Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 290819

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
419 AM EDT Thu Jun 29 2017


Longwave trough will reside over the northern U.S. and Canada
through the end of the week, while shortwave troughs embedded within
the larger feature pass through the Great Lakes. This will keep
unsettled weather over the area into the first part of the weekend.

The first upper wave is currently working into the northern Great
Lakes, and will push an area of surface low pressure across the U.P.
today into tonight. A couple of MCVs from upstream convection that
occurred over IA/WI/IL yesterday evening are working across the area
along with strong theta-e advection early this morning, bringing
showers and a few thunderstorms (mainly north of M-59). The activity
has been weakening as it moves towards Southeast Michigan and
encounters a drier and more stable airmass. Idea is that this area
of showers/tstorms will move east this morning, with subsidence
behind the upper waves and mid-level drying over Central Michigan
then yielding quieter weather for the middle part of the day.
Recovery of the airmass then becomes the deciding factor in whether
additional development of showers/tstorms occurs during the late
afternoon and evening. Hi-res models are split with solutions. Best
chance for redevelopment will be south of the I-69 corridor and
especially towards the Ohio border where deeper moisture will
reside. Warm and humid conditions are expected today, with max temps
in the low/mid 80s and dewpoints surging well into the 60s this
afternoon. Should also see a good pop of winds once we decouple late
this morning, with mixed layer supporting gusts to 35, or even 40
mph, per RAP/HRRR/NAM forecast soundings. Gusts should decrease by
mid afternoon however as low-level jet axis and stronger winds aloft
slide to our east. Severe weather potential this afternoon/evening
will hinge on airmass recovery following morning showers/tstorms and
clouds. Modestly strong wind field will exist over Southern Michigan
on the south side upper wave and surface low over the Northern Great
Lakes, with 30-35 knots of bulk shear in the afternoon per GFS/NAM.
If we can build enough ML CAPE, could see a few severe storms in the
afternoon/evening, with large hail and damaging winds the main
threat. Heavy downpours will also be possible.

Next round of convection to watch will likely occur overnight as
complexes of storms that develop late this afternoon/evening over
IA/MO move towards southern Michigan. Nocturnal resurgence of the
low-level jet stretching from the central Plains through the Ohio
Valley will help to maintain this activity to some degree, with up
to 1500 J/kg of CAPE keeping severe threat into the late night
hours. Other concern for convective development, including a few
severe storms, will be as a secondary warm front lifts into Southern
Michigan, potentially allowing storms to become surface based while
low-level shear increases, but CAPE should fall to less than 800
J/kg, again limiting threat and coverage of severe weather. Other
noteworthy item in the forecast tonight is the expectation of a warm
and humid night, with low temps only falling into the upper 60s to
near 70.

Next of the larger synoptic waves embedded within the longwave
trough that will impact Michigan now dropping through the Pacific
Northwest and will track into the Upper Midwest Friday, allowing
surface low pressure to lift up through Michigan. Secondary warm
front will continue lifting northward through the area during the
day, ushering in additional warm air and moisture. Severe storms
will again be possible, with strong flow once again residing over
the area and a potentially better build-up of instability during the
day. This will once again depend on overnight and early day
convection, which could again limit instability.



The region will remain under a moderate southerly wind today, as low
pressure slowly tracks across the upper peninsula.  These speed will
be magnified over Saginaw Bay and over western Lake Erie, where
channeling and alongshore flow respectively will enhance gusts.
Small craft advisories are in effect through this 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 tonight into Friday. The warmer
air will fuel increased thunderstorm activity as low pressure over
the northern Great Lakes drags a diffuse surface trough through the
region Friday into Saturday.



Lingering remnants of a weakening thunderstorm complex will maintain
the potential for lighter showers/isolated thunderstorms through the
morning period.  Rainfall amounts thus far largely arriving as
forecast, with totals generally ranging between one quarter and one
half inch where more widespread coverage was noted.

Greater stability in the wake of this complex does cast doubt in the
prospects for renewed thunderstorm development through the remainder
of the daylight period.  Expectations remain that any additional
development today will tend to focus south of the I-69 corridor,
with the greatest potential closer to the Ohio border.  Once again,
average rainfall amounts of less than half an inch are anticipated,
but localized higher amounts in excess of an inch area possible
should more concentrated areas of thunderstorms materialize this
afternoon and evening.  Potentially active period for showers and
thunderstorms will exist tonight through Friday night, although
placement of the more concentrated development remains less certain.

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.


Issued at 1147 PM EDT Wed Jun 28 2017


The remnants for the convective complex over Wisconsin earlier is
now working across wrn Lower Mi. Although this is weakening, showers
with a few embedded thunderstorms look probable for the first two to
possibly four hours of the TAF period. In the wake of this activity,
mid level subsidence will hinder additional convective development
during the morning through at least mid afternoon. RAP model
soundings remain supportive of carrying low level wind shear through
daybreak. The onset of daytime heating will quickly transition the
low level wind shear to mechanical turbulence during the morning.
Further deepening of the mixed layer Thurs afternoon will support
gusty s-sw winds, over 25 knots at times.

For DTW...The weakening of the upstream convection will remain
supportive of keeping thunder out of the metro TAF during the
overnight, with the better chances still north of Detroit. Low level
moisture advection during the course of the morning will increase
the chances for clouds based below 5000 ft.


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

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


MI...Beach Hazards Statement through this evening for MIZ049.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.




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