Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 111131
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
631 AM EST Sun Dec 11 2016

.NEAR TERM...(Today)
Issued at 329 AM EST Sun Dec 11 2016

...Widespread snow arriving today...

High impact weather potential: accumulating snow all areas into this
evening.

High pressure centered over the Mid-Atlantic coast, with ridging
extending n and nw into northern Ontario. Low pressure is emerging
from the central high plains, with a long swath of synoptic snow
extending from the Dakotas into central/southern lower MI. The
snow will expand northward today, and exit early tonight. Snowfall
trends are the main concern.

Today...original surface low will dig into the s central states. An
associated inverted surface trof will become better defined with
time, and a 1009mb low will spin up in WI this afternoon. This
occurs as a compact but potent 500mb shortwave moves ese into
northern MN this afternoon. Moisture availability will increase as
the system makes eastward progress. Frontogenetic forcing is not
overly impressive; the 850mb thermal gradient barely tightens up
this morning, then relaxes considerably during the afternon. This
hints at the expected evolution of synoptic snow: the ongoing long
but somewhat narrow snow swath will morph into a broader snow plume
this afternoon as (weak) fgen forcing diminishes and is replaced by
a broader warm conveyor belt ahead of the developing WI surface low.

Ongoing lake effect snows in the Straits region will continue to be
displaced northward, as 1000-850mb winds become southerly
(eventually se by midday) and increase. Light synoptic snow is
already pushing into southern sections of the forecast area; it will
tend to stay south of M-32 this morning, then expand northward
rather quickly at midday into the afternoon. Precip will start to
wane toward early evening along the Lake MI coast of nw lower, as
the warm conveyor belt moves eastward while downsloping se sub-850mb
winds continue.  Liquid-equiv QPF looks to range from 0.10-0.15
inches near and north of a line from Empire to Rogers City,
increasing to near 0.40 near Saginaw Bay. Snow-liquid ratios will be
harmed this morning by the best omega being placed above the DGZ.
The two are better aligned this afternoon, though near Saginaw Bay
the deep isothermal layer warms to around -10c, leaving only a
skinny DGZ well above 600mb for a period this afternoon.

All told, synoptic snowfall totals (including early in the tonight
period) will be in the 2-3 inch across much of the forecast area,
only reaching 4-6 across the far se. Some lake enhancement will be
seen into Mackinac and se Chippewa Co in se 1000-850 flow; further
south a more southerly low-level flow largely precludes enhancement
into northern MI. Will tack on another inch or so into
western/central Mack, and another 2 inches in eastern Mack and se
Chip.

No changes to headlines. Max temps in the 20s.

&&

.SHORT TERM...(Tonight through Tuesday)
Issued at 329 AM EST Sun Dec 11 2016

Tonight...low pressure will deepen as it crosses northern MI, and
will be nearing Georgian Bay by morning. Warm conveyor will belt
continue to move off to east, and widespread snow will be exiting
this evening. Wraparound moisture/comma head will be crossing
Superior and upper MI late evening/overnight, but this portion of
the system will be poorly organized. A baggy pressure gradient in
the wake of the system will result in weak northerly 1000-850mb
winds overnight north of M-32, while somewhat more brisk wnw winds
will develop late to the south.  Cold advection will be weak
overnight, as the temp gradient is somewhat baggy as well. Low level
moisture is generally rather abundant, even as some drier mid-level
air arrives (especially over northern lower MI). This could be a
freezing drizzle scenario in some cases, but in this event the
airmass looks too cold. In general, expect patchy light snow to
linger even as widespread activity exits. Some lake effect will
develop into parts of nw lower MI (and perhaps far western Chip)
toward morning, boosting pops a little further. Nighttime accums 1
to 2 inches.

Not much of a temp fall tonight, with mins near 20f to the mid 20s.

Monday into Tuesday...

High Impact Weather Potential...Lake
enhanced southwest flow snow possible Monday night. Burst of snow
and gusty winds possible with arctic boundary late Monday night
into Tuesday morning.

Pattern Synopsis/Forecast...The sfc low is located in Georgian Bay
at 12z, with the lake aggregate trough stretched back into Lake
Superior. At 500 mb the shortwave trough is moving through E Upper
and N Lower during Monday morning. Looking at the 1000-850 mb layer
wind flow pattern, the winds begin to turn NW-ish around 12z/Mon
which should begin the lake effect that will probably last through
the end of this next week. With the water temperatures still running
around 7c in Lake Superior and 8-9C in Lake Michigan, will expect
that with any 850 mb temperature colder than -5 or -6c will get the
LES machine going. The limiting factors will be the wind direction
shifts that the models hint at happening every 3 to 6 hours. This
does not bode well for persistent snow bands to drop mass quantities
of snow.

However, Tuesday, the winds are more west all day long, which would
produce some moderate LES near KMGN due to Green Bay being open,
providing a long fetch (greater than 100 miles) and the models
hinting at moisture in the 850-700 mb layer of around 60-70%. The
limiting factors here would be that the 850 mb temperatures begin to
get colder than -20c which would curb the production of larger snow
flakes, making this more like a fine powder, than fluff of the
larger dendrites. Also, some of the more higher res models like the
NAM12 showing that the synoptic dry air may be able to work into N
Lake Michigan and limit the LES.

.LONG TERM...(Tuesday night through Saturday)
Issued at 329 AM EST Sun Dec 11 2016

Extended (Wednesday through Saturday)...Looking at the 1000-850 mb
wind flows from Wednesday through Friday, the winds will be W to NW
with 850 mb temperatures of -15c or colder. Friday, looks to have
then next major system with a low moving through the region warming
the forecast area up to almost 0c (850 mb), only to quickly fall
back into the -10c to -15c range as the low exits with another
arctic blast. So the general idea is probably around normal
precipitation, with at or below normal high temperatures until
Friday/Saturday when the warm advection pushes up back above normal
briefly before we cool off late on Saturday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 631 AM EST Sun Dec 11 2016

-SN invading with IFR conditions at times.

Low pressure will develop in WI this afternoon, and intensify as
it crosses northern MI tonight. -SN in advance of the low is
already impacting much of lower MI, and snow will become more
expansive (especially this afternoon). Prevailing IFR vsbys
expected for a good chunk of the day. IFR to low-end MVFR cigs
will linger into tonight, even after the more widespread snow
exits.

Light s to se winds today.

&&

.MARINE...
Issued at 329 AM EST Sun Dec 11 2016

Low pressure will develop in WI this afternoon, and intensify as
it moves to Georgian Bay by Monday morning. Se-erly winds will
develop in most places today, replaced by nw-erly winds by Monday.
Some spots will see gusty winds late tonight in the wake of the
system, especially south of Ltl Trav Bay on Lake MI. Will assess
need for small craft advisories over the next hour.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until 7 AM EST Monday for MIZ008-015>036-
     041-042.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

NEAR TERM...JZ
SHORT TERM...JZ/JSL
LONG TERM...JSL
AVIATION...JZ
MARINE...JZ


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