Marine Hail in Lake St. Clair, August 11, 2017

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
316 PM EDT Fri Aug 11 2017

.DISCUSSION...
Cold front extends from about Bad Axe southwest to Benton Harbor.
Shower and thunderstorms developed shortly afternoon in the vicinity
of the front as boundary layer capes up to 1500 joules broke the
cap.  Some storms have been strong to marginally severe with hail as
big as quarter size. Freezing levels only 12k ft with strongest
updrafts supporting up to 35k ft tops so far.  Activity
will continue into the evening before rapidly dissipating from loss
of diurnal heating.  The slow moving front will exit east shortly
after 00z supporting some shower activity into the early night far
eastern portions of the area.  The best concentration of
thundestorms will likely remain north of Detroit where 500mb cold
pool deeper and surface frontal convergence stronger. Lesser amount
of shower and thunderstorm activity is still possible Detroit on
south until around sunset.

There will be brief period of clearing behind departing front
before low clouds wrapping around departing low to the northeast
advect in bringing back mostly cloudy skies.  Broad 500mb trough
will linger over the Great Lakes Saturday aiding in a fair amount of
cu development.  A secondary cold front/surface trough will drop
southward through the Thumb in the afternoon.  This combined with a
few hundred joules of cape may produce a few showers as far south as
the northern Detroit area.  Highs Saturday will return to below
average ranging from nr 70 in the tip of the Thumb to mid 70s
elsewhere.

Weak ridging in the mid levels and surface high pressure will build
into the area Saturday night and Sunday bringing mostly clear skies
and the continued below average temps.  Decent radiational cooling
Saturday night will put lows in most locations in the low 50s with
some isolated upper 40s possible.  Sunday should be very pleasant
with plenty of sun and weak surface gradient, highs should upper 70s
to around 80 with a light wind.

A fairly quiet start for the first half of the extended forecast. A
broad surface high pressure system will continue to situate itself
across the Great Lakes Monday into early Thursday which will keep
conditions relatively dry, all while bringing a healthy amount of
sunshine to the region. A weak frontal zone poised to situate itself
across southern Michigan along with an upper-level trough with
embedded shortwaves will however bring the slight chance to see a
quick, pop-up rain shower Monday afternoon and evening. Otherwise,
better chances for rain and thunderstorms will enter Thursday into
Friday morning as an amplified ridge moves off to the east. PoP-
values will remain sub-30 percent as we lack model convergence, but
long-range models are picking up on decent forcing mechanisms
despite varying reasons. The GFS and to a lesser extent the ECMWF
push a warm front through southern Michigan throughout Thursday. The
GEM is more aggressive with a strengthening low pressure system,
which moves through southern Michigan Thursday morning into Friday
morning. High pressure is then expected to build back into the Great
Lakes by the weekend.

&&

.MARINE...

A weak low pressure system will track slowly from northern Lake
Huron into Ontario tonight. This system will pull a cold front
through the eastern lakes this evening which will continue to
produce the scattered thunderstorms. Southwesterly winds ahead of
the front will become northwest behind the cold front later this
evening and overnight. Winds across Lake Huron on Saturday will be
more north-northwesterly. A more unstable flow on Saturday should
cause gusts to increase closer to 25 knots across the Huron basin
with shoreline waves of 2 to 4 feet, just below small craft
criteria. Saturday night and Sunday will see a high pressure system
settle over the lakes for a light wind regime.

&&

.PREV DISCUSSION...
Issued at 119 PM EDT Fri Aug 11 2017

AVIATION...

Scattered thunderstorms already developing across central MI. Expect
these to be an issue at all sites until about 00z. Trying to time to
a two or three hour window beyond a best chance window will be
difficult with this setup. A brief window of scattered clouds after
00z before low level moisture wraps back into southeast MI after
06z. Enough of a gradient and lack of surface moisture will keep
that moisture as a stratus layer with ceilings just above IFR. That
stratus will slowly lift into broken ceilings with a more diurnal
flavor on Saturday morning, but will take until after 18z to get
above 3000 feet.

For DTW...Still highlighting 21-00Z for the best chance of afternoon
convection although some isolated cells could start initiating
near the airport between 18-19Z.

//DTW THRESHOLD PROBABILITIES...

* Low for ceilings at or below 5000 feet through 06z. High for
  ceilings below 5000 feet from 06Z tonight until 18z Saturday.

* Low for thunderstorms from 18Z-00z Friday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

DISCUSSION...DRC/AM
MARINE.......RBP
AVIATION.....RBP

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

Hazardous Weather Outlook
National Weather Service Detroit/Pontiac MI
320 AM EDT Fri Aug 11 2017

MIZ047>049-053>055-060>063-068>070-075-076-082-083-120730-
Midland-Bay-Huron-Saginaw-Tuscola-Sanilac-Shiawassee-Genesee-Lapeer-
St. Clair-Livingston-Oakland-Macomb-Washtenaw-Wayne-Lenawee-Monroe-
320 AM EDT Fri Aug 11 2017

This hazardous weather outlook is for southeast Michigan.

.DAY ONE...Today and Tonight

Scattered thunderstorms are expected today. There is a slight chance
of severe weather with the storms this afternoon. The strongest
storms will be capable of producing wind gusts to 60 MPH and hail to
one inch in diameter as they move to the east at 35 MPH. The storms
will be triggered by the interaction of an unstable atmosphere and a
cold front. The strongest storms are expected between 2 PM and 6 PM.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...
Dispatchers...please notify your emergency managers immediately.
Spotter activation may be needed this afternoon and evening.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-120730-
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-
320 AM EDT Fri Aug 11 2017

This hazardous weather outlook is for portions of Lake Erie, Lake
Huron and Lake St Clair.

.DAY ONE...Today and Tonight

Scattered thunderstorms are expected today. There is a slight chance
of severe weather with the storms this afternoon, mainly on Lake
Huron south of Port Austin and on Lakes St Clair and Erie. The
strongest storms will be capable of producing wind gusts to 50 knots
and hail to one inch in diameter as they move to the east at 30 knots.
The storms will be triggered by the interaction of an unstable
atmosphere and a cold front. The strongest storms are expected
between 2 PM and 6 PM.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...
Dispatchers...please notify your emergency managers immediately.
Spotter activation may be needed this afternoon and evening.

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

SC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
253 PM EDT FRI AUG 11 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0223 PM     HAIL             5 S CLARKSTON           42.67N 83.41W
08/11/2017  E0.75 INCH       OAKLAND            MI   AMATEUR RADIO

            PENNY SIZE HAIL REPORTED

&&

AM

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