Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 160510
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1210 AM EST Wed Jan 16 2019

.AVIATION...

An impressive surge of moisture is noted on radar across SW Lower
Michigan as freezing drizzle gets a boost from Lake Michigan. This
continues to expand eastward and southward across SE Michigan during
the early morning producing a light glaze of icing on objects and
untreated surfaces. Flight conditions are otherwise firmly in IFR
ceiling and visibility in the moist prefrontal southwest flow.
Passage of the cold front will disrupt the freezing drizzle
production and eventually produce a change to flurries or scattered
snow showers, first at MBS around 09Z to DTW around 12Z. Colder air
moving in with the front also produces ceiling and visibility
improvement into MVFR during the morning followed by a quick
decreasing cloud trend into the afternoon over moderate NW wind.

For DTW... Timing and intensity of freezing drizzle remains the
primary concern in the forecast for early morning as observational
evidence increases confidence in it reaching the terminal. A light
glaze of icing remains likely on objects and any untreated paved
surfaces before sunrise. A transition to IFR during the night
accompanies the freezing drizzle until passage of the cold front
around 12Z and after which steady improvement occurs during the
morning.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling below 5000 feet through the morning.

* High for ptype as -FZDZ until around sunrise.

&&

.PREV DISCUSSION...
Issued at 938 PM EST Tue Jan 15 2019

UPDATE...

Upstream observational trends indicate favorable conditions for
increasing coverage and intensity of freezing drizzle across Lower
Michigan during the night and the Winter Weather Advisory will
remain in effect through 10 AM.

Trends in late afternoon and early evening surface observations,
along with satellite and radar imagery, depict high surface moisture
and at least moderate inversion level forcing resulting in freezing
drizzle production across the Midwest/western Great Lakes. It is
notable that texture in the stratus remains visible even in IR
imagery post sunset which suggests strong shear across the top of a
very stable inversion to go along with a saturated/steep lapse rate
boundary layer profile. The 00Z DTX, GRB, and ILX soundings all show
the very favorable setup along with the moisture profile much warmer
than -10C that ensures a supercooled liquid hydrometeor. Surface
analysis also indicates additional potential for low level moisture
advection, in terms of surface dewpoint, out ahead of the cold front
from Iowa/Illinois across Lower Michigan. This is expected to
enhance the productivity of an already adequate boundary layer
moisture profile while the wind field remains strong in the
prefrontal southwest flow. Therefore, expect to see coverage
increase on radar and visibility drop across the region toward
midnight and last well into the overnight hours. The one wild card
to monitor is how the pattern changes upon passage of the cold front
which occurs around 4 AM in the Tri Cites to around 8 AM Ohio border
region. It is possible that a change to flurries or snow showers
could occur at or shortly after the wind shift as cold advection
takes the the boundary layer temperature profile into the -10 to
-15C range. However, the freezing drizzle leading up to that point
will have already set up a negative impact on the morning peak travel
period, so for now the expiration of the advisory remains 10 AM.

PREV DISCUSSION...
Issued at 314 PM EST Tue Jan 15 2019

A strong cold front pushing through the western Great Lakes will
enter lower Michigan late tonight and exit southeast Michigan
by noon Wednesday. Southwest flow will increase ahead of the
front advecting warmer air and low level moisture.  Temperatures
will rise to near freezing this evening then back off slightly for
the rest of the night. Plenty of low level moisture will be trapped
below an 850mb inversion with very dry air above.  Turbulent mixing
at top of the inversion will increase through the night generating
areas of freezing drizzle as ice condensation nuclei seeding from
clouds aloft will be absent for any snow production. Freezing
drizzle will start off as patchy but increase more in coverage from
north to south after midnight and until the front exits the north
around 12z and the south around 15z. Though only expecting a couple
hundredths of qpf this could be enough to cause some problems on
roadways and therefore will issue a winter weather advisory for
freezing drizzle.

After the front passes Wednesday morning, skies will clear for the
most part but strong cold air advection will keep temperatures
steady in the mid 20s north to around 30 south.  High pressure will
quickly move east across the northern Great Lakes Wednesday night
bringing clear skies in the beginning but high clouds from an
approaching system will increase keeping lows only in the teens.

