Severe Thunderstorm Warning 42, NWS Detroit, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
730 PM EDT SUN AUG 9 2009

.AVIATION...

UPSTREAM CONVECTIVE COMPLEX WILL CONTINUE TO PROPAGATE
EAST-NORTHEAST AND ACROSS THE SOUTHEAST LOWER MI OVER THE NEXT
SEVERAL HOURS AS IT WORKS INTO AN EXTREMELY MOIST/UNSTABLE AND
WEAKLY CAPPED ENVIRONMENT.  BASED ON LATEST RADAR TRENDS...ALL
TERMINALS WILL SEE TEMPO WORTHY MVFR/IFR CONDITIONS IN
THUNDERSTORMS...WITH A LONGER DURATION FROM PTK NORTHWARD.  MOIST
BOUNDARY LAYER CONDITIONS WILL THEN LEAD TO MVFR FOG DEVELOPMENT
OVERNIGHT.  VFR CONDITIONS UNDER A LOW LEVEL STABLE LAYER MONDAY
MORNING...BEFORE ANOTHER ROUND OF DIURNALLY ENHANCED SHOWERS/STORMS
DEVELOP IN ADVANCE OF A COLD FRONT INTO THE AFTERNOON.  STILL EARLY
TO INCLUDE A SPECIFIC THUNDER MENTION AND WILL CONTINUE TO HIGHLIGHT
THIS PERIOD WITH SHRA.

&&

.PREV DISCUSSION...ISSUED 354 PM EDT SUN AUG 9 2009

SHORT TERM...TONIGHT

HOT AND HUMID CONDITIONS WILL PERSIST WELL INTO THE EVENING HOURS AS
SURFACE DEWPOINTS HAVE BEEN HOLDING SERVE IN THE MID-70S.  THERE
ARE SIGNS THAT DEEPER BOUNDARY LAYER MIXING WILL HELP LOWER THESE
VALUES SLIGHTLY.  HOWEVER...MIN TEMPS ARE ONLY EXPECTED TO DROP INTO
THE LOWER-MID 70S.

KDTX RAOB FROM 18Z SHOWS A RATHER FORMIDABLE STABLE LAYER FROM
850-720 MB.  SOME LOW-CLOUDS HAVE FORMED UNDER THIS FEATURE AND ARE
IN THE PROCESS OF MIXING OUT.  EXPECT THAT BOUNDARY LAYER MIXING
WILL CONTINUE TO WORK AGAINST THIS CAP WELL INTO THE EVENING HOURS
AS ACCUMULATED HEAT IS TRANSPORTED VERTICALLY.  ANTICIPATE THAT
LOCAL DEVELOPMENT WILL BE LIMITED EARLY IN THE PERIOD - WITH THE
MAIN FOCUS FOR DEVELOPMENT POISED OVER NORTHERN LOWER MICHIGAN.  THE
CONVECTION UPSTREAM OVER ILLINOIS/WISCONSIN/IOWA SHOULD CONTINUE TO
EXPAND AND MOVE TOWARD THE EAST ALONG THE INTERSECTION OF THE FRONT
AND THE EDGE OF THE CAP.  THERE SHOULD BE AMPLE INSTABILITY / MLCAPE
> 2KJ/KG / IN PLACE OVER SOUTHERN LOWER MICHIGAN TO MAINTAIN THE MCS
FAMILY FROM THE WEST AND ANY ACTIVITY ALONG THE FRONT THAT DESIRES
TO SETTLE SOUTH INTO THE INSTABILITY RICH ENVIRONMENT.  THE
INTENSITY OF THE ACTIVITY WILL CERTAINLY BE IN QUESTION WITH THE
DIURNAL DOWNTURN PLAYING A ROLE - BUT AMPLE DEEP LAYER SHEAR / >
20KTS / SHOULD AID IN SUPPORTING CONTINUED ORGANIZATION.

HEAVY RAINFALL WILL ONCE AGAIN BE A CONCERN AS PRECIPITABLE WATERS
HOVER ABOVE 1.5 INCHES.  THOSE PLACES AFFECTED BY YESTERDAY/S AND
LAST NIGHT/S ACTIVITY WILL BE QUITE SUSCEPTIBLE FOR A RECURRENCE OF
FLOODING WITH ANY APPRECIABLE ACCUMULATIONS /ESPECIALLY ACROSS
LAPEER COUNTY WHERE FLOOD WATER HAVE BEEN SLOW TO SUBSIDE/.

