Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 081212 AAA

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
612 AM CST Thu Dec 8 2016

Issued at 603 AM CST Thu Dec 8 2016

See below for an aviation forecast discussion for the 12Z TAFs.


.SHORT TERM...(Today through Friday night)
Issued at 359 AM CST Thu Dec 8 2016

Light snow appears to be finally winding down over portions of the
eastern CWA, although the Coteau region will likely stay in it for a
longer duration. Winds continue to be breezy and gusty, thus
bringing some areas of blowing snow and lowered visibility. Had
earlier adjusted wx/POP grids to reflect likely/categorical POPs
with beefed up blowing snow mention. Will likely go back in and
adjust for the slowly waning coverage of snow. Looking upstream,
lots of breaks in the cloud cover, but patches of status continue to
float southeast with flurries/light snow within these areas of
stratus. Will try to account for this in the wx/sky grids as well.

Otherwise, today will still feature rather breezy winds and very
cold temperatures. Wind chills will be a big story this morning with
the western CWA seeing readings in the 15 below to 25 below zero
range. Will leave the Wind Chill Advisory as-is for right now,
although actual wind chill readings may not quite reach criteria,
but it`s close enough and the impacts will still be felt.

Arctic high pressure settles over the region tonight, which will set
the stage for some bitterly cold temps. Still a bit concerned about
any lingering cloud cover persisting tonight, plus any mid/high
level clouds moving in late tonight with the weak wave approaching
for Friday. Day shift will have to take another look at cloud cover
trends/potential and if it looks like a mostly clear night, will
likely have to "put all the chips in" and tank temps even lower than
what`s currently forecast. Current forecast lows are a bit on the
conservative side for the time being. Will also have to keep in mind
that Brown county may not fall as far as we think due to the lack of
snow cover.

Friday night temps are rather tricky as well. It`s one of these
scenarios where we will likely see a large drop early in the evening
once the sun sets and skies are still clear with light winds. But as
the night progresses, clouds will be on the increase with the
incoming storm system and easterly winds will be picking up a bit as
well. SuperBlend lows seemed a bit too warm over eastern areas where
it looks like skies will be clear with light winds for a longer
duration of time. Therefore, a collaborative effort was made to
lower MinT grid Friday night towards the colder end of guidance to
at least get a trend started until things become a bit more clear.

.LONG TERM...(Saturday through Wednesday)
Issued at 359 AM CST Thu Dec 8 2016

The overall flow pattern aloft in the out periods remains relatively
unchanged, with zonal or nearly zonal fast flow aloft being
interrupted occasionally when a shortwave riding the strong polar
jet intensifies/undergoes cyclogenesis and creates a somewhat more
amplified wave pattern aloft. Still looks like one such system is
lining up to impact some portion of the cwa mainly on Saturday, with
a couple more shortwaves noted in the 00Z GFS/ECMWF/Canadian worth
justifying small pops mention beyond the Saturday system through
Monday night. Then, for the time being, the extended reverts back to
"confidence too low to mention precip chances at this time". As for
the Saturday system, snowratios are still running anywhere from 16:1
to almost 20:1 when it`s supposed to be precipitating. Guidance
suggests there is still the potential for a range of 0.10-0.30inch
of water equivalent for this upcoming event, which translates to
roughly 1 to 5 inches of snowfall. Breezy east-southeast winds could
be developing on Saturday as well.

As for temperatures, the deterministic output from the 00Z solutions
continues to lend enough confidence to prognosticate below climo
normal temps in the out periods, but said model solutions are not
generating adequate run-to-run continuity and/or agreement with each
other to start straying all that much from Superblend guidance, just
yet. The 00Z GEFS/NAEFS output continues to slowly trend downward
(now more than 2 standard deviations below normal, especially from
Monday night through Wednesday). Now, if the deterministic GFS/ECMWF
could start consistently latching onto this elusive uber-cold air
(temps of -25C or colder) at 925hpa and both could agree on
timing/coverage/duration of this airmass, that time-range of Monday
night through Wednesday could perhaps be identified as a target of
opportunity to nudge forecast temps colder than Superblend guidance.


.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 603 AM CST Thu Dec 8 2016

Still a few pockets of stratus/light snow around the region this
morning. But, by and large, conditions are on the improving side
of things, as winds steadily decrease throughout the day while
high pressure builds into the northern plains. At this time, the
only terminal in MVFR or worse flying conditions is KATY (although
those pesky stratus streamers are still coming off Lake Oahe this
morning and occasionally make their way over the ASOS at KPIR).
Through late this morning, cigs could continue bouncing between
MVFR and VFR at any of the four terminals but the prevailing
cigs/visbies should be VFR for much of the TAF valid period,
especially after 18Z today.


SD...Wind Chill Advisory until noon CST /11 AM MST/ today for



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