Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 181736

Area Forecast Discussion
National Weather Service Aberdeen SD
1136 AM CST Sun Feb 18 2018

Issued at 1125 AM CST Sun Feb 18 2018

Did increase snow amounts slightly for tonight into Monday over
our western counties. Upgraded the Winter Storm Watch to a Winter
Storm Warning, and included an additional line of counties based
not only on the snow expected tonight through Monday, but the
additional batch of snow sliding into those counties Monday night.
There will be a short lull in the moderate snow Monday morning,
but still expecting around an inch during that 6 hour period with
wind gusts around 20kts. Since most of the snow is expected to be
out of Dewey County earlier than the rest, shortened the end time
to 06Z Tuesday. Will be looking at the need for potential Winter
Weather Advisories for counties east of this area, for the light
to moderate snow Monday night into early Tuesday morning.


.SHORT TERM...(Today through Monday Afternoon)
Issued at 332 AM CST Sun Feb 18 2018

Warm air advection is currently ongoing over this CWA ahead of an
area of low pressure over northeast Wyoming. With the WAA, light
snow has developed this morning, mainly for locations along the
ND/SD border. Snowfall amounts under a half inch is expected. The
surface low pressure should be located over this CWA during the mid
morning hours with warm temps in our east, while the our west will
see CAA developing. Models continue to suggest the pcpn associated
with this low pressure remaining over North Dakota with little
expected in this CWA. By 18Z, CAA will overtake the CWA with gusty
northerly winds expected.

As one surface low pressure departs the region today, another one
begin impacting western South Dakota late this afternoon. This
system, along with upper level jet support will spread accumulating
into central South Dakota, Pierre area, mainly after 0Z Monday. Snow
should gradually progress northeast through the night with most of
the CWA seeing at least some accumulating by 12Z Monday. The
location of the heaviest snowfall STILL remains unclear at this
time. Consensus suggests the heaviest snowfall of 2 to 4 inches
could occur from Pierre, to Redfield, to Ortonville MN. Additional
light snow will be possible on Monday, but overall amounts should be
low. Several CAMS are suggesting a break on Monday between this
storm system and the second one on Monday night. 24-hour storm total
snowfall yields 3 to 6 inches in central South Dakota, and 1 to 3
elsewhere in our CWA. With a low forecaster confidence in seeing
winter storm criteria snow, will maintain the current watch.

.LONG TERM...(Monday Evening through Saturday)
Issued at 332 AM CST Sun Feb 18 2018

During most of the long term, the models maintain a western conus
trof, with a predominate west to southwest flow across the forecast
area. The main activity during the period will be Monday night into
Tuesday. All models now show a deformation zone forming across the
CWA said time period. Of course individual snow bands are a bit
different among the models, with the GFS now holding onto pcpn the
longest on Tuesday, which is contrary to past runs. Given cold
airmass that will be in place, don`t have much of an issue with
progged QPF amounts of up to a quarter inch. Snow ratios are pretty
high, pushing 20:1 or greater, so 3 to 5 inches of snow appears
appropriate Monday night and Tuesday before the accumulating snows
end. Isolated higher amounts are possible with any heavier bands
that may form.  Temperatures will start the period well below
normal, but then should trend toward normal by week`s end.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 1125 AM CST Sun Feb 18 2018

MBG has been stuck under a 015-020 deck since 1537Z, with no signs
of VFR ceilings and vis at all getting out of it through the
period. These mid clouds will sink across the rest of the forecast
area today, within the next couple of hours at PIR and ABR. Expect
much of the impact snow wise to slide into PIR, with snow starting
this evening and continuing through at least the morning hours


SD...Winter Storm Warning from 6 PM CST /5 PM MST/ this evening to 6
     AM CST /5 AM MST/ Tuesday for SDZ016-017-033>037-045-048-

     Winter Storm Warning from 5 PM this afternoon to 11 PM MST
     Monday for SDZ015.



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