Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210110
AFDDTX

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

.UPDATE...

The deepening sfc low is now over southeastern Lake Superior,
while the cold front extends across SW Lower Mi. The front will
track across the forecast area late this evening. The main
instability axis has shifted east of the area. Ascent ahead of the
cold front will still trigger some scattered showers late this
evening prior to the arrival of the mid level dry slot now
advancing across Lake Michigan. Overall, the going forecast for
tonight looks in good shape with a steady post frontal drop in
temps and humidity. An update will be issued to remove the mention
of thunderstorms and carry just scattered showers through the rest
of the evening, with dry conditions expected overnight.

&&

.PREV DISCUSSION...
Issued at 645 PM EDT Sat AUG 20 2016

AVIATION...

The cold front will track across Se Mi between 02Z and 04Z. Pre
frontal instability has been on the wane. There will however remain
enough moisture and forcing to produce periodic showers (perhaps an
isolated TSRA) prior to fropa. The passage of the front will be
marked by a veering of the wind to the west-southwest. The deepening
surface low lifting across ern Upper Mi will sustain ample boundary
layer mixing, holding wind speeds in the 10 to 15 knot range through
the night. Ceilings will remain variable during the evening, then
trend toward MVFR overnight as low level moisture becomes trapped
under a developing inversion.

For DTW...The lack of lightning over the past hour suggests most
convection through the rest of the evening will be brief heavy
showers. Fropa timing at metro looks to be around 03Z. Ceilings are
expected to be quite variable at metro through the night as the
better chances for widespread MVFR is expected to hold from PTK
northward.

//DTW Threshold Probabilities...

* High in ceilings below 5000 ft tonight through Sunday.

PREV DISCUSSION...
Issued at 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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 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.

&&

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...DG
MARINE.......SF
HYDROLOGY....SF


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