Severe Thunderstorm Warning 35, NWS Detroit, MI

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

.SHORT TERM...TODAY AND TONIGHT

THE MAIN WEATHER CONCERN FOR THE REST OF THE DAY IS THE ONGOING
SEVERE WEATHER THAT DEVELOPED THIS AFTERNOON. A WEAK COLD FRONT
SHOWN ON 18Z SURFACE ANALYSIS IS LOCATED ALONG THE I69 CORRIDOR.
THIS FRONT IS THE FOCUSING MECHANISM FOR THE THUNDERSTORMS THAT
DEVELOPED THIS AFTERNOON AND WILL CONTINUE UNTIL AROUND 10 PM. A
VERY UNSTABLE BOUNDARY LAYER UNDER THE NOSE OF A 50KT JET WITH GOOD
DIFLUENCE AT 500MB IS AIDING THESE STORMS. 0-1KM ML CAPE VALUES NEAR
2000 J/KG WERE REALIZED BY THESE STORMS AS THEY WERE QUICK TO GO
SEVERE ONCE THE CU FIELD DEVELOPED AROUND 17Z. DTX 18Z RAOB SOUNDING
ALSO INDICATED MAXIMUM CAPE VALUES OF OVER 3000 J/KG.

ANOTHER MILD NIGHT IS IN STORE WITH LOWS RANGING FROM THE LOWER 60S
TO THE NORTH UP TO MID 60S AROUND DETROIT IN THE URBAN HEAT ISLAND.
DEWPOINTS SHOULD REMAIN IN THE LOW 60S OVERNIGHT IN THE WAKE OF THE
COLD FRONT. THOUGH THERE IS SOME DRY AIR ADVECTION...THE SURFACE
REMAINS MOIST ALL THE WAY BACK UP INTO CANADA WITH DEWPOINTS SHOWING
IN THE 50S. AFTER A BRIEF PERIOD OF CLEARING SKIES IN THE WAKE OF
THE COLD FRONT LATE THIS EVENING...CLOUDS WILL DEVELOP ONCE AGAIN AS
A SECONDARY SHORTWAVE TROUGH MOVES THROUGH SOUTHEAST MICHIGAN. HIGH
PRESSURE WILL THEN BUILD IN TO OUR WEST EARLY FRIDAY MORNING HELPING
TO SCOUR OUT ANY LINGERING CLOUDS.

&&

.LONG TERM...FRIDAY THROUGH WEDNESDAY

RATHER DIFFUSE SYNOPTIC COLD FRONT WILL SETTLE SOUTH EARLY FRIDAY AS
A SECONDARY WEAKER TROUGH DROPS THROUGH DURING THE DAY.  ENOUGH
MOISTURE AND LOW LEVEL CONVERGENCE WILL EXIST TO GENERATE POCKETS OF
DIURNAL CU...BUT THE DEEPER MOISTURE WILL BE EFFECTIVELY SHUNTED
SOUTHWARD WITH THE INITIAL FRONTAL PASSAGE...SO NO ADDITIONAL
PRECIPITATION IS ANTICIPATED DURING THE DAY.  SUBTLE COLD AIR
ADVECTION WITHIN THE LOW LEVEL NORTHERLY FLOW WILL TAKE THE EDGE OFF
THE RECENT 90 DEGREE READINGS.  PREDOMINANT FLOW OFF THE COOLER LAKE
HURON WATERS WILL HOLD TEMPERATURES IN THE UPR 70S-LWR 80S ACROSS
PORTIONS OF THE THUMB...WITH READINGS RECOVERING TOWARD THE MID-UPR
80S ELSEWHERE.

LOW TO MID LEVEL RIDGE AXIS WILL SHIFT ACROSS THE GREAT LAKES FRI
NIGHT INTO SATURDAY...AS A STRONG SHORTWAVE PUSHES INTO THE NORTHERN
PLAINS.  EASTWARD EXTENSION OF DEVELOPING WEAK WARM AIR
ADVECTION/MOIST ISENTROPIC ASCENT IN ADVANCE OF THIS SYSTEM WILL
REMAIN LARGELY NORTH AND WEST OF THE AREA DURING THE DAY...WITH A
DRIER LOW LEVEL AIRMASS PRECLUDING PRECIP DEVELOPMENT PRIOR TO 00Z.

