Area Forecast Discussion
Issued by NWS Aberdeen, SD

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000
FXUS63 KABR 190349 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
949 PM CST Sun Feb 18 2018

.UPDATE...
Issued at 932 PM CST Sun Feb 18 2018

Jet streak of 130+knots overhead helping to enhance the band of
snow extending from swrn SoDak out into central SoDak at this
time. Moderately strong frontogenesis showing up between 700hpa
and 500hpa is teaming up with mostly moderately strong synoptic
scale lift and should continue to see a banded snow feature over
the region way out into the wee hours of the morning. Expecting to
see the snow band occasionally tighten up and increase to heavy
snow intensity with -EPV* hanging around in/above the best areas
of synoptic scale lift through appx 09Z Monday. The wild-card in
situations like this is always the low level cold dry air
entrainment that eats away at the chance for the snow`s northern
edge to reach the ground before evaporating/sublimating. The 00Z
KABR RAOB showed the low level cold dome was already appx 5kft
deep.

For the evening update, no notable changes made to the snow
forecast over central SoDak, where the focus is for tonight into
the first part of Monday, and where the Winter Storm Warning
resides. Evening update guidance did nudge qpf up a few
hundredths over central SoDak, but the impact on snow accums was
minimal. Where changes were made included lowering qpf/snow
amounts across far north central SoDak over into nern SoDak and wc
MN where this previously mentioned dry air will limit, if not
eliminate, most of the accumulating snow chances tonight into
Monday, mainly along and north of a line from McLaughlin to
Aberdeen to Milbank. South of that line tonight still has a chance
at seeing up to an inch of snow accumulation through mid-day
Monday. No other weather elements of the forecast were adjusted
this evening. Updates are out.

UPDATE Issued at 531 PM CST Sun Feb 18 2018

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

&&

.SHORT TERM...(This Evening through Monday)
Issued at 342 PM CST Sun Feb 18 2018

The low pressure system/cold front has been able to sink southeast
of the forecast area this afternoon, with temperatures slowly
falling throughout the day behind this boundary. The coldest air
will remain over our northwest counties, where 850mb temps fall to
around -18C by daybreak Monday. This area will have a better chance
of falling below 0F, while the rest of the area stays mainly in the
single digits above zero.

The 500mb low deepening over the Pacific Northwest will push a large
trough across the western half of the nation tonight into Monday
morning, with plenty of moisture overspreading the area. Already
seeing snow at MBG and north of PIR this afternoon, with some
flurries at NWS ABR around 20Z. This lines up well with some of the
CAM solutions. Have sped up the onset of snow for this event. Still
feel that the headlines (Winter Storm Warning for much of our
southwest) is in good shape timing and amount wise. Continue to
highlight a long term event, with 2 distinct periods of interest
across the forecast area. For the HWO it ends up being 3 periods of
snow amounts mentioned, due to the different temporal breakdown
needed for that product. The focus for tonight through Monday should
be Stanley and Jones (and surrounding areas) with 3 to 8 inches of
snow possible. The combination of this snow (with ratios around near
18:1) and winds gusting around 25kts have been productive in
reducing visibility to 2-4SM at MBG. This will likely be common
through the night. Expect snow ratios to increase in the cooling air
to closer to 22:1 by the end of the afternoon Monday. The focus for
stronger winds will likely be over the eastern half of the forecast
area, where lighter snow is anticipated. With plenty of cold air
sinking in, temperatures will remain in the single digits to teens
above zero for highs Monday.

.LONG TERM...(Monday Night through Sunday)
Issued at 342 PM CST Sun Feb 18 2018

Light snow will likely be ongoing across the area at the beginning
of the period (Monday evening), with another round of somewhat
heavier snow approaching from the west. The models remain in decent
agreement that a moderate to heavy band or two will set up, but
continue to differ on strength and exact location. The boundary
south of the region will be continuing to drop south, so will lean
toward the southern parts of the CWA likely seeing the highest
amounts of snow. An additional 2 to 5 inches looks possible during
the Monday night/Tuesday morning time frame. Winter Storm Warnings
and/or Winter Weather Advisories will remain in effect through
Monday night into Tuesday morning.

High pressure moves in behind the exiting system on Tuesday, and
will result in dry, but cool, conditions across the area through the
latter part of the week. A system tracking from the Southern Plains
to the eastern Great Lakes may bring some light snow to the
southeastern part of the area Thursday night, then another high
pressure system will bring back dry conditions for the weekend.

Temperatures will be below normal early in the period, with highs in
the single digits and teens Tuesday and Wednesday. Will see near to
slightly above normal temperatures for the remainder of the period,
with highs in the 20s to lower 30s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
Issued at 531 PM CST Sun Feb 18 2018

Weather conditions are going to be less than congenial over the
next 24 to 48 hours. The worst of it is going to impact KPIR
during this 24 hour TAF valid period. Don`t expect VFR to be a
prevailing weather condition at any of the TAF sites (although, in
the first 12 hours of these TAFs, VFR may be "tempo"-rarily
observed at times) between now and the end of the day Monday. A
complex weather scenario involving more than one area of low
pressure will bring some light to occasionally moderate snowfall
to all four terminals between now and mid-day Tuesday. But for
now, the focus will be on tonight and Monday, and the area likely
to be impacted the most by falling/blowing snow and sub-VFR
visbies is KPIR.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 3 PM Monday to 6 AM CST Tuesday for
     SDZ005-009-010.

     Winter Weather Advisory from 6 PM Monday to noon CST Tuesday for
     SDZ006>008-011-018>023.

     Winter Storm Warning until 6 AM CST /5 AM MST/ Tuesday for
     SDZ015>017-033>037-045-048-051.

MN...Winter Weather Advisory from 6 PM Monday to noon CST Tuesday for
     MNZ039-046.

&&

$$

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



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