Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 061949

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
249 PM EST Tue Dec 6 2016


Deformation zone associated with low pressure and parent southern
stream shortwave will lift through the eastern forecast area during
the late afternoon to early evening period as this feature tracks
from Ohio into the eastern Great Lakes this evening. Area of rain
will accompany this deformation axis, but end steadily from south
to north across the area between 21z-02z as support from right
entrance region of anti-cyclonic jet over Ontario/Quebec shifts
northeastward. Rain may linger a few hours longer into the evening
over the Thumb as left exit region of jet stream punching into
central Great Lakes around strong northern stream upper low over
northern Minnesota overlaps briefly with initial jet support. All
activity should safely exit northeast of the forecast area between
10 pm and midnight.

Attention will then turn to the aforementioned upper low pressure
system to the west/northwest. During the Wednesday to Thursday time
frame, this low will elongate as it tracks north of the Great Lakes
and then become an open as it continues into Quebec. While synoptic
scale precipitation over the area will be all but non-existent, the
deepening full latitude upper trough covering much of North America
will allow much colder air to settle into the central Great Lakes,
which, in turn, will activate the Lake Effect "machine".

This will be especially true from Wednesday night into Thursday as
cold air deepens over area with spoke of H85 air around -15c crosses
region and is gradually modified from heat flux from Great Lakes.
Best focus for lake effect snow shower activity will shift from the
middle of the forecast area Wed night to I-94 south Thursday as mean
flow veers from west to northwest with eastward progression of the
upper level trough axis. The most active period during this midweek
period will come on Thursday as fetch of cold air over Lake Michigan
will be longer with cyclonically curved northwest flow and low level
inversion heights rise a couple thousand feet and allow for more
intense snow showers which will have a better chance of crossing
east into southeast Michigan.

Temperatures will stair step down over the next few days with highs
in the middle 30s Wednesday and upper 20s to around 30 Thursday. Low
temperatures in the 20s will be common over the next several days as
this cold air builds across the Great Lakes.

Slight chance for precipitation exists Friday into Saturday as cold
W/NW winds pushing over a warmer Lake Michigan brings the chance to
see brief lake effect flurries/light snow, as temperatures struggle
to push into the lower 30s for a daytime high. Next potential for
significant precipitation accumulation returns Sunday into Monday as
a weak low from the Central Plains pushes into the Great Lakes
region. ECMWF model is pushing slightly cooler air into SE MI,
compared to yesterday`s 06Z run, increasing confidence that we will
see mainly a snow event, with GFS and GEM models producing snow.
Future model runs will help alleviate uncertainty regarding timing
and snowfall amounts. Additional chances for light accumulation will
be possible Tuesday into Wednesday as a cold front brings returning
chances of snowfall. Otherwise, temperatures throughout the early
part of next week will struggle to break the freezing mark,
especially after next Tuesday/Wednesday`s cold front.



Southeast winds in the 20 to 30 knot range over Lake Huron will
shift to the west-southwest by tomorrow morning, as strong surge of
cold advection works into the Central Great Lakes. Westerly wind
gusts of 30 to 34 knots are expected during Wednesday, with any
marginal gusts to low end gales being brief and highly localized,
thus no gale warning or watch will be issued. Small craft advisories
remain in effect and have been extended into Thursday morning as
frequent gusts of 25 to 30 knots continue. Winds shifting to the
northwest and gradually diminishing as we Head into Friday. Winds
look to be light on Saturday as high pressure slides through, with
strengthening southerly flow on Sunday.


Issued at 1156 AM EST Tue Dec 6 2016


Light rain spreading into much of southeast Michigan this afternoon
will allow for expansion of low MVFR ceilings. Easterly winds
around 10 knots will weaken and shift to southwest early this
evening, becoming stronger and gusty (20 to 25 knots), ushering in
colder and drier air to the State. Difficult call on whether or
not mvfr ceilings will hold on, as inversion heights lower below 3
kft. With moisture flux coming off Lake Michigan, will maintain
the ceilings inherited from 12z tafs, but confidence is not high,
as there is a solid chance for breaks in the clouds late this
evening into tomorrow, especially across southern taf sites.
Flurries possible tomorrow morning across northern taf Sites.

For DTW...Light rain arriving will allow for low MVFR cigs, with
reasonable shot at IFR vsby`s and/or cigs late today as rain tapers
off to drizzle. Gusty Southwest winds developing late this evening
ushering in drier and colder air, and have elected to include a
tempo for SCT clouds (4Z to 7Z) before more solid low mvfr
stratus returns Wednesday morning, but confidence is not high for
this scenario (Higher confidence PTK northward), and skies could
remain SCT for much of the Tonight into Wednesday morning period.

//DTW Threshold Probabilities...

* High for cigs below 5000 ft through early this evening, medium
  from mid evening onward.

* High confidence precipitation type will be rain this afternoon.


Lake Huron...Small Craft Advisory until 5 AM EST Thursday FOR LHZ441>443.

     Small Craft Advisory from 10 PM this evening to 5 AM EST Thursday
     FOR LHZ421-422.

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



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