Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 272018

Area Forecast Discussion
National Weather Service Aberdeen SD
218 PM CST Sun Nov 27 2016

Issued at 216 PM CST Sun Nov 27 2016

Visbies are improving so the dense fog advisory has been
terminated. Showers of rain are lifting northward across the CWA
at this time (still south of US Highway 212. Updates are out.

UPDATE Issued at 1150 AM CST Sun Nov 27 2016

One more update to the forecast as the pesky dense fog just won`t
go away or mix out across far northeast South Dakota and west
central MN. Have extended dense fog advisory to 00Z (6pm CST).
Perhaps once rain begins falling across the area, fog will begin
mixing out. Updates are out.

UPDATE Issued at 1127 AM CST Sun Nov 27 2016

See below for an aviation forecast discussion for the 18Z TAFs.

UPDATE Issued at 911 AM CST Sun Nov 27 2016

First morning update just highlights the extension of the dense
fog advisory across far northeast South Dakota into west central
MN out to 18Z today. Area webcams and surface obs continue to
indicate the fog is quite dense and widespread over that area.
Updates out.

UPDATE Issued at 525 AM CST Sun Nov 27 2016

See updated aviation discussion below.


.SHORT TERM...(Today through Tuesday Afternoon)
Issued at 307 AM CST Sun Nov 27 2016

Two main items of concern for the forecast, the dense fog in the
very near term and then the strong, potentially record breaking
low for KABR, for tonight into early next week.

First for the fog, this fog has been persistent over central MN
and steadily shifted west into far northeast South Dakota this
past evening. Have seen widespread 1/4mi visibility with the fog
and the going dense fog looks to be in good shape for that area.
GOES FLS IFR probs have a good handle on the westward
extent in the current dense fog advisory and are hinting at some
fog farther to the west. That shallow/patchy dense fog has been
seen at times in Brown and farther southeast towards
Clark/Hamlin counties. While webcams are sparse, not seeing too
much for thick fog, so will continue to go with the SPS through
8am for the patchy fog. The main question is how long the fog
will last. high resolution models show this fog sticking around
through much of the morning for the far northeastern CWA before
visibilities gradually lift into the afternoon (similar to
yesterday in central MN). After discussion with
surrounding offices, will hold on to current dense fog end time
and monitor through the morning hours for extension. While temps
remain in the think there is the potential for light
icing and slick spots on roads and will continue that mention in
the statements.

Outside of the fog, expect some high clouds to start the day
before thicker clouds quickly move in during the late morning and
afternoon associated with the low that will move into the area.
This low will rapidly develop and move northeast today as a strong
shortwave and pv anomaly (currently over the four corners region)
moves into the region. Models are continuing to show an upper 970s
low over far northeast SD by 12z Monday, which should produce a
new November SLP record at KABR. Plenty of lift present with the
shortwave and low, so expect rain to quickly move into the
area late this afternoon and into the early evening hours. Behind
the initial surge of precipitation, models are indicating a dry
slot to slide just to the SE of the CWA but most of the CWA will
be experiencing lighter precipitation associated with the surface
and mid level low over the area, thus held on to higher end PoPs.
The biggest uncertainty is the amount and location of
precipitation on the back side of the low associated with the nose
of the TROWAL. The location will be key, as colder air will be
working into the area as that precipitation occurs and changing it
over to snow. GFS/ECMWF are fairly consistent with surface/upper
low track and have similar thermal fields, while the NAM is a
little farther to the west and colder. Will trend towards the
GFS/ECMWF idea for the tonight through Tuesday period. That will
hold off the change over to snow over the far west until late
evening and shortly after midnight towards KMBG. Expect that
transition to continue eastward through the night, reaching the
James River valley around 12z. Will continue Thunder mention with
weak MUCAPE values and marginal 700-500mb lapse rates and
showalter values.

The low will slowly wobble and weaken around the SD/ND/MN border
through Monday night before beginning to slide to the southeast
across MN on Tuesday. With that location and abundant moisture in
place, expect fairly steady light precipitation to be ongoing
through much of the Mon-Tue period. While precip will start
as snow aloft, there may be enough low level warming to mix
the snow with or change it over to rain at times, especially over
the southern and eastern portions of the CWA Monday afternoon. Do
wonder if models are overdoing surface temps a touch and with
wetbulb0 heights only above 700ft from the Coteau and eastward
could see p-type being more snow than the forecast currently
indicates for Monday afternoon. Will need to watch over the next
couple of shifts.

While the precip and snow will be persistent, not expecting too
much of an impact or significant accumulations (generally an inch
or two every 12 hours). In addition, with temperatures rising to
around or just above freezing during the day on Monday/Tuesday,
that should help keep the roads more on the wet side outside any
of the stronger periods of snow. Finally, there will be breezy NW
winds developing Mon afternoon and continuing into Tuesday. Going
consensus looks pretty good with gusts to 30kts towards KMBG. With
warm temps and generally more of a wet snow, don`t expect too much
blowing snow through Tuesday, although there could be some light
drifting snow over the northwest CWA at night when temps cool
slightly. That idea is supported by the Baggaley blowing snow
model which struggles to give probabilities of blowing snow
exceeding 20% on Tuesday when snow is occurring.

.LONG TERM...(Tuesday Evening through Saturday)
Issued at 307 AM CST Sun Nov 27 2016

A large upper level trough will be over much of the country when the
extended period begins, with the main low center spinning over
Minnesota. The amplitude of the trough begins to get dampened by mid
week, with a brief return to ridging Friday and Friday night before
another shortwave approaches Saturday.

At the surface, a strong low pressure system will be centered over
Minnesota Tuesday night, then remains there before drifting off
toward the Great Lakes Wednesday night. Will still see decent
chances of precipitation Tuesday night and Wednesday, with light
snow likely lingering into Thursday night as well. Snow
accumulations Tuesday night into Wednesday may be an additional 1 to
3 inches. The remainder of the period looks dry at this time as high
pressure slides across the region Friday and Saturday.

Daytime highs will be in the upper 20s to mid 30s through the
period, with overnight lows in the upper teens to mid 20s.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 1127 AM CST Sun Nov 27 2016

The far eastern portion of the CWA is still socked in with IFR or
worse cigs and vsbys in fog. These conditions may very well
persist into the late afternoon hours before there is any notable
improvement. The rest of the CWA may be VFR right now, but short
range aviation forecast guidance suggests that by 03Z tonight,
widespread ifr cigs and mvfr/ifr visbies will be underway at all
four terminals as low level moisture streams northward into the
cwa. Rain is also still on schedule to reach terminals within this
CWA mainly between 21Z and 01Z, continuing during the evening and
overnight hours. The rain looks to switch over to snow across the
northwestern CWA late tonight.




LONG TERM...Parkin
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