147
FXUS63 KAPX 081132
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
632 AM EST Sun Dec 8 2024

.KEY MESSAGES...

- Mixed precip tonight, with small snow accums north of M-32.

- Wintry mix Monday into Monday night

- Accumulating lake effect returns for midweek

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 337 AM EST Sun Dec 8 2024

Pattern/synopsis: 991mb surface low is ne of Georgian Bay, along
the Ontario/Quebec border. A cold front extends w from the low
toward eastern upper MI, then curves sw across central WI. Temps
are mild, upper 30s to lower 40s across the area, though cooler
air is starting to spread back into the eastern UP. A surface
ridge axis extends n-s across MN.

Forecast: Some sprinkles/light rain is developing over far
northern lower MI. Low clouds are extensive north of M-72, but
this moisture is, and will remain, shallow. A few spits of rain
are possible today off of Lake MI into nw lower MI, and a few
flurries are similarly possible in eastern upper. But most
precip should not be impactful. However, the n-s ridge axis will
cross the area this afternoon, and stronger return flow ahead
of our next will be impinging late in the day. For late
afternoon and very early evening, a warm-advection wing of
precip could start to reach Leelanau Co and nearby areas. This
would mostly fall as rain.

Tonight, a complex surface low will advance eastward from the
northern plains. Deep theta-e advection ramps up in central and
northern sections of this forecast area. A warm-frontal slug of
precip will develop eastward over our heads, then lift northward
across and out of the area tonight. Associated pops will be
highest near, and especially north of, M-32. Expected QPF
tonight is around 0.25" in eastern upper MI, decreasing as you
head south. Behind the warm frontal band, low-level moisture
increases and deepens. Spotty Light precip will eventually
develop behind this band overnight, across northern lower MI.

P-type tonight: warmer air will be steadily returning to the
area. Where pops are highest (near/north of M-32), thermal
profiles favor snow at onset. There`s a smaller chance of
mostly rain in south. As the night proceeds, the rain-snow line
will gradually march north, reaching the Straits by 4 am. It
won`t make a lot of further progress, with a mix pushing into
Mackinac and se Chippewa Cos. The Sault looks to stay all snow,
though with lowering snow-liquid ratios with time. For most of
the area, this rain-snow line looks relatively "clean", with
only small chances for the more "exotic" p-types. However,
gridded forecasts do produce a small area of -FZRA potential
centered on Otsego Co (of course). Surface temp recovery will be
slowed in our higher elevations, and our most northerly higher
terrain areas will thus stand the best chance of just a touch
of icing.

Snow amounts 1-3" in eastern upper MI, around an inch in
Emmet/Cheboygan Cos, less south.

Max temps today are occurring early this morning, with most
places in the 30s to lower 40s thru the daylight hours. Lows
tonight in the 20s in eastern upper MI, near 30f to the mid 30s
in northern lower (where temps will slowly rise overnight).

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 337 AM EST Sun Dec 8 2024

PATTERN SYNOPSIS/FORECAST:

Surface low to our northeast over Ontario as of 4z...on cusp of PV
disturbance and nose of a 140+kt NW-SE oriented jet stretching back
into central Canada...atop a NW-SE oriented baroclinic zone
stretching from Saskatchewan to New Hampshire. Generally west to
southwest low-level flow on the upwind side of this boundary,
particularly here in MI, with temps rising into the 40s through 4z.
Pattern breakdown imminent over the western US as energy punts
eastward into the PacNW...where another clipper is strengthening
amid good dynamics and excellent Pacific moisture. (Anomalous pwats
around or greater than 0.5 inches stretch largely from the Pac NW
coast to the Great Lakes.) Upper low over the SW US slowly trekking
eastward, slowed by a ridge over the Gulf of Mexico, allowing for
excellent return flow into the Lower MS Valley.

