Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 141032
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
532 AM EST Thu Dec 14 2017

.NEAR TERM...(Today through Tonight)
Issued at 347 AM EST Thu Dec 14 2017

...Cold/Snowy pattern continues...

High Impact Weather Potential...Accumulating lake effect/enhanced
snow to end the work week.

Pattern Synopsis/Forecast...The train of short waves out of Canada
continues...cycling through persistent deep long wave troughing
that spans much of eastern NOAM. Our most recent system is kicking
through the eastern Great Lakes region heading off the Atlantic
coast. Next short wave is organizing over the Hudson Bay region
and will be diving down through the region later tonight through
Friday. In the interim...weak surface high pressure and drier air
is building into the region giving us a bit of a break from the
snow such as it is...although northerly flow lake snow showers
continue along both coasts (especially the Grand Traverse Bay
region) as well as in eastern upper Michigan. Per radar trends and
available sfc obs...snow showers appear more modest at the
moment...although Bufkit forecast soundings suggest convective
cloud layers are likely cutting through the DGZ...possibly leading
to a good fluff factor (just waiting for that 6 am phone call
with 5 inches overnight).

As mentioned above...next Canadian short wave will dive down
through the northern Great Lakes region later tonight through
Friday night. This will help gin-up another area of low pressure
over Lake Superior...likely aided by the lakes low level heat
plume...which will then migrate down across Lake Huron through
Friday. Not much by way of synoptic snowfall anticipated with this
one. But main impact will come with another big uptick and round
of lake induced snow showers...with potential for heavier
accumulations.

Much of today should end up "not bad" as weak surface high
pressure and pocket of dry air slides through. Ongoing northerly
and eventually northwesterly flow lake effect snow showers will
persist and shift back eastward across eastern upper and northern
lower Michigan through the day. Plenty of over-lake conditional
instability of course. But lower inversion heights/overall drier
antecedent conditions and backing winds should temper snow
accumulations...perhaps an inch or two where snow showers are most
persistent (again...barring that 6 am call).

Lake effect snows ramp up tonight...especially overnight...as
aformentioned short wave/associated bullseye of QG-forcing for
ascent swings down into the region. Bufkit soundings reveal
increasing or nearly non-existent inversion heights/moderate to
extreme lake effect conditions with lake induced CAPES approaching
1K J/KG and lake induced EQLs up over 15K feet. Conditions persist
through Friday/Friday night and promise to deliver another drawn
out period of moderate to heavy lake snows.

Of course greatest accumulations will ultimately depend on how
lower level mean winds develop and change in time. Tentatively for
tonight...anticipate a W or slightly WSW mean low level wind
which typically targets areas just north of M-32...particularly
the Petoskey area and points east into Cheboygan county given the
longest fetch out of Green Bay and across Little Traverse Bay.
Will start with snow accumulations of 3 to 6 inches in that area.
Slightly lower amounts further south through Charlevoix and Antrim
county where terrain will come into play. Minor accumulations
elsewhere.

Headline-wise...at this juncture we do not have any locations with
forecast 12 or 24 hour warning snow accumulations through Friday.
Close...but not there. We will eventually need winter weather
advisories at a minimum for lake effect snow...most likely across
the tip of the mitt and down into the M-32 corridor as well as
Mackinac county if heavier lake convection on Superior sags into
that area. But since it`s a late day 1 through day 2 forecast
plan on holding off for now and allow day crew to make the final
determination.

&&

.SHORT TERM...(Friday through Saturday)
Issued at 347 AM EST Thu Dec 14 2017

...Moderate snow for some on Friday...

High Impact Weather Potential...Moderate snowfall likely through
first part of Friday night, especially within WNW to NNW flow
snowbelts.

Pattern Synopsis/Forecast...Potent shortwave trough will drop
into the Upper Great Lakes on Friday as a closed upper low rotates
through southern Ontario. At the surface, a deepening surface low
initially over Whitefish Bay will trek across northern Lake Huron,
with a trailing back door cold front dropping through Michigan
Friday night. A band of isentropic lift stretching from northern
MN into southern Lower MI looks to just nose into our southwestern
counties late Friday night into Saturday morning as heights aloft
begin to climb. Canadian surface high will sit over Ontario on
Saturday, extending into northern Michigan and likely offering a
momentary lull from snow activity...though keeping things cold with
dry, northeast flow.

Primary Forecast Concerns...Snow amounts Friday through midnight
Friday night.

Favorable synoptic lift coming into play for northern Michigan on
Friday with the incoming shortwave and later the closed upper low.
Conditions will come together for decent lake enhancement as well
for portions of eastern Upper and northwest Lower Michigan. Low
level moisture looks good initially with PWATs near 0.25", but
moisture will gradually be stripped out from top down as the day
progresses. This will also bring about a slow lowering of inversion
heights (initially around 10 kft) through the day. Steep low
level lapse rates indicate rather robust lake-induced instability
thanks to delta Ts around 20 degrees or better. Now, fluctuating low
level wind direction due to the slowly departing surface low
will likely limit organization of the bands and their respective
snowfall impacts to some degree. However, general flow pattern and
otherwise favorable ingredients add confidence to the idea of
moderate snowfall at least within the favored WNW to NNW snowbelts.
Additionally, moderating surface temperatures with highs in the 20s
will place the DGZ square in the middle of the low level maximum
omega. Current snowfall forecast from Friday through midnight Friday
night calls for around 3 to 6 inches (with locally higher amounts
possible) for much of Charlevoix, Antrim, Otsego, Crawford, and
Kalkaska counties. Will have to monitor trends today, but there will
likely be a need for winter headlines through midnight Friday night
for at least this general area.

.LONG TERM...(Saturday night through Wednesday)
Issued at 347 AM EST Thu Dec 14 2017

High impact weather potential...Perhaps some accumulating snowfall
towards the middle of next week.

Northern Michigan looks to finally catch somewhat of a break from
relentless day after day snowfall for the first part of the period
as upper flow pattern becomes more zonal. Temperatures will moderate
through Monday, perhaps even into Tuesday, especially at 850mb.
Can`t rule out snowfall entirely through this timeframe, but the
pattern doesn`t look nearly as harsh as it`s been lately.

Tuesday into Wednesday will usher in a return to a more active
pattern as a deeper trough plows through the Great Lakes, followed
by a glancing shot of colder air. This will likely lead to some more
lake effect for the middle of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 532 AM EST Thu Dec 14 2017

Overall MVFR cigs with lake clouds and light snow showers will
persist at the terminal sites through today...particularly at TVC
and MBL where some VSBY reductions will occur this morning. CIGS
may briefly improve to VFR in spots this afternoon.

Another low pressure system slides down through the region later
tonight through Friday. This will bring another uptick in lake
effect snow shower coverage/intensities in the NW lower Michigan
snow belt areas...with the heavier snow showers impacting PLN
through Friday morning.


&&

.MARINE...
Issued at 347 AM EST Thu Dec 14 2017

Gustier northerly winds will persist through the morning
hours...particularly on the Lake Huron side...as low pressure
system continues to peel away from the western lakes region. Will
maintain small craft advisories on the Huron side for
now...although we may be able to trim headlines a bit earlier.

Lighter winds and waves for tonight. But gusty winds return again
for Friday and Friday night...with more marine headlines likely.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LHZ348-
     349.
LM...NONE.
LS...NONE.
&&

$$

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


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