Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 100200

Area Forecast Discussion
National Weather Service Gaylord MI
900 PM EST Fri Dec 9 2016

Issued at 900 PM EST Fri Dec 9 2016

Lake aggregate troughing and associated low level convergence axis
analyzed from eastern Lake Superior down through central and
southern Lake Huron. Regional MRMS radar loop reflects the
pattern, with some semblance of a mesolow trying to form over SE
Lake Superior near Whitefish Bay and a couple strong lake bands
converging into Alger and Schoolcraft counties. Converging lake
convection also evident across northwest/north central lower
Michigan with embedded heavy pockets of snow impacting parts of NW
lower Michigan this evening.

Rest of tonight: Per hi-res guidance, low level convergence axis
will pivot eastward into Lake Huron while low level mean flow off
Lake Michigan backs westerly by morning. Ongoing mass of lake
convection slides across northern lower Michigan this evening,
with WNW to W flow lake snow showers eventually refocusing back
into NW lower Michigan and ultimately up into the tip of mitt
areas by morning as winds back westerly. Heaviest snow showers
will continue to produce one to two inch (or more) per hour
snowfall rates, although convection will remain a bit on the
transient side. But where snow showers are most persistent
(Antrim, Kalkaska, parts of Otsego and Charlevoix counties)
nighttime accumulations should easily run 3 to 6 inches with
locally higher amounts likely. Advisories or course will remain

Eastern upper Michigan is a bit more tricky. Hi-res guidance
develops a well defined mesolow across SE Lake Ontario with
strongest convergence and heaviest/most persistent lake snows
remaining focused just back into Luce/Alger/Schoolcraft counties,
perhaps just sneaking into the Whitefish point/Paradise area.
Going forecast and lake snow advisory reflects that idea which I
will leave alone for now. Possible that heavier bands get further
eastward across Chippewa county and require increasing forecast
snow amounts...perhaps into lake effect snow warning territory.


.NEAR TERM...(Tonight and Saturday)
Issued at 327 PM EST Fri Dec 9 2016

...Lake effect snow to continue...

High Impact Weather Potential: Accumulating lake snows tonight into

Pattern Synopsis/Forecast: Lake effect snow showers continue as cold
and moist air filters across the big waters. Initial north/northwest
flow has slowly backed more northwest with time. While this has
disrupted what had been well developed banding, this transition has
brought more widespread snow showers to the traditional snow belt
locations, some of which have been briefly heavy. Plenty more cold
air and synoptic enhanced moisture set to cross the area yet
tonight, helped along by passage of subtle mid level wave within
broad upper level northwest flow regime. This will allow the lake
processes to continue, and may actually see some overnight
intensification as that wave arrives and the atmosphere "stabilizes"
from diurnal influences. Gradual infiltration of drier air and
further backing of low level winds should really start to disrupt
organized lake processes Saturday afternoon, but not before several
more inches of additional snow fall.

Primary forecast concerns: Placement/intensity (additional snow
accumulations) of lake snows tonight and associated headline

Details: Thermodynamic profiles remain excellent tonight into the
early part of Saturday, with inversion levels up near 10kft and
omega pegged in a completely in cloud dendritic growth layer.
Kinematics more troubling, with strong hints of potential meso-low
formation over both northern Lake Michigan and the southeast basin
of Lake Superior. General backing of winds should continue, with
lake aggregate troughing/possible meso-low formation potentially
really enhancing localized convergence.

Off Lake Michigan...Per pattern recognition and hi-res model
guidance, target area for northwest lower should transition to
points north of M-72 through the overnight, with some hints of that
enhanced convergence axis setting up along the M-32 corridor (others
possible further north pending that meso-low development). Loss of
diurnal influences likely to result in renewed banding structures,
although perhaps not with the organization experienced last night.
Still think snowfall rates up to and exceeding one inch per hour are
possible, especially where convergence is maximized. Upshot to the
above, expect several more inches of snow to target areas along and
west of interstate 75 and north of M-72 tonight into the first part
of Saturday. Given thermodynamics and high snow-to-liquid ratios (in
excess of 20 to 1), not out of the question some localized areas
could see quite hefty snow totals by morning. Not overly confident
on exact placement or potential high end amounts, so will simply
cover favored areas with a winter weather advisory, using verbiage in
such to highlight concern for heavier snow potential.

