Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181100
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
600 AM EST Mon Dec 18 2017

.AVIATION...

Conditions likely to remain somewhat variable through the morning
period, as deeper low level moisture takes some time to work back
into the region following an overnight warm frontal passage.
Upstream trends and latest model guidance do still suggest that a
more extensive coverage of IFR or low MVFR restrictions should
emerge today as greater saturation finally commences. This occurs as
a combination of low stratus/fog within some pockets of light rain
through the morning, before the fog component diminishes during the
latter half of the day. No real evidence exists to suggest that a
low stratus won`t persist right through tonight. Southwest winds
increase overnight, minimizing the potential for renewed fog
development.

For DTW...Upstream observational trends support renewed expansion of
low stratus over the terminal during the late morning period. Lower
confidence on an eventual reduction in visibility in shallow fog,
but MVFR a possibility yet this morning.  Winds prevailing out of
the southwest through the period.

//DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less through tonight.

&&

.PREV DISCUSSION...
Issued at 349 AM EST Mon Dec 18 2017

DISCUSSION...

Starting off with a little weather across lower MI as a warm front
lifts north through the area toward a stall front laid out across
mid MI. A shortwave ejecting out of the mid level trough over the
southwest conus will track along the front through southern lower MI
this morning and into the afternoon hours while a pv filament along
the longwave trough axis drops into the state. There has been decent
low level moisture present across the area for a couple days and
appears there will be a weak thermal ridge ahead of the shortwave
with enhanced 850mb moisture transport with it. Add in a brief
window with right entrance jet dynamics aloft skirting across
mid/northern MI and looks like chances are increasing for a period
of precipitation this morning. Main question for the forecast
through this afternoon will be ptype. Thermal profile north of I69
is cold enough for frozen precip, with soundings showing some ice
crystals at onset this morning. Mid level moisture gets stripped
away fairly quickly leading to more of a drizzle or freezing drizzle
setup. This leads to the second question, will the precip arrive
before the mid level moisture vacates or before the warm air pushing
north makes it too warm at the surface to allow freezing drizzle.
All in all with a low qpf scenario as advertised by most of the
hires suite, think any freezing drizzle that occurs should have
minimal impact. Areas of drizzle or light rain showers should linger
into the afternoon across eastern portions of the CWA as broader
area of lift with the height fall center passes.

Weather quiets down during the mid week period as longwave pattern
flattens out with the jet focused over the US/Canadian border. This
keeps the bulk of energy over southern Canada with only a short wave
clipping the northern Great Lakes Tuesday. We will stay on the warm
side of the jet allowing highs once again into the low to mid 40s. A
cold front will dig down through the northern/eastern Great Lakes
Tuesday night on the nose of a flaring up 150+ knot jet. Not much
moisture to support any precip, but temps will drop for Wednesday
back just below mid December average into the low/mid 30s.

Slight warming trend for Thursday as the main thermal gradient
meanders slowly back north again as shortwave ridge slides over the
region. This is in response to a developing system over the plains
that will lift through the Ohio Valley and Great Lakes Friday and
Saturday. This is a larger more developed system that will carry
much more moisture with it (GFS advertising near 1" PWAT) as it is
able to tap into Gulf moisture. Both the GFS and ECMWF have been
showing this system for a couple days now but continue to bounce
around with track of the low and thus strength/orientation of
frontal boundaries. Ptypes may be a concern early and late in the
event depending where the low and lead warm advective flank sets up,
but bulk of precip on Friday night looks to be liquid as the warm
sector reaches north into Ontario.

In the wake of this system, cold air will return for the foreseeable
future. Models have been quite persistent in deepening the longwave
trough over the west/central conus with a surge of cold air from
northern Canada. 850mb temps dropping into the Midwest have been
colder than -30C for a few models runs now.

MARINE...

Light wind and low waves will continue over all marine areas today
as a weak low and warm front move through the central Great Lakes.
This low will bring some areas of light rain and fog during the
daylight period. A strong low pressure system organizing over
central Canada today will track into the Hudson Bay region tonight.
Winds will respond to the increasing pressure gradient downstream,
leading to strengthening southwest flow overnight. The potential for
a period of gusts to gales will exist over the open waters, despite
the diminishing overlake stability as warmer air works into the
region. Strong cold front attendant to this low will then sweep
across the region on Tuesday. This will bring a longer window for
potential gales Tuesday and Tuesday night, as instability deepens
again under colder post-frontal westerly winds.  Winds ease into
Wednesday as high pressure settles over the marine areas.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from midnight tonight to 4 AM EST Wednesday for LHZ362-
     363-462.

     Gale Warning from midnight tonight to 4 PM EST Tuesday for LHZ421-
     441.

     Gale Warning from 4 AM Tuesday to 4 AM EST Wednesday for LHZ361.

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

$$

AVIATION.....MR
DISCUSSION...DRK
MARINE.......MR


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