Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 101731
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1231 PM EST Sun Dec 10 2017


.AVIATION...

Overcast VFR will deterioriate to MVFR over most of the area as a
moisture axis sweeps through the area this afternoon. Embedded light
snow within isentropic ascent ahead of the front may bring a brief
bout of snow showers roughly 19-02z this aftn moving from NW to SE
through the area. Wind will veer to NW behind the front before
turning light southerly by Monday morning in advance of an
approaching low. MVFR and light snow will overspread the area mid to
late Monday morning.

For DTW...Light snow is expected to begin as early as 15z Monday
morning. Moderate snow resulting in any appreciable accumulations
will hold off until late Monday aftn.


//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5ft.

&&

.PREV DISCUSSION...
Issued at 254 AM EST Sun Dec 10 2017

Discussion...

A strong lobe of vorticity rotating around base of mean upper low
centered over/east of James Bay will brush the northern lakes area
and push a weak surface trough into the region late today. Hires
models, including hrrr/ruc13, all support the idea of a decent
convergence region setting up south of this feature this afternoon
over the northern forecast area. West-southwest flow trajectory will
most likely allow a lake effect plume to funnel into area along and
norther of the I-69 corridor. Models suggest low level inversion in
the 5-6kft range by late in the day in the 5-6kft area, which should
support cloud depths sufficient for decent snow showers activity in
this banding. Previous forecast addressed this well, and still feel
that local snow amounts up to an inch will be possible before the
aforementioned surface trough works through and breaks up the better
snow bands into an area of flurries/scattered light snow showers.

Broadening out across the rest of NOAM, water vapor imagery shows
our next system of interest coming onshore in northern British
Columbia early this morning. This shortwave, while somewhat compact,
looks to be rather vigorous in its satellite representation. This
feature will top the western NOAM upper ridge, dig into the midwest
early Monday and then lift across the Ohio Valley into Monday night.
as it is overtaken by much larger PV anomaly that drops quickly SSE
from Nunavut.

Hires models suggest there will be an interesting interplay between
these features as they phase over/just east of the region. For our
purposes, the quicker this phasing begins, the more influence the
Gulf/Alaska shortwave will have on parts of the area, namely in the
form of additional light snowfall as some form of a deformation zone
precipitation follows the initial light snow. It is very difficult
to interpret the Arctic shortwave(s) given current the satellite
representation that far north, but model trends suggest potential of
this system exceeds our recent light snowfall.

If nothing else, the track of this shortwave from the Gulf/Alaska is
allowing for a plume a slightly better moisture from the Pacific (H7
specific humidities of 2 g/kg, pushing 3 g/kg in H85-H7 layer) which
should support several inches of snow (capped by how quickly the
lift translates east through the area). It will also be interesting
how the lake aggregate modulates low level features as the influence
of the main Arctic wave begins to influence the overall scenario.
This mesoscale influence from the Great Lakes seemed piece meal in
respect to yesterday`s system, but perhaps another couple of days in
this cold airmass will allow for a more organized response. Would
guess this will have a neutral to slightly positive influence on the
strength of low level forcing with this system attm.

Cold airmass of the past week deepens further as colder air of the
season spills in the north in the wake of Monday`s system thanks to
the strong influence of the Arctic stream. Highs Tuesday/Wednesday
will only reach the low/mid 20s-upper teens/low 20s respectively.
Low temperatures in the single digits Tuesday night will also allow
wind chills to dip below zero.

While some moderation in this pattern still seems plausible into
next weekend, it comes as a result of significant jet stream energy
from the Pacific region flattening the western NOAM upper ridge and
allowing for a broader NOAM trough. So, any milder temperatures back
into the 30s to 40ish? will come at the price of unsettled weather
as a series of shortwaves ride through the region within this active
northwest storm track. Meanwhile, the cold air remains poised rather
near the Canadian/US border.

MARINE...

Westerly flow, mostly in the 20 to 25 knot range over Lake Huron
today will shift to the northwest by this evening as a cold front
slides through. Winds will weaken tonight into Monday as low
pressure advances pushes into the region from the west. Deepening of
the surface low to the east of the Great Lake Monday Night and
Tuesday and an influx of arctic air will lead to a high probability
of northwest gales on Tuesday. In fact, gusts of 40 knots or
slightly greater are possible early Tuesday morning.  In addition,
the degree of cold air will also support high probabilities of
freezing spray and snow squalls. Winds willundergo a gradual
weakening trend Wednesday as high pressure attempts to expand into
the area from the west.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from late Monday night through Tuesday evening for
     LHZ361>363-421-441>443-462>464.

     Small Craft Advisory until 4 AM EST Monday for LHZ441.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....JVC
DISCUSSION...DG
MARINE.......SF


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