Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 090323

Area Forecast Discussion
National Weather Service Gaylord MI
1023 PM EST Fri Dec 8 2017

Issued at 1019 PM EST Fri Dec 8 2017

A very complex weather pattern out there tonight. An alberta
clipper is approaching from western Lake Superior, and is
enhancing ongoing lake effect. The difficult part is that the
winds are becoming very light and variable to some degree. This is
definitely resulting in a degree of uncertainty on where exactly
the highest amounts of snow will be, and where other areas of nrn
Michigan could see some unexpected higher amounts. There really
isn`t much of a consensus on a clear picture, but the greatest
degree of confidence is around the GTV Bay region. Did increase
amounts to as much as 6 inches there, but there could definitely
be higher amounts. Enhanced lake effect snow out over Lake Huron
could make it into Drummond Island, NE lower, or even add to snows
through the Straits where there has been decent snows ongoing this
evening. The impact of it all is whether additional counties need
to be in advisories. Have increased snows in these areas to show
the potential for more than anticipated snow, but will have to lay
off on additional advisories for now, and monitor radar to govern
any future needed headlines. There is sufficient evidence that
Chippewa county can be let go from their advisory now, and
Otsego county can be let go of the advisory close to midnight.


.NEAR TERM...(Tonight through Saturday)
Issued at 310 PM EST Fri Dec 8 2017

...Lake Effect Snow Showers Continue...

High Impact Weather Potential...Snow showers across the western
parts of northern Lower.

Pattern Synopsis/Forecast...Another wave moves into the upper trough
across the Great Lakes Saturday with a surface low pressure system
moving across Southern MI during the day. Lake effect snow will
continue with 850mb temperatures in the low teens.

Primary Forecast Concerns...Current W-WNW flow bring LES bands into
Gaylord, Charlevoix, Boyne City areas this afternoon. 1000-850mb
winds slowly back through the rest of the afternoon and drier air
continues to move into the area. This should help to push LES bands
away from areas that received snow this morning.

Low level flow becomes SWerly tonight which will help LES bands
develop over the Lake Michigan shoreline counties. This along with
moisture and lift ahead of the surface low should bring low-end
advisory level snows to those areas overnight. Continued LES and
departing surface low will then bring more snow showers to the
region Saturday. Flow eventually backs to N or NNW Saturday
afternoon which helps LES become more focused along the Lake
Michigan shoreline from TVC south. Snow amounts during the day
Saturday appear to be light at this time.


.SHORT TERM...(Saturday night through Monday)
Issued at 310 PM EST Fri Dec 8 2017

...Off and on Lake Effect Snow...

High Impact Weather Potential...It is possible that some of these
bands, as they transition from one wind flow regime to another, will
produce Higher impact weather especially on Monday as the south
winds over Lake Michigan, may enhance precipitation.

Pattern Synopsis/Forecast...Classic Ridge/Trough 500 mb flow pattern
with the trough over Hudson Bay. This allows either spokes of energy
from the 500 mb low to rotate into the Upper Great Lakes, (Saturday
night/Sunday) or as a potent shortwave, that rides over the 500 mb
Ridge along the Pacific coast and into the Northern Plains, spinning
up a sfc low that stays just to the south of the forecast area, and
keeps us in the cold air for synoptic snow/lake enhancement

Primary Forecast concerns...Saturday night, the main concern is the
NW to NNW flow that evolves into a W pattern by 12z. Temperatures
are definitely cold enough, with the water temperatures around +8c
and the 850 mb temperatures running from -14c to -16c over N Lake
Michigan and NW Lower around 00z/Sun, and warming to -9c to -12c by
12z. The HiResW-ARW seems to have the best handle on the bands and
where we would typically find the snow. Smoothed out the rougher
bands in the grids with the GFS and SREF. However, since this is
mostly LES, this is subject to change, as the bands merge and
realign with the wind patterns.

Sunday, as the 500 mb shortwave/clipper moves out of the region the
LES will be weaker, as the extra forcing from the wave moves to the
east. Most amounts should remain under an inch.

Sunday night into Monday, Main concerns will be the amount of
moisture in the 850-700 mb layer as the GFS/NAM show <40% RH in the
layer pushing into the region. The ECMWF is much more moist, and
could be onto something initially under the NNW flow. However, the
1000-850 mb ridge axis approaches the Lake Michigan shoreline by
06z. This will switch the wind direction as it moves into the region
by 09z, pushing the winds more WSW to SW over the forecast area. The
GFS/NAM continues the drier air with a slightly slower transition.
After 12z, the warm front moves into the region, the winds turn
south and the lake enhancement starts. The second concern will be
the SW to S flow will enhance the amounts in western parts of
Mackinac and Chippewa counties. The general amounts from the
synoptic portion of the system will be primarily south of M-32.

.LONG TERM...(Monday night through Friday)
Issued at 310 PM EST Fri Dec 8 2017

High impact weather: Periodic lake effect snows with enhanced snow
from several clipper systems throughout the extended period.

The extended period will see lake effect snows and a few clipper
systems bringing widespread snow throughout the forecast period.
Some accumulations will occur, but can`t pin point exactly where the
highest accumulations will be at this time...although it would
probably be safe to say that the favored locations in northwest flow
in eastern upper and northwest lower will be the likely targets for
the most. Highs will continue to remain below normal for this time
of the year...only reaching into the 20s, with Tuesday and Wednesday
being the coldest with a push of arctic air into the region...only
reaching into the teens. Lows Wednesday morning will drop into the
single digits negative and positive.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1019 PM EST Fri Dec 8 2017

A very complex weather pattern this TAF period. Low pressure near
western Lake Superior drops into lower Michigan Saturday morning,
then lifts through Lake Huron Saturday evening. Current westerly
low level flow will become highly variable as low level troughing
crosses later tonight through Saturday morning. The flow then turns
northerly Saturday and Saturday evening with the eastward passage
of the low pressure, before returning to westerly later Saturday
night with the approach of the next low pressure and cold front.
These varying winds, combined with lake effect being enhanced by
an Alberta clipper tonight into Saturday morning will result in
localized moderate snowfall amounts, but there is is some amount
of uncertainty. The better snowfall is expected to be in and
around the GTV Bay region, impacting MBL/TVC the most, with
general snowfall amounts ranging 3 to 5 inches. Locally higher
amounts are certainly possible. Through Saturday and Saturday
night, more typical lake effect snows develop from north flow
regimes to WNW through Saturday night.


Issued at 310 PM EST Fri Dec 8 2017

W to WNW winds will continue to gust to around 25kts before
subsiding some this evening. Small Craft Advisories will be needed
again on Saturday for the Lake Michigan and maybe the Lake Huron
nearshores as another storm moves across the area.


MI...WINTER WEATHER ADVISORY until 7 AM EST Saturday for MIZ020-025-
     WINTER WEATHER ADVISORY until midnight EST tonight for MIZ019-
LH...SMALL CRAFT ADVISORY from 7 AM Saturday to 5 PM EST Sunday for
LM...SMALL CRAFT ADVISORY from 7 AM Saturday to 5 PM EST Sunday for


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