Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 091714
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
Issued by National Weather Service DULUTH MN
1114 AM CST Tue Jan 9 2018

.SHORT TERM...(Today and tonight)
Issued at 420 AM CST Tue Jan 9 2018

Early this morning, a broad area of low clouds/stratus and fog
plagued a large part of the mid Mississippi River Valley,
northeast into the southern Great Lakes. This area of moisture,
plus the added stronger southeasterly flow developing later today
in the boundary layer, should be enough to generate areas of fog,
low clouds across most of Minnesota late tonight. In addition to
the fog, patchy drizzle will form. The current forecast has most
of the patchy drizzle in east central Minnesota, and west central
Wisconsin after midnight. However, I wouldn`t be surprised to see
this area expand to the west and southwest as moisture surges
northward ahead of the developing winter storm.

Due the increasing moisture, fog and some light precipitation
developing, icing is possible. This is highly dependent on surface
temperatures. With the stronger winds developing, and models not
doing well on temperatures, I am leaning more toward drizzle/light
rain, other than freezing precipitation. Only areas in central
Minnesota, and west central Wisconsin where the snowpack is
deeper, temperatures cooler, does the concern of freezing
precipitation become more questionable. Plus, the amount of QPF is
rather low, so icing problems will be concentrated on elevated
surfaces, bridges and overpasses if the precipitation develops.

Models have been too conservative on temperatures the past two
days, and with current readings already 2 to 6 degrees warmer than
models indicate, I have increased temperatures a few degrees from
yesterday. Tonight`s temperatures will likely be nearly steady or
only fall a couple of degrees from Tuesday highs due to the
stronger winds anticipated.

.LONG TERM...(Wednesday through Monday)
Issued at 420 AM CST Tue Jan 9 2018

The long term focus was on the expected winter storm to impact a
large chunk of the region in various degrees of intensity Wednesday
night through Thursday.

Wednesday will begin in the low/mid 30s with perhaps some drizzle
around. Some of this may freeze on untreated surfaces early, but
temperatures will warm into the upper 30s to low 40s by afternoon.
The area will remain in the warm sector into Wednesday evening
before the cold front marches steadily eastward Wednesday night.
Mid level frontogenetic snow band over the Dakotas will push into
western MN during the evening, and likely weaken as it reaches
southwest-central Minnesota. A secondary band will then develop
further east with lower level frontogenesis, somewhere from south
central MN to northwest Wisconsin. Models have been shifting this
area with each run. After extensive collaboration with surrounding
offices and WPC, left the blend largely in place but added a bit
of WPC QPF in to better account for where many ensemble members
paint the heaviest snow. This is placed similarly to the very
steady NAM, generally from the Mankato area northeast through the
metro into northwest Wisconsin. ECMWF and 06Z GFS are a little
further east, but the GEFS fits more with the idea of the 00Z GFS
and the NAM. Looking through each of the 50 ECMWF ensemble
members, almost all of them have a similar look to the narrow
heavy band of snow but each are slightly different with their
placement. Generally, they are hovering across eastern MN and far
western WI, so feel pretty confident in this area seeing the
heaviest snow. 4 to 7 inches are expected, heaviest occurring in
about the width of a county. Needless to say, it`s another
splitting hairs winter storm forecast which have been all too
common in recent years around here. A Winter Storm Watch has been
issued for these areas.

The snow may be preceded by a mix of sleet and freezing rain
depending how much quicker the low level cold air arrives and when
precip begins. Neither will accumulate much, but it could cut
down some on the snow totals on the eastern side of the heavy
swath.

There will likely be a minimum in snow accumulations between the
western MN state line and a line from New Ulm to St. Cloud if it
doesn`t fill in. However, given the uncertainty in the forecast
and collaboration with surrounding offices, hoisted a watch for
these areas as well for the potential for 3 inches and blowing
snow. Several of these counties may fall under an advisory
eventually though, particularly where wind gusts won`t be strong
enough to produce blizzard conditions. This includes the Alexandria,
Little Falls, and St. Cloud areas.

The strongest winds are expected in the MN river valley from west
central to south central MN where gusts of 40 to 45 mph are
possible. Instability/steep lapse rates through the deep low
level DGZ will probably keep snow showers going. If 3 or so
inches do fall, then blizzard conditions will be possible with the
addition of widespread blowing snow. The best chance of this
occurring is where the winds will coincide with the heaviest
accumulations over south central MN.

Following this system, it will get very cold again. Reinforcing
surges of arctic air are expected into at least early next week,
with highs in the single digits and lows in the teens to 20s below
at times. There`s also a weakening system that could bring some
more light snow to Minnesota Friday/Friday night. Accumulations
look light.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1114 AM CST Tue Jan 9 2018

VFR conditions will prevail through the daylight hours then MVFR
ceilings will develop this evening at all sites. As low as MVFR
visibility is possible due to fog/intermittent drizzle (possibly
freezing drizzle at sites that fall below freezing) late tonight
into Wednesday morning. Ceilings may fall as low as IFR towards
daybreak Wednesday morning then recover to MVFR through the day
Wednesday. Winds will become gusty out of the south-southeast to
south at some sites across southern Minnesota tonight, then not as
strong during the day Wednesday.


KMSP...

High confidence in VFR conditions through the daylight hours
(around 03z) then moderate confidence in MVFR ceilings developing
this evening and overnight. A period of IFR ceilings is possible
towards daybreak Wednesday morning but confidence is low. MVFR
ceilings persist through the day Wednesday. Drizzle may result in
as low as MVFR visibility overnight into Wednesday morning.
Freezing drizzle possible but kept it out of the TAF for now as
temperatures should remain above freezing overnight.

/OUTLOOK FOR KMSP/
Wed...MVFR to IFR with DZ/RA to SN late. Winds S 5-10 kts becoming
NW. Accumulating snow likely after 06z THurs, heavy snow possible
by 12z Thurs.

Thurs...IFR with SN/+SN before 21z. Improving to VFR late. Wind
NNW 15G25 kts.

Fri...VFR. Wind NE 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...JLT
LONG TERM...BORGHOFF
AVIATION...JJM



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