Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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260
FXUS63 KDTX 231914
AFDDTX

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

.DISCUSSION...
Hot day today as mid level ridge axis continues to slide in from the
west.  Atmosphere over the area is relatively dry per 12z dtx
sounding with pw around an inch.  This is seen as dewpoints that
started the day around 70f have fallen to as low as the low 50s
with diurnal mixing.  This drier air has allowed temperatures to
climb well into the 90s most locals under sunny skies.  Humidity has
also continue to fall helping to offset the higher temperatures as
far as heat indices have gone past two days.  Expect mostly clear
skies rest of this afternoon and evening with a few cu along
some lake breeze boundaries and some high thin cirrus from convection
over Wisconsin may be seen towards sunset.

Very hot and humid air over the Mid West will begin working its way
toward southeastern Michigan overnight as temperatures this
afternoon out there have climbed into the upper 90s with dewpoints
around 80.  Will see dewpoints bottom in the 50s most location early
tonight then rise into the 60s by daybreak. Mid and high level
clouds will also be on the increase later as convection over
Minnesota and Wisconsin in the highly unstable airmass works its
way east.  This convection will weaken as enters the western
portions of the CWA as better instability will continue to remain
just to the west so will just carry slight chc for precip far western
portions of the area.

Hot moist air will quickly overtake the forecast area Sunday ahead
of approaching cold front that will push through Sunday night.
Showers and thunderstorms Sunday will be dependent mostly on any
type of meso boundaries for initiation so precise time or location
will be hard to come by.  So expect showers and thunderstorms to be
scattered and not an all day event.  Temperatures will also be
dependent on how much if any precip occurs early in the day and
amount of cloud cover.  If precip is scarce early and enough
sunshine occurs, could easily see temps in the mid 90s with mid 70
dew points leading to possibly a heat advisory.  If rain is a bit
more widespread in the morning along with clouds, then most locations
may only see upper 80s to around 90.  At this point looking how
substantial the heat is to the west today and lack of any solid
focus for convection initiation, feel like low to mid 90s are more
likely.

Cold front will slowly move through the forecast area Sunday night
and exit the area by mid Monday morning.  Scattered showers and
thundestorms expected to accompany frontal passage.  There is a
marginal risk for severe weather as forcing is mainly frontal
convergence as upper dynamics will lag the front and also be far
removed to the north.  The main threat will be wind gust from load
shedding of precip as pwats will be quite high.

Monday still remain quite warm as frontal passage is more of drier
air then cooler.  Expect highs still in the upper 80s to around
90 far south as clouds exit the state by afternoon.

Absence of forcing and fairly weak mid/upper-level flow indicated by
midrange guidance argues for a dry forecast Tuesday/Wednesday.
Shortwave energy for the end of the week will cause the flow to
transition to more broadly trough-y, which may be enough to generate
periods of rainfall late week into next weekend. Still low
confidence on narrowing down the timing so broad chance PoPs will
suffice for now. Temperatures expected to remain above normal
Tue/Wed before easing back toward normal Thu into the weekend.

&&

.MARINE...

Light wind conditions will transition to modest south/southwest flow
on Sunday. Speeds will increase the most across Lake Huron into the
15-20 knot range with lighter wind conditions on Lake St. Clair and
Lake Erie. The wind will transition to lighter northwesterly Sunday
night into Monday. Thunderstorms are possible toward daybreak
Sunday...especially across Lake Huron. Additional thunderstorms are
possible again later Sunday and will mainly affect Lake St. Clair
and Lake Erie.

&&

.HYDROLOGY...

Showers and thunderstorms are possible early Sunday and again toward
Sunday evening. Any activity Sunday morning should be weakening as
it moves across Southeast Michigan - resulting in amounts generally
less than a half inch. Thunderstorms that develop later Sunday will
be capable of heavier downpours and localized rainfall amounts
exceeding one inch.

&&

.PREV DISCUSSION...
Issued at 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.
&&

$$

DISCUSSION...DRC/DT
MARINE.......Mann
HYDROLOGY....Mann
AVIATION.....Mann


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