SHORTWAVE WILL CLOSE OFF WHILE MOVING INTO THE NORTHERN GREAT LAKES
SATURDAY NIGHT...SENDING A COLD FRONT EAST AND THROUGH SOUTHEAST MI
OVERNIGHT. CONVECTION EVOLVING UPSTREAM DURING PEAK HEATING WITHIN
A ZONE OF INCREASING LARGE SCALE ASCENT...LOW LEVEL CONVERGENCE AND
MID LEVEL THETA-E ADVECTION WILL TRANSLATE EASTWARD. MODELS NOW IN
REASONABLE AGREEMENT WITH THE TIMING INTO SOUTHEAST MICHIGAN...
BRINGING THE BULK OF THIS ACTIVITY THROUGH BETWEEN 04-12Z.
THERMODYNAMIC PROFILE BECOMES UNIMPRESSIVE THIS FAR EAST WITH THE
THE OVERNIGHT TIMING...WITH LATEST GUIDANCE INDICATING MINIMAL
MIXED LAYER/SURFACE BASED CAPE.

RAPID POST-FRONTAL DRYING EARLY SUNDAY IN ADVANCE OF THE BROADENING
UPPER LOW ROTATING ACROSS THE UPPER PENINSULA.  ADDITIONAL
CONVECTION MAY DEVELOP BY LATE AFTERNOON/EVENING...ESPECIALLY
NORTH...AS LAPSE RATES INCREASE IN RESPONSE TO COOLING MID LEVEL
TEMPERATURES.  THIS SUPPORTS MAINTAINING A LOW POP ON SUNDAY.  UPPER
LOW WILL MAINTAIN CONTROL THROUGH THE EARLY TO MID WEEK PERIOD AS
IT SLOWLY SETTLES SOUTH AND EAST ACROSS THE REGION.  THIS SETUP WILL
CONTINUE TO FAVOR SCATTERED SHOWER/THUNDERSTORM DEVELOPMENT THROUGH
AT LEAST WEDNESDAY WITH AN EMPHASIS ON THE DIURNAL COMPONENT GIVEN
THE PRESENCE OF THE MID LEVEL COLD POOL/STEEP LAPSE RATES.  THE
LOWERING THICKNESSES WILL TRANSLATE INTO COOLER DAYTIME READINGS
THROUGH THIS PERIOD...WITH HIGHS GENERALLY HOLDING BELOW NORMAL IN
THE 70S.

&&

.MARINE...

A WEAK COLD FRONT AND UPPER LEVEL DISTURBANCE WILL CONTINUE TO
DEVELOP THUNDERSTORMS INTO THIS EVENING. 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.

&&

.PREV DISCUSSION...ISSUED 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.

&&

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

&&

SHORT TERM...DRK
LONG TERM....MR
MARINE.......DRK
AVIATION.....DRK

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
340 PM 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-
340 PM EDT THU JUN 25 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 10 PM FOR ALL OF
SOUTHEAST MICHIGAN WITH THE EXCEPTION OF MIDLAND...BAY AND HURON
COUNTIES.

THUNDERSTORMS WILL CONTINUE TO DEVELOP INTO THE EVENING HOURS.
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 WILL MOVE EAST-SOUTHEAST AT 20 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 THROUGH
WEDNESDAY AS A LOW PRESSURE SYSTEM LINGERS OVER THE REGION.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION HAS OCCURRED.

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-
340 PM 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

SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 10 PM FOR THE NEARSHORE
WATERS FROM PORT HURON TO PORT SANILAC.

THUNDERSTORMS WILL CONTINUE TO DEVELOP INTO THE EVENING HOURS.  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 WILL MOVE EAST-SOUTHEAST AT 20 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 THROUGH
WEDNESDAY AS A LOW PRESSURE SYSTEM LINGERS OVER THE REGION.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION HAS OCCURRED.

MR

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

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