LONG TERM...MONDAY THROUGH NEXT SUNDAY

STRONG UPPER TROUGH SEEN ON WATER VAPOR IMAGERY WILL TRACK INTO THE
WESTERN GREAT LAKES MONDAY THEN ACROSS LOWER MICHIGAN MONDAY NIGHT
PER LATEST MODEL GUIDANCE. THIS WILL PUSH A SURFACE TROUGH AND COLD
FRONT DOWN ACROSS SOUTHEAST MICHIGAN...RESULTING IN NUMEROUS SHOWERS
AND THUNDERSTORMS ON MONDAY. GFS AND NAM DIFFER SLIGHTLY WITH THE
SURFACE PATTERN BY TOMORROW...WITH THE GFS RIDING A SURFACE WAVE UP
AHEAD OF THE MAIN COLD FRONT AS IT PUSHES EAST ACROSS THE WESTERN
GREAT LAKES. GFS ALSO BRING A SECONDARY WARM FRONT UP INTO SOUTHERN
LOWER MI AHEAD OF THIS FEATURE...AND USES THIS BOUNDARY AS A FOCUS
TO GENERATE PRECIPITATION ACROSS MAINLY CENTRAL MICHIGAN TOMORROW.
NAM AND THE EURO BOTH KEEP THE SURFACE WAVE...WHICH IS STILL
ORGANIZING OVER THE SOUTHERN PLAINS...WELL TO OUR SOUTH AND GENERATE
MORE OF A DIFFUSE PRECIPITATION SHIELD. ALL MODELS DO HOWEVER SHOW A
GOOD AMOUNT OF INSTABILITY BUILDING BY AFTERNOON AS HEAT AND HIGH
DEWPOINTS REMAIN IN PLACE...AND 12Z NAM SB CAPE VALUES ECLIPSE 2500
J/KG...WITH NO CAP IN PLACE. WILL THEREFORE RETAIN A MENTION OF
SEVERE WEATHER IN THE HWO AND WATCH TO SEE HOW THINGS EVOLVE
CONVECTIVELY OVER THE NEXT 18 HOURS. MODELS HAVE SLOWED THE
PROGRESSION OF THE COLD FRONT...WITH MORE OF A MONDAY NIGHT THROUGH
TUESDAY AFTERNOON TIMING NOW. HAVE ACCORDINGLY ADDED A MENTION OF
THUNDERSTORMS FOR TUESDAY TO COVER THIS SCENARIO...THOUGH IT WILL BE
A RACE TO FIRE OFF CONVECTION BEFORE MID LEVEL DRY AIR ARRIVES.

HIGH AMPLITUDE UPPER RIDGE WILL BUILD INTO THE PLAINS ON TUESDAY
THEN SLOWLY MIGRATE ACROSS THE EASTERN U.S. THROUGH THE
WEEKEND...BRINGING AN EXTENDED PERIOD OF SURFACE HIGH PRESSURE
ACROSS SOUTHEAST MICHIGAN. MODELS ARE IN GOOD AGREEMENT WITH H500
HEIGHTS BUILDING TO AT LEAST 588DM WEDNESDAY AND BEYOND...AND HAVE
THEREFORE HUGGED THE HIGHER (AND EVEN GONE SLIGHTLY ABOVE) GUIDANCE
VALUES. TEMPERATURES SHOULD RUN ABOVE NORMAL THROUGH THE PERIOD WITH
FAIRLY LIGHT WINDS...DRY WEATHER...AND AMPLE SUNSHINE. GFS
ADVERTISES AN UPPER TROUGH REPLACING THE RIDGE BY
SUNDAY/MONDAY...HOWEVER WILL STICK TO THE TIGHTER CONSENSUS OF THE
EURO/GEM/UKMET AND KEEP WHICH INSTEAD KEEP THE VERY STRONG RIDGE
INTACT.

MARINE...

