Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 172300

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
700 PM EDT Thu Aug 17 2017


Weak convection along trough axis extending from low pressure to the
north will progress east/northeast of terminals during the first
hour or two of the forecast. VFR to occasional MVFR cigs will trend
to MVFR late tonight as low level moisture wraps back southeast into
the area as the low continues through the northern Great Lakes into
Ontario. Breezy southwest winds (20-25 knots) can be expected around
this low on Friday with slowly improving cigs (which should be VFR
by the end of the forecast period).

For DTW...Only a stray shower or two expected early with SCT-BKN
cigs bordering on VFR/MVFR. Wrap around moisture will bring better
coverage of MVFR cigs late tonight into Friday. Gusty southwest flow
will ensue by mid/late morning with wind gusts nearing 25 knots
during best mixing on Friday. Improving cigs/decreasing winds are
then expected late in the forecast.


* Low in thunderstorms 00z-02z.

* Medium in ceilings AOB 5000 ft this evening, higher late tonight
  into Friday.


Issued at 300 PM EDT Thu Aug 17 2017


A very moist but debris laden warm sector now overtaking southeast
Michigan, the arrival accompanying a secondary low level theta-e
surge and the associated arcing line of showers/thunderstorms. The
early afternoon timing of the precipitation effectively shrinking
the window for recovery. There is a narrow corridor of clearing now
migrating into the backside of this cloud debris field, allowing for
some degree of destabilization aided low 70s dewpoints. SPC
mesoanalysis indicates roughly 500-700 J/KG of MLCAPE within this
zone as temperatures bounce back toward the 80 degree range. It will
be within this axis where some renewed development remains plausible
this evening as a pre-frontal trough sweeps through. Latest hi-res
guidance suggests a low coverage, as convective growth continues to
fight modest instability, with paltry low level lapse rates. The
background deep layer wind field will remain supportive of
convective organization should instability allow for more robust
updrafts, but certainly a very conditional severe weather risk at
this stage.

Mid level circulation will lift from lake superior this evening to
south-central Ontario by midday Friday. Trailing shortwave pivoting
around the southern periphery of this system will track across
central lower MI overnight into Friday morning. An increasingly
component of dry air advection ongoing through this time becomes a
strong limiting factor in sustaining rainfall chances. Isolated
potential for a few showers/sprinkles given the accompanying
increase in cva with this wave, but certainly nothing organized
given the downturn in deep layer moisture quality and unfavorable
timing at the diurnal minimum.

Period of 850-925 mb cold air advection emerges by Friday morning,
likely accompanied by some expansion in lower stratus. Weakly
cyclonic mid level flow augmented by the diurnal process likely
sustains a high degree of cloudiness through the daylight period,
particularly with northward extent. Moisture depth and forcing is
lacking, suggesting shower production will be limited. Firm gradient
extending out from the system over Ontario will make for breezy
westerly conditions. Highs arriving largely within the 75 to 80
degree range.

Next shortwave sliding through the broaden background troughing
timed to arrive late Friday night into early Saturday. Brief uptick
in mid level dynamics with this system may prove sufficient for a
quick shot of rainfall/embedded thunder, before increasing mid level
stability/subsidence takes a progressive hold from northwest to
southeast through the latter half of Saturday. With good prospects
for some late day recovery, highs in the vicinity of 80 degrees will
be attainable.

Surface high pressure centered across the Ohio Valley on Sunday and
the majority of Monday will keep conditions dry as south/
southwesterly winds help raise daytime high temperatures well into
the 80s for both days. Rain and thunderstorm chances will gradually
ramp up late Monday into Tuesday as upper-level troughing with
embedded short-waves starts to build across the Great Lakes aloft. At
the surface, persistent southerly winds will allow a sufficient
amount heat and moisture to build in across the state, producing
sufficient conditions for shower and thunderstorm chances. A cold
front is also expected to move through late Tuesday, which will
provide additional lift for shower and thunderstorm development.
Behind the cold front, dry air will filter back in from the
northwest, bringing quiet conditions for the late half of next week.
The cold front will act to keep temperatures capped in the 70s for a
daytime high Thursday, and if the GEM and ECMWF models pan out, highs
in the 70s will persist into the weekend.


South-southeast winds generally in the 15 to 20 knot range this
afternoon will shift to the southwest tomorrow behind the cold front
which is tracking through this evening. Post frontal cold air
advection will boost the over-lake instability profile, and allow
for peak wind gusts more in the 20 to 30 knot range. Wind and waves
will then decrease over the weekend as high pressure builds into the
Great Lakes region.


Tropical airmass sliding east of southeast Michigan this afternoon,
and drying has commenced. None-the-less, scattered heavy rain
producing thunderstorms remain possible through early this evening
with leftover daytime instability. With the thunderstorm coverage
expected to be limited and progressive nature of activity, not
expecting flooding as additional basin averages look to be quarter
of an inch or less. However, localized quick half an inch to one
inch total remains possible with the strongest storms.


MI...Beach Hazards Statement until 10 PM EDT this evening for MIZ049.

Lake Huron...Small Craft Advisory from noon to 8 PM EDT Friday for LHZ443.

     Small Craft Advisory until 8 PM EDT Friday for LHZ441-442.

     Small Craft Advisory from 10 AM to 8 PM EDT Friday for LHZ421-422.

Lake St Clair...Small Craft Advisory from noon to 8 PM EDT Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from noon to 8 PM EDT Friday for LEZ444.




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