Area Forecast Discussion
Issued by NWS Gaylord, MI

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878
FXUS63 KAPX 090412
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1112 PM EST Thu Dec 8 2016

.UPDATE...
Issued at 842 PM EST Thu Dec 8 2016

...Lake effect machine running full bore...

Best lake effect parameters coming together this evening into
Friday as coldest air (-14C to -18C H8 temps) descends into the
northern lakes pushing delta T`s into the 20s, coupled with large
scale cyclonic flow and deep moisture. Lake convection has been
and continues to be a bit transient and broken as low-mid level
mean flow is just getting settled into a NW/NNW direction. But
most persistent snow showers do appear to be settling into areas
essentially west of U.S. 131 and particularly around the Grand
Traverse Bay area. Per radar snow accumulation estimates and
observations, heaviest lake convection is producing snowfall rates
around an inch per hour.

Rest of tonight, high resolution guidance (and trends) suggest
mean flow will remain settled into a 320-330 degree direction with
weakening winds and decreasing LLWS. This should allow some fairly
vigorous lake banding to set up overnight into Friday morning with
the biggest impact likely around the Grand Traverse Bay area with
a nice connection back into central Lake Superior. Anticipate inch
per hour snowfall rates, and possibly better. Of course transient
nature of lake effect will not likely lead to continual inch per
hour snows at any one spot. But where snow showers persist the
longest, certainly a good 4 to 6 inches of snow just tonight is a
good bet.

Have tweaked snow accumulations tonight through Friday based on
accumulations thus far and expectations for Friday as low level winds
back a bit more westerly during the day. Warnings and advisories
still seem well placed. But I may also add Presque Isle and Alpena
counties into the advisory mix given that nice persistent lake
band stretching from eastern upper Michigan down along the Huron
coast of those 2 counties.

&&

.NEAR TERM...(Tonight)
Issued at 320 PM EST Thu Dec 8 2016

...More Lake Effect Snow...

Favorable parameters to support more lake effect snow showers.
Lake/850 mb delta ts in the lower 20s...moisture in the 850/700 mb
layer of a robust 80 to 90 percent and inversion heights of close to
9,000 feet on average. Oh yeah, along with short waves embedded in
the flow evident on water vapor imagery enhancing activity from time
to time. These factors will pretty much all continue through the
near term and into the beginning of the short term as well. The main
near term forecast concerns revolve around the evolution of the lake
effect as well as current headlines and additional snow
accumulations.

Tonight...The flow continues to veer into the northwest across the
forecast area this evening and pretty much holds into the overnight
hours. This should focus best lake effect snow bands along and west
of Interstate 75 in northwest lower. However...mesoscale guidance
does not push activity quite as far west as previous guidance. This
is alright because this would still line up with current headlines
with several inches of more snow in the warning counties and a few
more in the counties with advisories.

&&

.SHORT TERM...(Friday through Sunday)
Issued at 320 PM EST Thu Dec 8 2016

Friday...

Continued northwest flow to start with a backing into the
west northwest in the afternoon. This should lead to a shift in the
lake effect snow bands (further inland). In addition...a convergent
band enhanced by a decent short wave in the afternoon should enhance
activity across portions of Otsego and Antrim counties at a minimum.
Expect a few to as much as several more inches. Headlines will
likely have to be extended with a few counties possibly having to be
upgraded to warnings (but will give the current headlines a while
to verify before changing any of them at this time).

Ground zero (where the sweet spot for the most snow falls) may be
along the southern Antrim/northern Kalkaska line where upwards of a
foot or more of accumulation is possible by Friday afternoon.

AJS

Friday night through Sunday...

...Plenty more snow chances...

High Impact Weather Potential: Accumulating snows through the period.

Pattern Synopsis/Forecast: Winter assault expected to continue for
the foreseeable future as cold air remains entrenched across the
Great Lakes. Current troughing does relax temporarily heading
through this weekend, setting up a more zonal flavor to the pattern.
This, however, does not mean conditions will quiet down, as fast
moving waves embedded in this flow regime bring additional snow
chances to start next week. Combine that with persistent lake snows,
and some of the snow belt regions are likely looking at some
appreciable snow accumulations by this time next week.

