Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 290104
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
904 PM EDT Wed Jun 28 2017

.UPDATE...

Mid level moisture advection this evening proved rather efficient in
generating at least light showers across much of the area. Mid level
moisture transport has been focused across central Lower Mi. This
has led to more persistent showers across the Saginaw Valley and
thumb regions. Earlier model solutions strongly suggested that the
better convective potential through the overnight would shift to the
northern Great Lakes as a longer wavelength trough rotating across
the nrn Great Lakes lifts the low level jet into nrn Michigan. The
ongoing quasi stationary MCS now over the WI/IL/IA border region adds
a level of uncertainty to this. Recent satellite/radar trends
suggest a little more stationary forcing has set up across central
Michigan. The resultant MCV from this convective complex may sustain
this region of enhanced moisture convergence across the northern
sections of the forecast area into the overnight. The approach of
this MCV combined with increasing elevated instability through the
overnight will support a chance for thunderstorms. An update will be
issued to further increase convective chances across the northern
portions of the forecast area. The convectively induced troughing to
the west may actually force some enhanced short wave ridging across
Lake Erie, which may be enough to limit convective chances to the low
chance category across the southern portions of the forecast area
(metro Detroit and points south).

The elevated instability overnight will be marginal, so severe
weather is not expected. Given the excessive rainfall across Central
Michigan this past week, current radar trends bear some watching. The
expectation is for the convection to weaken as it pushes toward the
Saginaw Valley, which should prevent excessive rainfall totals.

&&

.PREV DISCUSSION...
Issued at 701 PM EDT Wed Jun 28 2017

AVIATION...

Ongoing mid level moisture transport has resulted in high based
light showers across the area. Low to mid level moisture transport
will increase during the course of the night, which will support a
continued chance of showers. Weak elevated instability will arrive
late this evening. While this will support a chance of a few
thunderstorms, probabilities are under 30 percent. The more
persistent showers and best chances for thunderstorms will be at
MBS, where moisture convergence will be greater. There will be some
decrease in sfc winds this evening with loss of daytime heating. As
the low level wind fields increase (45-55kts at 2-3k ft after 04Z),
a mention of low level wind shear remains justified in the TAFS
overnight into early Thurs morning.

For DTW...The initial surge in mid level moisture may support some
light showers at the start of the TAF forecast. Chances for showers
during the remainder of the night is still quite low as the better
moisture transport will become focused north of metro Detroit. Low
level moisture advection Thurs morning will support sct to perhaps
broken ceilings below 5k ft by mid to late Thurs morning.

//DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less overnight through Thursday
  morning. Moderate Thursday afternoon.

* Low in thunderstorms tonight and Thursday morning. Moderate late
  Thursday afternoon and evening.

PREV DISCUSSION...
Issued at 341 PM EDT Wed Jun 28 2017

DISCUSSION...

Surface low pressure advancing towards the northern Great Lakes
region will continue to push a warm front up across northern WI and
into western MI.  Convection from this morning has slowly weakened
and continues to do so as it crosses into Michigan.  The warm front
did spark development out ahead of the the morning convection as it
moved across eastern WI.  This is what we have been watching with
the activity slightly outpacing some of the model data.  12Z
soundings from both DTX and APX showed quite a bit of drier air in
the column with the ridging that has been in place.  While this has
helped in holding off precip, moisture advection coming into the
area should help in maintaining some of the precipitation. Forecast
is on par with the trends as the northern half of the CWA will see
better chances for activity through the later afternoon and into the
evening. Rainfall amounts are expected to stay on the lighter side
through early Thursday morning, generally less than half an inch.

Surface based convection has already started to develop back across
the Midwest this afternoon.  This activity is expected to weaken as
it pushes east overnight. Activity is then expected to increase in
coverage Thursday morning as the area remains in the warm sector
coupled with the advancement of the warm front across the area.
There is still uncertainly in just how much coverage there will be
as it moves into the warm sector tomorrow morning. With instability
increasing, SPC has nudged both the marginal and slight risks
northward with main concerns for strong winds during the afternoon
and evening periods. Going into Friday, chances are still there for
storms as the cold front pushes through.  Friday looks to be the
best chance for storms as opposed to Thursday, but again will be
dependent on how convection from the previous day plays out.  The
entire CWA continues to be highlighted in slight risk for Friday.

Warm air advection will continue to bring warmer temperatures into
the area through the end of the week.  Highs on Thursday are
expected to be the warmest for the week with highs warming into the
lower 80s.

A wet weather pattern looks to be in store for Southeast Michigan
during the weekend into early next week. The first wave of low
pressure will move in on Saturday bringing the chance for showers
and thunderstorms diminishing by the afternoon hours. A high
pressure system will then build into the Great Lakes region on
Sunday, bringing relatively dry weather, however, an isolated shower
would not be out of the question. Another wave of low pressure will
then move through the region Monday evening into Tuesday allowing
for chances of showers and thunderstorms yet again. High pressure
then looks to move into the area on Wednesday, bringing drier
conditions. Temperatures will remain seasonal, with high
temperatures hovering around the upper 70s to low 80s, and overnight
lows in the 60s.

MARINE...

Low pressure developing over the western Great Lakes will continue
to support increasing southerly wind over marine areas tonight
through Thursday. Moderate speed will be more common over Saginaw
Bay and over western Lake Erie where channeling and alongshore flow
respectively will enhance gusts. Small craft advisories are in
effect overnight through Thursday evening for these areas as well as
for Port Austin to Harbor Beach around the tip of the Thumb. This
wind pattern will bring in warmer and more unstable air into the
region before easing Thursday night into Friday. The warmer air will
fuel increased thunderstorm activity as low pressure over the
northern Great Lakes Thursday drags a diffuse surface trough through
the region Friday into Saturday.

HYDROLOGY...

Low pressure tracking into the northern great lakes tonight will
pull a warm front into lower Michigan. Thunderstorms in progress
over the Midwest and western Great Lakes will tend to focus more
along this front through central lower Michigan overnight through
Thursday morning. Rainfall amounts are generally expected to be in
the range of one quarter and one half inch north of I-69 through
Thursday morning. Locally higher totals around 1 inch will be
possible due to clusters of thunderstorms.

Additional storms may develop throughout Thursday and Thursday night
as warm and increasingly humid air builds into the region but with a
focus more to the south of the I-69 corridor. Average rainfall
amounts will be generally less than one half inch, but localized
higher amounts in excess of an inch will once again be possible
within any more concentrated areas of thunderstorms. This will be
followed by another low pressure system tracking west of the region
that will maintain the threat for thunderstorms Friday and Friday
night.

The potential for flooding will be dependent on the cumulative
rainfall totals during this active period. Should a more focused
region of heavy rainfall emerge, then the potential for a
corresponding rise of area rivers and streams, as well as minor
flooding will be possible. Central Lower Michigan will remain most
susceptible as the area continues to recover from recent flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from midnight tonight to 10 PM EDT Thursday
     for LHZ421-422-441.

Lake St Clair...NONE.
Michigan waters of Lake Erie...Small Craft Advisory from midnight tonight to 4 PM EDT Thursday for
     LEZ444.

&&

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...SP/MV
MARINE.......BT
HYDROLOGY....BT


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