429
FXUS63 KABR 250302 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
902 PM CST Sun Nov 24 2024

.KEY MESSAGES...

- Light snow expected this evening across central/south central
  SD into northeast SD and west central Minnesota. Generally a
  trace to 2 inches expected.

- There is a 20 to 30 percent chance of light snow Wednesday
  morning through the afternoon over portions of northeastern SD
  into west central MN.

- High confidence on much below normal temperatures by the end of
  the week through the weekend, with highs in the lower teens to
  20s and lows in the single digits above zero to the single
  digits below zero.

&&

.UPDATE...
Issued at 854 PM CST Sun Nov 24 2024

Have been tracking a band of light to moderate snow move across
parts of central and northeast South Dakota since late this
afternoon and early this evening. It is now mainly confined to
zones east of the James Valley; across northeast and east central
South Dakota and west central Minnesota. It will all be mostly
done and east of our forecast area by midnight or shortly after.
Updated PoPs earlier this evening to update chances based on the
latest radar trends and surface observations. Will continue to
track this the remainder of the evening. No other changes
anticipated through the rest of the overnight hours.

UPDATE Issued at 539 PM CST Sun Nov 24 2024

See the updated aviation discussion below for the 00Z TAFS.

&&

.SHORT TERM /THIS EVENING THROUGH MONDAY NIGHT/...
Issued at 335 PM CST Sun Nov 24 2024

Will be watching the band of light snow moving/developing eastward
across the region into the evening hours. Models have increased QPF
slightly across the eastern CWA, and have followed suit in the
forecast. Radar imagery as of 3PM CST shows snow across southwest
and south central SD, and expect this to continue moving/developing
eastward into the evening hours. Latest forecast brings generally a
trace to 2 inches from south central SD up through northeast SD into
west central MN. Best potential for 1 to 2 inches looks to set up
over the eastern CWA into west central MN, where 700mb frontogenesis
may contribute to slightly heavier totals. HREF Grand Ensemble
probability for an inch+ (assuming 10:1 snow ratios) shows about 50-
80% across the eastern CWA. The probability for 2+ inches drops off
quite a bit, but is still around 20-40% over far northeast SD into
west central MN. Also increased PoPs from the previous forecast
across south central SD into the eastern CWA, while also pushing
them westward a bit.

Turning to cloud cover, stratus continues to blanket most of the
CWA, but recently the far northwest CWA has seen the stratus depart,
and models continue to show a slow departure of the clouds from west
to east overnight into Monday morning. In fact, HREF ensemble mean
cloud cover shows mostly sunny skies across the area on Monday.

As for temperatures, low-level cold air advection ramps up across
the CWA overnight as 925mb temps cool to -7C to -10C. Overnight lows
are a bit tricky as breezy northwest winds and clouds have to be
balanced with the strengthening cold air advection. LAV guidance
shows lows may not be reached until about 15Z Monday morning.
Looking at teens for most areas by the time we get to Monday morning.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 335 PM CST Sun Nov 24 2024

Main concern in the long term will be the colder temperatures for
the end of the week into next weekend where our first below zero
temp readings of the season are becoming likely! Starting out
Tuesday morning, an elongated area of high pressure will be over the
Northern Plains into Canada, with zonal winds aloft. This high will
be shifting out of the area as models agree as a large area of low
pressure setting up from MT and southeastward through Colorado
through the day into the evening, with a Co low forming. Aloft, a
positive tilted shortwave will move from the northwest over the
Northern Rockies (northern stream), as split flow continues, with
zonal flow over the central Rockies to central Midwest on the
downwind side of a trough, with the axis moving in over the western
CONUS (which helps the CO low form). With the CWA on the the
northeast side of this large area of of low pressure (and high
moving out), we will see surface troughing through Tuesday evening
into early Wednesday.

As this upper wave moves southeast over the Northern Plains, Clusters
1 and 2 (majority EC) is way more aggressive on chances of snow for
the area than GEFS/GEPS Clusters from this shortwave which makes
sense giving EC was showing a deeper wave aloft and slower compared
to the other models. This is seen in the EC meteograms which have
peak chances of snow topping out at 40-50% at the ASOS sites. Latest
NBM keeps this chance ranging from 15-30% over portions of north
central to northeastern SD/western MN Wednesday morning through the
afternoon with the highest chances occurring along the ND/SD border.
Probability of 24 hr snow> 0.5", ending Thursday morning, is 5-10%
GEFS and 20-30% EC. Of note, EC also tries to bring this CO low a
bit northward than GEFS and if this pans out, expect an increase in
pops over the southern CWA.

With northwest flow behind the first wave, another shortwave will
push southeast over the Northern Plains/Canada Wednesday evening
into Thursday with strong northwest flow behind it Thursday night
into Friday on the backside of it (50-60kts). At the surface, its
low will track southeast out of northwestern Canada and over
~Manitoba/Ontario border by 12Z Thursday (model depending) as its
mainly dry arctic cold front is forecasted to sweep across the CWA
during this time with the CWA behind the cold front by Thursday
morning. A strong arctic high will filter in behind it and remains
the dominant weather feature. Within this northwest flow several
embedded shortwaves are possible bringing a 15-20% chance of pops
Saturday, however, confidence remains low to due model variability
this far out.

Cold temps will stick around Tuesday and Wednesday with highs in the
20s to around 30 which is about 5-10 degrees below average. Lows
will range in the single digits to around 11 which is about 3-7
degrees below average. We get that first taste of arctic air for the
end of the week as overall highs are only forecasted from 10-11
degrees to 20s across the CWA and lows down to the lower single
digits to below zero. Highs will be about 10-20 degrees below
average and lows about 10-15 degrees below average! Latest NBM
probability of low temps below zero Friday morning to Monday morning
range from 20-75% with the highest chances over the James River
Valley.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 539 PM CST Sun Nov 24 2024

Terminals KABR,KATY,KPIR,KMBG

MVFR/IFR cigs and vsbys in -SN will remain possible at the
KABR/KATY terminals this evening. There is a short window still
possible for occasional MVFR cigs and -SN at KPIR the next couple
hours early this evening before improvements take hold for good.
North to northwest winds will remain gusty tonight into Monday
before beginning to diminish toward the end of this TAF set. The
low MVFR cigs/stratus will clear out of central South Dakota early
this evening but persist across northeast South Dakota going into
the late evening and early overnight. Those lower cigs will
eventually clear out over KABR/KATY between about 03Z-09Z. Expect
VFR conditions for all the TAF sites during the daytime hours on
Monday.

&&

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

$$

UPDATE...Vipond
SHORT TERM...TMT
LONG TERM...MMM
AVIATION...Vipond