Off Lake Superior...Much tougher call here, with that lake induced
low and potential cold air drainage off the Canadian Plateau
expected to really play havoc with low level wind trajectories. Snow
showers will initially linger this evening in favored northwest flow
areas, with pattern recognition of the above favoring focus for
heavier snow showers toward Whitefish Point and Paradise overnight
into early Saturday. If cold air drainage is strong enough, could
easily see snow showers pushing completely into Luce County.
Snowfall rates easily in excess of one inch per hour are expected if
enhanced banding is realized, with that favored area once again
across far northwest Chippewa County. A small area for sure, but
felt it worthy to go ahead and extend the current headline through
Saturday morning.

As mentioned, dry air and further backing of winds should decrease
both snowfall intensity and coverage heading through Saturday


.SHORT TERM...(Saturday night through Monday)
Issued at 327 PM EST Fri Dec 9 2016

Saturday night and Sunday...

...Widespread Sunday Snow Potential...

High impact weather potential: Heavy snow potential across at least
southern 1/2 of the area on Sunday, with Lake Huron enhancement

Pattern Synopsis/Forecast: The lake effect machine gradually ending
Saturday evening as inversions continue to fall with decreasing mean
layer moisture.  As winds back more to the southwest, lingering lake
effect will shift toward the Straits.  Guidance continues to
struggle with the next shortwave and associated surface reflection,
as energy pushes out of the mid-Mississippi valley and into the
southern lakes.  Euro remains the weakest with said feature, sliding
a relatively weak open wave across the lakes on Sunday with limited
moisture/forcing producing light snow across the area.  NAM quite a
big stronger showing a stronger phased system over the lakes
resulting in quite a bit heavier precipitation.  No doubt there will
be at least some lighter snows developing across at least northern
lower on Sunday with increasing isentropic upglide and deepening
moisture (but how much?).  Will place the highest POPS and
accumulations over the southern 1/2 of the area, closer to deeper
moisture/forcing.   Will need to closely watch the Lake Huron
shoreline for lake enhanced snow Sunday afternoon, with enhanced
convergence and favorable thermal profiles supporting at least some
lake contribution.


Sunday night and Monday...

Broad WAA and isentropic lift will continue across the area Sunday
evening ahead of the surface low. The NAM remains the aggressive
solution with the nose of a 40+ knot low level jet brushing our
southeast. In contrast, the ECMWF confines the LLJ to the Ohio
Valley, while the GFS and CMC are more middle of the road with a
modest 20-30 knot LLJ nosing into southern Michigan. Given
increasing spread in GEFS and SREF members beginning Sunday evening
(seen particularly in snowfall plumes), a model blend is preferred
at this time over any particular solution. Models do agree that the
best moisture will be found around Saginaw Bay and south where PWATs
will approach a half inch. Surface low will travel northeast across
northern Lower, reaching Lake Huron by Monday morning. Bulk of the
widespread snow will end quickly on the backside of this low and
associated cold front, but a potent mid level shortwave will provide
an enhanced possibility of lingering snow across the northern part
of the area through early Monday. CAA from cyclonic flow over Lake
Superior and northern Lake Michigan will then lead to some lake
effect snow showers on Monday across eastern Upper and northwest
Lower, as soundings show steepening mid level lapse rates with
increasing low level instability by afternoon.


.LONG TERM...(Tuesday through Friday)
Issued at 327 PM EST Fri Dec 9 2016

A cold and active pattern will continue across the country and Great
Lakes through the period. Broad upper troughing, almost nearly
zonal 500mb flow, will linger over the Great Lakes and northern
Plains through the work week, anchoring a chunk of polar air
(850mb temps around -22c) over the state. This will generate well
below normal afternoon highs in the teens through Friday. Westerly
flow lake effects will combine with a weakly organized system
passing through the Great continue periods of snow
across much of northern Michigan through the forecast period.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 707 PM EST Fri Dec 9 2016

Lake effect snow showers continue, primarily impacting KTVC and
KPLN through tonight. Winds will back more westerly late tonight
through Saturday and push most persistent snow showers up into the
tip of the mitt and KPLN terminal site.

Otherwise, a mix of VFR to MVFR cigs anticipated through Saturday.
Occasional IFR vsbys within the heaviest snow showers.


Issued at 327 PM EST Fri Dec 9 2016

Marginally gusty northwest winds and numerous lake effect
snow showers to continue tonight into Saturday morning. Winds back
southerly and decrease some Saturday night.


MI...WINTER WEATHER ADVISORY until noon EST Saturday for MIZ016-017-
     LAKE EFFECT SNOW ADVISORY until noon EST Saturday for MIZ008.
LM...SMALL CRAFT ADVISORY until noon EST Saturday for LMZ345-346.


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