Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 101756
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1256 PM EST Tue Dec 10 2019

.UPDATE...
Issued at 1153 AM EST Tue Dec 10 2019

A quick update..The snow bands are shifting now to the more west
to wsw orientation that they are expected to for tonight. As this
has been happening the dominate band in NE Kalkaska county is
beginning to diminish. Haven`t gotten any reports out of that area
this morning, but based on the band and the 7.6" report from
Mancelona this morning, wouldn`t be surprised if there is an 8 or
10+" amounts in there somewhere. So with this event winding down,
will keep the current advisories and begin to look ahead for
tonights headlines up near Emmet/Cheboygan counties and probably
Western Chippewa county as well.

&&

.NEAR TERM...(Today through Tonight)
Issued at 213 AM EST Tue Dec 10 2019

...Sharply colder with lake effect snow showers...

High impact weather potential: Turning much colder with accumulating
lake effect snow showers in our traditional snow belt locations of
eastern upper and northwest lower Michigan. Periods of reduced
visibility and snow-covered roads likely.

Pattern synopsis/forecast: Low pressure responsible for yesterdays
inclement weather now well off to our northeast...racing across
central Quebec. Core of mid level trough digging into the far
western Great Lakes, with its attendant much talked about Arctic
plunge punching southeast across southern Canada into the northern
Mississippi valley and northern Great Lakes (current readings well
below zero across portions of Minnesota). Leading edge of this
Arctic airmass making quick progress into our area on gusty
northwest winds. Deformation driven snows from earlier this evening
have largely ended, replaced by organizing lake snows into our
traditional snow belt locations. Combination of these snow showers
and gusty winds no doubt leading to some hazardous driving
conditions at times.

Cold air plunge will continue as trough axis swings right overhead
through tonight. Resultant temperatures will be well below normal
for this time of year, with wind chill reading several degrees
colder yet. Lake effect snow showers will most definitely continue
right through the period.

Primary forecast concerns/challenges: Lake effect snow accumulations
and impacts...with attendant headline considerations.

Details: Mid-winter like conditions expected across the Great Lakes
today and tonight, with high temperatures today remaining in the
teens and 20s, with lows tonight falling into the single digits and
lower teens. While wind gusts won`t be too extreme, it will
definitely be breezy enough to make it feel several degrees
colder...with wind chill readings tonight perhaps dipping below zero
at times. Simple extreme magnitude of the over-water thermal gradient
will continue to generate lake effect snow showers right through
tonight. For northwest lower snow belts, best parameters occur this
morning, with strong lift/convergence pegged in the heart of the
dendritic growth layer. A steadily backing wind field will limit
duration of any intense bands at any one location, but wouldn`t be
at all surprised to see at least a few inches fall very quickly
under any organized banding structures. Development of terrestrial
cape and a steadily thinning of large scale moisture should result
in a noted downward trend in snow shower organization this
afternoon. Would expect to see reorganization tonight as land based
cape is lost, this despite a lack of any good synoptic contribution.
Winds continue to slowly back, becoming west/southwest overnight.
This should target areas north of M-32 for better accumulations,
with the M-68 corridor and points north likely seeing at least a few
inches of additional snow by morning.

A bit more of a challenging forecast for our famous eastern upper
snow belts as those backing winds and potential development of lake-
induced low pressure tonight play havoc with placement of better
snow shower potential. Latest trends support maximized lake snow
parameters occurring today, with slowly backing winds allowing the
full length of Lake Superior to be utilized. Moisture tied to
passing mid level wave and lake-induced equilibrium levels topping
10kft (lake-induced cape up near 800 joules/kg this afternoon)
support intense snowfall rates, at times likely exceeding an inch
per hour. However, much like northern lower, those backing winds
should prevent long duration of these heavier snow rates. Still,
could easily see 4 to 6 inches, locally higher, for areas near
Paradise and Tahquamenon Falls by early this evening. Could also see
a period of heavier snows target the SOO this afternoon, although by
that time would expect snow bands to be much more
transient...reducing snowfall accumulation potential. Latest
guidance trends continue to advertise development of low pressure
across the eastern basin of Lake Superior tonight, forcing a
decidedly more backed flow across eastern upper Michigan. This
should result in better lake snow pushing north and offshore of
Whitefish Point later this evening, not returning until passage of
surface trough Wednesday morning.

Headline considerations: Will trim a few counties out of the
inherited winter weather advisory across northwest lower, with best
bands expected to impact the Charlevoix/Antrim/western Otsego
corridor this morning. May eventually need to expand these
advisories north into the Tip of the Mitt counties tonight as winds
back southwest. As for eastern upper, given heavier snowfall rates
expected to materialize today and anticipated snowfall amounts, have
opted to include northwest Chippewa county into the winter weather
advisory...running through midnight.

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 213 AM EST Tue Dec 10 2019

High Impact Weather Potential: Mainly light lake effect snow & cold
temperatures continue Wednesday.

