Severe Thunderstorm Warning 42, NWS Detroit, MI

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
307 AM EDT THU JUL 18 2002

A LOOK AT THE WATER VAPOR LOOP SHOWS SOUTHEASTERN MICHIGAN LYING IN
BETWEEN A CUT OFF UPPER LOW OVER MISSOURI AND THE MAIN BRANCH OF THE
JET ACROSS THE NORTHERN GREAT LAKES. A SHORT WAVE TROUGH IS ALSO
NOTED ACROSS NORTHERN MINNESOTA. THE SURFACE ANALYSIS SHOWS A WEAK
WAVY FRONT EXTENDING FROM CENTRAL WISCONSIN TO NORTHERN LOWER
MICHIGAN THEN INTO CENTRAL LAKE HURON. KAPX 88D HAS SHOWN THE
CONVECTION ALONG THIS BOUNDARY TO HAVE COMPLETELY DIMINISHED. NOT
MUCH UPPER LEVEL SUPPORT ALONG THIS FRONT...SO I EXPECT THAT IT WILL
TAKE INCREASING DIURNAL INSTABILITY TO ALLOW CONVECTION TO REDEVELOP
ALONG THE FRONTAL BOUNDARY.

BOTH THE LATEST RUC AND MESO ETA BRING THE SURFACE FRONT INTO THE
TRI CITIES AND THUMB BETWEEN 09Z AND 12Z THIS MORNING...THEN SHOW
THE FRONT SAGGING SOUTH ACROSS THE FORECAST AREA DURING THE DAY AS
THE NORTHWEST FLOW ALOFT INCREASES. WITH THE SURFACE HIGH ACROSS
NORTHERN ONTARIO PROGGED TO WEAKEN AND WITH AMPLE HEATING SOUTH OF
THE BOUNDARY...I SUSPECT THAT THE MODELS MAY BE BRINGING THE FRONT
THROUGH THE FORECAST AREA A LITTLE TOO FAST. A NARROW RIBBON OF
HIGHER 850MB THETA-E WILL ADVECT INTO THE AREA ALONG AND JUST BEHIND
THE FRONTAL BOUNDARY. WITH SOME BOUNDARY LAYER CONVERGENCE ALONG THE
FRONTAL BOUNDARY AND INSTABILITY ON THE INCREASE...I EXPECT
CONVECTION WILL REFIRE TODAY. MODIFIED MESO ETA SOUNDINGS FOR 88/68
FOR DETROIT SHOW 2300 J/KG CAPE WITH LIS NEAR -6C. 0 TO 6 KM SHEAR
VALUES ARE QUITE WEAK AND WET BULB ZERO HEIGHTS WILL BE AROUND 12K
FT...SO SEVERE THREAT APPEARS TO BE LIMITED. WITH PRECIPITABLE WATER
INCREASING TO AROUND 1.75 INCHES AND K INDICES IN THE MID AND UPPER
30S...LOCALIZED HEAVY RAINFALL WILL ACCOMPANY THE STRONGER
THUNDERSTORM UPDRAFTS. LACK OF REAL UPPER LEVEL DYNAMICS SUPPORTS
JUST SCATTERED CONVECTION...SO NOT EXPECTING EVERYONE TO SEE THIS
MUCH NEEDED RAINFALL. PRECIP CHANCES WILL BE LOWEST ACROSS THE
SAGINAW VALLEY AND THUMB WHERE THE FRONT WILL MOVE THROUGH EARLIER
IN THE DAY. WITH THE RUC SHOWING SOME WEAK SYNOPTIC LIFT IN THIS
AREA AS THE SHORT WAVE OVER MINNESOTA TRACKS ACROSS NORTHERN
MICHIGAN LATE THIS MORNING AND EARLIER THIS AFTERNOON...AND WITH THE
MESO ETA SHOWING POST FRONTAL INSTABILITY AND WEAK CONVERGENCE...I
WILL MAINTAIN CHANCE POPS IN THE NORTH.

AFTERNOON TEMPS WILL BE STRONGLY DEPENDANT ON THE AMOUNT OF CLOUD
COVER AND MOVEMENT OF THE FRONTAL BOUNDARY. I WILL STICK CLOSE TO
PREVIOUS FCST AND GUIDANCE TEMPS WITH HIGHS RANGING FROM NEAR 90 IN
THE SOUTH TO THE LOW 80S IN THE NORTH.

