Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 032102
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
302 PM CST Sat Dec 3 2016

.SHORT TERM...(This evening through Sunday)
Issued at 302 PM CST Sat Dec 3 2016

The focus remains on the next round of snow, for tonight through
Sunday. The snowfall forecast was generally increased a bit, and
enough so near the North Shore along the higher terrain of Cook
County, to warrant a winter weather advisory.

Snow will spread into the Northland tonight into Sunday because of
the deep saturation that will come from the combination of humid
southerly flow and synoptic lift from a couple troughs of low
pressure which will move into the region. An upper-level trough,
which was over the central Dakotas as of this discussion, will
lift into eastern North Dakota and northwest Minnesota this
evening, and its synoptic lift will begin to saturate the
atmosphere, developing/spreading snow across northwest and north-
central Minnesota late this evening and around midnight.
Then...the main, deep trough will cause more widespread falling
heights and synoptic lift across the region later tonight and
Sunday when it moves through the Dakotas tonight and into
Minnesota/Wisconsin Sunday. The snow will gradually shift east
through the Northland Sunday afternoon, and will likely linger
over the Arrowhead and parts of northern Wisconsin into Sunday
evening. There could be periods of rain/snow mix, or melting snow,
when some areas of the Northland reach temperatures in the lower
30s Sunday afternoon, but much of the rest of the area should
maintain snow with the temperatures near freezing. The 5 to 10
mph winds should not dramatically affect the visibility with the
falling snow, but stronger flow over Lake Superior could lead to
areas of more significant visibility reduction along the North
Shore, such as along Highway 61.

Much of the Northland can expect about 1" to 2" of snowfall.
Snowfall between 2" to 3" is likely for the Price County area of
northwest Wisconsin and for much of the Minnesota North Shore,
including the higher terrain of Duluth.

The greatest amounts of snowfall are expected for the higher
terrain along the far North Shore of Cook County, where 2" to 4"
is now forecast, including areas near and inland from Lutsen,
Grand Marais, and Grand Portage. Increased the snowfall forecast
about an 1" or so from the previous forecast. The GFS20 and NAM12
time/height profiles for the north shore, such as Devils Lake,
suggest considerable upward vertical motion and saturation around
the secondary favorable dendritic growth zone layer around -2 to
-5 degrees Celsius Sunday afternoon and early evening. While this
dendritic growth zone layer is not as significant as the dendritic
growth zone layer around -15 degrees Celsius, the model agreement
between the GFS and NAM are increasing our confidence in a period
of larger snow flakes falling along the far North Shore, resulting
in quicker accumulation of snowfall. Also, considering the
moisture lake enhancement from the strong southerly flow over Lake
Superior, the Lake will help to replenish moisture as it is snowed
upon the North Shore. Confident in at least the 2" to 4" to issue
a winter weather advisory, and may need to increase with
subsequent updates when more high resolution model guidance comes
into play.

.LONG TERM...(Sunday night through Saturday)
Issued at 302 PM CST Sat Dec 3 2016

The remnants of a shortwave trough that is forecast to bring the
Northland snow during the day Sunday will eventually move out
Sunday night and Monday morning. A low-amplitude mid-level ridge
with associated subsidence will keep conditions quiet and dry
Monday morning before another area of low pressure makes its way
into the region. The center of the low pressure looks to stay to
the west over North Dakota and into southern Manitoba and
southwestern Ontario, Canada. Models are showing good agreement in
bringing a good push of 850-700 mb warm air advection, with some
strong 850 mb southerly winds. While temperatures will warm to
above freezing in most places, chances of a rain/snow mix will
return with this set- up. This shouldn`t last long though as the
cold air on the windward side of the low takes over the warm air.

Winds will veer from the southeast to the southwest during the
day Tuesday as the cold air ushers in. Sfc pressure gradient looks
to tighten as well, so winds could get gusty, with gusts up to 25
knots possible. There is still some uncertainty regarding
precipitation coverage as the synoptic models are differing on
Tuesday. The 03.12z ECMWF keeps the Northland drier than the
corresponding GFS due to the GFS keeping the low pressure center
closer to the International Border than the ECMWF. The
Canadian/SREF models don`t lean in either direction at this point,
so the model solutions will need to be watched as we get closer to
this. A shift southeast in the low track would result in more
likely snow, as well as some blowing snow with the gusty winds.

The other story will be the strong cold air advection on the
backside of this low. Models have actually trended colder than
yesterday`s runs, with GFS/ECMWF 925 mb temps between -15 and -20
degrees C in the Thursday and Friday time period. This is expected
to result in low temperatures into the single digits in Minnesota,
with lower teens in northwest Wisconsin, Friday morning and
Saturday morning. During this period, lake enhanced snowfall is
also possible in the Lake Superior snowbelt. Thursday through
Friday night looks to be the primary time for this to occur as 850
mb temps drop to as low as -19 degrees C and plenty of isentropic
lift develops as the 1000-850 mb winds turn southeast, with values
up to -10 ubar/s. Bumped up PoPs from the consensus blends to
account for this.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1143 AM CST Sat Dec 3 2016

Mainly MVFR cigs, with some isolated pockets of IFR cigs, have
persisted over the Northland this morning, with ceiling heights
generally between 1-2.5 kft. Not expecting this to change through
the rest of the day as we are pretty well socked under this
stratus deck. There is a more BKN cloud deck just to the southwest
of BRD TAF site, moving northeast, so tried to capture that for
later this afternoon.

The next big concern will be of some snow possible later tonight
and into Sunday morning. This is expected to lead to reductions in
vsbys down to 2-3 SM. The highest likelihood of reduced vsbys will
be along our southern tier of counties, including BRD and HYR.
These conditions may also creep further north into the HIB and DLH
areas.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  25  34  26  35 /  60  60  20  30
INL  22  34  24  33 /  40  50  20  30
BRD  28  34  25  35 /  50  40  10  40
HYR  25  34  26  37 /  50  60  20  20
ASX  26  36  29  38 /  20  60  20  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Weather Advisory from 9 AM to 9 PM CST Sunday for MNZ021.

LS...None.
&&

$$

SHORT TERM...Grochocinski
LONG TERM...JTS
AVIATION...JTS


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