Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231131
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
631 AM EST Fri Feb 23 2018

.AVIATION...

Persistent near-surface dry air has held off onset of drizzle for
most areas, despite lowering stratus deck solidly into IFR/LIFR.
Surface temps above freezing will limit any freezing drizzle threat
early this morning, with rain expected to be the ptype as precip
gets ongoing after 12z with low pressure tracking by to the
northwest. Expecting generally light showers with the activity,
although a few heavier elements will be possible 13z-15z. Rain
quickly ends 16z-18z but IFR/MVFR stratus/stratocu prevails through
evening. Stratus lifting to MVFR looks most likely after 00z as
winds shift more westerly with time.

For DTW...IFR/LIFR ceilings continue through the morning hours, with
brief IFR vis restrictions due to drizzle. Drizzle transitions to
light showers 12z-16z before tapering off. IFR/MVFR ceilings hold
strong through at least evening as daytime mixing coupled with
increasing west/southwesterly wind attempts to break up the stratus
deck.

/DTW THRESHOLD PROBABILITIES...

* High for cigs below 5 kft through this evening.

* High for rain as ptype.

* Low for ceilings below 200 ft through this morning.

&&

.PREV DISCUSSION...
Issued at 348 AM EST Fri Feb 23 2018

DISCUSSION...

A moistening 2000 ft deep low level easterly flow maintaining
residence locally early this morning, tucked beneath a broadening
region of mid level warm air advection sustained under increasing
southwest flow. Lack of greater ascent thus far mitigating a more
productive precipitation response, with simply some hints of drizzle
noted on radar at times along the IN/MI border. This strip of higher
near surface saturation will begin to work into southern sections
going forward this morning, presenting a window for some drizzle to
emerge. Highest potential with southward extent prior to 13z, where
temperatures now reside at or above freezing. A slowly warming
thermal profile in combination with the lack of coverage/intensity
will minimize freezing rain/drizzle potential and any resultant
ice accretion.

Shortwave embedded within the mean southwesterlies will shear across
lake Superior today. This trajectory will position the strongest
forcing to the northwest. Southeast Michigan will see a quick shot
of stronger isentropic ascent within the broader corridor of warm
air advection anchoring the eastern flank of this system. This will
provide a small window during the late morning period for a greater
coverage of light rain. Aggressive mid level drying in the wake of
the attendant frontal passage will then bring a progressive end to
precip chances by early afternoon. Generally milder conditions today
as low level flow briefly turns southerly. Highs ranging from mid
40s north to near 50 south. Cooler air then drains back in tonight
under veering low level flow as high pressure briefly builds across
the northern great lakes. This will land lows Saturday morning back
around or just below the freezing mark.

Strong height falls spilling into the desert southwest will
reinvigorate the southwest flow over the weekend, prompting a strong
upper jet response and subsequent northeast transport of gulf
moisture within the warm sector. Retention of drier easterly low
level flow sustained by high pressure anchored to the north may
provide a defined northern gradient to the lead moisture axis
anchored within the blossoming moist isentropic ascent wing. This
will leave areas closer to the Ohio border with the greatest
potential for witnessing some light precipitation on Saturday. A
marginal thermal profile with sub-freezing early day wet bulb
temperatures suggest a brief light mix is plausible before diurnal
warming tips the ptype solidly to liquid. Afternoon temperatures
again largely climbing into the 40s.

Dynamic system rapidly lifts into the western great lakes during the
latter half of the weekend. Period of strongest ascent associated
with this system centered Saturday night, translating into
widespread rainfall but with the heaviest qpf axis likely contained
within any convection to the south. Strong early day cold frontal
passage and a trailing firm pressure gradient as the surface low
steadily deepens while racing north will then bring dry but gusty
conditions on Sunday. The potential will exist for a period of gusts
to reach or exceed 40 mph during this time.

MARINE...

Weak low pressure will track northeast across the northern Great
Lakes today with light to occasionally moderate southeast flow
gradually veering to the southwest with time. High pressure will
then build into the region from the west with continued light flow
veering northerly with time. The flow will become east/southeasterly
late Saturday and into Saturday night ahead of developing low
pressure across the central Plains. This area of low pressure will
rapidly deepen as it tracks northeast across the northern Great
Lakes, leading to decreased stability and a tight pressure gradient
across the local waters. Gale Watches will go into effect for all of
the Lake Huron waters late Saturday night through Sunday for
potential gusts approaching 40 knots.

HYDROLOGY...

Flood Warnings remain in effect for most of the primary river basins
over southeast Michigan as water levels begin to slowly recede. Weak
low pressure tracking northwest of the region will bring a period of
light rainfall today, with amounts under a quarter of an inch.
Another low pressure system will track northwest of the region late
Saturday night and into Sunday. With slightly better moisture to
work with, rainfall amounts of a quarter of an inch to half an inch
will be possible. This rainfall is not expected to have any
significant impacts to local rivers and streams.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from Sunday morning through Sunday evening for LHZ363-
     421-422-441>443-462>464.

     Gale Watch from late Saturday night through Sunday evening for
     LHZ361-362.

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

$$

AVIATION.....IRL
DISCUSSION...MR
MARINE.......IRL
HYDROLOGY....IRL

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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