Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 241133 AAA

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
533 AM CST Sat Feb 24 2018

Issued at 528 AM CST Sat Feb 24 2018

See updated aviation discussion below.


.SHORT TERM...(Today and Tonight)
Issued at 303 AM CST Sat Feb 24 2018

Fog continues across the James Valley, Coteau, and into western
Minnesota. This will likely remain in place until snow starts to
fall in the area later today.

The main question is how much snow will the area receive today?
While the upper trough is positively tilted currently, it becomes
more negatively tilted as it heads into the Dakotas/Minnesota
later today. This is the impetus for rapid mid level frontogenesis
and thus generation of snow. GEFS and SREF are both on the order
of .2 to .3 inches QPF for the Watertown area, .1 to .2 for
Aberdeen, and around .1 for Pierre area, so that kind of gives us
a range of values assuming a 15:1 to 20:1 ratio of 1 to 5 inches
across the CWA. The deterministic NAM looks like the high end of
guidance while the GFS deterministic is a bit more modest. Omega
values as the trough transitions increases to 10 to 20 microbars
between 15Z and 21Z with the GFS being a tad faster which is also
the reason for the lower QPF. Again, this is mainly at the
600-500mb levels with less lift in the low levels, but it still
appears that this will occur over a deep dendritic growth zone,
which may push up the snow ratios some. CAMS suggest there also
may be more convective/banded type elements, so there will
probably be a tighter gradient to the western edge of the
snowfall, and probably more variation in totals which sets it
apart from the last 2 events which were much more uniform.

The rapidly deepening surface low is placed well to the east and
will generally have limited effect on the pressure gradient. With
only around a 6-8mb gradient from southwest to northeast, and a lack
of strong thermal advection on the backside, winds are only going to
average around 10 to 20 MPH range. While that may be enough to
cause some minor blowing and drifting of the very light snow in
place, as well as what is expected to fall, its probably not all
that significant to this event.

Overall, only made some minor adjustments in snow totals, again
on the 2 to 5 inch range for counties in the Advisory. Did adjust
timing on the advisory however to better match short term
CAM/ensemble guidance.

.LONG TERM...(Sunday through Friday)
Issued at 303 AM CST Sat Feb 24 2018

The extended period starts off with surface high pressure to the
south of the region, and low pressure to the northwest. The pattern
will be dominant until Tuesday, when high pressure slides across the
area. Around mid week, a low pressure system will slide somewhere
across the central part of the country, but the models are currently
in terrible agreement with where that will be. The ECMWF takes it
across the Southern Plains, the GFS across northern
Oklahoma/southern Kansas to the central Great Lakes, and the
Canadian across Kansas to Iowa/southern Minnesota/southern
Wisconsin. The Canadian is the only solution at this time to have
precipitation reach the Aberdeen CWA, but the GFS is close.
Therefore, will stick with small pops for the Wednesday afternoon
through Thursday afternoon time frame for the eastern half of the
CWA. High pressure brings a return to dry conditions on Friday.

Temperatures will be fairly mild, with highs mainly in the upper 20s
to upper 30s, and overnight lows in the teens.


.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
Issued at 528 AM CST Sat Feb 24 2018

Patchy fog will continue to be possible for a few hours early this
morning across mainly the far eastern CWA. An area of snow will
work its way up from the southwest today, with IFR/MVFR cigs and
MVFR vsbys expected with the snow. The snow will come to an end
during the early evening hours, with VFR conditions then
prevailing overnight.


SD...Winter Weather Advisory from 9 AM this morning to 9 PM CST this
     evening for SDZ006>008-011-017>023.

     Dense Fog Advisory until 8 AM CST this morning for SDZ006>008-

     Winter Weather Advisory until 6 PM CST this evening for SDZ036-

MN...Winter Weather Advisory from 9 AM this morning to 9 PM CST this
     evening for MNZ039-046.

     Dense Fog Advisory until 8 AM CST this morning for MNZ039-046.



SHORT TERM...Connelly
LONG TERM...Parkin
AVIATION...Parkin is the U.S. government's official web portal to all federal, state and local government web resources and services.