Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 221656 AAB

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1056 AM CST Wed Feb 22 2017

Issued at 1034 AM CST Wed Feb 22 2017

Continue to watch an area of showers with isolated thunder moving
east along the ND/SD border. At times, this cluster is actually
producing pea sized hail. Have made a few adjustments to POPs
based on current radar trends. Otherwise, expecting partly to
mostly cloudy skies today, with cooler temperatures over northern
areas. Based on low level cold air advection patterns today over
the northern tier of counties, have dropped highs there just a
touch. Still seeing some fog across the extreme northeast CWA and
had already inserted that into the forecast earlier this morning.
Shortwave energy moving east across the Dakotas today and may see
some of this wrap-around activity move into the northern counties
by this afternoon. Latest model data coming in suggests the storm
system for tomorrow and Friday may be south of the watch area and
may need to make some adjustments to the current watch counties.


.SHORT TERM...(Today through Friday Afternoon)
Issued at 421 AM CST Wed Feb 22 2017

Southwest flow aloft and some minor weak waves are helping to
generate high based showers this am. CAMs continue this trend for
most of the day, although exact tracks seem to vary across the
forecast area. Added mention of thunder with the steep mid level
lapse rates evident in NAM BUFKIT soundings.

We also can see a backdoor front has now moved through the northern
half of the CWA. Low level cooling is expected through the day. Add
in the cloud cover and thus anticipate temperatures will probably
stall at some point before falling this afternoon. Upstream
observations also indicate some stratus/fog and light drizzle, which
may also move south into the CWA later today.

Main focus will be the shortwave ejecting into the Central Plains
Thursday, lingering into Friday. NAM/GFS BUFKIT soundings suggest
that there will be enough cold air within the profile to support a
predominantly snow P-Type, which is backed up by GEFS ensemble P-
Types. BUFKIT profiles also suggest a deep dendritic growth zone
with omega values centered therein, topping out between 10 and 20
microbars. Q vectors point to an interaction between the
departing right entrance region and an approaching left exit
region phasing just to our south, which explains the rapidly
deepening low, down to 989mb over northwest Iowa in the GFS, and
high omega values.

With an ideal set up for heavy snow in SD/NE, the main question is
how far north this will extend. The GFS is the preferred model at
this point, as it has shown a slight shift to the north. The
ECMWF/Canadian have also been rather consistent with the more
southward track, and fail to bring much precipitation into even the
southern CWA. The NAM is an extreme outlier with its preposterous
QPF/Snow amounts thanks to 40 microbars of lift. SREF supports
numbers closer to the GFS, with a 30-60% chance of exceeding 8
inches across southern CWA counties.

GFS 1/2km winds increase 40-50kts out of the northeast, with NAM
BUFKIT mixed winds in the 20-30kt sustained with 40kt gusts -
although again am using caution as the NAM has much stronger winds
about this system. Regardless, expect strong winds in combination
with the snow to cause significant visibility issues. Due to the
combination of SREF probabilities/GFS snow totals, and impact from
blowing snow, have issued a winter storm watch for central and
northeast counties.

.LONG TERM...(Friday Evening through Tuesday)
Issued at 421 AM CST Wed Feb 22 2017

By the start of the weekend, winds and perhaps some blowing snow
across the east will be all that`s left of the storm system slated
to impact the region at the end of the week. As troughing or more
zonal flow and resultant lower upper level heights dominate the
extended, temperatures will return to more typical readings for late
February. Highs in the upper 20s to 30s are expected through the
middle of next week.

While some isolated areas of snow showers will be possible over the
weekend as shortwaves move through the upper flow, the next best
chance of accumulating snow will be Monday night through Tuesday
night. A surface low will traverse the central plains and an upper
low will dip into the Dakotas providing some additional energy. Any
snow accumulations appear to be light at this time, around 2 inches
or less.


.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
Issued at 532 AM CST Wed Feb 22 2017

Isolated showers and thunderstorms are moving across northern SD
this morning. Lightning may be possible near KMBG and KABR with
these showers. Added in a mention of VCTS for KMBG, but still too
uncertain for KABR at this time. MVFR/IFR stratus will begin to
impact the region this afternoon and evening ahead of an
approaching winter storm system.


SD...Winter Storm Watch from Thursday afternoon through Friday
     morning for SDZ033-035>037-045-048-051.

     Winter Storm Watch from Thursday evening through Friday
     afternoon for SDZ008-018>023.

MN...Winter Storm Watch from Thursday evening through Friday
     afternoon for MNZ046.



SHORT TERM...Connelly
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