I EXPECT THE FRONT TO BE LINGERING IN THE SOUTHERN COUNTIES THIS
EVENING. SURFACE DEWPOINTS LOOK TO BE SLOW TO FALL OFF...SO SHOULD
SEE LINGERING INSTABILITY NORTH OF THE FRONT INTO THE EVENING. I
WILL THUS CARRY CHANCE POPS EVERYWHERE THIS EVENING. MODELS ARE
SHOWING SOME DISAGREEMENT ON HOW FAR SOUTH THE FRONT WILL MOVE
TONIGHT AND INTO THE DAY ON FRIDAY. THE AVN/NGM/CANADIAN SOLUTIONS
ALL CARRY THE FRONT SOUTH OF THE STATE LINE EARLY FRIDAY MORNING AND
THEN STALL THE BOUNDARY OUT ACROSS THE NORTHERN OHIO VALLEY DURING
THE DAY. THE ETA HOWEVER TRIES TO DEVELOP A WEAK WAVE ALONG THE
BOUNDARY AND THUS SHOWS AMPLE LOW LEVEL CONVERGENCE AND INSTABILITY
ACROSS THE FAR SOUTHERN COUNTIES THROUGH THE DAY FRIDAY. NOT READY
TO BUY INTO THIS IDEA...BUT SINCE ALL MODEL SOLUTIONS HAVE TRENDED
SLOWER WITH THE SOUTHWARD MOVEMENT OF THIS FRONT ON FRIDAY...I WILL
CARRY A CHANCE OF THUNDERSTORMS IN LENAWEE/MONROE COUNTIES. THE ETA
SOLUTION SHOWS MORE LOW-MID LEVEL MOISTURE LINGERING ACROSS THE REST
OF THE FORECAST AREA ON FRIDAY. I WILL THUS KEEP A MENTION OF PARTLY
SUNNY SKIES. DRYER AIR SHOULD FILTER INTO THE REGION LATE FRIDAY AND
FRIDAY NIGHT UNDER NORTHEAST FLOW TO CLEAR SKIES OUT.

A SFC HIGH PRESSURE RIDGE ON SATURDAY AND DRY AIR WILL KEEP SKIES
MOSTLY SUNNY...WITH TEMPERATURES IN THE 80S.

.DTX...NONE.

CONSIDINE

MIZ047>049-053>055-060>063-068>070-075-076-082-083-190200-

HAZARDOUS WEATHER OUTLOOK FOR SOUTHEAST MICHIGAN
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1041 AM EDT THU JUL 18 2002

...SEVERE WEATHER POTENTIAL STATEMENT FOR SOUTHEAST MICHIGAN...

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.

HAZARD...
SCATTERED THUNDERSTORMS WILL OCCUR ACROSS SOUTHEAST LOWER MICHIGAN
THIS AFTERNOON INTO TONIGHT.  THESE THUNDERSTORMS ARE EXPECTED TO
REMAIN BELOW SEVERE LIMITS.

DISCUSSION...
A COLD FRONT WILL CONTINUE TO PRESS SOUTH ACROSS SOUTHERN LOWER
MICHIGAN THIS AFTERNOON.  MOISTURE AND INSTABILITY AHEAD OF
THIS FRONT WILL RESULT IN SCATTERED THUNDERSTORMS ACROSS ALL OF
SOUTHEAST LOWER MICHIGAN.  THE VERTICAL WIND FIELD IN THE ATMOSPHERE
IS EXPECTED TO REMAIN WEAK TO MINIMIZE THE SEVERE WEATHER POTENTIAL
FROM HAIL AND WIND.  HOWEVER...WITH THE MOISTURE IN PLACE SOME
THUNDERSTORMS WILL HAVE THE POTENTIAL TO PRODUCE HEAVY AMOUNTS OF
RAIN IN A SHORT PERIOD OF TIME...UP TO ONE INCH WITHIN ONE HOUR.

THE COLD FRONT WILL MOVE THROUGH THE TRI CITIES AND THUMB EARLY THIS
AFTERNOON...THEN MOVE THROUGH THE FLINT...PONTIAC AND PORT HURON
VICINITY BETWEEN 4 AND 6 PM...THEN BECOME NEARLY STATIONARY ACROSS
THE SOUTHERN COUNTIES TONIGHT.  THUNDERSTORMS WILL DIMINISH AS THE
FRONT PASSES THROUGH THE NORTHERN COUNTIES...ALTHOUGH SCATTERED
THUNDERSTORMS WILL CONTINUE ACROSS THE SOUTH TONIGHT.  AGAIN...NONE
OF THESE THUNDERSTORMS ARE EXPECTED TO REACH SEVERE CRITERIA.

THUNDERSTORM MOVEMENT WILL BE TO THE EAST BETWEEN 10 AND 15 MPH.

SPOTTER ACTIVATION...
SPOTTER ACTIVATION IS NOT ANTICIPATED THIS AFTERNOON OR TONIGHT.

OUTLOOK FOR FRIDAY AND SATURDAY...
A CHANCE OF THUNDERSTORMS SOUTH OF INTERSTATE 94 ON FRIDAY AND NO
HAZARDS ARE FORECAST ON SATURDAY.

STAY TUNED TO NOAA WEATHER RADIO... OR LOCAL MEDIA OUTLETS... FOR
THE LATEST FORECAST INFORMATION FROM THE NATIONAL WEATHER SERVICE.
YOU CAN ALSO OBTAIN THE LATEST FORECAST ON THE NATIONAL WEATHER
SERVICE WEB SITE.

HTTP://WWW.CRH.NOAA.GOV/DTX/ (ALL LOWER CASE)

BGM