Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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347
FXUS63 KDTX 140805
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
305 AM EST Thu Dec 14 2017

.DISCUSSION...

The strong clipper, which set record daily snowfall records at
Detroit and Flint yesterday (6.3/7.9 inches respectively), already
over/near State College Pennsylvania (as of 8Z), with subsidence and
drying taking place over southeast Michigan this morning. Still
contending with Lake Effect snow showers over the eastern Thumb
Region, but this activity should be moving offshore shortly after
12z, as winds shift to the northwest, and surface ridge builds into
the region today. With the fresh snow cover, even with a good deal
of sunshine, expecting highs only in the upper teens to around 20 C,
as mixing depths come up short of 2 kft.

Deep PV anomaly dropping south from the Arctic circle will move over
Ontario by Friday morning, with the extension/trough axis sliding
though the Central Great Lakes during Friday. With this forcing and
associated surface trough, snow showers are expected with about 1.75
G/KG of specific humidity at 850 mb to work with. Even after the
trough passage, westerly flow off Lake Michigan and cold advection
will result in steep low level lapse rates as we head into the
afternoon/early evening. Deep layer of supersaturation with respect
to ice, 25 to 50 J/KG of surface based Cape embedded within the DGZ,
and winds around 35 knots at the top of the boundary layer will
support possible snow squalls. Even outside of any squalls, probably
looking at gusts of 25 to 30 mph with the deeper mixing. Enhanced
blowing snow may be a concern due to the powdery snow left over from
yesterday`s snow storm. Temperatures falling into the lower 20s
within the heavier activity assuring roads becoming snow covered
and/or icy, along with the brief near white-out conditions possible.
Expecting many locations to receive a quick inch or two during the
Friday-Friday evening period.

Pretty good chance of additional snow Friday Night Into Saturday, as
as low level frontal boundary hangs around the I-94 corridor, with
mid level fgen flare-up farther north as moisture advection takes
place from the Midwest. 850 mb specific humidity progged to climb to
around 2.5 G/KG (per 00z EURO). Seems like another narrow swath of
inch or two is possible as the frontal boundary lingers into
Saturday, but uncertainty on the exact position, with waning FGEN on
Saturday as a flat upper level ridge builds in.

Dampening upper level wave ejecting out of the Baja California area
looks to be tracking through the Ohio Valley on Sunday, caught up in
the southwest flow of the upper level trough situated over the
Rockies. With the system sliding off to the east along or just south
of the Michigan border, our warm up looks to be tempered, but
temperatures still likely climbing above the freezing mark. None-the-
less, some type of light wintry mix remains possible in the Sunday-
Monday time frame.

&&

.MARINE...

Northeast winds gusting into the 25 to 30 knot range will steadily
ease and back to the northwest this morning. In response, waves in
the 5 to 7 foot range will gradually subside and shift east away
form the nearshore waters. Small Craft Advisories will continue into
the afternoon due to the waves. The next clipper disturbance will
arrive on Friday, bringing a renewed threat of snow squalls to Lake
Huron. While winds will likely gust into the 25 to 30 knot range,
both in the southwest and northwest flow ahead of and behind this
system, widespread gale conditions are not anticipated. Wind will
ease into Saturday as Arctic high pressure brushes by to the north.

&&

.PREV DISCUSSION...
Issued at 1202 AM EST Thu Dec 14 2017

AVIATION...

Snow is diminishing rapidly late this evening evidenced by lower
reflectivity returns on regional radar mosaic. Expectations are for
MVFR cig heights with flurries for a couple of hours. Low confidence
in what sort of mixed boundary layer light snow could develop in the
cold air advection. No signal to really latch onto, so will go dry
the remainder of the night. Surface ridging and height rises will
support loss of cloud by mid to late morning with VFR conditions.
MVFR cig heights forecasted to develop quickly Wednesday evening in
response to old Lake Michigan plume advecting over the terminals.

For DTW...Surface wind directions turning northerly will allow drier
air to push into the terminal, ending the light snow. MVFR cigs to
largely hold this morning with erosion of low level cloud, VFR skies
late morning. MVFR cigs back into the area Wednesday evening in
response to lake effect cloud pushing overhead.

//DTW THRESHOLD PROBABILITIES...

* High confidence in cigs at/below 5000 ft agl through 12Z


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 6 AM EST early this morning for
     MIZ049-055.

     Winter Weather Advisory until 8 AM EST this morning for MIZ063.

Lake Huron...Small Craft Advisory until 4 pM EST this morning for
LHZ421- 441>443.

     Small Craft Advisory until 5 AM EST early this morning for LHZ422.

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

$$

DISCUSSION...SF
MARINE.......DG
AVIATION.....DG


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at www.weather.gov/detroit.



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