Winter Weather Advisory 13, NWS Aberdeen, SD

Big Stone County, MN, Traverse County, MN, Brown County, SD, Buffalo County, SD, Campbell County, SD, Clark County, SD, Codington County, SD, Corson County, SD, Day County, SD, Deuel County, SD, Dewey County, SD, Edmunds County, SD, Faulk County, SD, Grant County, SD, Hamlin County, SD, Hand County, SD, Hughes County, SD, Hyde County, SD, Jones County, SD, Lyman County, SD, Marshall County, SD, McPherson County, SD, Potter County, SD, Roberts County, SD, Spink County, SD, Stanley County, SD, Sully County, SD, Walworth County, SD

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1122 PM CST Mon Dec 13 2021

.UPDATE...
Issued at 526 PM CST Mon Dec 13 2021

The forecast remains on track this evening. No major changes are
planned.

&&

.SHORT TERM...(This Evening through Tuesday Afternoon)
Issued at 227 PM CST Mon Dec 13 2021

The tranquil weather before the storm, that's the short term. Mid-
level ridge will continue to build across the region through
Tuesday, as energy digs toward southern California. A quite warm
airmass will advect into the forecast area, with H850 temps
exceeding +12C across much of the area Tuesday afternoon. Only
caveat will be mixing depths over the region, and southerly breezes
aren't typically great for maximum mixing. BUFR soundings do
indicate a bit better boundary layer mixing out west, and thus
temperatures out over the Missouri valley should be milder vs the
eastern CWA. Here in the east, except for perhaps over the higher
elevations of the Coteau, mixing will be much shallower. So, in the
east will stick closer to the model blend. Pretty much did a blend
of NBM and 75th percentile NBM for highs on Tuesday For lows didn't
stray too far from NBM which does okay when there is some mixing
that takes place due to LLJ, etc.

.LONG TERM...(Tuesday Evening through Monday)
Issued at 227 PM CST Mon Dec 13 2021

Main focus for the long term forecast is potent storm quickly moving
through the north central CONUS Wed-Wed Night. Confidence is high on
the winds and in general the track of the low, but precipitation
timing/amounts, and to some extent type, is still pretty low
confidence at this point.

Upper trough currently off the western CONUS will come on shore
Tuesday and quickly lift to the east-northeast through the central
Plains Wed Aftn/Evening and into the Great Lakes by 12Z Thursday. A
strong surface low will accompany this, developing in the lee of the
Rockies in NE CO on Wednesday morning and tracking with the quickly
moving upper trough. There continues to be variability in the models
with the intensity and exact track of the low, but it should track
from NE CO to around the SD/NE/IA border area by 21Z Wed and then
quickly towards western Lake Superior by 03Z Thursday. As the
previous AFD highlighted, still various intensities of the low in
the EC-Ens/GEFS/GEPS members, anywhere from low 970s to mid-high
980s, with the stronger lows on the northern side of the previously
mentioned mean track. So with that track, expect to see a period of
at least advisory winds across the area. The strong winds will start
Wednesday afternoon and should peak during Wed evening and then
diminishing during the overnight hours. Comparing
deterministic/ensemble output, seems pretty consistent in seeing 35-
45kts gusts during the peak periods, but the peak winds will depend
on the depth of the mixing as the cold air surges in under the NW
winds. Deterministic models in Bufkit showing 50-55kts at or just
above the inversion around 850mb, so do feel that some high wind
criteria gusts are possible, which has some support in the 06Z NBM
v4.1 experimental data, which has some pockets of 50-80 percent
probs of gusts being at or above 48kts, with the full CWA having at
least a 30 percent prob.

On to the precipitation...00/06Z EC-Ens/GEFS/GEPS showing a variety
of areas of increased probabilities of 0.1" of liquid or 1" of snow
over this period. That being said, starting to see a trend in the EC-
Ens and now the 12Z GEFS, of the greater probabilities being farther
southeast and located more to the immediate north-northwest side of
the surface low. This had the latest probs of 0.1" of liquid being
the highest over southeast SD and into southern MN, with probs being
50 percent or greater to the southeast of a line from Murdo to
Miller to Sisseton. If that trend continues, that will reduce some
of the broader impacts from the precipitation side of things, but
would still expect some impacts where the snow occurs with the
strong winds. Looking at the latest deterministic runs, plenty of
dry air in place in the mid levels ahead of this system, which
should keep the area largely dry through mid day on Wed. Then we'll
quickly get the deeper moisture, both from the surface low and also
a secondary area to the northwest from the leading edge of the upper
trough. With some of the latest trends, this secondary area may
produce an inch or two of snow over north central SD, with a gap
between the two precip areas. With the uncertainty in the
precipitation location/amounts, there remains questions on
precipitation type too. As the profiles saturate, we should see the
profile cool and largely eliminate the warm nose that will be in
place. Thus, feel that we'll likely see a pretty quick transition to
a sub-freezing profile. But there is a concern for the lack of ice
present in the cloud between the two precipitation areas, which is
apparent in the latest deterministic soundings and also in the NBM
output. So where the deep moisture ends up being present, we'll see
snow and then where it isn't located, a wintry mix depending on
surface temps.

Finally for this system, blowing snow concerns. Areas with existing
snow over the south/eastern CWA will likely have crusted over with
the above freezing temps yesterday, today, and tomorrow. So existing
snow pack is not blowable and any impacts will be highly dependent
on new/falling snow. As mentioned previously, that exact area is a
little uncertain, so blowing snow potential is uncertain and will be
fine tuned in the next day or so.

For the rest of the extended forecast, there will be a couple
shortwaves moving through the area (Fri aftn/night and again late in
the weekend into Sun night), which could produce light snow.
Otherwise, temperatures will be near or slightly below normal after
the mid week event.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 1121 PM CST Mon Dec 13 2021

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are expected through the period.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

UPDATE...Wise
SHORT TERM...TDK
LONG TERM...SRF
AVIATION...Wise