Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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627
FXUS63 KDTX 250403
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1203 AM EDT THU AUG 25 2016

.AVIATION...

The weak surface pressure trough over SE Michigan around midnight
will give way to more of a neutral westerly flow prior to sunrise.
This should support some combination of fog and stratus as a
restriction in the moist sector ahead of the cold front. Strength of
the wind favors more stratus over MBS to FNT and more fog across the
DTW corridor before improving around mid morning, just in time for
the next round of showers to arrive ahead of the front. The cold
front itself will then slide through the region during peak
afternoon heating and bring a chance of thunderstorms, all of which
will be east of the terminals by evening.

//DTW Threshold Probabilities...

* Moderate for ceiling 5000 ft or less during remainder of
  tonight through afternoon.

* Medium for thunderstorms mid to late afternoon.

&&

.PREV DISCUSSION...
Issued at 957 PM EDT Wed AUG 24 2016

UPDATE...

Mesoscale subsidence trailing the mid level MCV will produce a
considerable break in showers/storms through much of the night.
The localized mid level subsidence and negative theta-e advection
will then give way to a resurgence of moisture transport ahead of
the cold front late tonight through Thursday morning. This will
support another round of showers and ordinary thunderstorms ahead
of MCS/MCV development from the central plains into the midwest.
The MCV is expected to to spread over lower Michigan during late
Thursday morning into afternoon and increase coverage of
showers/storms as outlined in the day shift discussion which
remains solidly on target. The forecast update will just refine
timing on low end chance pops for the rest of tonight before
ramping back up into likely during Thursday morning.

PREV DISCUSSION...
Issued at 312 PM EDT Wed AUG 24 2016

DISCUSSION...

Decent MCV exiting Northern IL will track across far Southern Lower
MI through this evening. The hi-res models continue to have a robust
response to this feature, especially south of I 69. Will continue to
let the forecast work a few more hours despite radar trends and have
the likely POPs for the south half of the forecast region.
Thoughts on severe weather and flooding from earlier discussion
still largely on target. Severe threat, and even generic
thunderstorm threat is rather minimal. ML CAPEs were around 500 J/kg
with a 30kt low level jet feeding on the back side of the MCV. The
low level jet will also continue to advect some good moisture as
precipitable waters get to around 2 inches. While the storms should
continue to move to the northeast around 30 mph, the high water
content with the forcing on the back side of the MCV continuing to
feed the system could lead to a couple of rounds of showers and
storms with heavy rainfall for a few isolated locations,
especially from Detroit on south. Subsidence behind this MCV will
end most of the shower and storm threat after about 02z until the
next convective system moves into the state from the west and
southwest around 12z Thursday.

The Thursday system is associated with a good shortwave and a
surface low riding along the cold front.  Lower MI will be in the
right rear entrance region of a good jet over the northern Great
Lakes.  500 mb winds get up to 50 kts with 0-6 km shear from 30-40
kts. Question will be the amount of instability. Both the NAM and
GFS keep the best instability south of the border, but with that
type of forcing would just need to squeeze a little instability into
Southeast Michigan to have a decent threat of severe winds with the
storms. Enough forcing to have likely POPs for areas south of a OZW
to PHN line.

Drier air works into the forecast area from 21z to 03z Thursday
evening for a mostly clear night. That dry air holds in place for
Friday morning, but then a return in moisture will bring broken
cumulus and cirrus by the afternoon for partly sunny skies.  The mid
and high level moisture continues to advect on good and deep
southwest flow Friday night into Saturday with plenty of cloud cover
expected. Saturday will stay dry as all of the instability and
forcing stays west of the forecast area.

Medium-range model consensus supports a deamplifying wave transiting
Lake Superior Saturday night. Best precip chances for now over the
Saginaw Valley closest to the best forcing/moisture advection. Weak
frontal boundary tracks through Sunday, but this will warrant only
low chance PoPs as there is little upper support. Dry forecast
favored for early next week with surface high attempting to build
into the Great Lakes. Above-normal temperatures are forecast Sunday
into early next week.

MARINE...

Moderate southerly flow in advance of a slowly approaching front
will be accompanied by showers an an occasional thunderstorm through
this evening. Another round of thunderstorms will sweep across the
southern waters on Thursday before winds veer to light to moderate
west northwest for the remainder of the week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...RBP/DT
MARINE.......JVC


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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