Severe Thunderstorm Warning 29, NWS Detroit, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
138 PM EDT THU JUN 25 2009

.AVIATION...

VERY UNSTABLE ATMOSPHERE IN PLACE ACROSS ALL TAF SITES THIS
AFTERNOON SOUTH OF A COLD FRONT LOCATED ACROSS MID MICHIGAN. CU FIELD HAS
BEGUN TO DEVELOP AS SHOWN ON VISIBLE SATELLITE AND SHOULD INCREASE
IN COVERAGE WITH THE ABUNDANT LOW LEVEL MOISTURE IN PLACE. STRONG
INSTABILITY IN COMBINATION WITH GOOD UPPER LEVEL SUPPORT WILL
PROVIDE A VERY GOOD CHANCE FOR THUNDERSTORMS TO IMPACT TAF SITES
EARLY THIS EVENING. MOST OF THE ACTIVITY SHOULD EXIT THE SITES BY
ABOUT 10 PM. WILL MONITOR STORM DEVELOPMENT AND AMEND TAFS AS
NECESSARY FOR TIMING. OVERNIGHT...SKIES SHOULD CLEAR AS WINDS BECOME
NORTHERLY BEHIND THE PASSING COLD FRONT.

&&

.PREV DISCUSSION...ISSUED 358 AM EDT THU JUN 25 2009

SHORT TERM...TODAY

A WEAK ILL-DEFINED SURFACE BOUNDARY IS SHOWN EXTENDING ACROSS
CENTRAL MICHIGAN ON THE 07Z SURFACE ANALYSIS. THIS FRONT WILL
PROVIDE A FOCUS FOR THUNDERSTORM DEVELOPMENT TODAY AS IT SLIDES SOUTH
INTO THE HUMID AND UNSTABLE AIRMASS ACROSS SOUTHERN MICHIGAN. SOME
CONVECTION IS STILL POSSIBLE ACROSS THE SAGINAW VALLEY AND THUMB
LATER THIS MORNING ALONG THE FRONTAL BOUNDARY AS WEAK SHORT ENERGY
NOTED UPSTREAM OVER WISCONSIN PASSES ACROSS LOWER MICHIGAN.

MORE NUMEROUS CONVECTION IS EXPECTED DURING THE AFTERNOON AS THE MID
LEVEL WAVE NOW OVER THE MANITOBA/ONTARIO BORDER SLIDES ACROSS THE
NORTHERN GREAT LAKES AND AMPLIFIES...ALLOWING MID LEVEL HEIGHTS TO
DROP ACROSS SOUTHERN MICHIGAN. ADDITIONAL UPSTREAM SHORT WAVE ENERGY
AND CONVERGENCE ALONG THE SURFACE FRONT AND/OR OTHER SURFACE
BOUNDARIES WILL HELP FOCUS CONVECTIVE DEVELOPMENT THIS AFTERNOON.
THE UPPER FLOW WILL ALSO BECOME INCREASINGLY DIFFLUENT DURING THE
COURSE OF THE DAY...AND EXIT REGION JET DYNAMICS WILL INCREASE AS
THE UPPER JET MAX OBSERVED OVER SOUTHERN SASKATCHEWAN ON THE 00Z
UPPER AIR PLOTS DIVES INTO THE WESTERN GREAT LAKES. UPSTREAM 00Z
SOUNDINGS REVEALED A DEEP ELEVATED MIXED LAYER...WHICH WILL ADVECT
ACROSS THE FORECAST AREA TODAY AND COMBINE WITH DAYTIME HEATING AND
MOISTURE POOLING ALONG THE SURFACE FRONT TO CREATE AMPLE
INSTABILITY. MODEL SOUNDINGS INDICATE 0-1KM MIXED LAYER CAPE
APPROACHING 2000 J/KG. A 40-45KT 500MB WIND MAX IS EXPECTED TO
PROGRESS INTO THE STATE DURING THE AFTERNOON...ACCOMPANIED BY A
SURGE OF MID LEVEL DRY AIR. THESE FACTORS WILL FAVOR LINEAR
CONVECTIVE MODES WITH THE THREAT FOR DAMAGING WIND GUSTS. GIVEN THE
POTENTIAL FOR PREFRONTAL TROUGHING/LAKE BREEZE BOUNDARIES/CONVECTIVE
OUTFLOW...STORM RELATIVE HELICITY MAY FAVOR SOME SUPERCELLS EARLY IN
THE CONVECTIVE EVENT. ALL THESE FACTORS HAVE LED TO SPC PLACING ALL
OF SOUTHEAST MICHIGAN IN A SLIGHT RISK FOR SEVERE WEATHER ON THE DAY
ONE OUTLOOK.

