Beach Hazards Statement 12, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1150 PM EDT SAT AUG 20 2016

.AVIATION...

Post frontal cold air advection and a deepening low level inversion
will support the development of shallow clouds during the early
morning. In addition to post frontal moisture, there is also some
degree of moisture flux off Lake Michigan. While ceiling heights
will be somewhat variable this morning, the predominate trend will
be toward lowering into the low end MVFR range. The onset of daytime
heating will deepen the boundary layer late in the morning into the
afternoon, lifting cloud bases to VFR. There will be some diurnal
showers Sun afternoon, coverage and intensity may not quite justify
mention in the terminals attm.

For DTW...Observational trends suggest at least some partial
clearing during the first few hours of the terminal forecast before
low stratus envelopes metro Detroit.

//DTW Threshold Probabilities...

* Medium in ceilings below 5000 feet early this morning, high after
  10Z through late Sun afternoon.

&&

.PREV DISCUSSION...
Issued at 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 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.

&&

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

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
858 PM EDT SAT AUG 20 2016

MIZ047>049-053>055-060>063-068>070-075-076-082-083-210815-
MIDLAND-BAY-HURON-SAGINAW-TUSCOLA-SANILAC-SHIAWASSEE-GENESEE-LAPEER-
ST. CLAIR-LIVINGSTON-OAKLAND-MACOMB-WASHTENAW-WAYNE-LENAWEE-MONROE-
858 PM EDT SAT AUG 20 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THERE IS A CHANCE OF THUNDERSTORMS WEDNESDAY NIGHT THROUGH
THURSDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-210815-
LAKE ST. CLAIR-
MICHIGAN WATERS OF LAKE ERIE FROM DETROIT RIVER TO NORTH CAPE MI-
LAKE HURON FROM 5NM EAST OF MACKINAC BRIDGE TO PRESQUE ISLE LT
BEYOND 5 NM OFF SHORE-
LAKE HURON FROM PRESQUE ISLE LIGHT TO STURGEON POINT MI BEYOND 5NM
OFF SHORE-
LAKE HURON FROM STURGEON POINT TO ALABASTER MI BEYOND 5NM OFF SHORE-
OUTER SAGINAW BAY SW OF ALABASTER TO PORT AUSTIN MI TO INNER SAGINAW
BAY-INNER SAGINAW BAY SW OF POINT AU GRES TO BAY PORT MI-
PORT AUSTIN TO HARBOR BEACH MI-HARBOR BEACH TO PORT SANILAC MI-
PORT SANILAC TO PORT HURON MI-
LAKE HURON FROM PORT AUSTIN TO HARBOR BEACH BEYOND 5NM OFF SHORE-
LAKE HURON FROM HARBOR BEACH TO PORT SANILAC BEYOND 5NM OFF SHORE-
LAKE HURON FROM PORT SANILAC TO PORT HURON BEYOND 5NM OFF SHORE-
858 PM EDT SAT AUG 20 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE ERIE...LAKE
HURON AND LAKE ST CLAIR.

.DAY ONE...TONIGHT

GALE WARNINGS ARE IN EFFECT LATE TONIGHT FOR CENTRAL AND NORTHERN
LAKE HURON. SMALL CRAFT ADVISORIES HAVE BEEN ISSUE FOR LATE TODAY
INTO TONIGHT FOR THE REST OF THE MARINE ZONES. SEE THE LATEST MARINE
WEATHER MESSAGE FOR DETAILS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE GALE WARNINGS AND SMALL CRAFT ADVISORIES REMAIN IN EFFECT
ON SUNDAY. SEE THE LATEST MARINE WEATHER MESSAGE FOR DETAILS.

AFTERNOON SHOWERS MAY ALSO PRODUCE WATERSPOUTS ON SUNDAY. THERE IS A
CHANCE OF THUNDERSTORMS WEDNESDAY NIGHT THROUGH THURSDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.

YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

SC