330
FXUS63 KFSD 072320
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
520 PM CST Fri Feb 7 2025

.KEY MESSAGES...

- Snowfall forecast amounts/timing largely remain on track for
  tonight-Saturday. Highest amounts of 2 to 4 inches remain over
  southwest MN where the Winter Weather Advisory is in place.
  Snow totals around an inch as far west/south as Huron, Sioux
  Falls, and Spencer.

- Temperatures cool significantly for most of the upcoming
  week, however the incoming airmass remains fairly typical for
  the second week of February. A few days with below zero low
  temperatures possible this week.

- Beyond Saturday, no significant snow risks ahead, though an
  area of light snow could accompany/follow the arctic front
  passage on Monday-Monday night. A lower confidence system
  moves in again by the end of next week.

&&

.DISCUSSION...
Issued at 257 PM CST Fri Feb 7 2025

LATE THIS AFTERNOON-SATURDAY: While today has been on the quiet side
across our local area, the initial snow from this system has been
falling over far southern North Dakota much of today, and has begun
expanding into far northern South Dakota since late morning. This
band appears to be focused close to a zone of strong frontogenesis
around 600mb which will extend east into portions of central MN as
we head toward evening.

Closer to home, a relatively dry/mild southeast flow has prevailed
for much of the day, reinforcing a dry layer below an expansive mid
level cloud deck. This dry low level air will initially slow the
development of snow into our forecast area through the early
evening, but persistent warm advection and increasing mid level
frontogenesis ahead of the approaching surface/upper level wave
should produce enough lift to allow for fairly rapid expansion of
the snow through the latter half of the evening across portions of
southeast/east central South Dakota and into southwest Minnesota.

The wave and associated stronger lift still look to move east of the
area pretty quickly, with the heaviest snowfall expected northeast
of a Brookings-Worthington line between midnight and 9am Saturday. A
nearly isothermal saturated profile near to slightly warmer than the
Dendritic Growth Zone (DGZ), along with relatively light winds
during this window, will provide good conditions for snowflake
growth, which could lead to higher snowfall accumulation rates at
times. In fact, the HREF does show mean snowfall rates of 1/4 to
1/2" per hour sliding through portions of southwest Minnesota, with
a low (<20%) probability for snowfall rates exceeding 1"/hour. So
while the heaviest snow may not last more than 4-6 hours in any one
location, we are still looking at a most likely range of snowfall
between 2 and 4 inches, with locations from Marshall to Windom
seeing a low (<20%) chance of exceeding 4 inches.

As noted by the previous shift, the post-frontal cold advection on
Saturday will aid in mixing some stronger wind gusts to the surface,
mostly in the wake of the falling snow. ARW/HRRR tend to perform
well in these cold advection regimes, and both models indicate winds
atop our mixed layer topping 25kt across southwest MN, with stronger
winds topping 35kt across southwest portions of our forecast area.
Thus will continue to favor the higher end of wind guidance for
Saturday, which could lead to areas of blowing/drifting snow into
the afternoon hours. In addition, a trailing weak wave combined with
the thermal profile cooling further into the DGZ may allow light
snow to linger near/east of I-29 through midday. As a result of the
stronger winds and later end to light snowfall, have extended our
advisory through 3 pm Saturday.

SUNDAY ONWARD: With focus on the near-term snowfall, did not much
time to examine the mid-long range for fine details. In the broad
view, highlights include a secondary push of cold air dropping into
the northern Plains for the start of the work week. With low level
temperatures falling back into the DGZ, any low level clouds will
support production of flurries/light snow, and models are latching
onto some light QPF/snowfall during this time Monday afternoon and
night. The coldest air of the week will follow this into Tuesday and
Tuesday night, and while not anomalously cold aloft for this time of
year, our fresh snow cover in parts of the area will help surface
temperatures colder with highs Tuesday in the single digits above
zero, and lows Monday night-Tuesday night in single digits and teens
below zero. May see additional cold weather headlines in some of the
colder areas on these nights.

Midweek looks to be relatively quiet, but some model solutions are
hinting at a stronger wave kicking out of the Rockies into the
Plains by late next week. Model agreement is low, and thus so is
confidence in any specific details for this period, aside from the
fact that temperatures look to remain cold enough that snow would be
the primary precipitation type.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 515 PM CST Fri Feb 7 2025

Light snow will overspread the area from northwest to southeast
tonight and continue into Saturday morning west of the James
River Valley, and into the afternoon east of there. With that,
ceilings and visibilities will fall into the MVFR/IFR range.

Southeasterly winds this evening will transition to northerly
overnight, gusting 20 to 30 kts through the day on Saturday.
This could result in patchy blowing and drifting snow, mainly
through east central SD and southwestern MN where snowfall
amounts will be highest.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...Winter Weather Advisory from midnight tonight to 3 PM CST
     Saturday for MNZ071-072-080-081.
IA...None.
NE...None.

&&

$$

DISCUSSION...JH
AVIATION...JM