Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 051640

Area Forecast Discussion
National Weather Service Duluth MN
1040 AM CST Mon Dec 5 2016

Issued at 1040 AM CST Mon Dec 5 2016

After taking a fresh look at the short-term guidance and in
collaboration with neighboring offices decided to expand the
Winter Weather Advisory across northern Minnesota. Low pressure
deepening over the Red River Valley this evening combined with
strong warm air advection along its associated warm front will
result in a period of moderate to at times heavy snow for parts of
northern Minnesota. While amounts may be on the low end for an
advisory (our criteria is 3-5 inches in 12 hours), the potential
for the heaviest snow to develop over the Duluth metro during the
evening commute was a factor in deciding to expand the advisory.
Shifting winds could result in more rain than snow right along the
lake shore - will take a closer look at this as the rest of the
12z model suite and additional short-range guidance rolls in later
this morning. Went fairly aggressive on the ending time for the
advisories in north-central MN and the Southern St Louis/Carlton
zone due to clear indications of a dry slot developing, which
seems likely given the strength and expected evolution of this
low pressure system. Not much of a change for northwest Wisconsin
- there will be a sharp eastern gradient for the heaviest
snowfall, so did not consider an advisory outside of north-central
and northeast Minnesota.

UPDATE Issued at 614 AM CST Mon Dec 5 2016

Please see the new 12Z Aviation Discussion below.


.SHORT TERM...(Today through Tuesday)
Issued at 450 AM CST Mon Dec 5 2016

At 4 am, skies were generally cloudy across the Northland. There
was some clearing across the far south, and areas of fog
developing as skies cleared. Temperatures ranged from the mid 20s
in the clearing areas, to the upper 20s and lower 30s across the
rest of the area. Some very light patchy freezing drizzle or snow
was also found across the area this morning.

The main focus for today through Tuesday will be the potential
for accumulating snow across the Northland. An upper level
shortwave will eject out of the Rockies this morning, as surface
low pressure develops in the Plains. The low is expected to
strengthen considerably as it lifts rapidly to the north northeast
by tonight, reaching the Red River Valley by late today, and
northwest Ontario by late Tuesday. The low will take on more of a
negative tilt as it pushes across Minnesota, eventually becoming
vertically stacked over Ontario. The first batch of precipitation
should arrive this afternoon over the south, and then spread
northward tonight and Tuesday. Given strength of WAA and FGEN, as
well as onshore flow/upslope conditions, became concerned about
the potential of locally heavy snow across the North Shore, and as
a result, we have issued a winter weather advisory for the
Minnesota Arrowhead. Total snow accumulation should reach 3 to 6
inches in that area, especially along the higher terrain adjacent
to Lake Superior.

A dry slot will then push in from the south tonight, bringing a
decrease in precipitation to southern and southeastern locations.
Snowfall amounts today into Tuesday should range from less than an
inch in the south to 3 to 6 inches in the Arrowhead.

.LONG TERM...(Tuesday night through Sunday)
Issued at 450 AM CST Mon Dec 5 2016

Main challenge in the long term continues to be a slow-moving cutoff
low and related precipitation chances and amounts.

Stacked low pressure will be found over northern Minnesota or
northwest Ontario Tuesday evening and will slowly move northeastward
toward Quebec through the end of the week. Much colder air will pour
into the region thanks to parcel trajectories from northern Canada
into the Upper Midwest. Along with the colder airmass, abundant
moisture will be available for precipitation. Deterministic guidance
has phased back into relative agreement tonight with the handling of
the low track and precipitation placement. Expect light snow to
continue over my northwest zones before tapering off to scattered
snow showers during the day Wednesday. Another 1 to 3 inches of
accumulation are possible overnight in those areas, with lower
totals elsewhere.

The low will shift eastward across northern Ontario on Wednesday
with a period of moist northwest flow expected over northeast
Minnesota and northern Wisconsin. This wind and moisture
configuration is favorable for the development of a gravity wave in
the vicinity of the North Shore as far south as Douglas and Bayfield
Counties. Precipitation placement with these terrain-induced
perturbations is highly dependent on the wind direction, speed, and
moisture depth. Given these caveats, stuck close to a blend of the
higher resolution models for POPs Wednesday afternoon and early
Wednesday evening.

Lake enhanced snowfall should begin in earnest over the northwest
Wisconsin snowbelt areas Wednesday night and will likely continue
into the weekend. Due to extensive cloud cover during the past two
weeks, satellite-derived lake surface temperatures are not
available. The few reports of municipal intake water temperatures
suggest the lake has cooled a bit to between 43 and 46 degrees.
Using those values yields between 300 and 700 J/kg of lake-induced
CAPE during the latter portion of the week. A deep antecedent cloud
layer will be primed for efficient snow production over portions of
Bayfield, Ashland, and Iron Counties Wednesday night through Friday
morning, with light snow showers likely continuing into Saturday
morning. Significant snow accumulation is likely early Thursday
morning into Thursday evening, with periods of heavy snow possible.
Drier air aloft and increasing wind shear are expected to taper the
heavy snow down to snow showers late Thursday night through early
Saturday morning. Several inches of additional accumulation are
likely during that period.

The cutoff low and associated longwave trough is expected to be
located over New England by Friday afternoon. Another weak shortwave
could move through the region Friday night and Saturday which would
squeeze out a few light snow showers over much of the area. The
upper level pattern transitions to a more progressive quasi-zonal
flow behind the departing low Saturday through early next week.
Another storm system may pay a visit to the Northland Saturday night
through Sunday with another few inches of snow possible.

Temperatures will trend colder this week with readings below to much
below normal. Overnight lows may drop to near zero over portions of
north-central and northeast Minnesota Thursday night through
Saturday with wind chills a few degrees below zero.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 614 AM CST Mon Dec 5 2016

MVFR/IFR overcast skies linger across northeast Minnesota and
northwest Wisconsin this morning. Partial clearing had developed
overnight over portions of west-central and central Minnesota,
including BRD. However, the clearing resulted in some fog and low
stratus development. Think the stratus may lift/clear briefly this
morning or early this afternoon before next round of moisture
arrives ahead of approaching low. Light snow or a rain/snow mix
will spread northward this afternoon and early this evening. Best
chance of the mix will be at DLH and HYR, while light snow seems
favored at INL and HIB. The snow may develop north of BRD so left
only VCSH in the forecast there. Confidence with this forecast
package is average through 20Z and below average thereafter.


DLH  33  23  27  16 /  80  90  40  30
INL  32  24  29  17 /  20  80  70  50
BRD  35  24  26  14 /  60  70  30  20
HYR  35  26  27  18 /  50  60  30  20
ASX  38  28  31  20 /  60  70  30  20


MN...Winter Weather Advisory from 6 PM this evening to 6 AM CST
     Tuesday for MNZ010-011-018-019-026.

     Winter Weather Advisory from 6 PM this evening to noon CST
     Tuesday for MNZ012-020-021.

     Winter Weather Advisory from 4 PM this afternoon to 6 AM CST
     Tuesday for MNZ037.



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