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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
705 PM EDT Sat Jul 30 2016



Aviation...

Scattered showers/thunderstorms have expanded back over areas south
of kptk early this evening as influence of next shortwave pivots
into far lower Michigan. This activity will fester into the evening
and may impinge on terminals south of kptk. Will include vcsh at
this time and monitor for any stationary cell that develops over or
near a terminal. Hires models suggest activity will flare up again
overnight roughly kfnt north as fgen forcing increases as this wave
lifts over the area. Will include prob30 for kmbs, which stands the
best chance of activity later. More widely scattered shras/tsras
will linger into Sunday as well, but coverage should wane with time.

//Dtw threshold probabilities...

* medium for ceilings aob 5kft this evening.

* Low for tstorm impacting kdtw.

&&

Previous discussion...
issued at 331 PM EDT Sat Jul 30 2016

Discussion...

Persistent low amplitude longwave trough remains over the western
Great Lakes and looks to stay that way until it releases eastward
Sunday and Sunday night. A train of shortwaves has tracked through
the flow across southern Michigan over the past couple days and has
resulted in showers and thunderstorms throughout the region, each
aided by a very moisture rich environment in a deformation region
spread across lower Michigan. Todays activity has weakened
significantly over the last couple hours but deformation and
isentropic ascent remain strong enough to keep showers going along
and north of M-59. Earlier activity has produced a notable change in
the forecast for this evening and overnight in the form of a strong
subsidence region generally along and south of I-94 (which happens
to be one of the areas hardest hit with heavy rainfall and flash
flooding). This shows up well on the visible satellite with the
cloud field quickly eroding. This region had been advertised by most
models to be favored for the next round of thunderstorms this
evening as the next wave ejects out of the base of the trough, but
now looks to be stable aloft and looks like the jet streak is aiming
a bit further south as well. Cannot rule anything out with this
airmass we are dealing with though. A lack of forcing has not
prevented thunderstorm development thus far and don't see it
shutting US down tonight. Have dropped the likely pops down to
chance expecting the most widespread activity to stay south of the
state line along the differently heating boundary and region of best
jet forcing. Will carry likely pops for ongoing convection along I-
69 northward and a blanket chance for the rest of the night for
renewed nocturnal activity across the area. With the wealth of
moisture in the column (pwats over 1.5 inches) and slow storm
motions, the threat of heavy rainfall will continue tonight. Did
notice one storm actually put out an outflow boundary this afternoon
too, so cannot rule out a wind gust to around 30 mph.

The longwave trough will eject eastward Sunday and Sunday night
which will finally bring some building height back into the region
on Monday. Lingering mid level cool pool and the backside of the
deformation axis will linger through most of the day which may be
enough to pop a few more showers before conditions begin to improve.
Will hold onto a chance pop Sunday before tapering off pops all
together overnight.

Tuesday through saturday: basic scenario shows building high
pressure over the southern U.S. With an upper level disturbance
centered over northern Manitoba pushing northeast. This combination
of systems will effectively combine to send several waves of low
pressure through Southeast Michigan. Chances of showers and thunderstorms
will develop late Tuesday and persist through the workweek...as weak
surface lows are pulsed up. High temperatures will be on an upward
trend through the week hitting the upper 80's by the end of the
workweek. Dew point temperatures also look high...anticipate another
round of hot and muggy.

Marine...

Small craft advisories remain in effect as persistent moderate to
fresh onshore flow builds significant wave heights into the 3 to 5
foot range this evening. Winds and waves will then gradually
diminish late tonight through Sunday being replaced by a light to
moderate breeze through midweek. Thunderstorms are possible over the
waters today...Sunday...and again on Wednesday.

Hydrology...

Pockets of heavy rain producing a half to quarter of an inch per
hour will be possible for the remainder of the evening. Lesser
coverage of storms is anticipated on Sunday. Slow-moving storms
containing heavy rain will still be possible, but will largely be
confined to the southern half of the forecast area during peak
heating.

&&

DTX watches/warnings/advisories...
Michigan...Beach hazards statement until 10 PM EDT this evening for miz048-049-
055-063.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for lhz421-422-
441>443.

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

$$

Aviation.....Dg
discussion...drk/de
marine.......jvc
hydrology....jvc



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