Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 070833

Area Forecast Discussion
National Weather Service Gaylord MI
333 AM EST Wed Dec 7 2016

.NEAR TERM...(Today and Tonight)
Issued at 333 AM EST Wed Dec 7 2016

...Turning colder with developing lake effect snow showers...

High Impact Weather Potential...Developing lake effect snow showers
with some accumulation combined with blowing snow.

Pattern Synopsis/Forecast...Initial cold front has pushed east of
Michigan early this morning. CAA has begun in earnest across the
Western Great Lakes region in the wake of the cold front. Increasing
over-lake instability combined with deep cyclonic flow via
vertically-stacked low pressure centered near the arrowhead of
Minnesota has lead to the commencement of lake effect snow shower
production. Latest KAPX base ref loop shows a steady increase in
lake effect snow bands across NW Lower Michigan over the past few
hours...targeting far NW Lower Michigan for highest POPs attm under
the direction of W/SW low level flow off of Northern Lake Michigan.
Overall pattern will evolve into an increasingly favorable lake
effect snow environment over the next 24 hours. CAA will continue to
increase over-lake instability as 850 mb temps cool to -13 C by late
tonight. Deep cyclonic flow will remain overhead...and will further
sharpen with the approach of the upper trough axis and surface
response as it reaches Upper Michigan by late tonight. Area of
deeper moisture associated with this secondary trough will begin to
push into Upper Michigan this afternoon...and will then spread SE
into Northern Lower Michigan tonight. Low level wind trajectories
will shift to the west early this morning...and eventually to the NW
throughout the afternoon. Winds will continue to gust to 20 to 30
kts thru tonight...with some higher gusts expected especially along
the Lake Michigan shoreline.

Primary Forecast Concerns...Main forecast issue is the combined
impact of falling and blowing lake effect snow for locations
targeted by the most persistent snowfall. Deeper moisture will not
arrive until tonight...especially late tonight across Northern Lower
Michigan. Also...development of favorable wind trajectories will not
truly occur for Chippewa county until later tonight. Increasing over-
lake instability and cyclonic flow will certainly continue to result
in a gradual increase in areal coverage and intensity of lake effect
snow showers over the next 24 hours. However...still appears snow
and blowing snow worthy of a headline will likely hold off until
late tonight. New snow amounts today will generally be an inch or
less...with another 1 to 2 inches tonight with blowing snow. In
coordination with adjacent offices...will elevate ongoing Winter
Storm Watch to Winter Storm Warnings and Winter Weather Advisories
beginning late tonight for the combination of falling and blowing
snow (see additional information regarding headlines below). Temps
hold nearly steady today in the upper 20s to around 30...and will
only cool a few degrees tonight.


.SHORT TERM...(Thursday through Friday night)
Issued at 333 AM EST Wed Dec 7 2016

...Lake effect snow machine kicks into high gear...

High Impact Weather Potential...Lake effect snow showers will
intensify on Thursday, continuing into Friday. Areas of blowing snow
as well as significant accumulations are expected in the snowbelts
along Lake Superior and Lake Michigan and will make for an extended
period of difficult or hazardous travel.

Pattern Synopsis/Forecast...A broad upper trough will establish
itself over the Great Lakes region Thursday into Friday, flattening
out as it moves east of the area Friday night. An Arctic airmass
settling over the region will allow for periods of lake effect snow,
with enhanced snowfall on Thursday due to a surface trough dropping
south through the area.

Primary Forecast Concerns...Pattern will become increasingly
favorable for efficient lake effect snowfall Thursday into Friday.
Water temperatures over eastern Lake Superior currently range from 5
to 8C and over northern Lake Michigan 8 to 10C. 850mb temps will be
falling to around -10 to -16C from Thursday through Friday night,
yielding delta Ts of 15 to 20+. Moisture through the period will be
also be favorable with 850-700mb RH generally 80-90 percent or
higher. Impressive low level negative omega will also coincide with
the dendritic growth zone for much of the period Thursday through
Friday night, making for efficient snow production. Aside from
convergence axes setting up along the Lake Superior and northern
Lake Michigan shorelines through the period, a surface trough will
push southward across the area on Thursday and provide additional
lift. With winds veering to the NNW behind this trough, lake effect
snow bands will change their orientation with impacts migrating
south over time and becoming focused over the Grand Traverse Bay
area and points south through Friday afternoon. In addition, a tight
gradient will allow for gusty winds that will lead to areas of
blowing snow, mainly through Thursday evening. Winds will then
slacken a bit, backing to the WNW late Friday afternoon and evening
which will shift LES bands back to the north Friday night. A passing
shortwave will also cross eastern Upper Friday night adding to snow
potential there.

