Severe Thunderstorm Warning 65, NWS Detroit, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
315 PM EDT THU JUL 13 2000

MAIN CONCERN THIS FORECAST CENTERS AROUND THUNDERSTORM INITIATION
AND SEVERE POTENTIAL.

THUNDERSTORMS NOW DEVELOPING ACROSS UP AND NORTHERN WI IN TROUGH
THAT WILL SHARPEN THROUGH THE EVENING AND CROSS CWA DURING THE NIGHT
AND INTO FRIDAY MORNING.

SYNOPTIC SCALE SUBSIDENCE SHOULD KEEP SKIES MOSTLY CLEAR FOR THE
EVENING HOURS ACROSS MOST OF THE CWA. EXCEPTION WILL BE SAGINAW
VALLEY WHERE BETTER MOISTURE...COMBINED WITH HIGHER
INSTABILITIES...AND APPROACHING TROUGH COULD SET OFF AN EVENING
THUNDERSTORM. OTHERWISE...EXPECT MOST OF THE ACTIVITY TO BE CONFINED
TILL AFTER MIDNIGHT. EXPECT THE FRONT...AS DETERMINED BY BEST MESOETA
SURFACE CONVERGENCE TO APPROACH THE SAGINAW VALLEY AROUND
06Z...THEN REACH METRO DETROIT AROUND 15Z FRIDAY. SURFACE BASED
CONVECTIVE PARAMETERS ALONG THE FRONT LOOK TO APPROACH AROUND 1000
J/KG AT MAXIMUM...BUT CIN VALUES ALSO SIGNIFICANT UPWARDS OF 100
J/KG. SO...POTENTIAL FOR SURFACE BASED CONVECTION LOOKS TO BE
MARGINAL. HOWEVER...ALOFT...PLENTY OF SUPPORT FOR CONVECTION WITH
850-500MB LAPSE RATES EXCEEDING 7C/KM...WHILE 850MB LI/S ARE AROUND
MINUS 4. AS WAS THE CASE YESTERDAY...MESOETA SPINS UP AN IMPRESSIVE
UVV FIELD ASSOCIATED WITH AN UPPER/LOWER LEVEL
DIVERGENCE/CONVERGENCE COUPLET AROUND 06Z ACROSS THE NORTHERN CWA...
AND SPINS THIS FEATURE SOUTH ACROSS ENTIRE CWA BY 12Z. MAIN SEVERE
THREAT LOOKS TO BE FROM HAIL...WITH WET BULB ZERO HEIGHTS AROUND
9500 FEET COINCIDENT WITH FRONT. WIND POTENTIAL IS MITIGATED BY
ELEVATED NATURE OF CONVECTION...SO DO NOT EXPECT THAT TO BE THE
PRIMARY THREAT. THEREFORE...STILL THINK THAT MOST LIKELY
SCENARIO...OF APPROACHING SEVERE LIMITS /HAIL TO ONE HALF INCH/...AS
DISCUSSED IN MORNING SEVERE WEATHER POTENTIAL STATEMENT LOOKS GOOD.

FRONT WILL SLOW FRIDAY MORNING AS IT APPROACHES SOUTHEAST LOWER. LOW
PRESSURE WILL SWING ACROSS THE SOUTHERN AND EASTERN HALF OF THE CWA
TOMORROW WITH GOOD SURFACE CONVERGENCE...AND CAPES...IN EXCESS OF
2500 J/KG EXPECTED ACROSS FAR SOUTHEAST LOWER...INCLUDING DETROIT.
WITH INSTABILITY STRONG...THUNDERSTORMS ROOTED IN THE BOUNDARY
LAYER...AND WET BULB ZERO HEIGHTS RUNNING AROUND 9000 FEET...WOULD
APPEAR TO BE A SLIGHT CHANCE OF SEVERE HAIL...CONFINED MAINLY TO FAR
SOUTHEAST PORTION OF CWA.

