National Weather Service - Area Forecast Discussion

000
FXUS63 KAPX 041949
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
249 PM EST Sat Dec 4 2021

.NEAR TERM...(Through Tonight)
Issued at 248 PM EST Sat Dec 4 2021

High Impact Weather Potential: Lake effect snow/blowing snow
continues with the primary impacts continuing across portions of
eastern upper Michigan.

Pattern Synopsis/Forecast: Impressive 130+ kt northern jet streak
remains draped across the northern Great Lakes early this afternoon
with broad/weak troughing overhead. Embedded within this is a more
apparent shortwave, currently slipping by to our north while
attendant weak low pressure meanders toward the Ontario/Quebec
border. These features will trek east by this evening as upstream
high pressure settles overhead by mid-evening into the overnight
hours, albeit won`t be around for long as primary focus for the
forecast period will revolve around the Sunday-Monday time frame --
in more detail below.

Primary Forecast Concerns: Continuing lake effect snow/blowing
snow with the primary impacts across Chippewa County.

Lake effect snow showers continue this afternoon in earnest across
Chippewa County into portions of Mackinac County, and to a much
lesser extent across the typical WNW flow snow belts of northern
lower. Ample over-lake instability continues across far northern
areas with delta Ts ~20C over Superior, plenty of moisture extending
through a 8kft inversion, and omega pegged squarely in a 3-4 kft
deep DGZ. Similar conditions will remain in place through this
evening before slowly rising mid-level heights and incoming high
pressure alluded to above really make their effects felt heading
into tonight with low-level moisture stripping out, inversion
heights crashing to sub-5kft, and low-level winds gradually taking
on a more southerly component with time.

Across northern lower, less favorable moisture profiles continue
with forecast soundings continuing to display an unfavorable
inverted-V at the low-levels due to abundant near-surface dry air.
Certainly some snow showers will roam areas south of the bridge as
has been the case for much of the afternoon, but with less
coverage/intensity. The only blemish to this area may fall across
the Tip of the Mitt where preconditioning off of Lake Superior has
allowed banding to extend through the straits into Lake Huron. Will
have to keep an eye on this to see if it sags into Emmet/Cheboygan/
Presque Isle counties. None the less, limited overall accumulation
expected, but some brief reductions to visibility and quick accums
leading to snow-covered roads possible.

With respect to amounts this evening, an additional 1-3" (locally
higher) across northern Chippewa County seems reasonable before snow
shower activity really wanes by late evening. Blowing/drifting snow
also remains possible with continued gusts of 20-30 mph. No changes
planned to eastern upper winter wx advisory through 03z. Localized
amounts of an inch or so possible across the Tip of the Mitt/
northwest lower with lesser amounts elsewhere. Lows tonight mainly
in the 20s, but wouldn`t be surprised to see a few colder readings
as breaks in the clouds and briefly lighter winds may result in a
brief period of decent radiational cooling.

Attention then rapidly turns to the upstream system for Sunday-
Monday (see short term section below). It`s possible isentropically
driven snow showers arrive across far west/southwest areas toward
Sunday morning.
&&

.SHORT TERM...(Sunday through Monday night)
Issued at 248 PM EST Sat Dec 4 2021

...Winter storm with lake effect to follow...

High Impact Weather Potential: Moderate to high. Several inches of
snow Sunday with system along with potential freezing rain/drizzle
and sleet. Additional accumulating lake effect snow Monday.

Pattern Synopsis:

The upper-level pattern will quickly amplify Sunday as an impressive
trough digs across the central CONUS. Strong forcing aloft will lead
to cyclogenesis in lee of the Rockies and deepen this low near 990mb
as it treks across the northern Plains and into the northern Great
Lakes Sunday night. Longwave troughing will continue to slide over
the Great Lakes on Monday as the associated cyclone continues to
deepen and moves into Quebec by Monday night. Surface high pressure
will build into the region behind the system Monday night underneath
subsidence aloft.

Forecast/Details:

As well-advertised in past days, an impactful winter storm is set to
reach northern Michigan Sunday and create hazardous weather and
travel conditions through the short term period. Heavy snow
associated with the system is anticipated Sunday and Sunday night,
especially across eastern upper, while additional accumulating lake
effect snow is expected across parts of the area Monday and Monday
night. The following will detail each of these events:

1.) Heavy snowfall and wintry mix Sunday - Sunday night

Snowfall will begin Sunday morning across far SW portions of the
area near Manistee/Benzie counties. Strong mid-level warm/moist
advection northward across the area will help drive a frontogenetic
snowband that is expected to lift NE across the CWA through Sunday
morning/early afternoon. With amplified forcing, snowfall rates of
1"/hr will certainly be possible with this band. Forecast soundings
display a very favorable environment to support higher snowfall
rates and snow-to-liquid ratios with a saturated isothermal layer
extending a few thousand feet through/near the DGZ. Thus, a quick 2-
3" will be possible as this band moves through Sunday morning across
parts of northern lower. Higher snowfall rates and wind gusts of 20-
30 mph will lead to blowing snow and hazardous road conditions at
times.

