Severe Thunderstorm Warning 142, NWS Detroit, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
810 PM EDT TUE AUG 22 2000

WARM FRONT LOCATED ACROSS CENTRAL LOWER MICHIGAN AT THE MOMENT...AND
AHEAD OF STRONG MID-LEVEL WAVE MOVING ACROSS SOUTHERN WISCONSIN...
THUNDERSTORMS HAVE DEVELOPED ALONG THIS FRONT.  DEVELOPMENT AIDED IN
WEST-CENTRAL LOWER MICHIGAN BY DEW POINT POOLING NEAR BIG RAPIDS...
WHICH HAS REACHED 70 DEGREES...AND FAIRLY GOOD SURFACE CONVERGENCE
LOOKING AT THE SURFACE OBSERVATIONS IN VICINITY OF THE WARM FRONT.
MSAS INDICATED LIFTED INDEX AT 21Z OVER SOUTHWEST MICHIGAN REACHED
AS LOW AS MINUS 8 TOWARD BIG RAPIDS...BUT SINCE THAT TIME...THE
INSTABILITY MAX HAD SHIFTED SOUTHWEST COURTESY OF NO RAIN TO LOWER
THE SURFACE TEMPERATURE...AND 81/75 AT COLDWATER.

LATEST RUC SHOWS THAT THE WEAK SURFACE LOW OVER EASTERN WISCONSIN
WILL CONTINUE TO MOVE EAST ALONG THE WARM FRONT...WEAKENING EVEN
FURTHER BUT MAINTAINING AT LEAST A WAVE ON THE FRONT AS IT HEADS
ACROSS THE SAGINAW VALLEY AND THE THUMB OVERNIGHT.  THE UPPER WAVE
MOVES THROUGH QUICKLY OVERNIGHT...AND BEING CLOSER TO THE FRONT AND
THE TRACK OF THE SURFACE WAVE...PROLONGED RAIN WILL OCCUR FROM
MIDLAND AND SAGINAW EAST TO BAD AXE AND SANDUSKY.  LOCALLY HEAVY
RAIN IN THE CURRENT ZONE FORECAST FOR THAT AREA LOOKS VERY GOOD.
INSTABILITY ON THE LATEST MSAS FALLS OFF QUICKLY IN SOUTHEAST
MICHIGAN WITH THE INSTABILITY GRADIENT NORTH TO SOUTH ACROSS
SOUTH-CENTRAL LOWER MICHIGAN.  FOR THE REST OF THE EVENING...EXPECT
SHOWERS AND THUNDERSTORMS MAINLY NORTH OF INTERSTATE 69 ALONG THE
SURFACE BOUNDARY AND AHEAD OF THE WEAKENING SURFACE WAVE.

OVERNIGHT...RUC PROGS 500MB AND 700MB TEMPERATURES TO FALL A COUPLE
OF DEGREES AS THE UPPER WAVE MOVES THROUGH...WITH 850MB TEMPERATURES
REMAINING ABOUT THE SAME...NEAR 15 TO 17 DEGREES C.  THIS
DIFFERENTIAL TEMPERATURE ADVECTION RESULTS IN RUC PROGGED LIFTED
INDICES FROM THE 850MB LEVEL TO FALL TO MINUS 7 IN SOUTHEAST
MICHIGAN BY 06Z OR SO.  500MB WINDS REACH 45 KNOTS...WITH 850MB
WINDS AROUND 20 KNOTS.  AT THE 500MB LEVEL...LEFT EXIT REGION OF 40
KNOTS JETLET HEADS ACROSS THE THUMB WITH THE RIGHT ENTRANCE REGION
OF 50 KNOT 500MB WINDS PROGGED ACROSS NORTHEAST LOWER MICHIGAN AND
LAKE HURON AROUND 06Z.  THUNDERSTORMS SHOULD CONTINUE TO DEVELOP
THROUGHOUT SOUTHEAST MICHIGAN...BUT AT THIS POINT IT WOULD APPEAR
THAT THE HEAVIEST RAIN AND THE MOST ORGANIZED THUNDERSTORMS WILL BE
OVER THE NORTH PART OF SOUTHEAST MICHIGAN.

