Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231000
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
600 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.

&&

.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.

PREV DISCUSSION...
Issued at 1157 PM EDT Fri Jul 22 2016

AVIATION...

Clear sky will continue through the night and morning over SE
Michigan. The weak front/moisture boundary settling through central
lower Michigan is still expected not to produce ceiling or
visibility restrictions as it takes most of the night to reach the
Ohio border. VFR will then continue through the day as weak high
pressure follows and produces light/variable wind becoming light
northwest by afternoon. A combination of the high exiting eastward
and lake breeze consolidation will produce light easterly wind by
Saturday evening.

For DTW... Favorable operational conditions will be in place through
the day. Wind will be light westerly to light and variable under
clear sky through the morning. A late wind shift toward the
northeast to east is possible by Saturday evening.

//DTW Threshold Probabilities...

* none

PREV DISCUSSION...
Issued at 339 PM EDT Fri Jul 22 2016

Discussion...

The dewpoint has fallen into the 50s in Huron County on a light west
wind, well ahead of the approaching moisture boundary.
Downsloping off the glacial ridge appears to be the only
explanation. Regardless, the heat advisory is dropped for Huron as
dewpoint front will be arriving shortly anyway.

Veering deep layer flow and weak height falls as a shortwave tracks
northeast of the Great Lakes region is modeled to shunt this
boundary about halfway through the CWA overnight. Upper 50s or low
60s dewpoints will dominate across the north. Southward progress
will slow upon the departure of height falls. However, second and
stronger wave presently over Manitoba will sweep east taking roughly
the same road within the mean flow and kick the boundary safely out
of the area by around sunrise. Low 60s (or lower) Tds areawide by
midmorning, with the exception of the immediate Ohio border where
some of the guidance is allowing 70s dewpoints to creep back in
during the day. Very dry airmass beneath strong subsidence will set
the stage for a clear and hot day as the NAM indicates dry adiabatic
mixing to 750mb. The only thing preventing area wide mid/upper 90s
will be the lake aggregate high present under weak gradient
conditions. An easterly gradient, lake breeze, or a combination of
both will spread into the area during the afternoon confining highs
to around 90 north of I-69. Locations south of M-59, aside from
higher elevations, should easily reach the mid 90s. The heat
advisory will not be extended due to the low humidity as well as the
opportunity for relief tonight as dewpoints fall.

Sunday`s forecast is lower confidence. The trough over the Pacific
Northwest will eject east northeast as it tracks toward Hudson Bay
by Sunday night. Emerging low-level jet over the northern plains
will likely foster thunderstorms/possible MCS over the Dakotas/Upper
MS valley Saturday into Saturday night. The remnants of the MCS and
attendant convectively enhanced wave will wash over the area late
Saturday night and the first half of Sunday. At this time, the
prospects for organized convection locally appears rather poor given
northward displacement of the LLJ and lacking SB instability early
Sunday. The more interesting period will be late Sunday evening into
Sunday night per current NWP timing. Height falls and modest PV
advection juxtaposed with the lower tropospheric warm conveyor
and a moderate wind field could yield convection worthy of keeping
an eye on. Southerly gradient will spell a return to muggy
conditions, but highs on Sunday will be limited to around 90 on
account of cloud cover.

Deeper moisture progged to exit by Monday with drier dewpoints
filtering in as well. Model consensus supports high pressure
building in at the surface and lingering into Wednesday promoting
mainly dry weather. Temperatures will still be above normal with 850
mb temps in the upper teens and guidance indicating highs in the
upper 80s, but not quite as warm as the current airmass. Low
predictability toward the end of next week, but a general trend
toward lowering heights/broad troughing supports transition to a
less-warm and possibly wetter pattern.

MARINE...
A dew point boundary working southward across southern Lake Huron
and the Thumb may produce an isolated shower or thunderstorm late
this afternoon and evening across southern Lake Huron.  Other then
that, high pressure over the Mid West will provide a west northwest
flow across the lakes through Saturday morning.  As the high passes
through, winds will become light and variable Saturday afternoon.
Winds will become easterly Saturday night then veer to the southwest
while increasing by Sunday afternoon ahead of an advancing cold
front. This front will bring showers and thunderstorms across the
lakes that will linger into Sunday night.  The new week will
start off with dry weather on a northwesterly flow.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory from 10 AM this morning to 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.
&&

$$

DISCUSSION...RBP
MARINE.......HLO
AVIATION.....BT


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