Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 181531
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1031 AM EST Mon Dec 18 2017

.UPDATE...
Issued at 1031 AM EST Mon Dec 18 2017

Warm front is holding south of our CWA late this morning. All of
Michigan remains in a rather soupy/saturated airmass along and
north of this boundary. Low stratus and fog continue to hang over
the entire Western Great Lakes region...with a few spots still
reporting some dense fog. Ample moisture and low level shear along
with weak lift north of the warm front continue to produce areas
of freezing drizzle and flurries across much of our CWA. Weak wave
lending support to this very light precip will exit our CWA this
afternoon...resulting in diminishing and possibly a temporary end
to the precip. Also...as temps warm into the mid to upper 30s...
the freezing drizzle will become plain drizzle...and any remaining
slick spots due to freezing drizzle will improve.

&&

.NEAR TERM...(Today through Tonight)
Issued at 340 AM EST Mon Dec 18 2017

...Milder but still some wintry concerns...

High impact weather potential...light wintry mix in spots today
and tonight. Potential for icy roads. Dense fog in spots along
M-55 this morning.

Warm front has lifted north into central lower MI. Two bands of
fgen- forced precip were impacting the region. One was decaying
over eastern upper MI, producing light snow. The other was more
convective-looking, producing snow showers in central and parts of
northern lower MI. These will all be diminishing during the
morning hours, as a sheared-out shortwave and associated fgen exit
the area. That leaves behind a sludgy airmass, plenty of low
clouds out there, and (south of M-32) some fog. Mainly just
nuisance- type wx today, but things get dicier tonight as a
shortwave moves ese- ward into the northern lakes.

Moist low-levels will maintain plenty of cloud cover today, even as
the mid/upper levels partially dry out behind the departing wave.
Bufr soundings emphasize the general mushy-ness of the situation,
with plenty of moisture below 3k ft, with occasional (cooler)
moist layers poking in and out between 5k and 15k ft. So we might
be able to establish some seeder-feeder processes at times, but
most of the time, this is a potential drizzle/flurry setup. Most
of northern MI will eventually warm above freezing by the end of
the daylight hours, but until then some patchy fzdz will also be
possible.

Fog is presently soupiest in the south, with dense fog at HTL/W
Branch/OSC, while CAD has improved to 1/2SM. With temps in the
mid/upper 20s (though heading upwards), some potential for a touch
of icing on some surfaces. This might also be a favorable zone
for freezing drizzle early on, in between the snow showers that
dot the region early this morning. Gave some thought for a dense
fog headline, but would only be for a few counties, and there`s
some potential for passing pre-dawn snow showers to disrupt fog.
Anticipate writing an SPS shortly to discuss fog and very light
icing potential in southern sections this morning.

Max temps today will eventually reach the mid 30s in most locales.

Tonight, another shortwave pivoting around the Hudson Bay low will
make a run at us. An associated cold front will cross most of
northern MI in the overnight hours. Narrow plume of better
isentropic ascent ahead of this front will contribute to some
precip tonight, especially in northern sections (closer to
stronger height falls). Models have trended a little slower in
breaking out precip, which should start to move into eastern upper
MI by late evening, but will be most expansive between midnight
and 5-6am. Pops will increase to categorical across much of
eastern upper (at least for a period), with likelys sneaking only
a bit south of the Bridge, and chance pops as far south as
Grayling. A warm nose at onset could result in a brief mix of
exotic p-types early on, but otherwise a surface-based warm layer
will determine p-type. That looks to be almost all snow in eastern
upper MI, with some rain mixing in near Lakes MI/Huron. More of a
rain-snow mix in northern lower MI, which will be largely
elevation-dependent (more snow inland, more rain near the coasts).

This is not remotely a freezing rain scenario in the classic sense.
But, given we`ve been in the deep freeze for almost two weeks, there
are concerns that ground/surface temps will not recover as quickly
as air temps today into tonight. That might allow for rain tonight
to freeze on some of our roads, even with air temps above freezing.
Too soon to pop an advisory for this potential, since pops/QPF do
drop off as one heads south into the rain zone. But will mention
the possibility of icy roads overnight in the HWO.