The heaviest snowfall on Sunday is expected to arrive Sunday
afternoon/evening across eastern upper MI. The aforementioned band
will move into eastern upper around noon while receiving lake
enhancement with SE winds coming off of northern Lake Huron.
Snowfall rates near 1"/hr may continue for a few hours across
eastern portions of Chippewa/Mackinac county during the afternoon
and evening should lake enhancement materialize. Wind gusts of 20-30
mph will also lead to some blowing snow concerns across eastern
upper and, with higher snowfall totals, create even worse road
conditions across this area. In total, 7-10" is expected by Monday
morning across most of eastern upper with locally higher amounts
possible with lake enhancement. Amounts of 4-7" are expected from M-
32 to the bridge with lessening amounts with southward extent. There
is a chance for sleet/freezing rain later Sunday afternoon and
evening mainly along and south of M-72, but confidence is currently
higher for sleet than freezing rain and associated icing conditions.
The best chance for any glaze of ice will come with potential
freezing drizzle Sunday evening/Sunday night across northern lower
as there will be a break in precip potential during the overnight
hours.

2.) Accumulating lake effect snow Monday - Monday night

As this system departs to the east, WNW/NW winds behind it will
usher in the coldest air of the season and associated lake effect
snow chances beginning Monday morning. A broad area of snow is
expected around sunrise as a secondary front moves through, but lake
effect snow is expected to organize over the following hours Monday
afternoon and evening. Increased moistening through the lower
troposphere is expected via forecast soundings with ample delta-Ts
and saturation extending through the DGZ. This may support an uptick
in lake effect snow intensity Monday late afternoon through Monday
evening. Several inches of snow will be possible in the hardest hit
lake effect areas of northern lower and eastern upper, along with
increased potential for blowing snow and drops in visibility. Wind
gusts will increase to 30-40+ mph at times Monday afternoon and
evening, especially near the lakeshores. Quickly deteriorating road
conditions will certainly be possible underneath the heaviest lake
effect snow. Chances will wane overnight heading into Tuesday.

&&

.LONG TERM...(Tuesday through Saturday)
Issued at 248 PM EST Sat Dec 4 2021

High Impact Weather Potential: Remaining fairly active with various
chances of additional wintry weather.

By early Tuesday, impressive troughing across the eastern Great
Lakes is expected to have trekked northeast across Quebec. While
enough lingering low-mid level cold air may prove to be enough to
continue scattered lake effect snow showers, latest trends suggest
upper-level subsidence and incoming sfc high pressure will aid to
fight much in the way of additional appreciable accumulation. Precip
chances across much of the area return Tuesday night into Wednesday
as another wave dives out of Canada toward the Great Lakes region,
although subtle forcing mechanisms bring higher than desired
uncertainty through this time frame. An active pattern looks to
remain in place toward the end of the week into next weekend with
seemingly better precip potential as guidance continues to hint as
strong upper-level forcing across the nation`s midsection.
Otherwise, chilly teens/20s for highs Tuesday gradually moderate
into the 30s as we head through the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 138 PM EST Sat Dec 4 2021

Lake effect snow showers/flurries this afternoon into this
evening, primarily at PLN and APN. Cigs primarily remain VFR this
afternoon, but some brief reductions to MVFR not out of the
question. Gusty winds continue into this evening before breifly
diminishing overnight. Attention turns to Sunday when a low
pressure system is expected to bring a mixture of snow and
possible freezing rain, along with another round of gusty winds.


&&

.MARINE...
Issued at 248 PM EST Sat Dec 4 2021

Windy conditions expected over the next several days. Ongoing WNW
small craft/gale force winds this afternoon diminish briefly
tonight. Strong low pressure moves through the northern Great lakes
Sunday-Monday with SSE winds pick up through the day Sunday,
gradually veering more westerly during the day Monday. Periods of
gale force wind gusts are possible through this time frame across
all nearshore zones.&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WATCH from Sunday afternoon through Monday morning
     for MIZ086>088-096.
     WINTER WEATHER ADVISORY until 10 PM EST this evening for MIZ086-
     087-095.
LH...SMALL CRAFT ADVISORY until 10 PM EST this evening for LHZ346>348.
     GALE WARNING until 4 PM EST this afternoon for LHZ346>348.
     SMALL CRAFT ADVISORY until 10 PM EST this evening for LHZ345-349.
     GALE WATCH from Sunday afternoon through Monday evening for
     LHZ345>349.
LM...GALE WATCH from Sunday morning through Monday evening for LMZ323-
     341-342-344>346.
     SMALL CRAFT ADVISORY until 10 PM EST this evening for LMZ323-341-
     342-344>346.
LS...GALE WATCH from Sunday morning through Monday evening for LSZ321-
     322.
     SMALL CRAFT ADVISORY until 10 PM EST this evening for LSZ321-322.
     GALE WARNING until 4 PM EST this afternoon for LSZ321-322.
&&

$$

NEAR TERM...MG
SHORT TERM...DJC
LONG TERM...MG
AVIATION...MG
MARINE...MG

NWS APX Office Area Forecast Discussion