Pattern synopsis/forecast: Well-advertised mid-upper level troughing
continues across the northern Great Lakes through the day Wednesday
with the core of the coldest air aloft becoming centered overhead...
evident by H8 temps falling to roughly -22 to -24 C. Continued lake
effect snow showers downwind of Lake Michigan and Superior will be
the result before heights begin to rise and weak warm air advection
takes over Wednesday evening - Thursday morning ahead of a compact
clipper system set to cross the region Thursday afternoon and
evening.

Primary forecast concerns/challenges: Lake effect snow chances and
amounts Wednesday. Cold temps/wind chills.

The core of the coldest air aloft continues to descend on northern
Michigan during the day Wednesday with H8 temps falling to -22 to
-24 C, and thus lake effect snow showers continuing through the
 day Wednesday. Certainly there`s more than impressive lake
 induced instability, but nearly all other attributes remain
 rather anemic through this time frame with nearly zero synoptic
 support/moisture above a 4 kft inversion and a DGZ rooted at the
 surface given such cold air aloft. Given that winds will slowly
 be veering more west- northwesterly through the midday and
 afternoon hours, would expect any relatively minor accumulations
 to be fanned out across a good chunk of northwest lower and
 northern Chippewa County. Expecting generally another 1-3 inches
 of fluffy accumulation across the hardest hit locations through
 the day Wednesday, although could foresee some locally higher
 amounts up to 5 inches near Whitefish Point stretching
 potentially over to locations near the Soo. Somewhat gusty
 surface wind gusts through this time frame may also yield pockets
 of blowing snow, especially across north- south oriented
 roadways.

Wednesday evening into Wednesday night, weak warm air advection
gradually increases from south to north... bringing a diminishing
trend to lingering snow showers through the overnight hours.
However, attention then transitions to a compact, quick-moving
clipper system set to cross the region during the day Thursday.
Could foresee an area of light snow spreading west to east across
much of northern Michigan as early as mid-late Thursday morning,
continuing into the afternoon before diminishing late in the day.
Latest trends suggest the bulk of accumulation (generally in the 1-3
inch range) with this system will fall across far northwest lower,
the Tip of the Mitt into parts of eastern upper with lesser amounts
as you head toward the M-55 corridor and toward Saginaw Bay.

Otherwise, the other story remains the season`s coldest air to date
with high temperatures on Wednesday in the teens for most across
northern Michigan. Combine that with an occasionally gusty west/west-
northwest wind alluded to above and wind chills are expected to
remain in the single digits below zero for much of the day leading
to a truly mid-winter feel. Wednesday night lows in the single
digits for most.

.LONG TERM...(Thursday night through Monday)
Issued at 213 AM EST Tue Dec 10 2019

High impact weather potential: Occasional chances for bouts of
wintry weather at various times through the long term forecast
period.

The aforementioned weak clipper system during the day Thursday may
yield a few lingering snow showers into Thursday night, although
with little impact anticipated by that time. Otherwise, while global
model guidance diverges in the degree of overall large scale pattern
amplification, occasional pieces of energy may prove to be enough to
bring occasional wintry precipitation chances to at least parts of
northern Michigan at various times through the remainder of the long
term forecast period. The first chance for this arrives during the
day Saturday with periods of light snow and/or mixed precipitation
possible.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1245 PM EST Tue Dec 10 2019

Lake effect snow bands continue this afternoon into Wednesday as
the low pressure continues to retreat east, and the cold air with
associated with the sfc high pressure continues to stream over the
relatively warm Great Lakes. Winds in the layer from the sfc to
about 5000 feet are beginning to the WNW and will continue to back
to the WSW by this evening. The change in direction will push the
snow bands from the TVC and MBL toward PLN. While light snow is
still possible at MBL and TVC, the MVFR/IFR category vsbys and
CIGS will be mainly limited to PLN where the the bands are
expected to reestablish themselves.

APN will see a brief lowering as the snow bands and clouds move
through the taf site while the bands shift with the wind
direction. For the rest of the TAF in APN, the cigs and vsbys will
remain VFR/MVFR.

&&

.MARINE...
Issued at 213 AM EST Tue Dec 10 2019

Coldest air yet this season will continue to overspread the Great
Lakes today through Wednesday, resulting in plenty of lake effect
snow showers. Gusty northwest winds this morning will likely subside
some this afternoon as they slowly back more west and southwest.
Winds will become gusty once again across all waters tonight and
Wednesday.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until 4 PM EST this afternoon for MIZ021-
     022-027-028-099.
     WINTER WEATHER ADVISORY until midnight EST tonight for MIZ086.
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-
     344>346.
LS...SMALL CRAFT ADVISORY until 7 PM EST Wednesday for LSZ321-322.
&&

$$

UPDATE...JL
NEAR TERM...MB
SHORT TERM...MG
LONG TERM...MG
AVIATION...JL
MARINE...MB


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