Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 061111

Area Forecast Discussion
National Weather Service Gaylord MI
611 AM EST Tue Dec 6 2016

.NEAR TERM...(Today and Tonight)
Issued at 305 AM EST Tue Dec 6 2016

...One more above normal day before cold air arrives tonight...

High Impact Weather Potential...Low. Increasing chances of mixed
rain and snow showers this afternoon and tonight.

Pattern Synopsis/Forecast...Narrow ridge axis continues to exit east
away from Michigan early this the far eastern edge of a
warm front/WAA wing lifts into NW sections of our CWA ahead of
deepening low pressure over the Northern Plains and Upper
Mississippi Valley. Latest base ref loop from KAPX shows a solid
area of mid level returns lifting NE thru Northern Lake Michigan
into Eastern Upper Michigan...with little in the way of any precip
actually reaching the ground attm. Deeper moisture and thus better
chances of precip remains further upstream in the vcnty of the cold
front which currently extends from NW Wisconsin thru Central Iowa
into Nebraska. Deepening vertically-stacked low will slowly make NE
progress out of the Northern Plains and into Southern Ontario over
the next 24 hours or so. Precip chances will be confined to Upper
Michigan this morning where deeper moisture will reside along and
ahead of the warm front. Better chances of precip will develop
across our entire CWA this afternoon and tonight as the cold front
and associated deeper moisture slide thru the area. CAA in the wake
of the cold front will begin to increase over-lake instability later
tonight...resulting in increasing chances of lake enhanced precip.

Primary Forecast Concerns...Precip type will remain an issue thru
this evening before CAA turns all precip over to all snow. Expect a
mix of rain and snow across Eastern Upper Michigan thru this morning
as temps hover in the upper 20s inland to the mid 30s near the
lakeshores...with little in the way of snow accumulation. As precip
chances increase across our entire CWA this afternoon and evening...
higher elevations will initially see a mix of rain and snow. This
mix will gradually spread into the rest of our CWA as the afternoon
and evening progresses with increasingly cold air sliding into the
area in the wake of the cold front. Precip will eventually switch to
all snow everywhere by around 06Z as temps fall into the mid to
upper 20s overnight. Although moisture will be sufficiently deep to
produce some light precip...narrow band of moisture will still be
limited and thus new snow amounts will remain minor...i.e. well
under an inch.


.SHORT TERM...(Wednesday through Thursday night)
Issued at 305 AM EST Tue Dec 6 2016

...Colder with lake effect snow...

High Impact Weather Potential...Lake effect snow showers will
develop on Wednesday, becoming more intense Thursday and Thursday
night. Several inches of accumulation will be possible within the
typical snowbelts along Lake Michigan. In addition, gusty winds will
cause blowing snow and reduced visibilities, making for difficult

Pattern Synopsis/Forecast...An elongated upper trough will develop
over the Great Lakes as a cutoff low drifts east across southern
Ontario. A significantly colder airmass will be supportive for
persistent lake effect snow showers, but veering low level winds
will shift the impact of snow bands southward along Lake Michigan.

Primary Forecast Concerns...Wednesday morning a vertically stacked
low will be located over the northern tip of Lake Superior.
Ingredients are coming together for a prolonged period of lake
effect snow across the Upper Great Lakes. Low level RH Wednesday
into Thursday across northern Michigan will be plentiful with 925-
850mb RH averaging 90 percent or higher. With 850 mb temps around
-12C, delta Ts will be around 20 degrees. Winds for most of
Wednesday will be brisk out of the SW with gusts of 30-35 mph
possible, higher along the coasts. LES bands are therefore expected
to initially affect eastern Upper and northwest Lower. PoPs will
increase through the day as mid level lapse rates steepen and the
capping inversion weakens and rises, especially north of M-32. Some
enhanced lift will come from an H5 shortwave as it passes across
northern Michigan Wednesday evening, mainly influencing areas north
of M-32.

A surface trough/wind shift line will then drop south through
northern Michigan Thursday morning, causing winds to gradually veer
to the NW by Thursday evening and to the NNW Thursday night. Low
level convergence along this line is expected to enhance the snow
potential, as will the erosion of the temperature inversion aloft.
In addition, favorable low level negative omega will coincide with
the dendritic growth zone for much of Thursday and Thursday night.
Despite the favorable setup for very efficient LES, the gradual
shift in wind direction will cause the bands to shift their
orientation, becoming more focused further south along the Lake
Michigan coast as the day/evening progress. This will act to temper
snow amounts for any given location, but areas around and south of
the Grand Traverse Bay area could easily see 6 inches or higher by
Thursday night.

Temperatures Wednesday and Thursday will top out in the upper 20s to
lower 30s with lows in the lower to middle 20s...closer to seasonal

.LONG TERM...(Friday through Monday)
Issued at 305 AM EST Tue Dec 6 2016

High Impact Weather Potential...

High impact weather potential: Accumulating lake effect snow
continues with some significant accumulations possible west of I-75
Friday - Friday night. Additional snowfall is possible on Sunday
across all of northern Michigan.

Focus early in the extended period continues around the ongoing lake
effect snow across the snowbelts of northwest Lower and eastern
Upper Michigan. Fairly good guidance agreement in H8 temps around
-13 C (delta Ts 20-22 C) becoming progressively colder throughout the
day Friday. Predominately NW winds to start the day should focus the
greatest potential along and west of US-131 and far western
Chip/Mack before the threat are subtly shifts northward as winds
slowly back WNW/W by Friday evening (thus focusing the heaviest lake
effect north of M-72/west of I-75). Signals continue to hint at
potentially significant accumulations (although hampered somewhat by
the aforementioned shifting/backing winds), which include steep low
level lapse rates, impressive subsidence inversion heights (15-20+
kft), and negative omega squarely in the DGZ at various points
Friday into Friday night. Decreasing lake effect PoPs will be the
rule Saturday, although expecting locations at least near the tip of
the mitt and eastern Upper to see additional snow showers, as winds
weaken and begin to veer with associated WAA ahead of a system
developing over the Plains. This sytem may be the next to provide
impact locally with widespread snow during the Sunday timeframe,
although a lack of guidance consistency will preclude much in the
way of details at this juncture.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 611 AM EST Tue Dec 6 2016

VFR conditions will deteriorate to MVFR as low clouds increase and cigs
lower with the approach of an upstream cold front. CAA behind this
front will increase over-lake instability and begin to produce
lake-enhanced clouds and precip tonight. Any precip this evening
should be a general mix of rain and snow...changing to all snow
overnight as colder air sweeps into the region.


Issued at 305 AM EST Tue Dec 6 2016

Winds and waves will reach SCA criteria today and tonight...and will
likely further strengthen on Wednesday in response to tightening
pressure gradient around deepening low pressure as it slides north
of Michigan thru Ontario and into Quebec by Wednesday night. Mixed
precip chances will also increase today and this evening as the cold
front moves thru the region. Precip will transition to all snow and
become lake-enhanced as strong CAA begins in the wake of the cold
front overnight and thru Wednesday and Wednesday night.


LH...SMALL CRAFT ADVISORY until 7 PM EST Wednesday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 7 PM EST Wednesday for LMZ323-341-342-
LS...SMALL CRAFT ADVISORY until 7 PM EST Wednesday for LSZ321-322.


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