Primary forecast concerns: Addressing what should still be fairly
vigorous lake snows Friday night into Saturday, and additional snow
chances with a fast moving wave Saturday night into Sunday.

Details: Lake parameters remain rather impressive Friday night into
the first part of Saturday, with inversion levels up to and just
short of 10k feet, and excellent moisture and omega pegged within
the cloud layer dendritic growth zone. Wind fields become just a
touch dicey with time, with strong guidance support (as well as
pattern recognition) of maturing lake aggregate troughing across the
area. Where this exactly sets up is still in question, but per that
pattern recognition, the favored area would be across the tip of the
mitt/far northern Lake Michigan and up into central upper. This
should only serve to enhance low level convergence across northwest
lower and west sections of eastern upper as winds slowly back with
time. This convergence may be further enhanced via development of
northeast drainage flow off the Canadian Plateau north of the SOO.
Upshot to the above, could easily see one or more lake bands
maintaining inch per hour snowfall rates, producing several more
inches of snow by the time things begin to weaken some later
Saturday. Little doubt extensions of current winter headlines will
be needed for some. Since this "event" is just really getting going,
and with lingering uncertainty of better band placement Friday night
into Saturday, will not do those extensions just yet.

While it won`t end, lake snows should become more disorganized and
lighter later Saturday into Saturday evening as wind fields
themselves become disorganized and better synoptic moisture
contribution departs. Still some lingering uncertainty with
depth/available forcing with fast moving low amplitude wave set to
impact our area Saturday night into the start of Sunday. As it looks
now, not expecting a ton of widespread snow with this system, with
trends supporting the best isentropic upglide/moisture convergence
remaining south of our area. Will need to closely watch the
shorelines for lake enhanced snow however, particularly across
northwest lower Michigan, with increased moisture and weak
wind fields perhaps supporting meso-low formations and areas of local
convergence. Much too earlier for any specifics, but have seen
similar looking patterns result in some rather hefty shoreline
hugging snow amounts. Something to watch for sure.

MSB

.LONG TERM...(Sunday night through Thursday)
Issued at 320 PM EST Thu Dec 8 2016

High Impact Weather Potential: Additional snow accumulations with
synoptic system Monday and continued lake effect afterward into mid-
week. Gusty winds and cold temperatures mid-week may bring single
digit, perhaps some negative, wind chills.

Guidance continues to wrestle with the details of a storm system
expected sometime around the beginning of the week. Initially
arriving Sunday, things have slowed the past few cycles and it looks
like it may near the area Monday now. Current passage through SE MI
would bring snow for much of northern lower, with heavier amounts in
the SE portion of the CWA with some lake enhancement off Huron in
the Easterly flow on the north side of the low. Lake effect will
continue behind the low as cold air continues to remain overhead.
The coldest air of the season so far will arrive mid-week, with high
temperatures in the teens and gusty winds combining for single digit
and below zero wind chills.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1110 PM EST Thu Dec 8 2016

Lake effect snow showers will continue to bring largely MVFR and
periods of IFR conditions to the terminal sites through Friday.
While all terminal sites will see snow showers to varying degrees
through the taf period, biggest impact through Friday morning
will be at TVC, where NW/NNW winds will continue to bring heaviest
snow showers through that area.

&&

.MARINE...
Issued at 320 PM EST Thu Dec 8 2016

Gusty northwest winds and lake effect snow showers to continue
through Friday, with SCA conditions on some nearshore waters.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING until 3 PM EST Friday for MIZ019>021-
     025>027-031>033.
     WINTER WEATHER ADVISORY until 3 PM EST Friday for MIZ016-017-022-
     028-034.
     WINTER WEATHER ADVISORY until noon EST Friday for MIZ018-024.
     LAKE EFFECT SNOW ADVISORY until 3 PM EST Friday for MIZ008.
LH...SMALL CRAFT ADVISORY until 5 PM EST Friday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 5 PM EST Friday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 5 PM EST Friday for LSZ321-322.
&&

$$

UPDATE...TBA
NEAR TERM...AJS
SHORT TERM...MSB/AJS
LONG TERM...ALM
AVIATION...TBA
MARINE...AJS



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