SURFACE DEWPOINTS ARE EXPECTED TO BE IN THE UPPER 60S/LOWER 70S
ALONG AN AHEAD OF THE SURFACE FRONT. WHILE THERE WILL BE SOME MID
AND HIGH LEVEL CLOUDS AROUND THIS MORNING...ENOUGH HEATING IS
EXPECTED TO CREATE ANOTHER HOT AND HUMID DAY. IN ANTICIPATING A
LATER START TO CONVECTION ALONG AND SOUTH OF I-94...MAX TEMPS NEAR
90 LOOK REASONABLE. MEANWHILE...IN ANTICIPATING EARLY TO MID
AFTERNOON CONVECTION...WILL KEEP FORECAST HIGHS IN THE 80S NORTH OF
THE I-94 CORRIDOR.

LONG TERM...TONIGHT THROUGH WEDNESDAY

UPPER TROUGH WILL EXIT EAST OUT OF MICHIGAN EARLY TONIGHT AS UPPER
RIDGING BUILDS TO OUR WEST. THIS WILL ALLOW LOWER MICHIGAN TO FALL
UNDER THE INFLUENCE OF SURFACE HIGH PRESSURE...AND BRING AN END TO
ANY LINGERING SHOWERS AND THUNDERSTORMS DURING THE LATE EVENING.
SURFACE HIGH PRESSURE WILL THEN HOLD INTO SATURDAY AS THE UPPER
RIDGE AXIS SLOWLY TRANSLATES EAST ACROSS THE GREAT LAKES. SOME
QUESTION AS TO HOW MUCH INSTABILITY WILL BE PRESENT ON FRIDAY AS
LAKE BREEZES MOVE INLAND. GFS MODEL SOUNDINGS FROM 00Z INDICATE
ENOUGH WARMING ALOFT FROM THE RIDGE TO INHIBIT THUNDERSTORM
FORMATION...HOWEVER THE NAM IS A BIT STEEPER WITH THE MID LEVEL
LAPSE RATES AND ALLOWS A DEEPER LAYER OF INSTABILITY TO DEVELOP.
WILL CONTINUE TO FOLLOW THE MORE STABLE GFS AS UPPER RIDGING BUILDS
IN AND WATCH FOR ANY WESTWARD SHIFT WITH THE RIDGE AXIS WHICH COULD
PREVENT SOME OF THE WARMING ALOFT SHOWN ON THE GFS SOUNDINGS.

