Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 190539 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Aberdeen SD
1139 PM CST Wed Jan 18 2017

Issued at 1125 PM CST Wed Jan 18 2017

See below for an aviation forecast discussion for the 06Z TAFs.

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 06Z TAFS through 06Z Thursday Night)
Issued at 1125 PM CST Wed Jan 18 2017

Left KMBG in good VFR through most of the TAF valid period for
now. But, at KPIR/KABR/KATY staying with some IFR visby in fog for
the rest of the night. KABR and KATY are already in fog, but KPIR
is not yet. Still thinking there is the potential for a few hours
of IFR fog at KPIR before sunrise Thursday.

By the end of Thursday, will be starting to see a little bit more
of an advection component to low level moisture increases within
and beneath this pesky/strong low level thermal inversion. So,
guidance is considerably more aggressive bringing in low clouds
and/or fog redevelopment by late Thursday evening, in particular




SHORT TERM...Connelly
LONG TERM...Parkin
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