Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 211754

Area Forecast Discussion
National Weather Service Aberdeen SD
1254 PM CDT Tue Mar 21 2017

Issued at 1243 PM CDT Tue Mar 21 2017

Tracking the end of clouds over our northeastern corner, while
much of the rest of the area is slow to get rid of them. Highs in
the 30s still look good, although they could be a couple degrees
too high if the clouds hold on much longer. Initially added more
temporal resolution to the pops for overnight into Wednesday, but
the latest model solutions may have me cutting them down slightly
from what was originally posted with an earlier update. Will do
more investigating before making additional adjustments.

UPDATE Issued at 647 AM CDT Tue Mar 21 2017

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


.SHORT TERM...(Today through Thursday Afternoon)
Issued at 359 AM CDT Tue Mar 21 2017

This morning/Today: Area radars indicate precipitation becoming more
widespread across western and south central South Dakota this
morning. Area webcam and ASOS observations indicate rain at the time
of forecast issuance, however NAM BUFKIT soundings support the
profiles cooling more or less uniformly. There may be problems with
ice introduction initially as well, but ground temperatures are
above freezing so we shouldn`t have any issue with the air
temperature falling below freezing before the P-type changes to
snow. High pressure nosing into North Dakota/north central South
Dakota will cause profiles to dry through the day as well, which
will limit overall snow accumulation. Cold advection and cloud cover
will severely limit daytime heating.

Wednesday: Mid level warm advection will develop as a large scale
ridge aloft builds across the center of the country. A weak wave
riding the top of the ridge moves overhead between the morning and
afternoon hours. Warm advection precipitation will initially begin
as snow according to NAM BUFKIT profiles - with about 5 to 8
microbars of lift. As profiles warm aloft, lift moves out of the
dendritic growth zone, however low level warm advection doesn`t keep
up. This results in soundings shifting towards freezing drizzle as
the main P-type with less lift but saturation below 7-10ktf, and
surface and ground temperatures at/below freezing. Doubt there will
be much impact as temperatures warm above freezing as the morning
progresses but this will be something to monitor today/tonight.

We also anticipate strong southerly flow Wednesday with a 18-21mb
gradient across the state and pressure falls of 7mb/6hours. 1) this
will be close to advisory level winds and 2) if we do get any icing
this would enhance the difficulty of travel conditions.

Wed night/Thursday: With warm advection, cloud cover and strong
southerly flow, temperatures Wednesday night will probably remain
above freezing for the most part. We begin to see the initial
influence of the main upper low moving into the intermountain west
during the day, with rapidly warming profiles and upper vertical
motion resulting in rain showers.

.LONG TERM...(Thursday Evening through Monday)
Issued at 359 AM CDT Tue Mar 21 2017

When the period opens Thursday night, a deepening low pressure
system lifting out of the Four Corners region is beginning to
produce rain chances across the cwa mainly along and south of a line
from Pierre, SD to Graceville, MN. Becoming cut-off from the main
steering flow aloft and occluding on Friday, it appears that the
upper low of the system slowly works its way east across KS (even
into Friday night) while continuing to generate deformation
zone/TROWAL-forced precipitation chances across the aforementioned
portions of the cwa. Things should begin to dry out on Saturday, and
mainly dry conditions are probable through perhaps the first half of
Sunday, before west-southwesterly flow aloft sets up again. Embedded
shortwave energy within that flow regime is expected to bring
additional chances for precipitation heading into early next week.

Low level thermal advection does not appear to become overwhelmingly
warm or cold in the out periods. There will be the cooling effects
on the backside of the large central CONUS low pressure system early
on in the period. But then, during the second half of the weekend
into early next week, it almost appears as though thermal advection
is weak enough that airmass moderation from daily insolation becomes
the primary driver in how warm it will get Sunday and Monday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1243 PM CDT Tue Mar 21 2017

Some clearing is attempting to move in from the northeast,
allowing ABR to jump back to VFR in another hour or so. There have
been some MVFR ceilings at ABR, MBG and PIR early this afternoon.
Expect slowly improving conditions this afternoon. The next round
of precipitation will bring back MVFR to IFR ceilings overnight
into Wednesday from the southwest. Precip will mainly start off as
snow but could mix with light drizzle/freezing drizzle. Confidence
is not as high as originally expected on the intensity and areal
coverage of precipitation overnight into Wednesday, so stay tuned
for further updates.




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