WITH UPPER LEVEL LOW DROPPING JUST EAST OF CWA FRIDAY NIGHT AND
SATURDAY...ALONG WITH ASSOCIATED TROUGHS ROTATING ABOUT AT SURFACE
AND ALOFT...WILL KEEP CHANCE OF PRECIPITATION IN FOR THE ENTIRE
FORECAST PERIOD. CONVECTIVE PARAMETERS OFFER MINIMAL THREAT OF
THUNDERSTORMS ON FRIDAY NIGHT...AND JUST A SLIGHT CHANCE ON
SATURDAY. SO WILL LEAVE MENTION OF STORMS OUT FOR FRIDAY NIGHT...AND
ADD A POSSIBLE THUNDERSTORM FOR SATURDAY.

WILL KEEP TEMPERATURES CLOSE TO FWC NUMBERS.

EXTENDED...

AS UPPER LEVEL CUTOFF LOSES DEFINITION AND SLIDES INTO THE
SOUTH...UPPER LEVEL RIDGE POKES A NOSE INTO CWA BRINGING DRY WEATHER
FOR SUNDAY AND MONDAY AHEAD OF NEXT FRONTAL SYSTEM. MRF/ETAXX IN
GOOD AGREEMENT ON TIMING FRONTAL SYSTEM TO CWA IN TUESDAY/WEDNESDAY
PERIOD...WHILE CANADIAN MUCH QUICKER...MOVING FRONT THROUGH CWA ON
MONDAY. WITH TIMING OF SYSTEMS RECENTLY PROGRESSING SLOWLY WILL GIVE
THE NOD TO THE ETAXX/MRF TIMING AND LEAVE MONDAY DRY...WITH CHANCE
SHRA/TSRA FOR TUESDAY/WEDNESDAY. ETAXX PRO*GS 1026MB HIGH TO BUILD IN
ACROSS LAKE SUPERIOR WEDNESDAY NIGHT...WHILE MRF IS WEAKER AND
FURTHER EAST WITH HIGH. WILL START THURSDAY OFF DRY...GIVING THE NOD
TO ETAXX FOR NOW.

.DTX...NONE.

OKEEFE

MIZ047>049-053>055-060>063-068>070-075-076-082-083-141200-

SEVERE WEATHER OUTLOOK FOR SOUTHEAST MICHIGAN
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
630 PM EDT THU JUL 13 2000

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

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.

THERE IS A CHANCE OF THUNDERSTORMS THIS EVENING AND OVERNIGHT AROUND
THE TRI CITIES AREA. THERE IS A SLIGHT CHANCE THAT SOME OF THESE
STORMS COULD REACH SEVERE LIMITS AND SPOTTER ACTIVATION MAY BE
NEEDED. THERE IS ALSO A CHANCE OF THUNDERSTORMS OVER THE REST OF
SOUTHEAST MICHIGAN TONIGHT...AND SOME OF THESE STORMS MAY APPROACH
SEVERE LIMITS.

A WEAK COLD FRONT WILL MOVE THROUGH THE SAGINAW VALLEY THIS EVENING.
THIS FRONT WILL COMBINE WITH MORE HUMID AIR MOVING IN FROM WISCONSIN
AND ILLINOIS AND HELP GENERATE THUNDERSTORMS. THESE STORMS WILL MOVE
TO THE SOUTHEAST AT 30 MPH. IF STORMS DO BECOME SEVERE THE MAIN
THREAT WILL BE HAIL NEAR 1 INCH. WIND GUSTS NEAR 60 MPH CAN ALSO
OCCUR.

THUNDERSTORM ACTIVITY WILL INCREASE TOWARD MIDNIGHT AND SPREAD
SOUTHEAST OVER THE REST OF SOUTHEAST MICHIGAN DURING THE OVERNIGHT
HOURS. SOME STORMS ACROSS THE REST OF SOUTHEASTERN MICHIGAN WILL
APPROACH SEVERE LIMITS AS A STRONGER STORM SYSTEM APPROACHES FROM
THE WEST. HAIL WILL AGAIN BE THE MAIN SEVERE WEATHER
CONCERN...REACHING ABOUT ONE HALF INCH IN THE STRONGEST STORMS.
HOWEVER...WIND GUSTS NEAR 60 MPH WILL REMAIN POSSIBLE.

STAY TUNED TO NOAA WEATHER RADIO...OR CHECK YOUR LOCAL RADIO...
TELEVISION...OR CABLE TELEVISION STATIONS FOR LATER FORECAST UPDATES.

GROVER COSTELLO