SOUTHWEST GRADIENT FLOW WILL ELEVATE OVER THE STABLE MARINE LAYER.
A COLD FRONT WILL SETTLE SOUTHEAST ACROSS THE LAKES REGION LATE
MONDAY IN TO EARLY TUESDAY - VEERING THE WINDS TO MORE WESTERLY.
SHOWERS AND THUNDERSTORMS CAN BE EXPECTED BOTH TONIGHT AND MONDAY AS
THIS FRONT LUMBERS THROUGH THE REGION.  CONDITIONS APPEAR TO BE
RATHER TRANQUIL FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...HEAT ADVISORY...MIZ075-MIZ076-MIZ082-MIZ083...UNTIL 10 PM SUNDAY.

LAKE HURON...NONE.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

AVIATION.....MR
SHORT TERM...MANN
LONG TERM....HLO
MARINE.......MANN

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
128 PM EDT SUN AUG 9 2009

MIZ047>049-053>055-060>063-068>070-101000-
MIDLAND-BAY-HURON-SAGINAW-TUSCOLA-SANILAC-SHIAWASSEE-GENESEE-LAPEER-
ST. CLAIR-LIVINGSTON-OAKLAND-MACOMB-
128 PM EDT SUN AUG 9 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS THIS AFTERNOON AND TONIGHT AS
A FRONTAL BOUNDARY MEANDERS OVER CENTRAL LOWER MICHIGAN.
ADDITIONAL THUNDERSTORMS UPSTREAM ARE EXPECTED TO MOVE EAST ACROSS
THE AREA THIS EVENING.  THERE IS A SLIGHT CHANCE THE THUNDERSTORMS
MAY BE SEVERE. LARGE HAIL...DAMAGING WIND GUSTS...AND LOCALLY
HEAVY RAINFALL IN EXCESS OF ONE INCH ARE ALL POSSIBLE. THUNDERSTORM
MOTION WILL BE EAST AT 35 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A COLD FRONT MOVING THROUGH SOUTHEAST MICHIGAN ON MONDAY WILL
LIKELY LEAD TO THUNDERSTORMS...INTO MONDAY NIGHT. THERE IS A
CHANCE OF SEVERE WEATHER WITH THESE STORMS.

.SPOTTER INFORMATION STATEMENT...

DISPATCHERS PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING.

MIZ075-076-082-083-101000-
WASHTENAW-WAYNE-LENAWEE-MONROE-
128 PM EDT SUN AUG 9 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A HEAT ADVISORY REMAINS IN EFFECT. REFER TO THE LATEST URGENT
WEATHER MESSAGE FOR DETAILS.../NPWDTX/.

THERE IS A CHANCE OF THUNDERSTORMS THIS EVENING AND TONIGHT AS A
FRONTAL BOUNDARY MEANDERS OVER CENTRAL LOWER MICHIGAN AND
THUNDERSTORMS UPSTREAM MOVE ACROSS THE STATE THIS EVENING. THERE
IS A SLIGHT CHANCE THE THUNDERSTORMS MAY BE SEVERE. LARGE HAIL...DAMAGING
WIND GUSTS...AND LOCALLY HEAVY RAINFALL IN EXCESS OF ONE INCH ARE
ALL POSSIBLE. THUNDERSTORM MOTION WILL BE EAST AT 35 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A COLD FRONT MOVING THROUGH SOUTHEAST MICHIGAN ON MONDAY WILL
LIKELY LEAD TO THUNDERSTORMS...INTO MONDAY NIGHT. THERE IS A
CHANCE OF SEVERE WEATHER WITH THESE STORMS.

.SPOTTER INFORMATION STATEMENT...

DISPATCHERS PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING.

LCZ422-423-460-LEZ444-LHZ361>363-421-422-441>443-462>464-101000-
ST. CLAIR RIVER-DETROIT RIVER-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-
128 PM EDT SUN AUG 9 2009

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS TODAY AND TONIGHT AS A FRONTAL
BOUNDARY MEANDERS OVER CENTRAL LOWER MICHIGAN. THERE IS A SLIGHT
CHANCE THE THUNDERSTORMS MAY BE SEVERE. LARGE HAIL...DAMAGING
WIND GUSTS ARE POSSIBLE. THUNDERSTORM MOTION WILL BE EAST AT 35 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A COLD FRONT MOVING THROUGH SOUTHEAST MICHIGAN ON MONDAY WILL
LIKELY LEAD TO THUNDERSTORMS...INTO MONDAY NIGHT. THERE IS A
CHANCE OF SEVERE WEATHER WITH THESE STORMS.

.SPOTTER INFORMATION STATEMENT...

DISPATCHERS PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING.

MANN

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

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