Area Forecast Discussion
Issued by NWS Gaylord, MI

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271
FXUS63 KAPX 110849
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
349 AM EST Mon Dec 11 2017

.NEAR TERM...(Today through Tonight)
Issued at 347 AM EST Mon Dec 11 2017

...Another round of snow/lake effect snow...

High Impact Weather Potential...prolonged period of lake effect
snow for some areas through Tuesday night.

Pattern Synopsis/Forecast...Highly amplified pattern remains
intact of course with a sharp blocking ridge up through the
western CONUS and downstream troughing encompassing much of
central and eastern NOAM. We do have just a hint of low amplitude
short wave ridging sliding through the western lakes region
currently...and attending surface high pressure sliding through
the region. Thus...we have caught at least a little bit of a
break...although there remains some lighter NW flow lake snow
showers impacting some areas.

Upstream...a rather well defined short wave and attending surface
low is dropping quickly southeastward into the upper Midwest...with
a secondary piece of energy is noted over western Hudson Bay.
Warm advection "synoptic" snowfall ahead of the lead wave is
already sliding into Wisconsin and will be reaching us this
morning. This system will slip quickly southeast through the
western Great Lakes region into the Ohio Valley through this
evening before pivoting and substantially deepening heading into
the New England region on Tuesday. This will bring all areas some
light accumulating snow today. But...lake effect snow is another
matter.

Primary Forecast Concerns...SW flow lake enhanced snowfall on the
front end of this system...prolonged NNW flow lake effect snow and
gusty winds on the back.

As mentioned...short wave trough and attending surface low will
drop quickly southeastward through the western Great Lakes through
the course of the day. Upstream swath of warm advection forced
snowfall will overspread the region through the morning before
peeling off to the east through the afternoon. Shouldn`t be a big
deal overall with much of the CWA picking up and inch or two of
snow. However...S/SW flow ahead of wave coupled with increasing
forcing/synoptic moisture will bring several hours of enhanced
lake effect banding into the western portions of Mackinac county
and potential for 3, 4, 5 inches of snow. With that in mind...plan
on hoisting a winter weather advisory for Mackinac county for
today...focusing on the western/central part of the county.

Gets much more interesting tonight (and beyond). Clipper will be
pivoted through the Ohio Valley this evening before heading
northeastward toward New England...while secondary northernmost
short wave dives down through the western Great Lakes and brings
along a big plunge of arctic air. Fairly sharp low level trough
axis/cold front will be passing through the CWA this evening
ahead of the arctic plunge...likely accompanied by a period of
enhanced snowfall. Behind the trough...winds still looking to
turn sharply NNW and set the stage for a prolonged period of
healthy lake effect snows later tonight through Tuesday night.
Extreme instability (Bufkit forecast sounds at MBL/TVC give over
1000 J/KG lake induced CAPE) persistent NNW flow all suggest some
rather healthy snow totals along the Lake Michigan coastline from
Leelanau county southward...assuming the flow does lock in as
forecast. Coupled with gusty winds/blowing snow potential...plan
on issuing a winter storm warning for Leelanau through Manistee
counties as well as Grand Traverse county...bordered by an
advisory.


&&

.SHORT TERM...(Tuesday through Wednesday)
Issued at 347 AM EST Mon Dec 11 2017

...Frigid Arctic air and significant lake effect snow...

High Impact Weather Potential...Significant lake effect snow on
Tuesday around and south of Grand Traverse Bay. Blustery winds
will result in blowing snow and very frigid wind chills at times.

Pattern Synopsis/Forecast...Deep troughing overhead (2 to 3
standard deviations below the mean) will be reinforced by another
lobe of energy dropping south from western Ontario Tuesday morning.
Arctic air will surge southward with this trough on the backside of
an intense departing surface low, with 850mb temperatures dropping
to around -20C over northern Michigan. Surface ridge will drift
across the region Tuesday night into Wednesday, but lake aggregate
troughing will hold fast. Another incoming shortwave will
become sheared out as it passes through the region on Wednesday.

Primary Forecast Concerns...Cold temperatures, significant lake
effect snow, and Wednesday`s clipper system.

The coldest surge of Arctic air thus far this season will arrive on
Tuesday, though the airmass will moderate slightly as it plunges
south into the Upper Great Lakes. Not looking at any strong
temperature anomalies (only around 1 to 2 standard deviations below
the mean at 925 and 850mb), but this airmass will be significant
just because of it being the coldest thus far. Highs will be in the
teens both Tuesday and Wednesday for most. Lows Tuesday night (the
coldest period) will be in the single digits on either side of zero
everywhere except west of M-37. Factor in the blustery winds Tuesday
morning and somewhat brisk winds Wednesday morning, and wind chills
will plunge well below zero across much of northern MI both mornings.
If skies manage to clear out more than currently expected Tuesday
night, temperatures could drop even lower than the current forecast
east of I-75, but don`t expect the boundary layer will completely
decouple to allow for an ideal radiational cooling setup.

