Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 250745

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


Moisture plume (analyzed at 00Z between 1.75 and 2.0 inches) can be
seen on water working up from Mexico into the southern Great Lakes
between a large upper high over the southeastern U.S. and an upper
trough sinking from central Canada into the Northern Plains. Several
shortwaves/MCVs are evident within this plume stretching along a
warm front from the Plains into the Western Lakes. These waves and
the front should work into Southeast Michigan during the morning and
afternoon per latest model guidance. First round of showers/tstorms
triggered by these waves is now working across Lake Michigan. This
activity is expected to weaken as it crosses Southeast Michigan
during the mid to late morning as low-level jet support wanes. Some
of the higher-res guidance then suggests that instability will
struggle to recover enough to support much in the way of
thunderstorms later in the day, while other runs support enough
recovery for strong storms. This places us in a very familiar
situation of waiting to see how much the atmosphere can recover from
early convection before stronger forcing works in during the
afternoon. Strengthening mid-level wind field will increase 0-6km
bulk shear values to 35-40 knots by this afternoon, while forcing
from smaller waves is bolstered by surface trough and initial cold
front. Warm start to the day should help temps rise into the 80s,
with dewpoints near 70 helping to generate SB CAPE values likely
around 1000 J/kg or more. This will support a threat for severe
weather if instability can be realized from mid-afternoon through
early evening, with fairly unidirectional wind profile making
damaging wind gusts to 60 mph the biggest threat. Very high moisture
content will also bring the threat for very heavy rainfall and
localized flooding. Drier air will arrive tonight behind the surface
trough, and behind a stronger secondary front that will arrive
overnight. This will end the threat for rain and allow skies to
clear a bit.

Weak shortwave ridging will allow surface high pressure to build
over Michigan on Friday. Larger-scale subsidence should keep the
area dry even as a weak shortwave riding the periphery of the upper
high centered over the southern U.S. lifts up into Michigan. This
should allow for an increase in mid/high level cloudiness by late in
the day, with GFS/NAM model forecast soundings keeping the lower
levels dry. A warm front will lift through the western and central
Great Lakes Saturday into Saturday night in advance of a stronger
trough working through the Northern Plains and Upper Midwest. This
will bring increasing clouds (mostly cloudy skies) and chances for
showers and thunderstorms from at least the I-69 corridor northward.
Upper trough, favorable right entrance region forcing, and cold
front working through Saturday night and Sunday will expand chances
for showers/tstorms across all of Southeast Michigan. Temperatures
for the end of the week have been adjusted upwards as warm air
advection look much more robust in latest model runs. Highs both
Friday and Saturday look to reach near 80 to the mid 80s.



Modest west to southwesterly winds in the 10 to 20 knot range will
persist ahead of a slowly approaching cold front. Ahead of this
front, the potential continues to exist for showers and
thunderstorms from Saginaw Bay southward, particularly this morning.
The cold front is expected to track through the central Great Lakes
tonight. Overall, very little wind increase is expected behind this
weak system. Modest west winds are expected again for Friday before
shifting to the south on Saturday.


Issued at 1203 AM EDT Thu AUG 25 2016


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.


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



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