Area Forecast Discussion
Issued by NWS Twin Cities, MN

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178
FXUS63 KMPX 091755
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1155 AM CST Fri Dec 9 2016

.Updated for 18z taf discussion below...

.SHORT TERM...(Today and tonight)
Issued at 409 AM CST Fri Dec 9 2016

There are two primary concerns here in the short term, cloud cover
trends and the threat for continued flurries/light snow with any
cloud cover we see.

This morning, there is a 1040mb high centered over the Dakotas,
which keeps us within cyclonic flow of a sprawling low over eastern
Canada. Being on the western fringes of this cyclonic flow, we are
seeing larger holes appear in the clouds and there is a sizable one
across the center of the MPX CWA between cloud cover that brought us
our day of light snow yesterday thats moving into Iowa and another
batch of clouds up in northern MN that is slowly dropping south. And
with strong flow aloft, a batch of warm advective clouds moving out
across western Nebraska will be heading for southwest MN by the
afternoon. Forecast soundings show steep lapse rates developing
again with solar insolation, so expect the clearing to cloud up as
the mixed boundary layer develops.

As for these clouds, like we have seen the last couple of days, much
of these cloud layers will reside within the dendritic growth zone,
which means flurries/light snow will continue to be common. Have
high PoPs into the early morning, but do reduce them as we go
through the morning, though if what we are seeing across northern MN
this morning continues, we may need to increase PoPs considerably
across central MN as the batch of clouds to the north sags south.
Again, this would amount to a trace of liquid, but likely a couple
tenths of an inch of fluffy snow.

As for the wave coming across Nebraska, all of the guidance shows a
burst of deeper moisture and warm advection in the h85-h7 layer
working across the SD/Neb border and into southern MN. Given our
cold environment, we will have a deep DGZ once again. Moisture is
limited, but looping the satellite fog product this morning does
show moisture surging north across western KS, so this wave could
certainly produce more snow than what both hi-res and deterministic
models show. After coordination with FSD, we brought some
chance/slight chance pops into SW/SC MN. Once again, this would be a
little/no QPF snow that amounts to a couple tenths of accumulation.

For highs today, continued weak CAA will once again limit diurnal
temp rises to about 5 degrees from morning lows and we should highs
today a good 10 to 15 degrees below normal, though at least we will
get a break from breezy conditions we have seen all week. Lows
tonight will be driven by the amount of clearing we see. Several of
the models are showing clear skies developing over west central MN.
With a 1040mb high likely to centered over the Red River Valley, we
could really see temperatures tank out toward Alexandria. Stayed
close to a blend of the deterministic models for lows tonight, but
we could certainly see some double digit below zero lows out in
western/central MN if clouds clear out quick enough.

.LONG TERM...(Saturday through Thursday)
Issued at 409 AM CST Fri Dec 9 2016

Confidence has increased significantly overnight on the
likelihood of a long duration snow event this weekend. The
divergence of the various models runs over the past few
days/nights seems to have sorted itself out. What appeared to be
two weather systems moving through, one Saturday into Saturday
night and the other late Sunday into Monday, now appears as one
continuous event.

The thinking now is that a short wave will exit the northern
Rockies on Saturday and then deepen over the central and northern
Plains on Sunday. An area of surface low pressure will develop
over eastern Colorado on Saturday, move into the central Plains on
Sunday and reach the lower Great Lakes on Monday.

Snow will spread into western central and southwest MN by midday
Saturday and then reach into eastern MN and western WI during the
afternoon and evening. The snow then continues Saturday night and
Sunday as the surface low passes south of us. The snow would then
diminish from west to east Sunday night. FB pops were way too low
with likely to categorical pops used.

The best forcing and deep layer moisture pass across southern
MN/northern IA and the adjoining areas of WI during the
aforementioned periods. This is where 4 to 6 inches of snow is
likely to accumulate over two days. There could be some 8 inch
amounts around Albert Lea where a good cross-hair signature is
noted with the omega and dendritic growth zone. To the north, 3 to
4 inches are likely. The consensus from the surrounding offices
was to hold off on any watches/warnings/advisories to allow more
fine tuning of the forecast.

The next concern after the snow is an Arctic cold front that
remains on track to move through Monday night. This will usher in
the coldest air of the season for the mid to late week period. We
did raise winds Monday night rather significantly over the FB
winds. MOS guidance was primarily used. High/low temperatures
remain a grave concern behind the front. CIPS analog guidance
indicates December 17 1983 as the number one analog. This was a
brutally cold period that stretched through Christmas. One
difference with the 1983 analog is that deep snow covered the
region. A few downward tweaks were made to the temperature grids
for the mid to late week period as the FB grids are warmer by 5
to 10 degrees over most guidance. More work will be needed to
reach a consensus from surrounding offices as time progresses as a
considerable amount of time was spent overnight with the snow/pop
grids for this weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1155 AM CST Fri Dec 9 2016

Lower end MVFR cigs and some -shsn remains across much of the taf
area. Lower level moisture is trapped under the subsidence
inversion and will likely remain much of the first half of the
period...especially to the east. Various guidance has the clouds
moving slowly east this afternoon and should clear out of KAXN-
KRWF before more clouds move into the southwest by this evening.
Some weak lift moves across the far south into tonight and could
generate mainly a few flurries. KRWF may be affected by this but
kept that threat south for now. The next snow threat moves into
the southwest Saturday morning....possibly affecting KRWF by 18z.

KMSP...MVFR cigs remain over the east metro and they appear to be
on the edge of this through the afternoon. Will try and break it
out by late afternoon...with more clouds...mainly VFR...tonight
into Saturday morning. We could see some light snow or flurries
work into the area after 22z Sat. W-NW winds are less than 10kts
through period...and becoming light/vrbl overnight as the ridge
moves slowly east.

/OUTLOOK FOR KMSP/
Sat nite...MVFR/IFR in SN. SE wind 5-10 kts.
Sun...IFR/MVFR in SN. NE wind 5-10 kts.
Mon...MVFR/VFR with -sn possible. W wind 5-10 kts. Bcmg NW 15G25
overnight.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Weather Advisory from 9 AM Saturday to 3 PM CST Sunday
     for MNZ073>075-082-083-091-092.

     Winter Weather Advisory from noon Saturday to 6 PM CST Sunday
     for MNZ076>078-084-085-093.

&&

$$

SHORT TERM...MPG
LONG TERM...RAH
AVIATION...DWE



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