Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 171041
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
541 AM EST Fri Nov 17 2017


.AVIATION...

Subsidence will reinforce a strong inversion while high clouds
inhibit insolation. Confidence is therefore high that overcast low
VFR will persist through at least mid afternoon. Although cigs may
briefly scatter this evening, incoming showers will signal the
arrival of deeper moisture supporting eventual widespread IFR
overnight. Arrival of supporting LLJ will bring a brief period of
heavier rainfall overnight as well as introduce wind shear concerns
for PTK south. IFR and light rain or drizzle accompanied by
steady south wind will then persist for the remainder of the period.


//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft.

&&

.PREV DISCUSSION...
Issued at 313 AM EST Fri Nov 17 2017

DISCUSSION...

Surface high pressure ridge has broken up stratus deck somewhat
overnight leading to areas of clear skies which has allowed
temperatures to fall further into the 20s where this is occurring.
Low clouds will continue to slowly breakup through the morning
however mid and high level clouds are already streaming in ahead of
next system. Winds will gradually increase from a southeasterly
direction today as the surface high slides to the east.  This will
lead to mainly a cloudy day with highs reaching the low to mid 40s.

The next system will effect the area Friday night through Saturday
night.  Large mid level wave just off the coast of northern
California will move rapidly eastward while another wave in the
polar jet over northwestern Canada drops southeastward.  These two
waves will begin phasing over the western Great Lakes Friday night.
A lead cold front will push through the Great Lakes Friday night with
the southern end becoming stationary across southeastern Michigan as
surface low pressure begins developing over Illinois with the
phasing of the two waves. Strong moist advection in the lower levels
with produce solid band of showers along the front that will effect
the whole area Friday night. As the surface low tracks northeast
along the stalled front it will continue deepening providing plenty
of forcing and a decent amount of rain Saturday, especially across
the southern half of the area. Depending on the track of the low,
could see some thunder from the Detroit area southward from about
06-18z Sat. The GFS tracks the low right across Detroit which allows
warm warm sector to make it to about M59 corridor along with a
period of convective instability. This includes K indices to the low
30s along with slightly negative LIs and a brief period of several
hundred elevated joules of cape. The Canadian model is very similar
however the Euro takes the low across Toledo keeping any thunder
chance to the south. The NAM is the outlier with weaker phasing of
the waves and keeps the surface low weaker and way further south. In
any event will carry a slight chance for thunder southeast corner.
Depending on how far north the low tracks will depend how far the 50s
makes it. Right now will go with the GFS/Canadian track which brings
mid 40s across the north with 50s from the Detroit area south.

As the surface low pulls away to the east Saturday evening it will
continue to intensify.  This will bring a tightening gradient and
strong gusty winds Saturday night along with lingering rain showers
that will mix with snow, mainly north of Detroit before diminishing
by morning.

Cold air advection on strong and gusty northwest flow Sunday will
produce plenty of lake effect clouds and scattered snow showers or
flurries with highs mainly low to mid 30s.  Large high pressure will
bring clearing skies and warmer temps for Monday as highs climb back
in the 40s.  The rest of the week will be fair and seasonably with
only exception being Tuesday as a wave crossing the northern lakes
will drag a cold front through the area with little fan fare. Just
clouds and possibly few light rain showers mainly across the
northern half of the forecast area.

MARINE...

Quiescent conditions in the near term will give way to developing
strong southerly flow today as high pressure translates east. Stable
flow will limit wind gust potential but elevated wave conditions
will exist along the eastern shoreline of the Thumb. Small craft
advisories remain in effect. Wind will briefly diminish tonight into
early Saturday as approaching low pressure moves directly overhead.
In its wake...strong N to NNW wind will develop with sustained gales
possible over the southern half of Lake Huron by Saturday night.
Gusts to moderate gales will be common over most or all of Lake
Huron late Saturday into Sunday. Significant wave heights will reach
at least 12 feet and maximum wave heights will eclipse 20 feet in
favored parts of the southern basin. The existing Gale Watch is now
a warning. In addition...a new watch is now in effect for Inner Bay
and Lakes Saint Clair and Erie.

HYDROLOGY...

Two rounds of moderate rain will impact through the first half of
the weekend. The first batch of rain will arrive around 9pm local
time tonight. A widespread 0.3" to 0.5" of rain is forecast, mainly
focused in the 10pm to 4am time window. The second batch of rain is
forecast to lift through the area from south to north mid-morning
Saturday morning through Saturday afternoon. A widespread 0.5" to
0.75" in anticipated during the day Saturday before rain tapers off
during Saturday night. The bulk of this rain will fall between
roughly Noon and 5pm in the Detroit Metro Area. Localized amounts of
an inch will be possible during this time potentially leading to
minor urban flooding issues. 24-hour rain totals of 1 to 1.5 inches
are likely, especially in the Metro Area and surrounding suburbs.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 3 PM Saturday to 7 PM EST Sunday for LHZ361>363-
     462>464.

     Gale Watch from Saturday evening through late Saturday night for
     LHZ422.

     Small Craft Advisory from 3 PM this afternoon to 4 AM EST Saturday
     for LHZ441>443.

     Gale Warning from 7 PM Saturday to 7 AM EST Sunday for LHZ421-
     441>443.

Lake St Clair...Gale Watch from Saturday evening through late Saturday night for
     LCZ460.

Michigan waters of Lake Erie...Gale Watch from Saturday evening through late Saturday night for
     LEZ444.

&&

$$

AVIATION.....JVC
DISCUSSION...DRC
MARINE.......JVC
HYDROLOGY....JVC


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at www.weather.gov/detroit.


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