Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 062343
AFDDTX

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

.AVIATION...

A surface occluded front is exiting the terminal corridor at press
time and will take IFR out of the area by mid evening. This front is
associated with deep low pressure over the northern Great Lakes that
will force colder air into the region on moderate westerly flow.
MVFR ceiling observed over the Midwest will then fill in over Lower
Michigan during the night and last through Wednesday with a boost
from Lake Michigan. The shallowness of the cloud moisture does still
offer potential for a few breaks in coverage at times, especially
through the DTW corridor which will be on the southern fringe of
lake effect influence. Westerly surface wind gusting around 20 knots
will be the only other element of significance in the absence of
anything more than a snow flurry through the period.

For DTW... Departure of the front will produce rapid improvement
from IFR to broken MVFR by mid evening. Westerly wind gusting
around 20 knots will bring colder air into the region that will
maintain MVFR through Wednesday. DTW will be on the southern
fringe of lake effect influence which could result in some breaks
that will be addressed in shorter term updates.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less with some breaks tonight.
  Moderate Wednesday.

&&

.PREV DISCUSSION...
Issued at 249 PM EST Tue Dec 6 2016

DISCUSSION...

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.

MARINE...

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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

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.

&&

$$

AVIATION.....BT
DISCUSSION...DG/AM
MARINE.......SF


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