Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 270548 AAD

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1148 PM CST Sat Nov 26 2016

Issued at 1137 PM CST Sat Nov 26 2016

See the updated aviation discussion below.

UPDATE Issued at 816 PM CST Sat Nov 26 2016

Fog continues to advect west. Now added Roberts and Grant
counties into the dense fog advisory. For now most of the I-29
webcams are clear, with the exception of Victor which is just
beginning to show reduced visibility. Adjusted weather grids
accordingly. No other changes are planned to the forecast this
evening unless additional fog headlines are needed.

UPDATE Issued at 633 PM CST Sat Nov 26 2016

Issued a dense fog advisory for Big Stone and Traverse counties as
fog continues to advect west this evening. The Wheaton
observation site already dropped to 1/4 mile visibility and do not
expect any improvement through the night. Tough to see on current
satellite imagery due to high clouds also in the area, but will
continue to monitor through the evening in case additional
counties need to be added.


.SHORT TERM...(This Evening through Sunday)
Issued at 328 PM CST Sat Nov 26 2016

We will see the breakdown of the 500mb ridge overnight into early
Sunday as the large Pacific Coast trough moves east and stretches
from Alberta down through eastern WY and the 4-corners region by
late Sunday.

The weak pressure gradient overhead, and very light winds will be on
the way out as low pressure becomes better organized by daybreak
Sunday. In the meantime, fog over much of central MN will be
nearing our eastern counties, and may remain in place through the
overnight hours. Expect the low to be set up from MT through eastern
CO at 12Z Sunday and shift over the southern SD border by the end of
the day. Expect 6 hour pressure falls of 4-6mb Sunday afternoon.
Precipitation will edge northward, and mainly impact our central and
eastern counties shortly after 18Z as southerly low level winds
increase. 850mb winds get up to 30-35kts Sunday afternoon. Did not
put a lot of weight into the 12Z NAM qpf, wrapping more into our
western counties. Kept the higher precip over our south and east for
now. Did keep the potential for thunder over the southeastern cwa
as MUCAPE values peak in that region.

.LONG TERM...(Sunday night through Saturday)
Issued at 328 PM CST Sat Nov 26 2016

Not a lot of change now in the deterministic solutions regarding
this early week anomalously deep surface low/large upper system.
GFS/ECMWF/Canadian 12Z runs have all converged on an upper low track
through South Dakota into southeast North Dakota on Monday where it
stops and spins for appx 24 hours before shifting south and east out
of the region Tuesday/Tuesday night.

700-500hpa layer rh disappears for a time across the eastern
forecast zones after 06Z Monday, so lowered ForecastBuilder qpf
amounts some across the eastern zones Monday morning. There`s still
some smallish CAPE showing up in the BUFKIT output at
KABR/KATY/KAQP, so continued with the thunder mention across the
southeastern zones Sunday night. Highest pops continue to be focused
across the western half of the CWA, where either snow or a rain/snow
mix is expected to persist for much of the Monday through Tuesday
forecast period.

StormTotalprecipitation continues to be appx 0.25 to 0.75inches less
than national guidance qpf, but hopefully as this event continues to
draw closer, ForecastBuilder and the addition of CAM output can fine
tune these amounts. Likewise, given how warm it is in the boundary
layer, despite low level caa ramping up late Sunday night into
Monday morning, and how low the snow-ratios are on Monday (less than
10:1), StormTotalSnow remains less than 6 inches across portions of
north central/northeast South Dakota with the highest amounts
currently nestled between the MO River and the James River. Still
looks windy across central South Dakota Monday through Tuesday where
falling snow is expected to be occurring.

After one final vort-max rotates all the way around the upper low
and sweeps south-southeastward through the Red River valley on
Wednesday, precipitation chances pretty much dry up for the rest of
the week as surface high pressure sits down over the region. There
may be another upper wave starting to enter the northern plains
region from the northwest by Saturday, but for now will leave
Saturday dry.

Like yesterday, 925hpa temperatures do not fluctuate wildly during
the period, but the coldest air appears to be set up over the CWA by
Wednesday evening and remains over the region through Saturday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 1137 PM CST Sat Nov 26 2016

Dense LIFR fog has spread over much of Minnesota and far
northeast South Dakota and continues to very slowly move west.
While a more shallow IFR fog extends from KATY to KABR. Expect IFR
visibilities to continue through the night at KABR and
KATY...perhaps dropping to LIFR at times. Conditions should
gradually improve after 15Z Sunday. There will be a break where
VFR conditions return Sunday afternoon. However, a low pressure
system will move into the region later in the day Sunday. This
system will initially bring rain to the region, with lowering
ceilings and reduced visibility likely late in the TAF period.


SD...Dense Fog Advisory until 9 AM CST Sunday for SDZ008-021.

MN...Dense Fog Advisory until 9 AM CST Sunday for MNZ039-046.



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