109
FXUS63 KAPX 190300
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1000 PM EST Sat Jan 18 2020

.UPDATE...
Issued at 1000 PM EST Sat Jan 18 2020

Low pressure center continues to slide eastward away from Lower
Michigan late this evening. Secondary trough axis has pushed into
far Northern Lower Michigan. Surface winds have responded by
shifting to the north...and even to the NE across Eastern Upper
Michigan. This shift in low level winds behind the trough has
greatly diminished any lake contribution to snow production in
these areas. Have therefore cancelled the Winter Storm Warning for
all of Eastern Upper Michigan with only an inch or two of
additional snow expected overnight. All of Northern Lower Michigan
remains under a Winter Wx Advisory for now...but we should be able
to trim off our eastern counties from the Advisory later tonight as
winds shift to the N/NW in its wake and begin to mainly target
areas along and west I-75 overnight. Expect our snowbelt areas
across NW Lower Michigan will receive another 2 to 3 inches
overnight...with locally higher amounts possible.

&&

.NEAR TERM...(Through Tonight)
Issued at 312 PM EST Sat Jan 18 2020

...Heaviest snows target the snow belts tonight...

High impact weather potential: Organizing lake snows to bring
several inches of accumulation and attendant hazardous driving
conditions to our traditional snow belt locations. Lakeshore
flooding potential targets portions of the northwest lower coastline.

Pattern synopsis: Sub 1000mb surface low making its way steadily
east right across the heart of northern lower Michigan early this
afternoon, with the center of its mid level parent also working its
way east into western Lake Superior. Widespread snow continues
across portions of northern lower and eastern upper Michigan, with
total accumulations of several inches already reported. Pockets of
lighter snow continue off to our west and northwest as primary axis
of mid level support pivots across the northwest Lakes.

Low pressure will continue to steadily move east the remainder of
this afternoon and evening, reaching far southeast Ontario by the
early morning hours of Sunday. Upstream shortwave trough also works
east with time, with it and post-surface low cold air advection
continuing the threat for additional accumulating snow...with focus
for such increasingly directed into our traditional snow belt
locations.

Primary forecast concerns/challenges: Addressing additional snow
amounts and attendant headline decisions.

Details: As mentioned, surface low will make steady east progress,
exiting stage right by late this afternoon and early evening.
Strongest lift will exit with it. However, slower moving mid level
parent will follow, producing just enough forcing to likely keep
widespread light snow through much of the overnight (an additional
inch or so of snow, heaviest across eastern upper Michigan).
Addressing what should be burgeoning lake processes a much more
formidable forecast challenge. Initial surge of cold air advection
in a quickly veering low level wind environment is not overly
impressive...but should be just cold enough to entice the
development of lake moisture contribution into a slowly increasing
convective boundary layer (up around 8kft by later this evening).
Lake aggregate enforced surface trough extending back west from the
departing low into northern lower Michigan only adds to the
complexities. With all that said, do feel lake enhanced snow showers
will ramp up quickly this evening, targeting areas especially along
and south of M-32 where low level convergence is initially
maximized. Would like to see a better over-water thermal gradient
for more organized/intense lake processes, but still several more
inches of snow are possible this evening in those favored northwest
lower snow belts. Passage of main mid level wave later this evening
should overwhelm any lake aggregate effects, shunting surface trough
rapidly south, perhaps actually clearing our forecast area by
sunrise Sunday. Enhanced convergence along this trough should bring
a transient band(s) of heavier snow south into areas along and south
of Grand Traverse Bay through the overnight. Flow quickly veering
north and northeast for areas north of the big bridge should keep
any lake contributions to a minimum.

As for headlines: Tough call for eastern upper Michigan with minimal
additional accumulations expected through Sunday morning. Given
ongoing impacts from heavy snow and gusty winds, prefer to let
current winter storm warning alone, with the thought that the
overnight crew can end it much earlier than its 18z Sunday end time.
Winter weather advisories will remain unchanged across northern
lower with a combination of lingering "system" snow and those
developing lake processes. Even here, however, more than likely at
least a handful of the counties will be able to be cancelled earlier
than their current end time.

&&

.SHORT TERM...(Sunday through Tuesday)
Issued at 312 PM EST Sat Jan 18 2020

High Impact Weather Potential: Minimal for now

...Lake effect chances through Monday...

Pattern Synopsis:

Broad troughing will be in place over the eastern CONUS Sunday with
upper-level ridging west of the Great Plains. Saturday`s storm
system will continue to depart along the Atlantic coast with an
associated lake aggregate trough/secondary cold front draped across
northern lower Michigan. This is expected to sag south through
Sunday as a subtle shortwave moves across the Great Lakes overnight,
but timing is still uncertain. Strong surface high pressure will
continue to build into the Great Plains through the period due to
subsidence underneath the ridge-trough inflection point.