THE CHIEF THREAT FROM SHOWERS AND THUNDERSTORMS OVERNIGHT WILL BE
HEAVY RAIN.  K INDICES ARE PROGGED TO CLIMB TO AROUND 40...AND THIS
APPEARS REASONABLE GIVEN THE WEAK PRESSURE FALLS ASSOCIATED WITH THE
SURFACE AND MID-LEVEL WAVES SHOULD BE SUFFICIENT TO BRING INCREASINGLY
MOIST LOW-LEVEL AIR INTO SOUTHEAST MICHIGAN.  HOWEVER...WITH
THUNDERSTORMS DEVELOPING IN THE WARM SECTOR AND FAIRLY GOOD WINDS
FROM 850MB ON UP...AN ISOLATED STORM COULD PRODUCE A WET WIND NEAR
SEVERE LEVELS.  MARGINALLY SEVERE HAIL MAY ALSO OCCUR AS
TEMPERATURES ALOFT FALL SOME...BUT THIS WILL BE A LITTLE LESS LIKELY
WITH 00Z DTX RAOB SHOWING A FREEZING LEVEL OF 13600FT.

INCREASING DEW POINTS AND RAIN BOTH WILL CONTRIBUTE TO AREAS OF FOG
OVERNIGHT.  COORD WITH GRR AND SPC.

.DTX...NONE.

DJF

MIZ047>049-053>055-060>063-068>070-075-076-082-083-231000-

SEVERE WEATHER OUTLOOK FOR SOUTHEAST LOWER MICHIGAN
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
701 PM EDT TUE AUG 22 2000

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

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.

SHOWERS AND THUNDERSTORMS WILL BE NUMEROUS ACROSS SOUTHEAST MICHIGAN
OVERNIGHT.  THOUGH MOST THUNDERSTORMS WILL PRODUCE HEAVY RAINFALL
AND FREQUENT LIGHTNING...AN ISOLATED STORM COULD BE SEVERE...WITH
WINDS NEAR 58 MPH AND HAIL UP TO THREE QUARTER INCH IN DIAMETER.
SPOTTER ACTIVATION MAY BE REQUIRED.

A WARM FRONT EXTENDED ACROSS CENTRAL LOWER MICHIGAN DURING THE EARLY
EVENING.  IN ADDITION...A STRONG UPPER LEVEL DISTURBANCE WILL
SWEEP ACROSS LOWER MICHIGAN DURING THE NIGHT.  WITH MOIST AND
UNSTABLE AIR EXISTING ALONG AND SOUTH OF THE WARM FRONT...CONDITIONS
WILL BE GOOD FOR THE DEVELOPMENT OF THUNDERSTORMS.

THUNDERSTORMS ARE EXPECTED TO BEGIN IN THE SAGINAW VALLEY...
ESPECIALLY WEST OF MIDLAND AND SAGINAW...BY 9 PM.  OTHER SHOWERS
AND THUNDERSTORMS WILL GRADUALLY PROGRESS EAST...REACHING THE THUMB
AND THE FLINT AREAS BY MIDNIGHT...AND THE DETROIT AREA AFTER
MIDNIGHT.  THOUGH MOST THUNDERSTORMS WILL RESULT IN BRIEFLY HEAVY
RAIN AND FREQUENT LIGHTNING...A FEW STORMS WILL PRODUCE WIND GUSTS
TO 40 MPH AND SMALL HAIL.  HOWEVER...AN ISOLATED THUNDERSTORM COULD
BE SEVERE WITH WINDS TO 58 MPH AND HAIL TO DIME SIZE.

THUNDERSTORMS WILL MOVE TO THE EAST AT 40 MPH.  WITH HEAVY RAIN
OCCURRING IN THUNDERSTORMS...PERSONS PLANNING TO TRAVEL OVERNIGHT
SHOULD BE PREPARED FOR PONDING OF WATER ON ROADS.  STAY TUNED TO NOAA
WEATHER RADIO...OR YOUR FAVORITE MEDIA OUTLET...FOR THE LATEST
WEATHER INFORMATION.

DJF