Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 102330
AFDDTX

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

.AVIATION...

Ceilings gradually lowering within MVFR over the next several hours,
as low level moisture temporarily deepens in advance of a weak
boundary. This will be sufficient to generate a few light snow
showers/flurries, with some minor visibility restrictions possible
through midnight. A period of drier northwest flow then emerges
overnight, favoring a general clearing of low stratus from northwest
to southeast during the early morning period. Attention then turns
to advancing low pressure that will bring a period of widespread
snowfall to the region Monday and Monday night. Initial period of
lighter intensity snowfall expected to develop during the midday
period 15z-20z, where conditions largely remain at MVFR restrictions
outside of the heaviest bursts. Snowfall intensity will increase from
late afternoon into the evening period, with peak intensity and
accumulation potential centered between 6 pm and midnight.

For DTW...A few very light snow showers or flurries will accompany
the existing MVFR stratus across the airspace late this evening. No
accumulation expected. A period of clear sky across the lowest 5kft
a possibility during the early morning period, then back to MVFR as
light snow develops by 15z-16z Monday. Heaviest period of snow
expected late Monday into Monday evening, peaking 23z-05z.
Accumulation between 2 and 3 inches expected by early Tuesday
morning.

//DTW THRESHOLD PROBABILITIES...

* High confidence for ceilings aob 5000 feet through 06z, then low
  overnight. High in ceiling dropping below 5000 ft again by 16z
  Monday in developing light snow.

* High confidence in precip type being snow this evening and
  again Monday.

&&

.PREV DISCUSSION...
Issued at 345 PM EST Sun Dec 10 2017

DISCUSSION...

Several items of interest in the coming week across SE MI. First we
are monitoring a developing lake effect band coming off central Lake
Michigan this afternoon. Next up is a clipper that will track
through the souther Great Lakes Monday afternoon and evening
bringing the next round of accumulating snowfall. Coldest airmass of
the season then moves in through mid week dropping lows into the
single digits and holding highs around 20F. Additional light
snowfall could come at the end of the week with the next clipper
followed by a brief warm up next weekend.

First up is the potential convergent lake band this afternoon. Winds
have just flipped to the NW at Big Rapids showing the convergence
seen at the shoreline is now making its way inland but GRR radar is
less than impressive thus far showing the moisture plume enhancing.
In addition, hires models less impressed with the setup today as
they were previously. Lowered pops, qpf, and snowfall north of I69
this afternoon to mainly flurries or light snow showers with little
accumulation. The trough dropping into northern lower will reach the
Saginaw Valley around 00Z, which will then break up the convergent
feature as it continues southward through the state.

Models continue to come better in line in regards to the clipper and
associated snowfall on Monday. In addition to agreements in hires
models as they now begin to reach out far enough to forecast the
clipper, there are similarities between medium and long range models
as well. Bulk of the forecast remains unchanged as we still expect a
compact clipper to dig southward into the Ohio Valley Monday
afternoon before getting pulled back NE into a stronger PV anomaly
on the nose of a 150+ knot jet right on it`s heals. The speed of the
second wave seems to be difference in how the event plays out thus
far. A faster and stronger wave will phase the two earlier, which
will start ingesting the smaller clipper faster which pulls the
fgen/deformation forcing northeastward earlier. A slower or weaker
solution will allow the clipper to stay more compact and further
south keeping the main deformation band across the southern part of
the state. Adjustments have been made for location of highest
snowfall with qpf/snow amounts not much different. Still looking at
a wide swath of 1-2 inch snowfall across SE MI with a band of
heavier snow around 3 inches likely with the deformation band on the
northeast flank of the low. Currently this band looks to set up
between M59 and I94. A lead leaf of broad isentropic ascent ahead of
the broader trough will bring light snow showers to the area
starting 15-18Z with the heavier band occuring between 21-03Z.
Remnant light showers will taper off around 12Z Tuesday when drier
air moves in.

Northwest flow ramps up behind the departing wave which will usher
in the coldest airmass of the season thus far with 850mb
temperatures falling to -20C by Tuesday afternoon and -25C located
just north of Lake Superior. Tuesday will not be a pleasant day as
highs reach the low to mid 20s but winds gusting to 20-30 mph will
result in wind chill values in the single digits most of the day.

Cold arctic airmass remains over the Great Lakes on Wednesday,
preventing highs in our area from climbing out of the upper teens to
low 20s with wind chills hovering in the single digits. Surface
ridging between systems will keep the area quiet and allow for some
sunshine through the day. Temperatures Thursday begin a slow rebound
as the coldest air aloft moves off to the east. Models diverge on
the placement and strength of a potential shortwave/clipper pivoting
through on Thursday into Friday, but looking at another chance for
light snowfall across the region.

Above freezing temps to return to Southeast Michigan on Saturday;
jet energy will help flatten the ridge over the western CONUS and
allow for the trough over the eastern CONUS to ease up. Warm air
advection will set up ahead of a developing low in the northern
plains, with highs reaching a few degrees above normal on Saturday
and Sunday. The low pressure system is currently progged to move
over the northern Great Lakes on Sunday with the best of the forcing
displaced to our north; no significant precipitation amounts are
expected though some gusty winds will be possible with the
heightened pressure gradient.

MARINE...

Diminishing winds this evening will transition to light southerly
for most of Monday. Colder air will spread across the waters Monday
night with sustained near-gales forecast to gust to strong gales
early Tuesday morning through Tuesday afternoon. Significant wave
heights will reach 12 feet during this time with maximum wave
heights of 20 feet or higher. Gales will diminish late Tuesday.

&&

.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.....MR
DISCUSSION...DRK/TF
MARINE.......JVC

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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