Forecast/Details:

The main forecast challenge for this period will be the progression
of the lake aggregate trough/secondary cold front overnight Sunday
through Sunday morning as this will greatly influence lake effect
snowfall totals across northwest lower Michigan. Current thoughts
are that it will be at or south of our forecast area border by the
beginning of this period. This would lead to weaker northerly flow
across the area, along with drier air moving in behind. The
combination of wind shift and drier air aloft will change the focus
and intensity of lake effect snow. Areas of northwest lower mainly
south of Grand Traverse Bay could see lake effect snow Sunday after
the frontal passage, with diminishing intensity through the evening
as moisture continues to decrease.

However, if the shortwave has less of an impact on the aggregate
trough/cold front than currently expected and remains in the
forecast area into the morning, this opens the door for continued
lake effect snow accumulations in WNW near-surface flow. These
continued accumulations would likely be more intense than the
northerly lake effect behind the frontal passage, and possibly heavy
with enhanced forcing along the boundary itself. There is also a
slight chance that ascent aloft provided by the passing shortwave
could create mesoscale influences with the boundary to further
enhance snowfall in some areas. Like previously stated, more
confidence currently lies in this passage happening by the beginning
of this period.

Lake effect chances renew themselves on Monday as northwest flow
returns across northern Michigan. While forecast soundings show
fairly shallow moisture with saturated profiles remaining below
850mb, at least a portion of this layer should lie within the DGZ to
support snow production. Relatively small accumulations are
expected, but weaker flow could lead to an opportunity for mesoscale
processes to enhance snowfall in some areas with cold air over land
and still relatively warm water temperatures in northern Lake
Michigan. High temperatures Sunday and Monday are expected to be in
the lower 20s for most with chilly overnight lows in the single
digits and lower teens.

.LONG TERM...(Tuesday night through Saturday)
Issued at 312 PM EST Sat Jan 18 2020

High Impact Weather Potential: Minimal

A somewhat amplified upper-level pattern is expected across the
country Tuesday morning with ridging in place across the Great
Plains and a shortwave moving through the southeastern US. Surface
high pressure should continue to build eastward into the upper-
Mississippi Valley, eventually stretching across much of the eastern
CONUS by Thursday. A lack of moisture and forcing across the Great
Lakes hinders precipitation chances mid-week for the area. The short
dry stretch could come to an end Thursday-Friday, but much
uncertainty exists given differing guidance at that timeframe.
Temperatures are expected to warm slightly through the workweek,
reaching into the low to mid-30s across the forecast area. Overnight
lows will also be in the lower 20s for most.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 607 PM EST Sat Jan 18 2020

Low pressure currently centered over Northern Lower Michigan will
exit our region this evening. Synoptic snow produced by this
system will gradually transition to W/NW flow lake effect snow
showers this evening as ample moisture and sharp low level
convergence remains over the area in the wake of the low center.
Overall conditions will remain MVFR...dropping to IFR within some
of the heavier snow showers. Snow showers will continue overnight
and will then gradually diminish on Sunday as high pressure builds
into the region. W/NW winds will strengthen to 15 to 25 kts
across portions of NW Lower Michigan tonight...with higher gust
along the lakeshores. Winds will eventually shift to a more
straight north trajectory as a secondary trough drops thru the
region later tonight into Sunday.

&&

.MARINE...
Issued at 312 PM EST Sat Jan 18 2020

Passage of surface low will quickly swing the winds around
to the northwest and north tonight and Sunday. Increasing
instability and a tightening pressure gradient will result in gusty
winds, especially south of Sleeping Bear Dunes tonight where gale
force wind gusts are expected. Winds should quickly subside Sunday
night.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until 7 PM EST Sunday for MIZ020-021-
     025>027-031>033.
     LAKESHORE FLOOD ADVISORY until 10 AM EST Sunday for MIZ020-025-
     031.
     WINTER WEATHER ADVISORY until 1 PM EST Sunday for MIZ016-022-028-
     098-099.
     WINTER WEATHER ADVISORY until 7 AM EST Sunday for MIZ017-018-023-
     024-029-030-097.
     WINTER WEATHER ADVISORY until 1 AM EST Sunday for MIZ034>036-041-
     042.
LH...SMALL CRAFT ADVISORY until 4 PM EST Sunday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 4 PM EST Sunday for LMZ323-341-342-
     344.
     GALE WARNING until 10 AM EST Sunday for LMZ345-346.
LS...NONE.
&&

$$

UPDATE...MR
NEAR TERM...MB
SHORT TERM...DJC
LONG TERM...DJC
AVIATION...MR
MARINE...MB

NWS APX Office Area Forecast Discussion