Min temps around 30f to the lower 30s.

&&

.SHORT TERM...(Tuesday through Wednesday)
Issued at 340 AM EST Mon Dec 18 2017

...Turning colder with a little lake effect...

High Impact Weather Potential: Possible icy roads early Tuesday in
some spots.

Primary Forecast Concerns/Challenges: Chances for lake effect snow.

Steady cold advection Tuesday behind a departing surface cold front.
So after some lingering mixed rain and snow showers early, the lake
effect machine should fire up (at least to a certain extent). Plenty
of over lake instability with lake-850 mb delta ts slowly increasing
to near 20 Tuesday evening. Model soundings across northern lower
however still look fairly unimpressive with inversion heights only
4000-5000 feet. In addition, 850-700 mb rh is only about 55 or 60
percent and it is not centered in the dendritic growth zone. These
parameters are a little more favorable across eastern upper though.
So the bottom line is the expectation is for mainly light lake
effect snow showers in west northwest favored locations from late
Tuesday morning through Tuesday evening with the flow veering into
the northwest for overnight Tuesday into Wednesday morning.
Accumulations in the couple of inches range expected across northern
lower while eastern upper could push up into the few inch range
(maybe). Slowly falling temperatures through the 30s Tuesday with
highs Wednesday in the colder middle 20s to near 30.

.LONG TERM...(Wednesday night through Sunday)
Issued at 340 AM EST Mon Dec 18 2017

...Low pressure likely tracks into northern Michigan...

Extended models continue to struggle over the timing/track and
intensity of likely low pressure moving up from the Plains into the
Great Lakes later in the week. Notable trends over the last couple
of days: Slower and farther north. This results in adjustments to
the forecast. The first is to slow down the timing of incoming
mainly light snow chances Wednesday night into much of Thursday. The
second is to add in the likelihood of a mix with and possible change
over to rain Friday into Friday night (though much of eastern upper
could escape the warmer air and remain mostly all snow). Still lots
of uncertainty over the details but this system still has the
potential to disrupt travel (perhaps even in a major way). Colder
air and lake effect is likely to follow at some point Saturday
through the remainder of the weekend (these details are fuzzy too
unfortunately due to moisture/timing differences). It still looks
like another shot of arctic air dives into the region somewhere on
or about Christmas Day making for a rather frigid next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 655 AM EST Mon Dec 18 2017

IFR/LIFR cigs/vsbys to start the morning, improving to MVFR this
afternoon.

Southwest low-level flow will slowly increase into this evening,
ahead of a cold front that enters northern MI overnight. Plenty of
low level moisture remains in place ahead of the front, with
stratus/fog and plenty of LIFR/IFR conditions to start the day.
This will improve somewhat as warmer air works northward, and
anticipate improvement to MVFR this afternoon. The cold front
tonight could bring some rain/snow showers tonight, especially at
PLN. Otherwise MVFR cigs tonight.

Sw breezes today and this evening. LLWS tonight, just ahead of the
incoming cold front.

&&

.MARINE...
Issued at 340 AM EST Mon Dec 18 2017

Southwest winds will be push gale force for parts of today/tonight
on parts of Lake MI, ahead of the cold front that moves thru
overnight. Will evaluate the potential need for gale warnings
later in the morning. Otherwise, advisory-level conditions are
expected ahead of and behind the front.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from 9 PM this evening to 6 AM EST
     Wednesday for LHZ346>349.
     GALE WARNING from 7 PM this evening to 7 AM EST Wednesday for
     LHZ345.
LM...SMALL CRAFT ADVISORY from 2 PM this afternoon to 6 AM EST
     Wednesday for LMZ323-344>346.
     GALE WARNING from 7 PM this evening to 7 AM EST Wednesday for
     LMZ341-342.
LS...SMALL CRAFT ADVISORY from 9 PM this evening to 6 AM EST
     Wednesday for LSZ321-322.
&&

$$

UPDATE...MR
NEAR TERM...JZ
SHORT TERM...AS
LONG TERM...AS
AVIATION...JZ
MARINE...JZ



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