Area Forecast Discussion
Issued by NWS Gaylord, MI

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330
FXUS63 KAPX 110447
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1147 PM EST Sun Dec 10 2017

.UPDATE...
Issued at 926 PM EST Sun Dec 10 2017

A weak shortwave trough was overhead with a swath of added
moisture aloft pushing SE of nrn Michigan. This feature didn`t
really have a chance to enhance any lake effect snows since the
banding hadn`t really developed yet due to the disruption from the
earlier cold frontal snows. Banding has formed behind this
feature now however, but moisture was gradually thinning with time
and inversion heights were becoming shallower. High pressure will
work into the region over the next several hours before departing
east by Monday morning. This will weaken and back winds
significantly from NW to south by daybreak. As a result, lake
effect will gradually work it`s way closer to the shores or go
offshore. No more than a half inch in any area across NW lower or
Chippewa county. In this fast/progressive synoptic pattern, the
next Alberta clipper will quickly be pressing SE into the mid
Mississippi valley. Warm advection and deepening moisture, mainly
aloft, will be increasing through Monday morning. Light synoptic
snows will start spreading through nrn Michigan from west to east.
This will bring some light amounts of snow, but despite a shallow
inversion, will also feed and energize light lake effect snows
which may be scraping portions of NW lower shoreline, as well as
into western Mackinac county. That increased snowfall intensity
doesn`t really get going until later Monday morning.

&&

.NEAR TERM...(Tonight through Monday)
Issued at 325 PM EST Sun Dec 10 2017

...Lake effect snow tonight transitions to widespread synoptic
snow Monday...

High Impact Weather Potential...Accumulating snow.

Pattern Synopsis/Forecast...Sharp lake-enhanced trough axis has
dropped south into Northern Lower Michigan as expected this
afternoon...helping to enhance ongoing westerly flow lake effect
snow showers. Locations with the typical snowbelts have received the
brunt of the snowfall this afternoon...although even portions of NE
Lower Michigan are seeing brief bouts of heavy snowfall as a result
of strong convergence along the trough axis. While Eastern Upper
Michigan is still receiving lake effect snow showers...intensity has
waned with the departure of the trough axis. Thus have let the
Advisory expire as of 18Z for Chippewa county. Advisories still
remain in effect for the big 5 counties in NW/North Central Lower
Michigan where westerly flow combined with the trough axis continue
to produce periods of heavy snowfall.

As we head into tonight...low level flow will shift to the N/NW in
the wake of the departing trough axis. Lake snow bands will
reorganize and will continue to target the current advisory areas...
and will also begin to impact other areas around NW Lower Michigan
such as TVC and MBL. However...with surface ridging and drier low
level air building into our CWA tonight in the wake of the trough
axis...overall snow band intensity will diminish. Thus...expect
remaining snow bands at the time of Advisory expiration should have
weakened enough to not need any extension of the Advisory...at last
at this time.

Lake snow will continue to diminish overnight...and will begin to
transition to a light synoptic snow event as we head toward early
Monday morning. Low level winds will shift to a nearly straight
south trajectory...which is one of the few directions that brings
lake effect precip to a close across our CWA. Just as this
happens...synoptic moisture and isentropic ascent will begin to
increase from west to east across our CWA ahead of a fast-morning
low pressure system dropping SE out of South Central Canada into
Illinois and Indiana by 00Z Tuesday. QPF from this system will
likely be relatively low...producing sub Advisory criteria snowfall
for the day (i.e. an inch or two).

&&

.SHORT TERM...(Monday night through Wednesday)
Issued at 325 PM EST Sun Dec 10 2017

...Lake Effect First, then Cold Air...

High Impact Weather Potential...Lake effect snow and the coldest air
so far for Tuesday night/Wednesday morning.

Pattern Synopsis/Forecast...We continue with the ridge/trough 500 mb
pattern that has put the Upper Great Lakes into the cold air. This
has put us into a pattern of a clipper every other day with the next
two expected to be stronger than the previous. Monday night, the
next clipper looks to deepen the 500 mb trough, and then lift out
quickly on Tuesday, allowing for some clearing Tuesday night and
temperatures falling into the single digits over the forecast area.
Possibly below zero F in E Upper. Wednesday, the next clipper drops
into the Upper Great Lakes can kicks off the process all over again.

Primary Forecast concerns...Monday night into Tuesday, we transition
from synoptic to LES as the system moves to the east. Again, with
the cold air and relatively warmer water temperatures, we can get
light to moderate snow fall rates. The issue will be the persistence
of the bands. Winds turn to the north so most of the snow fall will
be along and west of US-131. Tuesday, the 850-700 mb layer begins to
dry out and the amounts begin to diminish to minor to light amounts,
mainly near Lake Michigan, which continues into Tuesday night.
Wednesday, the clipper begins to move into the Upper Great Lakes, so
we will see snow showers begin to move into the region by the
afternoon.

.LONG TERM...(Wednesday night through Sunday)
Issued at 325 PM EST Sun Dec 10 2017

High impact weather: Periodic lake effect snows with additional snow
possible from a couple clipper systems throughout the extended
period.

The extended period will continue with below normal temperatures
through Friday night. These cold temperatures will continue to
produce periods of lake effect/enhanced snows and produce wind
chills in the single digits below and above freezing through Friday
morning...with Thursday morning seeing the coldest of the
temperatures. Models are beginning to agree with yet another clipper
system moving into the Great Lakes region Saturday...tracking
through Lake Superior/Upper Peninsula. This track would provide us
with more normal temperatures on southerly winds and possibly some
rain mixing in at times with the snow both Saturday and Sunday
afternoons over portions of northern lower. Too much uncertainty
this far out in the forecast period to forecast any accumulations
that may occur. Highs will be in the 20s Thursday and Friday, and
then reach into the low to mid 30s for Saturday and Sunday. Lows
will be mostly in the single digits Thursday morning, single digits
to low 10s Friday morning, and then warming some each day of the
remainder of the period...with Sunday morning only dropping into the
low to mid 20s.

&&

.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...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...SMD
NEAR TERM...MR
SHORT TERM...JL
LONG TERM...TL
AVIATION...SMD
MARINE...MR



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