Area Forecast Discussion
Issued by NWS Aberdeen, SD

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000
FXUS63 KABR 190411 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1011 PM CST Wed Jan 18 2017

.UPDATE...
Issued at 1009 PM CST Wed Jan 18 2017

Made some adjustments to add fog mention in across mainly the
eastern half of forecast zones, especially areas that reached a
high temperature above freezing earlier. Plenty of night-time
hours for light winds and clear skies to produce areas of
radiation fog.

UPDATE Issued at 532 PM CST Wed Jan 18 2017

See below for an aviation forecast discussion for the 00Z TAFs.

&&

.SHORT TERM...(This Evening through Friday Night)
Issued at 314 PM CST Wed Jan 18 2017

Initially in this forecast period we are dealing with mild air
aloft, with 850mb temperatures +10 to +12C which represents the peak
warmth of the inversion. This airmass will keep temperatures
relatively/seasonally mild overnight - and with
sublimation/evaporation we could see fog but am not real confident
as guidance winds are 5kt or greater.

The mild air aloft will translate into another above average
temperature day Thursday, though winds will be light and mixing
limited so our deep snow cover will again have a deleterious effect
on highs.

A plume of moisture originating to the south will lift
into the CWA late Thursday. Not certain of this source region as
the connection to the gulf ends up east of the CWA. BUFKIT
soundings also continue to show saturation will be shallow - at
just 3 to 4kft AGL, which is usually not thick enough to generate
drizzle. However both the GFS/NAM are consistent in light QPF
production late Thursday through early Saturday. Thinking is most
impacted area will be eastern slopes of the Coteau with an upslope
component - and western Minnesota where the stratus layer is
deepest. The James valley looks to experience a downslope
component as well, and will probably be dry with just stratus. Ice
accumulation should be minimal regardless due to how shallow the
saturated layer is. Advection fog is also possible as
temperatures/dewpoints increase into the 30s.

A shortwave lifting northwards will begin to saturate the profile
early Saturday. Lift provided by the shortwave to generate ice will
allow for a transition to a wintry mix - probably dominated by light
snow - with peak inversion temperatures between +1 and +2C close to
the surface. Peak omega values are only between 5 and 10 microbars
so snowfall will be light with an inch or less accumulation.

The Missouri valley will probably be dry late Thursday through early
Saturday during all this, with cooler temperatures as the core of
warmest air moves to the east, and the dominating influence on the
temperature forecast is the deeper snowpack.

.LONG TERM...(Saturday through Wednesday)
Issued at 314 PM CST Wed Jan 18 2017

The extended period starts off with a weak low pressure system over
the northern plains, with ongoing precipitation likely across
portions of the CWA. Precipitation type will be tricky as
temperatures wobble on either side of freezing Saturday into
Saturday night. Will see a brief respite in precipitation Sunday
afternoon into the day Monday, then significant differences begin to
show up in the models. The Monday night/Tuesday storm system from
previous runs is now non-existent in the ECMWF, and is stronger and
further north in the GFS. The GFS solution would bring a prolonged
period of snow to the CWA Monday night into the day Wednesday, while
the ECMWF solution keeps the region dry. For now, will not bite on
the completely dry solution and keep a slight chance to chance
mention of precipitation.

The trend of above normal temperatures will continue into the early
part of the extended period, with highs in the 30s Saturday and
Sunday. Slightly cooler air then begins to work its way in from the
northwest, with temperatures trending downward each day to highs in
the mid 20s northwest to around 30 east by Wednesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 532 PM CST Wed Jan 18 2017

Going to break from what`s been being forecast in the TAFs over
the past couple of days. With the temperature reaching to above
freezing today at KPIR, KABR and KATY (promoting some snow melt),
fully expecting that tonight`s super-strong low level thermal
inversion will have some surface/near surface moisture trapped
within it to make fog with. The surface pressure pattern is also
shifting around to the point that light southerly winds will be
persisting at all four terminals (another variable that favors fog
around here) amid some weak pressure falls over the next 24
hours. Left KMBG in good VFR through the TAF valid period for now.
But, at KPIR/KABR/KATY did introduce some IFR visby in fog which
may or may not deepen enough to be reported as a very low IFR
ceiling. It`s possible that the winds at higher elevation KATY may
stay strong enough to support more of an IFR stratus layer
overnight, versus fog. Based off the already very impressive low
level thermal inversion showing up on tonight`s 00Z KABR RAOB, the
UPS fog technique and latest available short range guidance and
RAP model soundings fed through BUFKIT, thinking the addition of
some sub-VFR conditions overnight tonight is warranted.

&&

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

$$

UPDATE...Dorn
SHORT TERM...Connelly
LONG TERM...Parkin
AVIATION...Dorn


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