Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 270546
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
146 AM EDT Thu Apr 27 2017


.AVIATION...

The rogue strong to severe thunderstorm cluster that was tied largely
to the lead edge of upper level diffluence and midlevel moisture
advection has exited the Thumb. Localized subsidence in the wake of
this convection along with the configuration of the upper level jet
maximums support quiet weather for the remainder of tonight. A few
convective cells along a line from NE of Grand Rapids to Claire need
to lift through the region yet, but this activity is expected to miss
KMBS to the north and west. Next chance of greater coverage of
precipitation and thunderstorms will be in 16-20Z time window as
pooled moisture ahead of a pre-frontal trough swings through
southeastern Michigan. Conditional to the development of the low-
topped convection either thunderstorms or showers, the potential will
exist for wind gusts with the activity. The other main narrative
will be the strong southwest winds that develop during the afternoon.
Current forecast data suggests wind gusts in the 30 to 35 knot range
will be possible.


//DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 ft or less Thursday afternoon.

* Moderate probability for thunderstorms between 16 and 20Z Thursday.

&&

.PREV DISCUSSION...
Issued at 837 PM EDT Wed Apr 26 2017

UPDATE...

Robust convection is maintaining intensity as it moves rapidly
through Indiana adding confidence that it will reach central Lower
Michigan in some form during mid to late evening. Hourly mesoanalysis
indicates the storms are operating in a strong wind profile with an
adequate combination of surface based and elevated instability. A
ribbon of 50 kt effective bulk shear extends northward from Indiana
into central Lower Michigan along the surface trough/lake breeze
hybrid where showery convection lingers through the Tri Cities. The
wind profile will keep the Indiana convection more organized while
MUCAPE lingers around 1000 J/kg along a similar corridor. This is a
measure of instability that illustrates lingering potential as
surface based CAPE begins to diminish after daytime heating. The
latest projections suggest the strongest storms will move north of
the border while possibly brushing Lenawee and Washtenaw counties and
then track toward Howell, Flint, and the Tri Cities region during
late evening. The earlier update expanded chance POPs mainly west of
the U.S.23/I-75 corridor into the Flint, Tri Cities, and western
Thumb. Later updates are planned based on a downward intensity trend
while coverage remains on the numerous side through about midnight to
2 AM.

PREV DISCUSSION...
Issued at 344 PM EDT Wed Apr 26 2017

DISCUSSION...

Ample insolation combined with strong south/southeasterly transport
has supported a solid temperature rise this afternoon. The
temperature rise has been slightly muted east of the limiting
streamline (evidenced by the density discontinuity observed as a
fine line in KDTX reflectivity imagery) attendant to the west end of
Lake Erie (owing to widespread lake shadowing withing the strong
flow). Temperatures west of the boundary have touched 80F, while
remaining in the lower to mid 70s in the lake shadows.

Moisture quality is slowly increasing over western Lower Michigan -
as witnessed by increasing boundary layer cumulus and even some
small scale shower development. The ribbon of better lower-
tropospheric moisture is expected to slip east through the next
several hours. An isolated shower or two is possible as this occurs;
however, given the slightly lower surface temperatures and resultant
slightly more stable environment, expectations are for any robust
development to tied to the better congestus field along the lee of
Lake Michigan convergence zone. This feature is expected to sweep
northeast and may eventually affect the Saginaw Valley during the
evening.  Otherwise, high level cloudcover is expected to slowly
overspread the region during the evening hours, as convection over
the mid-Mississippi valley continue to mature.

The mature surface low, located over northern Wisconsin, will
continue to move north/northeast. The accompanying cold front is
roughly aligned along the mean steering flow vector - which will
limit the eastward progression through the night. Consequently, the
deep moisture plume along the cold front will take all night to
advance east into portions of Southeast Michigan. Additionally, the
quality of the deep moisture will decrease substantially as it loses
connection with moisture transport from the Gulf of Mexico.

During the day Thursday, the cold front will be dominated by
confluent flow - limiting the ability to provide a solid ribbon of
ascent. Therefore, expectations are for only a couple of broken
lines of convection along the boundary as it slides through during
the midday hours. Instability along the boundary is expected to be
rather meager - but may be sufficient to produce some scattered
thunderstorm activity. The flow in the column will remain strong and
will support gusty conditions across all of Southeast Michigan, with
the possibility of convectively enhanced gusts certainly possible
(thus the SPC Marginal Risk for severe weather).

The next is the series of strong western CONUS systems will dig into
the southern Plains by Saturday. Moisture transport in response the
deepening surface low will set the stage for period rainfall chances
across the southern Great Lakes region starting late Friday. The
system is expected to strengthen substantially through the weekend
and lift northeast into the western Great Lakes region by early
Monday. During the development timeframe, several waves of rainfall
will be possible across southeast Michigan.  Cooler than normal
conditions are expected for several days in the wake of the system.

MARINE...

Moderate pre-frontal southeast wind will remain in place through
tonight. Existing higher degree of stability will continue to limit
higher gust potential, with gusts capped at or below 25 knots during
this time.  Winds will turn to southwesterly as a cold front slips
through by late Thursday.  The combination of increasingly gusty
conditions and a period of wave heights above 3 feet will lead to a
marginal small craft condition Thursday across Saginaw Bay and the
lake Huron nearshore waters.  There will be a low probability for
thunderstorms with the cold frontal passage early Thursday
afternoon.  Winds and waves will diminish Thursday evening as high
pressure builds into the region.  Lower southwest winds speeds
expected Friday as this high sustains a weaker gradient.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 AM this morning to 10 PM EDT this
     evening for LHZ421-422-441>443.

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

$$

AVIATION.....CB
UPDATE.......BT
DISCUSSION...Mann
MARINE.......MR


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