A wave and weak surface low in the southern stream will move quickly
through the Ohio Valley Thursday and Thursday night.  This is a
little further south then previous model runs had and keeps the
heaviest snow just south of the border. Some light snow is possible
Thursday/Thursday night from this system with the best chance closer
to the Ohio Border where less then an inch likely. Temperatures will
be seasonably Thursday with highs around 30 and lows low to mid 20s.

Subtle recovery in heights aloft and surface high pressure ridging
in from the northwest look to keep Friday and Friday night quiet and
dry. A renewed flow of cooler air will keep temps near seasonal
normals while mostly cloudy skies remain overhead.

Attention in the extended forecast remains turned to the dynamic
system progged to develop over the southern Plains late Friday and
swing up through the Ohio Valley Saturday and Sunday. Interaction
between potent northern and southern stream troughs over the Great
Lakes and favorable right entrance jet dynamics in the presence of a
sharp baroclinic zone will aid in the strengthening of this system.
SE Michigan remains positioned on the northwest side of the track of
the surface low which is a favorable location for accumulating
snowfall potential. The latest runs of long range models are in
fairly good agreement that the heaviest snowfall will be located to
our south over central Ohio, but this has plenty of time to change
as additional data is gathered this week. Ample cold air - temps in
the lower 20s - will be in place to ensure all snow at the event
onset, which will likely be Saturday morning. Snowfall may continue
into Sunday morning. This system will continue to be monitored in
coming forecast updates as details regarding snowfall timing and
intensity need to be worked out.

Regardless of snowfall potential this weekend, main story for Sunday
into the early week will be the arrival of the coldest air mass of
this season so far. 850mb temps will plummet to around -22 to -25C
by Sunday afternoon as frigid arctic air rushes in in the wake of
the aforementioned system. Highs will struggle to break out of the
mid teens on Sunday with a brisk north-northwest wind resulting in
wind chills in the negative single digits to teens the entirety of
the day. The thermal trough axis will pass overhead late Sunday but
plenty of cold air will linger through Tuesday and keep temps well
below normal. Monday morning lows will fall to around 0 degrees with
wind chills in the negative teens. Potential exists for snow showers
Monday in this cold air mass as shortwave energy pivots overhead.

MARINE...

Gusty southwest flow will continue into the evening hours as the
region remains in between deepening low pressure to the north of
Lake Superior and high pressure over the lower Mississippi Valley.
Gusts of 25-30 knots will be common over much of the Lake Huron
waters, strongest in portions of Saginaw Bay and into the central
Lake Huron basin due to funneling effects. As the area of low
pressure moves east towards Quebec tonight, a cold front will drop
south across the region with winds becoming northwest in its wake.
Colder air ushering in behind the frontal passage will result in
gale-force gusts across the northern and central Lake Huron basin
and Gale Warnings remain in effect tonight and into Wednesday.
Significant freezing spray will also be likely with a Heavy Freezing
Spray Warning in effect during the day Wednesday. Elevated waves
will also lead to hazardous conditions for small craft across outer
Saginaw Bay and all of the Lake Huron nearshore waters. Marine
conditions will begin to improve Wednesday night into Thursday as
higher pressure settles over the region.

PREV DISCUSSION...
Issued at 257 PM EST Tue Jan 15 2019

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Winter Weather Advisory until 10 AM EST this morning for MIZ047>049-
     053>055-060>063-068>070-075-076-082-083.

Lake Huron...Small Craft Advisory until 4 PM EST this afternoon for LHZ421-441.

     Small Craft Advisory from 4 AM early this morning to 4 PM EST this
     afternoon for LHZ442-443.

     Heavy Freezing Spray Warning from 7 AM this morning to 7 PM EST
     this evening for LHZ361>363.

     Gale Warning until 11 AM EST this morning for LHZ361>363.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...DRC/TF
MARINE.......IRL


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at www.weather.gov/detroit.



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