Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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590
FXUS63 KDTX 231702
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
102 PM EDT SAT JUL 23 2016

.AVIATION...

Light wind conditions with no restrictions will continue through the
rest of Saturday. Modest lake-breeze influence on winds will emerge
later this afternoon with preferred directions at the typically
affected terminals. High clouds will increase in coverage toward
evening from upstream thunderstorm activity. Some light fog may
develop toward daybreak, once again. Otherwise early Sunday,
conditions become more favorable for support of upstream
thunderstorms cascading across Lower Michigan.

For DTW...lake breeze from Lake Erie should work into the Metro
airspace toward 21z - but speeds should remain modest. Enough
boundary layer moisture may collect again tonight supporting a
period of MVFR light fog.

Some semblance of a weakening convective complex may affect the
airspace during the morning hours on Sunday. Additional thunderstorm
development is possible later closer to the incoming cold front.
Development of the second round is highly dependent upon the fate of
the first wave of activity.

//DTW Threshold Probabilities...

* Medium for visibilities reduced due to light fog / haze
* Low for Thunderstorms Sunday Morning
* Low for ceilings at or below 5kft Sunday

&&

.PREV DISCUSSION...
Issued at 314 AM EDT Sat Jul 23 2016

Discussion...

Drier, stable, and hot air mass in place over the forecast area for
Saturday. Should be full sunshine today with dew points in the 60s
and that should allow temperatures to again soar into the low to mid
90s for all locations away from the Thumb. Only upper 80s expected
there as winds become north and northeast during the afternoon off
of Lake Huron.

Will issue a heat advisory for the immediate metro Detroit area and
include Lenawee and Monroe Counties.  The dew point front is
struggling to make it through the forecast area. This in combination
with the urban heat island has kept temps and heat indices up around
80 all night. While heat indices will only reach 95 to 98 degrees
this afternoon it will be the third day of heat with its cumulative
effects on the population.

Tonight will be watching developing convection and a possible MCS.
It should remain mostly clear until well after midnight when clouds
from the approaching convection move over all of Lower MI.

All indications of a weakening or dissipating MCS will be moving
through central and/or northern Lower MI from 12z to 18z Sunday.
Will have the highest chances for the northern forecast area for
this scenario. In the wake of the dying MCS...skies will become
partly cloudy for the afternoon with warming in the mid levels to
effectively stabilize the atmosphere. If there is some decent sun in
the afternoon, may make another run toward 90 degrees. Dew points
increase to around 70 and that would bring some concern about
another heat advisory. A lot of uncertainty with any temperature and
heat index forecast on Sunday.

The cold front moves through Lower MI during Sunday night. Lower MI
gets into the right rear entrance region of 100 kt jet, there is
some shortwave energy in the base of the weak 500 mb troughing, and
models have ML CAPEs in excess of 2000 j/kg along the front. Still a
significant cap to overcome during the overnight hours, but thinking
the above mentioned forcing should be enough to get some scattered
convection. Wind fields become marginal for some organization Sunday
night with 0-6 km shear increasing to around 30 kts. However,
convection will have to be lifted from around 900 mbs to maximize
the CAPE and moisture which would suggestion any marginal risk for
severe weather may be mostly a borderline hail threat.

Front just clears Lower MI at 12z Monday, so will leave out any
chance of showers and storms for Monday. Skies will be clearing
through the day from northwest to southeast across the forecast
area. The atmosphere is still warm behind the front as 850mb temps
only cool about 2 C.  With the clearing skies and subsidence behind
the cold front, should be able to warm effectively and again may
touch 90 degrees in a few locations.

Should remain warm and dry through mid week. Then as 500 mb heights
slowly fall, the weather pattern gets a little cooler and unsettled
for the end of next week.

MARINE...

High pressure will bring dry conditions and fairly light winds to
the Central Great Lakes today and tonight. Southerly winds will
increase on Sunday as an area of low pressure tracks through
Ontario. Speeds look to reach between 15 and 20 knots over Lake
Huron, and 15 knots or less over Lake St Clair and Western Lake
Erie. The area of low pressure and approaching cold front will also
provide a chance for showers and thunderstorms Sunday and Sunday
night before dry weather returns for Monday. Winds will veer to the
northwest behind the front Monday, but look to remain at 15 knots or
less.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 10 PM EDT this evening FOR MIZ069-070-075-076-
     082-083.

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

$$

AVIATION.....Mann
DISCUSSION...RBP
MARINE.......HLO


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at www.weather.gov/detroit.



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