Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 172328 AAA

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
628 PM CDT Sat Mar 17 2018

Issued at 624 PM CDT Sat Mar 17 2018

See updated aviation discussion below.


.SHORT TERM...(This Evening through Sunday)
Issued at 310 PM CDT Sat Mar 17 2018

Cloud trends are probably the main forecast challenge through
Sunday. Currently, there are a couple of bands across the forecast
area, particularly over central and western South Dakota. These bands
have only shown a slight eastward movement through the day. With
easterly low level flow setting up, suspect there won`t be much
of a change in sky cover, and it may in fact expand further
across the area. We had fog last night, and guidance is suggesting
it again tonight. So, have put patchy/areas fog into the forecast
through Sunday morning. Overnight lows should be held up by the
abundant cloud cover.

Sunday will likely feature a fair amount of cloudiness, which will
probably limit temperatures to some degree.  The day should be
mainly dry, but with some chc rain far west toward evening.

.LONG TERM...(Sunday Night through Saturday)
Issued at 310 PM CDT Sat Mar 17 2018

Main focus of the extended is weather associated with an upper trough
that continues to sit and spin over the intermountain west, ejecting
a wave into the plains Sunday night. Best forcing with this system
is to the south, but overhead we can see in both NAM/GFS BUFKIT
sounds a shallow saturated layer, about 3kft thick (so no pre system
drizzle), with gradual saturation aloft in the dendritic growth
zone. There may be a warm layer as well, but as soundings saturate,
wet bulb processes move the line below 0C. Thus, precipitation type
will be mainly determined by temperatures in the lowest few hundred
feet, which are also hugging the rain/snow threshold. With the weak
lift, there may be enough daytime heating for melting as well
Monday. On the backside of the system we see a loss in the dendritic
growth zone so there may be some drizzle then, but with loss of lift
any ice should be minimal. So we are only looking at an inch or two

The active pattern continues as the longwave pattern shift overhead,
setting back up with ridging over the central CONUS around mid week.
During that transition there are additional weak waves embedded in
the flow, though again nothing looks very impressive.

There are also indications of a late week system within all suites
of deterministic guidance. Something to consider as guidance comes
into better alignment.


.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 624 PM CDT Sat Mar 17 2018

Abundant cloud cover will remain over the area tonight into the
day Sunday. VFR/MVFR cigs will gradually lower to IFR levels
overnight, then lift back to MVFR levels after sunrise Sunday.
Also expecting fog development overnight into the early morning
hours, with vsbys likely falling to MVFR levels.




LONG TERM...Connelly
AVIATION...Parkin is the U.S. government's official web portal to all federal, state and local government web resources and services.