STRONG UPPER LOW OVER BRITISH COLUMBIA WILL TRACK ACROSS CANADA AND
INTO THE WESTERN GREAT LAKES ON SATURDAY/SATURDAY NIGHT. THIS WILL
PUSH A STRONG SURFACE LOW ACROSS THE NORTHERN GREAT LAKES SATURDAY
NIGHT...THOUGH MODELS CONTINUE TO DIFFER ON WHETHER THE CENTER OF
THIS SYSTEM WILL PUSH ACROSS CENTRAL ONTARIO OR NORTHERN
MICHIGAN...LEADING TO SOME DIFFERENCES WITH WHERE THEY PLACE THE
FRONTAL BOUNDARIES/OCCLUSION AND INSTABILITY. RECENT SHIFT TO
NOCTURNAL TIMING OF FRONTAL/OCCLUSION PASSAGE WOULD BODE FAVORABLE
FOR SOUTHEAST MICHIGAN AS THIS WOULD KEEP THE HIGHEST SURFACE/MIXED
LAYER INSTABILITY WELL TO OUR WEST OVER WISCONSIN SATURDAY
AFTERNOON/EVENING. DID LEAVE SOME POPS IN FOR LATE SATURDAY
AFTERNOON...BUT THIS WAS MORE TO COVER UNCERTAINTY IN TIMING RATHER
THAN INSTABILITY AND LIFT AHEAD OF THE SYSTEM. 00Z GFS/NAM SOUNDINGS
ARE ACTUALLY QUITE STABLE NOW FOR SATURDAY AFTERNOON...ESPECIALLY IN
THE MID LEVELS. CHANCES FOR SHOWERS AND THUNDERSTORMS WILL BECOME
LIKELY OVERNIGHT ON SATURDAY AS THE SYSTEM MOVES ACROSS...WITH SOME
ACTIVITY LINGERING INTO THE FIRST HALF OF THE DAY ON SUNDAY. WILL
HAVE TO KEEP AN EYE ON MODEL TIMING HOWEVER...AS WE HAVE SEEN A
TENDENCY TO SLOW THINGS DOWN OVER THE PAST FEW DAYS.

MEDIUM RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE CANADIAN
UPPER LOW STALLING OVER THE GREAT LAKES SUNDAY THROUGH WEDNESDAY.
WHILE ANY SHORTWAVES AND FRONTS WILL BE HARD TO TIME...SUFFICIENT
MOISTURE AND GOOD INSTABILITY GENERATED FROM THE UPPER COLD POOL
SUPPORTS A BROAD-BRUSH CHANCE OF SHOWERS ALONG WITH DAYTIME
THUNDERSTORMS THROUGH THE PERIOD. HAVE ALSO COOLED THE FORECAST
SLIGHTLY AS WE SHOULD EXPECT BELOW NORMAL TEMPERATURES UNDER THE
UPPER LOW.

MARINE...

A WEAK COLD FRONT AND UPPER LEVEL DISTURBANCE WILL TRIGGER SEVERAL
ROUNDS OF THUNDERSTORMS TODAY. SOME OF THESE STORMS WILL BE STRONG
TO SEVERE WITH THE POTENTIAL FOR WIND GUSTS GREATER THAN 40 KNOTS.
WEAK HIGH PRESSURE WILL EXPAND ACROSS THE AREA ON FRIDAY AND LINGER
INTO SATURDAY...PROVIDING LIGHT WINDS AND IDEAL BOATING CONDITIONS.
A STRONG COLD FRONT IS FORECAST TO MOVE THROUGH THE REGION EARLY
SUNDAY. THIS SYSTEM WILL TRIGGER THUNDERSTORMS. COLD AIR ADVECTION
BEHIND THIS FRONT MAY BE STRONG ENOUGH TO CREATE SOME GUSTY WINDS
AND HIGHER WAVES SUNDAY INTO EARLY MONDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

AVIATION.....DRK
SHORT TERM...SC
LONG TERM....HLO
MARINE.......SC

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
437 AM EDT THU JUN 25 2009

MIZ047>049-053>055-060>063-068>070-075-076-082-083-260845-
MIDLAND-BAY-HURON-SAGINAW-TUSCOLA-SANILAC-SHIAWASSEE-GENESEE-LAPEER-
ST. CLAIR-LIVINGSTON-OAKLAND-MACOMB-WASHTENAW-WAYNE-LENAWEE-MONROE-
437 AM EDT THU JUN 25 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

