Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 091126
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
626 AM EST Sat Dec 9 2017

.NEAR TERM...(Today through Tonight)
Issued at 332 AM EST Sat Dec 9 2017

...Accumulating lake effect snow continues...

High impact weather potential...lake effect/enhanced snow.

A whole bunch of mesoscale nonsense playing out early this morning.
1005 mb surface low is in central WI, forced by a vigorous
shortwave digging toward southern Lake MI. A rather baggy pressure
field is found east and ne of the low, resulting in relatively
light wind fields. There are some indications of mesolows near the
Manitous...nw of Rogers City...and north of central/ eastern
upper MI (obvious on MQT radar). Best snowfall rates are
presently seen in southern portions of nw lower MI (as expected),
closer to the best synoptic-scale forcing, and with weak westerly
onshore flow. Somewhat stronger northerly winds will kick in
today as the low passes to our south. This will restore a more
normal/typical lake effect scenario...eventually.

But today will still be messy. Synoptic support for snowfall will be
departing fairly quickly this morning, but perhaps not quite as
quick as earlier thought. HRRR/Nam/RAP are supporting decent
precip rates in Manistee Co a bit past 12Z, before the synoptic
precip shield exits to the south. Potential for another inch or so
after 7 am warrants extending the winter wx advis for Manistee Co
(only) until later in the morning. The rest of the advisory
counties should be safe to expire at 7 am, if not sooner.

Some indications from the models of a mesolow in central Huron
drawing some snow back into ne lower MI from midday into this
afternoon. This idea is fine, but the Nam appears overdone in its
portrayal. It`s the only model with 0.20" of liquid QPF, with the
RAP and HRRR at 0.10" or less (the HRRR in particular is not
enthusiastic. Will allow for 1-2" of accums from Rogers down to
OSC.

Our departing system will leave behind nne 1000-850mb winds for a
period early today. That will contribute to a mid-lake convergence
band getting going on northern Lake MI as synoptic precip exits.
That band could be rather vigorous out over the lake, and as winds
back to the n and nnw this afternoon, it will come ashore into nw
lower MI. Places west of US-131 could pick a very quick
additional inch or so of snow this afternoon.

Through all of this, eastern upper MI is relatively quiet. Some
potential for a remnant vortice to push into Chippewa Co, especially
mid/late this afternoon. Expect any such feature to be poorly
organized, with accums under an inch.

Max temps will range thru the 20s.

Tonight...yet another shortwave will dig in far ne Ontario. This
will sharpen and eventually drag southward the lake aggregate
surface trof across central/southern Superior. This looks to
substantially amplify 1000-850mb convergence at the east end of
that lake, especially overnight. At least some potential for more
potent banding to poke into northern Chip Co from late evening
on. However, as of now, am concerned this flow will not be
northerly enough to bring better banding south of Paradise, at
least until almost daybreak. In fact, the 06z Nam has gone less
northerly than the 00z run, with resulting lake effect snow
impacting less of Chippewa. Will have 2-5" accums in far nw Chip,
but given the small area impacted and uncertainty as to how winds
will evolve, will decline to issue an advisory at this time.

Wnw to w flow elsewhere has much less moisture available (further
away from the digging shortwave and lake-aggregate surface trof),
and a much shorter fetch. Anticipate nmrs snow showers in the nw
lower snowbelt, with accums topping out in the 1-2" range (centered
on Antrim Co).

Min temps from upper single digits above zero interior eastern
upper MI, to around 20f for parts of the nw lower MI coast.

&&

.SHORT TERM...(Sunday through Monday)
Issued at 332 AM EST Sat Dec 9 2017

...A couple more rounds of generally light snow accumulation...

High Impact Weather Potential...Light snowfall amounts on Sunday in
the NW flow snowbelts, followed by a more widespread snow event on
Monday with generally light accumulations.

Pattern Synopsis/Forecast...A weak shortwave/clipper system will
brush eastern Upper early Sunday as it treks across southern
Ontario. This system will send a cold front southward through
northern Michigan during the day, ushering in another rather short-
lived blast of colder 850mb temperatures. Surface ridge of high
pressure will cross the region Sunday night, providing a brief
respite for much of the area from this active snowy pattern. Another
potent shortwave and clipper system will dive southeast from the
Dakotas on Monday, likely bringing a round of widespread
accumulating snow to northern Michigan through the day with some
lake enhancement as well.