Clipper to our northeast attm will drag a subtle BCZ over us
today...which will serve as a highway for that PacNW system to ride
eastward along tonight into Monday...as southwestern US low tracks
up into the OH Valley. This should drag a surface system through the
region Monday...with a secondary front dragging cooler air into the
region for Tuesday...as trough axis over the US sharpens
dramatically over the Great Lakes going into midweek. Sharpening
trough plus intensifying upper jet ahead of the trough axis will
drive development of a Nor`easter for midweek...and strengthen
cyclonic flow for us here in the Great Lakes as a potent upper low
sinks into the region...bringing another bout of very cold air to
the region for mid-late week (highs struggling to hit 20?). This
should also help to intensify lake aggregate troughing over the
region...setting the stage for another period of accumulating lake
effect snow, along with the potential for some breezy winds at
times...till surface high tries to sneak into the area and slacken
up the pressure gradient a bit for late week, perhaps. For the end
of next week...pattern appears relatively progressive/zonal...with
potential for a shortwave to cross the northern tier of the country
into the weekend. However...still quite a bit of uncertainty in the
strength/timing of this feature...which will need to be monitored in
the coming days.

Primary Forecast Concerns:

Potential for a wintry mix Monday into Monday night...The
Straits/EUP will likely be the battleground for most of the p-type
issues Monday, as the front should stall in this region as the
triple point with this system moves through.  Think this is where
the better precip rates will end up being...but also where the
thermal profiles could switch back and forth between snow, sleet,
and freezing rain as warm air passes by aloft during the day. Strong
low-level easterly flow expected with this system over the EUP,
too...which signals potential for dry advection out of
Canada...which could keep surface temps cold enough to warrant
concerns for greater ice accretion (if the warm nose aloft is deep
enough) and/or accumulating sleet that could also impact
travel/clean-up. Think at least a glaze to a few hundredths of ice
is possible across the EUP...with some probabilistic guidance
suggesting a worse-case-scenario of up to 0.10-inch of ice accretion
across parts of the EUP by Monday night. Still a fair bit of
uncertainty in the timing of the warm front/triple-point
passage...and how far north it ends up...but the timeframe of
impacts during the morning into at least midday for this region
seems the most reasonable attm...as the warm air could sneak far
enough north by afternoon to preclude further issues (and perhaps
melt some of what will have fallen). Not impossible this system ends
up being much colder than expected, which could shift ptypes and
accumulations further south than currently expected. Only other
ptype concern would be for parts of the interior higher terrain to
get some freezing drizzle at times as the dry slot tries to work in,
but where surface temps could be cold enough. Cold advection should
begin overnight Monday night as a trough axis swings through,
increasing potential for lake effect processes to start kicking up
again...and thermal profiles more supportive of snow again (though
if moisture isn`t deep enough...freezing drizzle could yet be on the
table into early Tuesday).

Accumulating lake effect returns for midweek...Think there will be
some lake effect on Tuesday with some disturbances moving through,
primarily focused in the usual lake effect zones (W/NW flow);
perhaps a few inches Tuesday night where the better bands set up.
Even so...think the best shot of accumulations will be Wednesday
with the primary trough axis and punch of much colder air...along
with some synoptic moisture. Think most areas could see a little bit
of snow, but the main event will be in the lake effect snow belts
again. Signals for weaker stability with this feature also hint at
potential for more bang for our QPF buck with this system. Still a
few days out, but certainly worth keeping an eye on as we could put
back (at least in the lake effect snow belts) a fair bit of the snow
we may lose in the next couple days with the warmth/rain. Also of
note is the potential for weak enough flow to allow for a
convergence band up in eastern Lake Superior again...potential of
which should be watched for Tuesday night into early Wednesday ahead
of the trough axis.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 632 AM EST Sun Dec 8 2024

Mix of MVFR and VFR cigs this morning, behind departing low
pressure. Weak ridge of high pressure moves in this afternoon,
before next system approaches tonight. Precip moves back into
the region tonight, CIU/PLN with IFR conditions in -SN (turning
to rain at PLN late). MBL/APN will see IFR cigs very late
tonight. TVC will be MVFR tonight.

Winds becoming light today.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 9 AM EST this morning for LHZ345-
     346-349.
     Small Craft Advisory until noon EST today for LHZ347-348.
     Small Craft Advisory until 9 AM EST this morning for LMZ323-
     341-342-344>346.
     Small Craft Advisory until noon EST today for LSZ321.

&&

$$

SHORT TERM...JZ
LONG TERM...FEF
AVIATION...JZ

NWS APX Office Area Forecast Discussion