Overall have gone with categorical PoPs in the snowbelts from late
Wednesday night through Friday afternoon. Forecast for this period
yields a total of 3 to 5 inches across Chippewa County as well as a
broad 5 to 8 inches in the snowbelts of northwest Lower, with
amounts closer to 10 inches around Grand Traverse Bay and south.
Though these amounts will fall over 36+ hours, expect an extended
period of hazardous travel with additional impacts from blowing
snow. Have therefore gone with Winter Storm Warnings around Grand
Traverse Bay and Winter Weather Advisories for surrounding counties
of northwest Lower through Friday afternoon. Also have a Lake Effect
Snow Advisory for Chippewa County for this timeframe.


.LONG TERM...(Saturday through Tuesday)
Issued at 333 AM EST Wed Dec 7 2016

High Impact Weather Potential...

High impact weather potential: Lake effect snow threat shifts toward
the tip of the mitt/eastern Upper Saturday. Widespread accumulating
snow possible late Saturday night - Sunday and again Tuesday.

Active weather will continue through the extended period with
several periods of accumulating snow possible. Initial lake effect
threat will gradually shift towards the tip of the mitt and eastern
Upper and winds weaken and begin to veer in association with WAA
ahead of the next potentially widespread snow maker. Isentropically
driven snow is expected to arrive after midnight Saturday night,
continuing through much of Sunday. As mentioned by the prior shift,
Sunday`s system has at least a brief tap to the Gulf moisture,
although PWs aren`t necessarily off the charts for this time of year.
At least a few inches of snow look possible with another possible
headline event looming. Late in the extended period, guidance hints
at an arctic front dropping out Canada into the northern tier of the
CONUS, thus providing another shot at synoptic snowfall followed by
renewed LES chances for the middle and end of next week.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1145 PM EST Tue Dec 6 2016

Gusty southwest winds will continue to overspread region overnight
in the wake of the front. Wind gusts of 20-30 kts will continue to
be likely - particularly at MBL/TVC/PLN - as cold air advection
commences. Generally MVFR ceilings will expand and prevail tonight
into Wednesday, thanks in large part to colder air crossing the
Great Lakes. Some light lake effect snow showers will develop during
the pre-dawn hours and into Wednesday at mainly PLN and TVC.
Reductions in visibility and accumulations are expected to be minor.
Heavier lake effect snows are expected Thursday and Thursday


Issued at 333 AM EST Wed Dec 7 2016

Gale forecast winds and high waves will continue to impact much of
our nearshore areas today into tonight as deep low pressure tracks
north of Michigan...keeping our area within a rather tight pressure
gradient. Strong CAA thru Thursday and increasing moisture as a
secondary trough swings thru the region will lend to increasing
areal coverage and intensity of lake effect snow showers...with the
greatest impact along the Northern Lake Michigan shoreline and the
Straits area as well as Whitefish Bay and the St Marys River


MI...WINTER WEATHER ADVISORY from midnight tonight to 3 PM EST Friday
     for MIZ016-017-019-022-028-033.
     WINTER STORM WARNING from midnight tonight to 3 PM EST Friday
     for MIZ020-021-025>027-031-032.
     LAKE EFFECT SNOW ADVISORY from midnight tonight to 3 PM EST
     Friday for MIZ008.
LH...SMALL CRAFT ADVISORY until 7 AM EST Thursday for LHZ348-349.
     GALE WARNING until 1 AM EST Thursday for LHZ345>347.
LM...GALE WARNING until 1 AM EST Thursday for LMZ323-341-342-344>346.
LS...SMALL CRAFT ADVISORY until 7 AM EST Thursday for LSZ321-322.


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