night of 30 to 40 mph expected. Both NAM and GFS soundings
indicate that gusts of 45 mph or greater are possible so further
increases may be needed.

SATURDAY INTO EARLY NEXT WEEK: Mid/upper trough axis continue to
dive south through Saturday, with low pressure stagnating over the
Hudson Bay through the early part of next week. This mid/upper
pattern coupled with arctic high pressure, keeps temperatures well
below average through this period. Confidence is high in well below
average temperatures. When compared to climatology, temperatures at
850 mb, 700 mb, and 500 mb all fall in the coldest 1%, with numerous
periods of 700 and 500 mb temperatures at or below climatological
minimums. Ensemble probability is high (> 80%) for low temperatures
below zero Sunday night into Monday. Additionally, ensemble
probabilities are high that areas from roughly Chamberlain to Sioux
Falls to Spencer, IA remain below zero through the day Monday.
Expect periodically breezy conditions with continued pushes of CAA
and mixing into stronger flow aloft. Any wind with these very cold
temperatures will lead to dangerous wind chills, with moderate to
high probability (30% or more) of wind chills -25 F or colder at any
time through at least Monday (highest chances at night). Cold
weather headlines will likely be needed, but will hold off to allow
for subsequent shifts to refine details.

All that information points to highs in the single digits either
side of zero into the teens above. Lows in the single digits and
teens below. One potential issue with the exact values could be the
lack of snowpack, which may keep us a couple of degrees warmer than
the NBM is trending. However, with temperatures this cold, a couple
of degrees warmer would still lead to dangerously cold temperatures
and wind chills.

Dry conditions expected through early next week. Ridging begins to
build and slide east mid week, which should begin to warm things up
a bit mid next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 522 AM CST Thu Jan 16 2025

VFR conditions expected through the period with prevailing high
clouds. Main concern is the winds and wind shifts. Anticipate a
shift in surface winds from northwesterly to southerly through
the day and into tonight, with another shift to west/northwest
overnight into Friday as a cold front moves across the area.
Winds gust to 20 to 25 knots (strongest tonight into Friday
morning) with gusts to 30 knots along the Buffalo Ridge.

LLJ will fluctuate in direction and speed as well, leading to
periods of LLWS this evening and into Friday morning.

&&

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

&&

$$

DISCUSSION...SG
AVIATION...SG