NUMEROUS THUNDERSTORMS ARE EXPECTED TODAY. THERE IS A SLIGHT
CHANCE OF SEVERE WEATHER WITH THESE STORMS. TIMING OF SEVERE
WEATHER WILL BE BETWEEN 1 PM AND 8 PM. THE STRONGEST STORMS WILL
BE CAPABLE OF PRODUCING WIND GUSTS TO 70 MPH AND HAIL TO ONE INCH
IN DIAMETER. THERE IS ALSO A SLIGHT CHANCE OF A TORNADO WITH THE
STRONGEST STORMS. ANY STORM THAT DEVELOPS WILL PRODUCE INTENSE
RAINFALL AND FREQUENT CLOUD TO GROUND LIGHTNING. THUNDERSTORMS
THAT DEVELOP BEFORE 3 PM WILL MOVE EAST AT 15 MPH. THOSE THAT
DEVELOP AFTER WILL MOVE SOUTHEAST AT 30 MPH.

A WEAK COLD FRONT WILL PUSH ACROSS THE REGION FROM THE NORTH TODAY.
HUMID AND UNSTABLE AIR ALONG AND IN ADVANCE OF THIS FRONT WILL
TRIGGER THE THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THERE IS A CHANCE OF THUNDERSTORMS SATURDAY NIGHT INTO SUNDAY AS A
STRONG COLD FRONT SLIDES ACROSS THE REGION.

THE CHANCE OF THUNDERSTORMS WILL CONTINUE THROUGH MONDAY AND TUESDAY
AS A LOW PRESSURE SYSTEM LINGERS OVER THE REGION.

.SPOTTER INFORMATION STATEMENT...
DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS AFTERNOON.

LCZ422-423-460-LEZ444-LHZ361>363-421-422-441>443-462>464-260845-
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-
437 AM EDT THU JUN 25 2009

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

.DAY ONE...TODAY AND TONIGHT

NUMEROUS THUNDERSTORMS ARE EXPECTED TODAY. THERE IS A SLIGHT
CHANCE OF SEVERE WEATHER WITH THESE STORMS. TIMING OF SEVERE
WEATHER WILL BE BETWEEN 1 PM AND 8 PM. THE STRONGEST STORMS WILL
BE CAPABLE OF PRODUCING WIND GUSTS TO 60 KNOTS AND HAIL TO ONE
INCH IN DIAMETER. ANY STORM THAT DEVELOPS WILL PRODUCE INTENSE
RAINFALL AND FREQUENT CLOUD TO GROUND LIGHTNING. THUNDERSTORMS
THAT DEVELOP BEFORE 3 PM WILL MOVE EAST AT 15 MPH. THOSE THAT
DEVELOP AFTER WILL MOVE SOUTHEAST AT 30 MPH.

A WEAK COLD FRONT WILL PUSH ACROSS THE REGION FROM THE NORTH TODAY.
HUMID AND UNSTABLE AIR ALONG AND IN ADVANCE OF THIS FRONT WILL
TRIGGER THE THUNDERSTORMS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THERE IS A CHANCE OF THUNDERSTORMS SATURDAY NIGHT INTO SUNDAY AS A
STRONG COLD FRONT SLIDES ACROSS THE REGION.

THE CHANCE OF THUNDERSTORMS WILL CONTINUE THROUGH MONDAY AND TUESDAY
AS A LOW PRESSURE SYSTEM LINGERS OVER THE REGION.

.SPOTTER INFORMATION STATEMENT...
DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS AFTERNOON.

SC

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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
144 PM EDT THU JUN 25 2009

MIZ068-251800-
LIVINGSTON-
144 PM EDT THU JUN 25 2009

...SIGNIFICANT WEATHER ADVISORY...

AT 143 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
RAPIDLY DEVELOPING THUNDERSTORM NEAR FOWLERVILLE...MOVING EAST AT 25
MPH.

ONE HALF INCH DIAMETER HAIL...WINDS UP TO 40 MPH...ARE POSSIBLE
WITH THIS STORM.

* THE THUNDERSTORM WILL BE NEAR...
  COHOCTAH AROUND 155 PM EDT...
  OAK GROVE AND HOWELL AROUND 200 PM EDT...

GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW
AROUND. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THIS STORM HAS
PASSED.

SF/DRC

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