Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 180131 AAB

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
731 PM CST Tue Jan 17 2017

Issued at 720 PM CST Tue Jan 17 2017

The only adjustments to the tonight period forecast center on the
potential for some strong downslope winds in the lee of the
prairie coteau of northeast South Dakota. Feeding all the latest
available guidance and observations (00Z KABR RAOB) through the
local office downslope winds checklist for objectiveness, reveals
output supportive of at least a moderately strong downslop wind
event, where sustained winds are between 30 and 40 mph and gusts
push 50 to 60 mph. There are already strong downslope winds and
blowing snow mention in the forecast for the typical wind-favored
areas. After reviewing all the 12Z output and noting the vertical
wind field and low level waa/thermal inversion already in play at
00Z, opted to hoist a Special Weather Statement (SPS) for the
coteau/downslope region for the overnight hours. There is plenty
of snow on the ground to blow around out in the area of concern.
But, it`s all pretty much more than a week old and may not blow
around all that much, even with wind gusts as high as 55 mph
thought to be possible. Will hold off issuing anything else
unless local law enforcement/emergency management requests it. The
worst of the strong winds looks to set up between 10 PM CST
tonight and 6 AM CST Wednesday. Travelers moving along that
familiar stretch of I-29/U.S. Highway 12 in northern Grant County
and southern Roberts County should be prepared for strong
west-southwestlery winds overnight.

UPDATE Issued at 528 PM CST Tue Jan 17 2017

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


.SHORT TERM...(This Evening through Thursday Night)
Issued at 226 PM CST Tue Jan 17 2017

As the night shift alluded to, despite milder air aloft and weak
westerly 925mb flow, temperatures have struggled to move much today.
Thats the gist of the next 24 hours as well thanks to ample snow
cover. The exceptions will be the Coteau region which I`ll explain
next - and around the periphery of the CWA where there is less snow
cover (south) and the higher terrain (west).

Westerly flow upwards of 30kts and a steep inversion will result in
Coteau downslope winds this evening through mid day Wednesday. These
favorable mixing conditions will allow for the warmer air aloft to
mix to the surface and keep temperatures mild overnight and into
Wednesday. Blowing snow will remain in the forecast for that area.

The only other aspect of the forecast that needs to be addressed is
increasing low level moisture around a weak surface low Wednesday
night into Thursday. Models show some light QPF/drizzle signature
but on closer inspection NAM/GFS BUFKIT profiles only show moisture
through the lowest 2-3kft and thus this will more than likely just
be a layer of stratus and is not thick enough to generate
precipitation with dry conditions aloft. As such, removed pops that
were introduced with the latest blended guidance.

.LONG TERM...(Friday through Tuesday)
Issued at 226 PM CST Tue Jan 17 2017

Main challenge in the extended period will be precipitation chances.
As low pressure strengthens over the central plains on Friday, may
see light precipitation develop over the eastern CWA. Warmer air
aloft may result in some sleet development, but chances look low at
this time. The precipitation will transition to rain/snow through
Sunday morning, before tapering off as high pressure moves in. The
next system looks to track somewhere across the central plains
Monday night into Tuesday. The GFS continues to indicate a more
southerly and slower track than the ECMWF, so for now will stick
with model consensus, keeping just some small pops in for now.

Warm air will be in place through the period, with daytime highs
mainly in the 30s through the period. Overnight lows in the teens
and 20s will be common.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 528 PM CST Tue Jan 17 2017

VFR conditions will prevail across the area through the TAF




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