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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
314 PM EST Monday Feb 8 2016

Discussion...

With surface temperatures holding in the upper 30 to low 40s this
afternoon...boundary layer warmth has remained sufficient in keeping
the returns streaming into Port Huron and the eastern thumb region
all rain. This precipitation will undergo a transition to all snow
this evening due both to nighttime boundary layer cooling and weak
low level cold air advection. These returns are associated with an
axis of middle level deformation extending from Northern Ohio into Southern Lake
Huron. The regional water vapor loop today has indicated some
moisture advection into this system ahead of a short wave impulse
now over the Ohio/Kentucky border. This short wave feature is associated
with the broad upper low centered over Lake Michigan. The short wave
impulse will be driven toward Southern Lake Huron overnight as the upper
low slides into northern Indiana. This will in turn drive the middle level
deformation across The Thumb region during the night. Latest hi res
suite all generally suggest the stronger push of deformation will be
a little slower to move through The Thumb region tonight as it
appears the middle level impulse will Foster a more compact region of
forcing. Meanwhile some convective showers have emerged under the middle
level cold pool over Southern Lake Michigan/SW lower Michigan. Some of these showers
may impact the far southern sections of the forecast area this
evening.

On Tuesday...the middle level short wave will hold nearly steady in the
vicinity of either the eastern thumb/Southern Lake Huron or just east of
metropolitan Detroit into Tuesday afternoon. The middle level impulse will then
lift northeast as the upper low opens up and lifts east late in the
day. There remains some degree of model uncertainty as to how
quickly the deformation region opens up and transitions west and
south. Recent model trends suggest it will take until Tuesday
afternoon/evening for the remnant large scale forcing to push
through the Saginaw Valley and into metropolitan Detroit/Ann Arbor and points
south. Steady cold air advection through the day will begin to boost
instability over Lake Huron. The departure of the system to the east
Tuesday night may be enough to force a lake enhanced surface trough into
The Thumb region...possibly boosting snowfall rates across Huron
County Tuesday night. Expect the remainder of the forecast area will
see snow transition to numerous/scattered snow showers. Residual deep layer
moisture and steep low level lapse rates could however support some
intense snowfall out of some of these snow showers.

As far as the Winter Weather Advisory...there will be no areal
extension of the advisory at this time. The potential for lake enhancement
within the middle level deformation will however support extending the
advisory end time a little later into Tuesday evening. The main
forecast uncertainties at this time revolve around how far west into Flint
and the Tri Cities regions the stronger deformation will occur on
Tuesday and how well the large scale forcing holds together late in
the day south of the M 59 corridor. Given fairly respectable
moisture quality with 850mb mixing ratios between 2 and 3 g/kg and
given a fairly deep layer of low static stability with the middle level
cold pool in the vicinity...there is likely to be some regions of
enhanced forcing which may support periods of high intensity
snowfall rates. These factors suggest some near term forecast
updates will be needed as this event unfolds. Taking into
consideration liquid to snow ratios around 10:1 tonight rising to
roughly 12:1 by late Tuesday and with total quantitative precipitation forecast /tonight through
Tuesday night/ possibly over a half inch in The Thumb to a tenth or
less south of M 59...total forecast snowfall of 3 to 7 inches look
reasonable in the advisory area /dropping to an inch or less south
of the M 59 corridor/.

Remainder of the forecast focuses on snow shower potential Wednesday
and cold temperatures Wednesday through the weekend. Surface low
continues to pull away Wednesday with upper trough axis sweeping
through. Surface flow turns northwesterly which is typically a drier
flow for Southeast Michigan. However...850 mb temperatures drop to near -20
resulting in good instability over the lakes. In addition...model
forecast soundings show the column saturated with respect to ice up past 10kft
early in the day...with deepening boundary layer resulting in steep
lapse rates and supersaturation with respect to ice in the dgz. Think we will
see at least a scattered coverage of snow showers with potential for
locally and briefly heavy bursts of snow. Total accumulations
Wednesday still likely around an inch or less for most areas.

High temperatures Wednesday through Friday expected to be a few degrees either side of
20 before a reinforcing shot of Arctic air blasts in Friday night
into the weekend. This will occur as the Arctic closed low sweeps
into southeast Canada...and a backdoor cold front turns surface
winds to a north-northwest direction. Fairly good confidence that this will be
the coldest airmass all year...with gefs mean 850 mb temperatures dropping
to around -25c. Heart of this cold air will be Friday night through
Sunday. Current forecast calls for low temperatures in the single digits
above and below zero Friday/Sat night...with highs mainly in the single
digits Sat. European model (ecmwf) MOS guidance is even colder. There is light
snowfall potential Friday along the Arctic front areawide...with
some concern for lake effect snow along the Huron shoreline Friday
night and Saturday.

&&

Marine...

Low pressure will settle over far Southern Lake Huron
tonight...strengthening in the process...which will allow for
expanding snow shower activity through tomorrow. Winds will be light
tonight...but gusting up to 20 knots across far Western Lake Huron.
As the low slowly pulls away tomorrow and cold air rushes into the
central Great Lakes...northwest winds look to be ramping up to 25 to
30 knots across much of Lake Huron Tuesday night...and persisting
Wednesday...with just a small decrease on Thursday. With the amount
of cold air coming in...freezing spray is expected...and may be
heavy. A renewed surge of Arctic air arrives by Saturday...allowing
for another round of stronger winds and likely freezing spray.



&&

Aviation...issued 1202 PM EST Monday Feb 8 2016

Timing of low cloud (mvfr) development remains the challenge this
afternoon...as colder air slower filters east through lower
Michigan...with middle level moisture backing in from the east. When
low clouds (mvfr) arrive (possibly holding off through early
evening)...next occur of business is snow shower activity...which
looks to be most prevalent across mbs/fnt late
tonight/tomorrow...where a light accumulation (couple inches) can
be expected. Confidence in flurries/light snow shower activity
included in the northern tafs for this evening is low.
Light...mostly northwest winds through tonight...will increase a
bit tomorrow with diurnal boost/better mixing supporting gusts of
20 knots or slightly better.

At dtw...
middle level cloud canopy in place to start the forecast
period...but low clouds (mvfr) will eventually work into the
terminal site from the west/southwest. Exact timing remains
difficult...as there will likely be some patches initially. A
surface trough looks to be tracking through late tonight...which
may help trigger light snow showers...but better activity is
expected later Tuesday as middle level moisture sinks south. Light
accumulation of snow possible...around 1 inch. Along with the
snow...northwest winds gusting up to around 25 knots during the
afternoon.

//Dtw threshold probabilities...

* low confidence for ceilings at or below 5000 feet this afternoon...medium
this evening...and high tonight into tomorrow.

* High confidence in precipitation type being snow tonight/tomorrow.

* Low confidence in northwest crosswind tomorrow afternoon.

&&

DTX watches/warnings/advisories...
Michigan...Winter Weather Advisory from 9 PM this evening to 9 PM EST Tuesday
for miz049-054-055-062-063.

Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Discussion...SC/dt
marine.......sf
aviation.....Sf



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