Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 070309

Area Forecast Discussion
National Weather Service Gaylord MI
1009 PM EST Tue Dec 6 2016

Issued at 958 PM EST Tue Dec 6 2016

Cold/occluded front extended from just west of the Sault, south
across north central and northeast lower Michigan late this
evening. Front will continue to push east tonight, and exit the
forecast area within the next hour or two. Just a few light
showers were noted along front over tip of the mitt and eastern
Upper - and they should exit eastern Upper by 05Z.

Colder air will steadily overspread region tonight behind front,
as winds turn gustier. Expect plenty of cloud cover to persist,
as 850 mb temps fall toward -10C overnight. APX model soundings show
moisture eventually extending up to near 850 mb, so this will be
just sufficient for some light lake effect snow showers to
develop over far northern Lake Michigan after roughly 05-07Z.
However, with very shallow low level moisture, expect lake effect
snow showers to remain scattered and quite light. Lows will fall
off into the 20s.


.NEAR TERM...(Tonight and Wednesday)
Issued at 345 PM EST Tue Dec 6 2016

High impact weather potential: None. Period of light rain and snow
late this afternoon and evening, with light snow showers developing
later tonight.

Pattern synopsis and forecast:

Deep vertically stacked low pressure system spinning over NW MN with
an occluded front extending south through WI/IL. A shortwave with
strong DPVA/deep layer -divQ along and ahead of this front is
working with minimal moisture while lifting through western Lake
Superior. This is only resulting in a narrow corridor of light snow
and rain working toward nrn Michigan. The deep moisture associated
with the srn shortwave lifting through the SE states, continues to
wrap deeper moisture toward Michigan on the nrn periphery of the sfc
low in the mid Atlantic. Earlier thinking was that this will likely
result in a expanding swath of light rain/snow with minimal QPF.
Best chances over NE lower/Lake Huron where there is longer time for
moisture to advect there. This is still the thought per latest
radar. Plus, hi-res data suggesting a farther south expansion of the
precipitation in a narrow corridor. Latest radar also suggesting
this is valid.

Heading into tonight, the occluded front will cross us by this
evening with the srn system moisture making it up through NE lower
and Lake Huron before the front exits east. Best chances for
rain/snow there. Behind the front, are the beginnings of the long
talked about cold advection. There is no pre-existing lake effect,
and moisture is shallow back behind the front. Thus, it`s gonna take
time for the lake effect machine to get going, but could see western
Chip/Mack seeing some flakes at nightfall while the low level flow
is more southerly. Then, WSW flow sets up and doesn`t want to budge
through Wednesday, particularly the 1000-850mb flow which will hold
in a WSW fashion. Temperatures cool to -11C to -13C which will allow
moisture to easily extend to where ice is introduced into the
shallow convection (inversion heights below 5500 feet), and a more
solid lock/high confidence in snow showers. These cold temperatures
will also eventually result in p-type being all snow over the warm
water too. The WSW flow will pinpoint rather light but persistent
snow showers from north of M-68 in nrn lower through eastern
Chip/Mack counties of eastern upper, including the Straits. Only an
inch or two over this entire time period, but it is interesting to
see there are a few members of SREF ensemble that show in excess of
4 inches through Wednesday. Winds get a little gusty Wednesday, so
some blowing snow expected.


.SHORT TERM...(Wednesday night through Friday)
Issued at 345 PM EST Tue Dec 6 2016

...Intensifying lake effect snow...

Increasingly favorable pattern with sufficient cold air to produce
lake effect snow through the period. Over lake instability looks
extremely good with lake/850mb delta ts through this time in the
lower 20s. The main forecast concern revolves around snow amounts
and possible winter headlines.

Wednesday night into Thursday...Southwest flow veering west through
the night with continued veering into the northwest Friday
afternoon. Moisture is also good (850-700 mb rh 80 to 90 percent).
So plenty of fuel and instability for lake effect snow showers. In
addition...models are in agreement that a convergence axis pushes
across eastern upper Wednesday night and far northern lower Thursday
which will likely intensity the snow. However...the bands are
expected to be shifting around and reorienting with time.

Thursday night into Friday...Flow settles into the northwest with
continued excellent moisture and instability. So more opportunity
for beefy lake effect snow bands.

Bottom line to all this is for the potential for several inches of
lake effect snow. Therefore...will issue a broad watch for much of
northwest and north central lower Michigan from midnight Wednesday
night into Friday afternoon. It may be tough to reach the 8 inches
in 12 hours and 10 inches in 24 hours warning level criteria.
However...want to heighten awareness since it`s still early in the
season (we may ultimately end up with lots of advisories and perhaps
a handful of warnings). Either way, there is still plenty of time to
figure out the details.

.LONG TERM...(Friday night through Tuesday)
Issued at 345 PM EST Tue Dec 6 2016

High Impact Weather Potential...Several inches snow accumulation
possible late Saturday night through Sunday

Active weather pattern will continue through the extended period.
Initial lake effect snow will give way to a potentially robust low
pushing through the northern Plains. There is a slight tapping of
Gulf moisture with this system, but PWAT values will only be
slightly above typical for this time of the year. Can certainly see
picking up at least a few more inches through the day Sunday, and
more substantial accumulations are not out of the question. Getting
a good fix on totals this far out is like trying to nail jello to a
wall, but this will be a system to keep an eye on for any possible
warnings or advisories.

The cold H8 air will also remain overhead, so lake effect behind the
exiting system will add more to the snowpack. Temperatures
will continue to run a bit below normal through the period.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 648 PM EST Tue Dec 6 2016

South to southeast winds will become southwest tonight as a sharp
front crosses northern Michigan. Wind gusts of 20-30 kts will be
likely behind the front tonight (from the SW) as cold air
advection commences. Forecast frontal passage as follows...TVC
around 00Z...PLN 02-03Z...and APN 04-06Z. Generally MVFR ceilings
will prevail tonight into Wednesday, thanks in part to colder air
crossing the Great Lakes.

A few light rain or snow showers will accompany front tonight,
with light lake effect snow developing later tonight and Wednesday
at PLN and TVC. Reductions in visibility and accumulations are
expected to be minor. Heavier lake effect snows are expected
Thursday and Thursday night.


Issued at 345 PM EST Tue Dec 6 2016

Upgraded nrn Lakes Michigan and Huron nearshores, including the
Straits, to a Gale warning, as low level temperatures get colder and
colder with a tightening pressure gradient settling in tonight
through Thursday. Overlake instability will be large with deep
mixing tapping low end gale gusts tonight into Wednesday night.
Conditions will remain gusty, but at this point speeds are not
expected to reach gales Thursday.

Also, lake effect snows will become more and more common over this
time period, with the worst of conditions Thursday as a fairly
potent band of snow is expected to sweep across the region,
followed by good lake effect Thursday night into Friday.


MI...WINTER STORM WATCH from late Wednesday night through Friday
     afternoon for MIZ016-017-019>022-025>028-031>033.
LH...SMALL CRAFT ADVISORY until 7 AM EST Thursday for LHZ348-349.
     GALE WARNING until 1 AM EST Thursday for LHZ345>347.
LM...GALE WARNING until 1 AM EST Thursday for LMZ323-341-342-344>346.
LS...SMALL CRAFT ADVISORY until 7 AM EST Thursday for LSZ321-322.


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