As for snow, forecast soundings show a very ideal lake effect setup
for areas south of Grand Traverse Bay on Tuesday. Steep low level
lapse rates and strong lake-induced instability. Inversion heights
at MBL approach 8 kft, and strong unidirectional NNW winds from the
surface through the upper levels will provide strong low level
convergence along the coast. Very impressive low level omega
coincident with the dendritic growth zone and pretty high RH from
the surface up through ~750mb. Thus, expecting some very impressive
snow bands to develop by daybreak Tuesday, and the hi-res ARW/NMM
show just that with banding focused from Leelanau County south to
Manistee throughout the day. Relied heavily on ARW/NMM QPF. This
would yield daytime snow accumulations of around 4-8 inches across
our southwestern counties, likely highest over Benzie and Manistee
counties. And, of course, this snowfall would be on top of what
falls in that area tonight. Hence the headline decisions
mentioned above. Do expect some NW flow lake effect off Lakes Huron
and Superior as well, but not of the same magnitude. Upstream
surface ridge sliding in Tuesday night will cause lake effect to
diminish in coverage and intensity with only light additional
accumulation expected through Wednesday morning. Next clipper system
will dive in from the NW late morning into the afternoon, but models
still don`t have its precise track pinned down. Only looking like
light snow accumulation potential from this system, however.

&&

.LONG TERM...(Wednesday night through Sunday)
Issued at 347 AM EST Mon Dec 11 2017

High impact weather potential...Ongoing lake effect snow with
additional enhancement from a clipper system or two.

A slow moderation in temperatures expected the remainder of the
week...even signals of temperatures climbing /above/ freezing this
weekend! But still an active wintry pattern to deal with in the
meantime with lake effect snow and an occasional clipper system.

Deep longwave troughing over the eastern CONUS is progged to
gradually lift NE heading into Thursday with upper flow turning
zonal for a brief time as the strong ridge out west begins to
flatten. Additional energy drops south from Canada on Friday,
yielding a sharp but quick moving trough over the region. Flow
then turns largely zonal again towards next weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1144 PM EST Sun Dec 10 2017

Light lake effect snow showers and flurries will gradually push
their way closer to the shorelines, or out over the Lakes through
the night as weak high pressure moves across the region and brings
weakening winds that back around to the south by daybreak. Little
to no accumulation for the remainder of the night. The next low
pressure and cold front will bring deepening moisture and light
system snow to the region Monday into Monday evening with a
general 1 to 2 inches of snow to all airports, maybe a shade
higher around MBL. The cold front crosses Monday night, and winds
shift and strengthen out of the NW/NNW and will be gusty.
Accumulating lake effect snows will develop and lead to another
general 1 to 3 inches, but amounts could be higher around MBL/TVC.


&&

.MARINE...
Issued at 325 PM EST Sun Dec 10 2017

Winds and waves will continue to reach SCA criteria into this
evening but will drop below criteria overnight as high pressure
builds into the Western Great Lakes region. Conditions will ramp up
again to SCA and possibly gale warning criteria Monday night into
Tuesday as northerly flow strengthens in the wake of a departing
area of low pressure. Lake effect snow showers will continue to
impact much of our nearshore areas tonight...but will transition to
a light synoptic snow event on Monday as that next area of low
pressure drops thru Michigan.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING from 10 PM this evening to 11 PM EST
     Tuesday for MIZ020-025-026-031.
     WINTER WEATHER ADVISORY from 10 PM this evening to 11 PM EST
     Tuesday for MIZ021-027-032-033.
     WINTER WEATHER ADVISORY until 6 PM EST this evening for MIZ015.
LH...GALE WARNING from midnight tonight to 6 PM EST Tuesday for
     LHZ347>349.
     SMALL CRAFT ADVISORY from 6 PM this evening to 6 AM EST
     Wednesday for LHZ345-346.
LM...GALE WARNING from midnight tonight to 6 PM EST Tuesday for
     LMZ323-342-344>346.
     SMALL CRAFT ADVISORY from 6 PM this evening to 6 AM EST
     Wednesday for LMZ341.
LS...GALE WARNING from midnight tonight to 6 PM EST Tuesday for
     LSZ321-322.
&&

$$

NEAR TERM...BA
SHORT TERM...MK
LONG TERM...MK
AVIATION...SMD
MARINE...MR



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