Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 261944
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 123 PM EDT Wed Apr 26 2017

AVIATION...

Continued dry low level conditions will favor a mainly clear sky
across the lowest 10k ft through this evening.  While instability
will increase as conditions turn warmer and more humid, potential
for showers and thunderstorms will largely remain to the west
through tonight.  The exception will be in the vicinity of MBS,
where a low probability exists as convection develops over northern
Illinois and tracks northeast early tonight.  Gusty southeast flow
through the latter half of the day, subsequently easing with sunset.
Best window for showers roughly 15z-19z Thursday as a cold front
lifts through.  Introductory mention of a low probability for
thunderstorms during this time.

//DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less.

* Low for thunderstorms Thursday.


&&

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

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

$$

DISCUSSION...Mann
MARINE.......MR
AVIATION.....MR


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