Primary Forecast Concerns...Snowfall amounts through the period,
particularly with Monday`s system.

Northwest flow behind Sunday`s cold front will combine with the
influx of colder 850mb temperatures (dropping to -15 to -20C) to
provide more favorable conditions for lake effect snow, especially
for eastern Upper and portions of northwest Lower. Added to the lake
effect will be some frontogenetic lift along the front, providing
additional support for snow showers as the front drops south through
northern Michigan. So, decent low level omega and inversion heights
around 5 kft or better with the front`s passage, but moisture
becomes more limited as the day progresses. All in all, snow totals
with this system generally look limited to an inch, perhaps up to 2
inches in the favored NW flow snowbelts.

Light lake effect snow showers may linger in the NW flow snowbelt of
eastern Upper heading into Sunday night, but nothing of any
significance as the surface ridge slides through.

Main snow concern through the period will be with Monday`s clipper
system. A band of increasing isentropic ascent will develop over the
Upper Midwest late Sunday night, sliding into northern Michigan
Monday morning as the clipper system becomes absorbed in the deep
troughing over the Great Lakes. A narrow ribbon of higher moisture
at the system`s core will pass by just to our southwest, but PWATs
>0.3" over northern Michigan will still be ample for perhaps around
2 to 3 inches of widespread snow accumulation during the day. Given
decent consensus among the models, there is a good amount of
confidence in this system at this time, but it will need to be
monitored over the next 24 hours or so for any possible deviations.
The fly in the ointment will be any possible lake enhancement that
develops off northern Lakes Michigan/Huron in the southeasterly flow
out ahead of this system, as suggested by the GFS and NAM.

.LONG TERM...(Monday night through Friday)
Issued at 332 AM EST Sat Dec 9 2017

High impact weather potential...Ongoing lake effect snow will be
enhanced by periodic snow from passing clipper systems. This could
yield some significant snow totals for some areas.

Monday night will get interesting as the departing clipper system
becomes absorbed in the longwave troughing pattern overhead,
deepening as it rotates off to our east. In its wake, a tightening
pressure gradient will quickly lead to somewhat windy conditions
near the lakes, especially over Lake Michigan where gales are
looking increasingly likely. As this system departs, Arctic air will
surge southward into the region, this round colder and lingering a
little longer than what we`ve grown used to so far this season.
We`ll be looking at nighttime lows in the single digits for many by
Tuesday night, even below zero in spots, particularly eastern Upper.
Highs Tuesday and Wednesday largely in the teens. Wind chills in the
negative single digits to teens by Tuesday night. Needless to say,
continued lake effect as a result through the week, particularly
across eastern Upper and northwest Lower. Temperatures will start to
moderate a tad through the second half of the week, but precip
pattern forecast gets a little muddied by model track differences
for another clipper system.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 626 AM EST Sat Dec 9 2017

Low pressure crossing southern Lake MI will continue to move off
the se. Associated system snow will wane this morning, mainly
impacting MBL. Lighter winds have allowed a variety of lake effect
snow showers to form. Some of these will impact TAF sites today,
especially APN, TVC, and MBL. Eventually we will see northerly
flow develop today, becoming wnw tonight. That will maintain a
chance for snow showers tonight for the nw lower MI sites. VFR to
MVFR conditions will be most common.

Northerly winds will become a bit gusty today, then weaken and
back toward the wnw tonight.

&&

.MARINE...
Issued at 332 AM EST Sat Dec 9 2017

Northerly winds will fairly quickly increase today, as low
pressure in se WI moves further se. Advisory-level conditions will
return on most, if not all, waters. A disturbance passing to our
north will maintain brisk conditions late tonight and Sunday.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until 7 AM EST this morning for MIZ020-
     025.
     WINTER WEATHER ADVISORY until 11 AM EST this morning for MIZ031.
LH...SMALL CRAFT ADVISORY until 5 PM EST Sunday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 5 PM EST Sunday for LMZ323-341-342-
     344>346.
LS...NONE.
&&

$$

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



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