Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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822
FXUS63 KDTX 280751
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
351 AM EDT THU JUL 28 2016

.DISCUSSION...

Cold front over northern Lower Michigan will slowly drop southward
today and tonight, while high pressure builds over the northern
Great Lakes. These features will combine to allow higher theta-e
currently over the southern 2/3 of Lower Michigan to gradually sink
southward. There is reasonably good agreement with this overall set-
up with the 00Z GFS and NAM. Models do show a weak shortwave
entering the western Great Lakes late today, then crossing southern
Michigan overnight. Confidence in these small-scale features is not
high however, given lack of model continuity over the past 24 hours
and the relatively small-scale of these features. This wave would
however aid in showers/tstorm development along the front, providing
support even after the diurnal cycle had completed. POPs today are
highest over the western and southern portion of the forecast area,
with a gradually trend of tapering off from north to south
overnight. Cooler northeast flow building in behind the front will
have more of an influence over the thumb, boosting stability and
likely eliminating chances for any convection there. Storms are not
expected to be severe with CAPE expected to stay below 1000 J/kg and
light wind field only providing bulk shear values of 15-20 knots.
Storms will however be capable of locally heavy rainfall.
Temperatures today will be heavily influenced by flow off Lake Huron
and the front dropping through the area. Highs along/south of M-59
should reach into the mid/upper 80s with early day sunshine helping
to boost those numbers. The remainder of the area will see low 80s
and even some 70s over the eastern/northern thumb. The front looks
to settle near the Ohio border by Friday, while high pressure
remains in place over the northern Great Lakes. GFS/Euro slowly
track a shortwave across the Midwest and Southern Great Lakes during
this timeframe and will keep a slight chance POP in there for Friday.

A good deal of uncertainty then enters the forecast Friday night and
Saturday as global models diverge with the way they handle upper
energy now aligned along a jet axis from British Columbia through
the Central Plains. While most models consolidate the various
shortwaves into a broad trough that tracks through the Ohio Valley
and Southern Great Lakes late Friday and Saturday, they differ with
the evolution of surface low pressure that develops and tracks out
ahead of this features. GEM has been the most aggressive for several
models runs now, and the NAM has the feature but is a day slower
than the other models. GFS/Euro offer a better solution but differ
with the surface low placement. (GFS slightly further south.) Euro
seems like a reasonable solution, and has been fairly stable over
the past few runs. Have introduced some mid-range over Southeast
Michigan Friday night into Saturday as a result. Euro catches mid-
level front as it drops through Michigan late Friday and begins to
increase convergence along this boundary as the low tracks just to
our south. Along with a chance for rain and mostly cloudy skies,
this scenario would also keep temperatures closer to 80 degrees for
an afternoon high Saturday.

Medium-range models are in good agreement with this system exiting
on Sunday and upper ridging over the central U.S. expanding into
Michigan early next week. GFS/Euro have trended stronger with upper
energy riding through Canada around the periphery of this ridge, but
vary widely with timing and placement. Overall expectation for next
week continues to be warming temperatures (back to at least
mid/upper 80s), with occasional chances for thunderstorms as waves
ride to our north.

&&

.MARINE...

High pressure expanding across the northern Great Lakes today will
force a cold front into southwest Lower Mi and northern Ohio by the
end of the day. The expected development of weak low pressure along
this front and building high pressure across the northern Great
Lakes will support increasing north-northeasterly winds across the
lakes today. Given the fetch and relatively warm water temperatures,
these winds will become rather gusty across Saginaw Bay and the
southern basin of Lake Huron. The expected winds and building waves
remain supportive of small craft advisory conditions for the
nearshore waters of Lake Huron. There will be some slight weakening
of the northeast gradient on Friday as the frontal boundary and weak
low pressure system slides to the mid Atlantic. However, there is
still likely to be some gusty winds over the warm nearshore waters
of Lake Huron, possibly requiring the extension of some of the small
craft advisories through Friday. Further weakening of the gradient
over the weekend will support reduced wind speeds and wave heights
and more favorable boating conditions.

&&

.PREV DISCUSSION...
Issued at 1254 AM EDT Thu Jul 28 2016

AVIATION...

Weak frontal boundary will sag south of the terminals overnight with
light northeast flow expanding through the forecast area. This flow
will persist Thursday and increase with better boundary layer mixing
and a tightening pressure gradient as low pressure ripples through
the northern Ohio Valley along this boundary. While diurnal cumulus
will be common, shras/tsras will focus south of terminals for the
most part. Chance seems to small to include as prob30 group attm.
That said, lower VFR cigs in the 7-10kft range will be more common
from midday into early evening.

For DTW...Northeast flow in wake of passing front will persist
throughout the forecast, increasing to 8-10 knots for a time during
best mixing Thursday afternoon. CIGS should remain above 5kft and
any shra activity will be spotty with low confidence in timing and
placement

//DTW Threshold Probabilities...

* Low for thunderstorms impacting KDTW Thursday afternoon.

* Low for ceilings at 5000 feet Thursday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from 11 AM EDT this morning through this
     evening FOR MIZ048-049-055-063.

Lake Huron...Small Craft Advisory from 11 AM this morning to 4 AM EDT Friday FOR
     LHZ421-422-441>443.

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

$$

DISCUSSION...HLO
MARINE.......SC
AVIATION.....DG


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