988
FXUS63 KABR 212328 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
528 PM CST Thu Nov 21 2024

.KEY MESSAGES...

- Patchy fog is possible tonight.

- Fresh snow cover could cause overnight low temperatures to fall
  into the single digits tonight. Otherwise, temperatures Friday
  and Friday night should be close to normal.

- There is a 15 to 25% chance of light snow over portions of north
  central and northeastern SD into west central MN Sunday
  through late Sunday night. Little to no accumulation is expected.

- Average to slightly below average temperatures this weekend and
  around 5 to 10 degrees below average early next week.

&&

.UPDATE...
Issued at 525 PM CST Thu Nov 21 2024

See updated aviation discussion below.

&&

.SHORT TERM /THIS EVENING THROUGH FRIDAY NIGHT/...
Issued at 117 PM CST Thu Nov 21 2024

At 1 PM CST, other than overcast skies on the Prairie Coteau and
west central Minnesota, the CWA is basically sunny or mostly sunny
with some higher level clouds streaming by. Temperatures under the
cloudy skies are in the upper teens to mid 20s (also the area with
the most snowfall the other day), while sunny sky areas were warming
through the 20s into the low 30s. Winds were northwest at 5 to 15
mph, with some areas east in the CWA gusting to around 25 mph at
times.

Surface high pressure is over the Missouri River valley region of
the CWA. It is forecast to re-align along the Dakotas border with
Minnesota by 12Z Friday. If the clouds over the eastern zones
dissipate or continue their move off into Minnesota, the portion of
the CWA that received 2in to 5-6in of snow Tuesday night into
Wednesday could be staring a clear sky/light wind night square in
the face; meaning there is the potential for low temperatures over
this new snowfield to bottom out a good 5 to 10 degrees (or more)
lower than surrounding bare ground areas. Have attempted to draw in
that potential some in the min T forecast grid, while maintaining
bordering CWA integrity with neighbors. There could also be some fog
on/near this snow field later tonight as winds go light and
temp/dewpoint depressions narrow to just a degree or two at the
surface. Also worth noting, the HREF skycover guidance is hinting
that the scattered coverage higher-level cloudiness happening now
will be ongoing overnight, which could end up pumping the breaks on
snowfield ultra-cold low temperatures, and on fog development.

During the day on Friday, there is an attempt made for low level WAA
over the CWA, in particular across the western third of forecast
zones (Missouri River valley region), in response to lee of the
Rockies/Black Hills surface pressure falls. So, fully expecting high
temperatures to warm into (at least) the low to mid 40s across much
of central and north central South Dakota.

Something to watch, though, is how far south into the CWA a shallow
cold airmass can push Friday night. The latest RAP output shows a
cold front beginning to work into Corson County by 00Z Saturday,
potentially reaching as far south as a line from Pierre to Miller to
Watertown to near Appleton, MN by 12Z Saturday.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 117 PM CST Thu Nov 21 2024

Starting out the long term on Saturday, models are consistent on a
ridge overhead with zonal winds turning southwesterly. Just west of
the ridge, the low continues to spin off the coast of WA/OR with a
trough, south of this low, extending over the Pacific Ocean. The
ridge overhead will slide eastward with a negative shortwave forming
over southern Alberta/Saskatchewan/northern MT along with several
embedded shortwaves/pulses over the Rockies Saturday evening. At the
surface, an elongated area of low pressure will form over this area,
pushing east/southeast with the broad surface low extending from the
Northern Plains southward through Texas by 12Z Sunday. The low then
track east/northeast Sunday into Monday with the upper level waves
following behind.

Models keep most of the precip along the ND/Canadian border Saturday
night through Sunday (closer to the 700-850mb low skirting east
within this wave). However, ENS brings the chance of precip a bit
further south, brushing our northern/northeastern CWA Sunday through
early Monday as it indicates the wave aloft plunging further south
than GEPS/GEFS. NBM does a good job indicating this with pops of 15-
25%, highest along the ND/SD border, with Ptype being mainly snow.
EC meteograms do indicate a 10-15% chance that ptype could be light
freezing rain/drizzle at 8D3 and less than 10% chance at KATY mixed
in with the snow early Sunday. EC soundings at 8D3/KATY shows a
potential warm nose (and dry air above this) with GEFS soundings for
these locations keeps the column at or below freezing indicating all
snow (which GEFS plumes do indicate). Low confidence exists on this
potential as of now. No ice accumulation expected with little to no
snow accumulations.

Otherwise, behind the system, high pressure moves in and will be the
dominant weather pattern through the midweek, keeping the area dry
and quiet. Aloft, winds will mainly be zonal through the midweek as
models indicate a broad positive tilted trough moving west to east
over the CONUS with lots of variability between the models on track
and intensity and whether it the pattern remains phased together or
becomes split flow. Both EC/GEFS do hint at a possible lee low
forming near CO/OK/TX area Wednesday and tracking northeast through
end of next week. Depending on track this may bring the return of
snow (under 20% chance for now). Confidence is low this far out on
the overall pattern and where/if precip will fall and where.

Temps will be around average to a few degrees below average for the
weekend. As that high moves in early next week, it will bring in
colder air with it with 850mb temps ranging to the single digits
below zero to -11C with the coldest air over the northern CWA with
GEFS being the most aggressive on this colder air. Temps are
forecasted to run about 5 to 10 degrees below average. Even colder
air is forecasted to move in for the end of the week (again GEFS
being the most aggressive) with 850mb temps ranging from -10 to -13C
by early Saturday morning with this colder air hanging around at
least through the early following week. Latest NBM has a 30 to 60%
chance of low temperatures below zero by Sunday morning (12/1) and
30-55% chance Monday morning (12/2). CPC highlights this well with a
slight risk (20%) of "Much Below Normal Temperatures" 11/28-12/4 and
a moderate (40% chance) over the north central CWA 11/28-11/30.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 525 PM CST Thu Nov 21 2024

Terminals KABR,KATY,KPIR,KMBG

For the most part, VFR conditions will prevail across the area
tonight and through the day Friday. The exception will be across
far eastern parts of the area where some patchy fog and MVFR cigs
may develop late tonight into Friday morning. KATY may be
affected.

&&

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

$$

SHORT TERM...Dorn
LONG TERM...MMM
AVIATION...Parkin