Area Forecast Discussion
Issued by NWS Gaylord, MI

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042
FXUS63 KAPX 081125
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
625 AM EST Thu Dec 8 2016

.NEAR TERM...(Today and Tonight)
Issued at 245 AM EST Thu Dec 8 2016

...Extended period of accumulating lake effect snow showers...

High Impact Weather Potential...Significant lake effect snow
accumulations combined with blowing snow today and tonight.

Pattern Synopsis/Forecast...CAA is in full swing across the Great
Lakes early this morning. Sharp secondary trough remains upstream...
extending from near James Bay thru SE Ontario into Lake Superior and
into the Upper Mississippi Valley. Ahead of this features...low
level winds are still from the W/SW across our CWA...directing the
majority of ongoing lake effect snow bands into far NW Lower
Michigan and the Straits area. Snowfall rates have generally been
less than an inch an hour so far...limited by inversion heights
holding around 3 kft and relatively shallow moisture attm. As we
head into today...deep cyclonic flow remains over the entire area
and is further sharpened as the upstream trough axis slides SE thru
our CWA by this evening. Low level winds will shift to the NW in the
wake of the trough axis...redirecting highest POPs and snow
accumulations into areas under the Winter Storm Warning...generally
west of I-75 in NW Lower Michigan. Winds will continue to gust to 20
to 30 kts today...producing areas of blowing snow as well.

Primary Forecast Concerns...Main forecast issue remains the combined
impact of falling and blowing lake effect snow for locations
targeted by the most persistent snowfall. Deeper moisture arrives
along and behind the trough axis. Also...inversion heights steadily
rise with the passage of the trough axis...becoming nearly non-
existent this afternoon into tonight. In addition...NW wind
trajectories will provide preconditioning from Lake Superior and
will maximize orographic lift within the higher elevations of NW
Lower Michigan. Expect snowfall rates will steadily increase this
afternoon and tonight as focus of highest POPS and snow
accumulations shift southward from the tip of the mitt into areas
along and west of US-131 from Bellaire...Mancelona and Kalkaska
westward to TVC...CAD and FKS. These locations which are currently
under the warning should receive 3 to 6 inches of new snow just
today...with an additional 3 to 5 inches tonight. Locations within
the advisory will see 2 to 4 inches of new snow today...with an
additional 1 to 3 inches tonight. Expect drifting and very low vsbys
due to falling and blowing snow...especially within heavier snow
bands.

&&

.SHORT TERM...(Friday through Saturday)
Issued at 245 AM EST Thu Dec 8 2016

...Lake effect snow continues...

High Impact Weather Potential: Lake effect snow across northwest
Lower and eastern Upper.

Pattern Forecast: Low pressure centered near James Bay and
associated surface troughing over the Great Lakes is clearly evident
on tonight`s water vapor imagery. Surface trough will continue to
drop southeastward across the northern lakes on Thursday, allowing
for winds to veer more north-northwest. CAA will ramp up as the
winds shift, especially Thursday night through Friday.

Primary Forecast Concerns: Lake effect snow. As mentioned above,
surface troughing pivots across the area on Thursday, allowing winds
to slowly veer from the current westerly direction to more of a
north-northwesterly flow with an effective stretch extending back
through Lake Superior to Lake Nipigon, which is expected to continue
into the day Friday. Forecast soundings for Friday continue to
depict very supportive LES conditions with delta Ts of 21-24 C, a
very subtle subsidence inversion around 7,500 ft, and negative omega
values pegged off the chart squarely in the DGZ at various times
Friday through Friday night. NNW boundary level winds stay fairly
stationary through the midday hours Friday, focusing the greatest
snow totals across the heart of the Winter Storm Warning area,
including Grand Traverse, Kalkaska, Leelanau, Wexford, and Antrim
where an additional 3-6+ inches is likely.

Friday afternoon, winds begin to back toward the WNW and eventually
westerly Friday night. This is again expected to create a more
disorganized banding structure and provide more of a spread out snow
accumulation across northwest Lower Michigan. Additional
accumulations on the order of 2-6 inches are expected Friday night
across the lake belts with the greatest amounts expected in WNW flow
favored counties including Antrim, Kalkaska, Charlevoix, and Otsego.
Fully expect the need to extend headlines through at least Friday
night for parts of NW Lower and likely eastern Upper; however,
seeing that the headlines just went into effect, will hold off on
fiddling with the expiration timing at this juncture. All in all,
storm total accumulations from early this morning through Friday
night expected to range from 8-14 inches with locally higher amounts
anticipated for the hardest hit locations across the warning
counties and 4-10 inches for those under an advisory.

Winds continue to back during the day Saturday with return flow
guiding lake effect toward the tip of the mitt and eastern Upper.
Another minor accumulation is expected for those locations.
Attention then quickly turns to a pronounced wave set to move from
the central plains into the Great Lakes late Saturday night into
Sunday...perhaps extending into Monday based on timing, which will
be discussed in more detail below.

.LONG TERM...(Saturday night through Wednesday)
Issued at 245 AM EST Thu Dec 8 2016

High Impact Weather Potential...

High impact weather potential: Accumulating snow likely during the
late Saturday night-Sunday timeframe. Lake effect snow ramps up
again toward the middle of next week. Gusty winds and cold
temperatures during the midweek timeframe as well.

Active weather will continue through the extended period with
several periods of accumulating snow possible. Aformentioned backing
winds are expected on Saturday ahead of the next system expected to
arrive late Saturday night into Sunday. Guidance disagreement in
terms of overall system development, strength, timing and precip
precip placement yields low confidence in the event details;
however, a consensus blend would suggest that isentropically driven
snow arrives very late 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. Another couple of
inches of accumulation will be possible with another possible winter
weather 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 what could be very cold temperatures and
renewed LES chances for the middle and end of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 625 AM EST Thu Dec 8 2016

Lake effect snow showers will continue to impact much of Northern
Lower Michigan thru Friday morning. Heaviest and most persistent
snow showers will shift focus southward from the tip of the mitt
to areas along and west of US-131 as low level winds shift from
the W/SW to the NW in response to the passage of a trough axis
today. Conditions will deteriorate to IFR within heavier snow
bands. Winds will continue to gust to 15 to 25 kts today...
diminishing to 10 to 20 kts tonight.

&&

.MARINE...
Issued at 245 AM EST Thu Dec 8 2016

Gale force winds and high waves will continue to impact much of our
nearshore areas this morning as deep low pressure remains NE of
Michigan...keeping our area within a rather tight pressure gradient.
Strong CAA 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 shifting from
the Straits and the tip of the mitt southward into areas along and
west of US-131. Winds and waves will diminish later tonight and
Friday as the pressure gradient loosens.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING until 3 PM EST Friday for MIZ019>021-
     025>027-031>033.
     WINTER WEATHER ADVISORY until 3 PM EST Friday for MIZ016-017-022-
     028-034.
     LAKE EFFECT SNOW ADVISORY until 3 PM EST Friday for MIZ008.
LH...SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LHZ348-
     349.
     GALE WARNING until 11 AM EST this morning for LHZ345>347.
LM...SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LMZ341.
     GALE WARNING until 11 AM EST this morning for LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY until 7 AM EST Friday for LSZ321-322.
&&

$$

NEAR TERM...MLR
SHORT TERM...MJG
LONG TERM...MJG
AVIATION...MLR
MARINE...MLR



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