Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 311938
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
338 PM EDT WED AUG 31 2016

.DISCUSSION...

Cold front currently across far se corner of state slowly pushing
southward.  Dewpoints ahead of the front in the low 70s lead to
afternoon cape values 1-1.5k joules, resulting in a thin line of
showers/thunderstorms to develop across southern Wayne and Washtenaw
counties.  These storms will continue southeastward and should exit
the state completely before 5pm.  Behind the front cooler and drier
air is filtering with back edge of post frontal clouds now along the
I-69 corridor.  Should see gradual clearing this evening from north
to south with diurnal cu north dissipating toward sunset.

Tonight through Friday morning,  sharp 500mb trough will slowly
swing southward across the area bringing the first fall like airmass
of the season as 850 temps fall to the single digits.  Wind flow
will become north-northeast over Lake Huron and forecast area.  Sfc-
850 delta-T of around 20C over Lake Huron will lead to several
hundred joules of cape and lake effect clouds that will advect over
most of southeast lower Michigan.  Some lake convergence banding and
sharp 500mb cyclonic flow with trough will lead to a slight chance
for showers beginning in the Thumb region and expanding southward
through the day.  A fair amount of clouds and mixing into 850mb
temps around 7c will yield highs Thursday in the upper 60s Thumb
Region to the low 70s far south and west.

Clouds will quickly dissipate toward sunset Thursday evening with
loss of heating and passage of 500mb trough axis leading to
mostly clear skies, though there will still be patches of lake
effect clouds as flow above boundary layer inversion will remain
rather strong from the northeast.   Surface winds should decouple
allowing for good radiational cooling sending temps down in the
upper 40s in the normally cooler locations to low to mid 50s
elsewhere.

Surface High pressure and 500mb ridging will provide clear skies,
low humidity and seasonably cool temps for the beginning of Labor
Day weekend.

All indications are for a quiet Labor Day weekend as the Great
Lakes remains under upper ridging between a western CONUS trough and
TS Hermine, which is forecast to track up the Eastern Seaboard.
Temperatures are expected to warm from near normal values on
Saturday to well above normal by Labor Day as a surface high shifts
east and southerly flow increases. Humidity values are expected to
be rather low during Labor Day weekend.

&&

.MARINE...

Northerly winds will increase tonight and Thursday as a second cold
front drops through the Central Great Lakes. Winds will be strongest
over Lake Huron, where gusts will reach between 25 and 30 knots. In
addition to the gusty winds, the long fetch over the length of the
lake will allow wave heights to build between 3 to 5 feet over
Southern Lake Huron by late tonight. A small craft advisory remains
in effect for the Southern Lake Huron nearshore waters with the
exception of inner Saginaw Bay. Winds will gradually decrease over
the region Thursday night and early Friday as high pressure slowly
builds into the area. High pressure will remain in control through
the weekend, bringing dry quiet weather and no marine concerns.

The deep layer of cold air surging southward over the warm lake
waters will also support waterspout development over all of the
Central Great Lakes both tonight and Thursday. Multiple waterspouts
were already observed Wednesday afternoon over Lake Superior.

&&

.PREV DISCUSSION...
Issued at 223 PM EDT Wed AUG 31 2016

AVIATION...

Surface cold front will continue exiting the area this afternoon,
allowing lower clouds to push south. A few showers have developed
south of DTW. These should continue to sink southward through the
afternoon. Moisture/clouds evident on satellite over Northern
Michigan will push southward tonight and Thursday in association
with a secondary cold front. Models suggest cloud deck currently
associated with this moisture will break apart to at least some
degree tonight as high pressure and subsidence begin to fill in over
the Central Great Lakes. This should keep clouds SKC-SCT for much of
the night before strengthening low-level flow turns off Lake Huron
late and promotes stratus development. This is mainly expected to
impact PTK and FNT, but will watch for potential for development
further southward. Wind speeds of 5-10 knots should inhibit fog
formation. Daytime heating...continued flow off Lake Huron...and
steep lapse rates yield high confidence with and MVFR ceiling
tomorrow.

For DTW...Linear extrapolation from satellite suggest SCT ceilings
by 21-22Z as clearing over Central Michigan makes it way southward.
Additional showers and thunderstorms today are expected to remain
south of DTW, but will impact the southern extent of the airspace.
Post-frontal winds will continue to increase from the N-NW this
afternoon, with speeds expected at or just exceeding 10 knots. Flow
will turn off Lake Huron tonight, allowing some lower clouds to
develop over portions of Eastern Michigan early Thursday morning. It
appears southern extent will be at or just south of PTK at this time
but will need to watch overnight.

//DTW Threshold Probabilities...

* Moderate in ceilings below 5000 feet through mid-afternoon. High
  tomorrow.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 8 AM to 10 PM EDT Thursday FOR LHZ442-443.

     Small Craft Advisory from 10 PM this evening to 10 PM EDT Thursday
     FOR LHZ421-441.

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

$$

DISCUSSION...DRC/DT
MARINE.......HLO
AVIATION.....HLO


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at www.weather.gov/detroit.



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