Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201843
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
243 PM EDT SAT AUG 20 2016

.DISCUSSION...

Deepening low pressure will track from eastern Wisconsin to the
eastern shores of Lake Superior this evening. Pretty decent model
agreement that this low will drop to near 990 mb during this time
frame. As this occurs, expect a pre-frontal trough to lift east to
northeast through the area this afternoon/early this evening with a
strong cold front to follow by midnight to 2 am or so. Showers and
thunderstorms will increase in coverage mid/late afternoon as this
trough works into the area.

While most of the thunderstorm activity to this point has been
embedded in a shield of stratiform rain, the individual line
segments of convection have been becoming better defined in terms of
small bowing features over southern Lake Michigan/SW Lower Michigan.
Given these features are more or less perpendicular to the mid level
flow, expect strong to severe wind gusts with some of this activity
as it rides 50 knot H5 flow into the Saginaw Valley in the 19z-20z
time frame and encounters MLCAPE of 1000-1500 J/kg.

Additional storms will also continue to fire south/southeast into
Indiana along next surge of higher theta-e air with this activity
lifting northeast into the remainder of the forecast area from late
afternoon into the early evening hours. While severe weather will
not be widespread, strong to severe wind gusts will likely be
embedded within the overall maelstrom of rain/thunderstorm segments.
Rain/thunderstorm chances will then persist through the evening as
cold front surges from its afternoon position from GRB to DVN into
Southeast Lower Michigan by around midnight. Thereafter, mid level
dry slot will bring an end to precipitation quickly overnight.

This low will then occlude overnight into Sunday east of Lake
Superior with mid level cold pool pivoting southeast around center
into lower Michigan during the day on Sunday. This should lead to
scattered showers with a few thunderstorms, particularly during
instability maximum mid/late afternoon as surface trough associated
with this secondary push of cooler air maximizes low level forcing
over area. Activity will then fade quickly Sunday evening with loss
of daytime heating and high pressure begins to build into area in
the wake of this passing trough. Cooler weather can be expected in
the Sunday to Monday time frame as this airmass of Canadian origin
builds through the region. Expect high temperatures to be limited to
the 70s both days.

Quiet weather is then expected through the first half of next week
as surface high pressure builds through the area. At the same time,
progressive upper level ridging will translate eastward across the
central Great Lakes. This should allow temperatures to build back
into the lower 80s Tuesday/Wednesday. Thereafter, upper troughing
builds eastward from western to eastern CONUS with shortwave energy
lifting into area from around this upper trough. This will lead to
increasing rain chances from late Wednesday into Thursday. Cooler
weather with high back into the 70s will follow late next week as
upper trough, albeit rather flat, shifts into the Great Lakes.

&&

.MARINE...

Deepening low pressure will head northeast through the Straights
this evening, supporting showers and thunderstorms. Strong cold
front will pass through late this evening/overnight, with southwest
gales expected after midnight for much of Lake Huron. Strongest winds
will be over northern Lake Huron tomorrow, as winds veer around to
the west, likely resulting in gusts of 40 knots as cooler air also
settles into the region, increasing the low level instability. With
the warm water temperatures, waterspouts also look to be a
possibility. Much quieter and favorable boating conditions early
next week as high pressure works through.

&&

.HYDROLOGY...

Periods of showers and thunderstorms expected through this evening
as strong cold front moves through the area. Progressive nature of
activity should limit flooding threat, but thunderstorms will
produce torrential rainfall, quick one inch or greater possible,
which could produce localized minor flooding in poorly drained
locations, especially in urban areas.

&&

.PREV DISCUSSION...
Issued at 1233 PM EDT Sat AUG 20 2016

AVIATION...

Showers and thunderstorms expected to overspread southeast Michigan
between 3-5 PM, with periods of showers and thunderstorms continuing
through the evening hours. A dry slot will then overspread the area
overnight, but enough low level moisture around expected to produce
low mvfr stratus deck, with the exception being across dtw/yip/det
where partial clearing is expected. Any clearing will fill back in
Sunday morning as cooler air filters in with gusty westerly winds
(20-25 knots by afternoon), but ceilings lifting to low VFR.

For DTW...Expecting thunderstorms to arrive around 20z, with period
of showers and thunderstorms persisting into the evening hours.
Banking on dry slot overnight and slight downsloping west-southwest
winds to help scatter out low level moisture, but confidence is
somewhat low.

//DTW Threshold Probabilities...

* High confidence in ceilings aob 5000 feet late this afternoon
  through this evening, low overnight, and medium Tomorrow.

* Moderate in thunderstorms late this afternoon and early evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from midnight tonight to 4 PM EDT Sunday FOR LHZ363-
     421-422-441-462.

     Small Craft Advisory until 4 PM EDT Sunday FOR LHZ442-443.

     Gale Warning from 4 AM to 10 PM EDT Sunday FOR LHZ361-362.

Lake St Clair...Small Craft Advisory until 4 PM EDT Sunday FOR LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT Sunday FOR LEZ444.

&&

$$

DISCUSSION...DG
MARINE.......SF
HYDROLOGY....SF
AVIATION.....SF


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at www.weather.gov/detroit.



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