Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 081141
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
641 AM EST Thu Dec 8 2016


.AVIATION...

Cold air advection in the 2500-5000ft agl layer occurred overnight
behind a secondary cold front. This caa has been sufficient in
increasing mixed layer into the -10-15C layer, important for ice
nucleation. Model data supports supersaturation with respect to ice
in this layer. Therefore, moving forward flurries and light snow
showers will be possible. Not expecting significant degradation in
aviation conditions due to snow showers. Reasons include: relatively
low mixing heights at 4000 ft agl, overall weak modeled convergence
signature over southeastern Michigan. The one feature that will be
worth monitoring is a mature convergence axis that will push
southward into the Saginaw Valley and northern Thumb region after
21Z.

FOR DTW... Cold, well mixed air mass will be responsible for
westerly gusts in the 20 to 25 knot range that will last through the
day. Expect flurries during the morning to build into scattered snow
showers at MVFR restriction during early to mid afternoon. There is
little forecast data that suggests snowfall accumulations will be
happen today.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less through tonight.

* High for snow as precipitation type.

&&

.PREV DISCUSSION...
Issued at 343 AM EST Thu Dec 8 2016

DISCUSSION...

There`s a few main points to hit on with this forecast package.
First will be the arctic outbreak that has initiated which will
bring below normal temperatures into next week. Next will be the
chances of lake effect snow through the end of the work week as a
result of the arctic air. And finally we`ll hit on the weekend
system that continues to look like it will produce snowfall
accumulations across the region.

The passage of a shortwave overnight has opened the door for the
first wave of cold air to enter the region. GRR radar has begun to
indicate lake effect snow starting to move inland as convective
depths increase. 850mb temps are on their way down from about -5C to
-15C with the latest surge of cold air. Winds will be westerly and
with convective depths only around 5kft, don`t think much
accumulation will occur over the east side of the state. Winds will
veer northwesterly this evening behind a second front dropping south
through the state. Hires models are actually showing this second
front bringing the better burst of snow to the area today.
Regardless, Duration for any location doesn`t look too long without
any real convergent bands setting up so accumulations should remain
below a half inch today and tonight.

Some lake effect snow could linger into Friday but high pressure
sliding through the Midwest into the Ohio Valley and weak shortwave
ridge will help dry the area out temporarily. Excessive cloud cover
will keep the high temps down around 30 with nighttime temps falling
to around 20.

Much attention remains on the potential system this weekend which
looks to bring accumulating snowfall to the region. Models continue
make adjustments as they try to latch onto the wave, but with the
storm still offshore they are struggling. The pattern to start with
is the persistent deep trough centered over the Plains. With the
strong jet streak rotating around the southern periphery of the
stacked low exiting the Great Lakes, the jet stream will weaken
across the country as the longwave pattern flattens. This will lead
to a more progressive pattern through the weekend. The Euro had been
trying to amplify the pattern as this system tracks across the
country but the latest run, 08.00Z, has made a sizable shift to
much flatter flow more similar to what the GFS has had a couple runs
now. Where does that leave us? It looks now that a lead shortwave
will eject out of the flow ahead of the main system, working across
the region Saturday night. There will be some upper level support
from a coupled jet along with isentropic ascent as the main
baroclinic zone resides just to our south. This scenario, with
models putting out 0.1-0.2 tenths of qpf could drop a couple quick
inches of snow. Next question is how much of a lull do we get before
the main system which will track somewhere through the Ohio Valley
or Southern MI Sunday night and Monday? The lead warm front and
isentropic ascent may fire right away Sunday, or there may be a
brief break before this ignites, but hard to tell at this point. GFS
does show deep moisture through the DGZ which would help snowfall
rates. So could see warm frontal snowfall Sunday and Sunday night
before the low arrives bringing the deformation axis through the
region Monday. Moral of the story is...models have been consistently
advertising the potential for a few inches of snowfall for the end
of the weekend into the beginning of next week. Forecast adjustments
will occur over the next couple days.

MARINE...

Westerly wind environment remains well mixed over Lake Huron this
morning as cold, cyclonic flow remains the dominant feature.
Windspeeds have consistently eased below gale force criteria. As a
result, the Gale Warning for central Lake Huron has been allowed to
expire this morning. A cold front will track from northern Lake
Huron this afternoon to Lake Erie tonight. Frontal passage will be
accompanied by a wind shift to the northwest in addition to an
increase in lake effect snow squalls. Building high pressure south
of the Great Lakes will allow moderate winds to take hold for the
end of the week before the arrival of the next low Sunday into
Monday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 PM EST this evening FOR LHZ421-422.

     Small Craft Advisory until 10 AM EST Friday FOR LHZ441>443.

Lake St Clair...Small Craft Advisory until 10 PM EST this evening FOR LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EST this evening FOR LEZ444.

&&

$$

AVIATION.....CB
DISCUSSION...DRK
MARINE.......CB


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