Severe Thunderstorm Warning 58, NWS Detroit, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
815 PM EDT FRI MAY 21 2004

.UPDATE...
CONVECTIVE POTENTIAL RECOVERING RAPIDLY AT THE END OF DAYTIME
HEATING. STORMS DEVELOPING OVER SW LOWER FOCUSED ON THE SURFACE TROF
FROM ABOUT PORT HURON TO LANSING. MID LEVEL LAPSE RATES ARE MODEST
IN THE SAGINAW VALLEY AND THUMB BUT CLOSE TO 7.5 C/KM NEAR THE OHIO
BORDER, ENOUGH TO HELP SUSTAIN THE MCS AS IT MOVES THROUGH LOWER
MICHIGAN THIS EVENING. EXPECT CONVECTION TO BE NEAR SEVERE LIMITS
ALONG AND SOUTH OF THE SURFACE TROF/INTERSTATE 69 THROUGH THE
EVENING AND EARLY OVERNIGHT HOURS. RAIN WILL BE WIDESPREAD OVER THE
SAGINAW VALLEY BUT STORMS LESS INTENSE. STILL HAVE A SHOT AT A LATE
NIGHT ROUND OF STORMS AS CONVECTION CONTINUES TO FORM OVER IOWA.

FORECAST UPDATE WILL REFLECT A TREND TOWARD INCREASING AREAL
COVERAGE DURING THE EVENING. FLOOD WATCH MESSAGE WILL BE UPDATED TO
REFLECT LATEST CONVECTIVE TRENDS.

&&

BT

.PREV DISCUSSION... ISSUED AT 300 PM TODAY
WE WILL EXTEND/HOIST FLOOD WATCH TO COVER ALL OF THE CWA THROUGH 6
PM SATURDAY (FOR NOW).  VERY ACTIVE WEATHER PERIOD SO THIS WILL BE
BRIEF.

SEVERE MCS/BOW ECHO PROGRESSING EAST WITH THE BOW APEX ACROSS
EXTREME SOUTHEAST LOWER MICHIGAN.  SEVERE WEATHER, FOR THE MOMENT,
WILL CLEAR THE REGION BY 20Z AS WE WILL BE ON THE SUBSIDENCE SIDE OF
THIS DEPARTING SYSTEM WITH RAIN GRADUALLY COMING TO AN END.  COLD
POOL ACROSS WISCONSIN HAS SENT THE OUTFLOW BOUNDARY ACROSS NORTHERN
ILLINOIS INTO CENTRAL IOWA.  NEW CONVECTION IS ALREADY DEVELOPING,
LIKELY INTO ANOTHER MCS, IN NORTHERN IOWA WHERE LOW LEVEL JET PER
PROFILERS IS FEEDING MOIST AIR NORTH ALONG THE BAROCLINIC BOUNDARY.
LATEST MODELS SUGGEST UPSTREAM MCS WILL TRACK INITIALLY NORTHEAST
THEN TURN EAST PER CORFIDI VECTORS AND THICKNESSES.  HOWEVER, THE
WARM FRONT WILL BE DISPLACED A BIT FURTHER SOUTH SO AT LEAST FOR NOW
THE THREAT FROM SEVERE WEATHER (HAIL/WIND) WILL BE LIMITED.  THE
MAIN CONCERN WILL BE FLOODING AS THE GROUND IS QUITE SATURATED AND
FLOOD GUIDANCE NUMBERS ARE LOWERING WITH TIME.

THE LOW LEVEL JET WILL STRENGTHEN OVERNIGHT (>50KTS) ACROSS THE
PLAINS AS TROF DIGS ACROSS THE ROCKIES.  THIS WILL BE SURE TO KEEP
ADDITIONAL THUNDERSTORMS DEVELOPING ALONG AND NORTH OF INTERSTATE 80
OVERNIGHT ACROSS THE PLAINS AND TRACK EAST ACROSS THE GREAT LAKES.
PWATS REMAIN WELL ABOVE 1.50 SO HEAVY RAINFALL A REAL CONCERN.

SEVERE WEATHER POTENTIAL PICKS UP ONCE AGAIN SATURDAY NIGHT INTO
SUNDAY AS IMPRESSIVE SURFACE WAVE DEEPENS A BIT AS IT TRACKS TOWARD
THE GREAT LAKES.  STRONG LOW LEVEL JET COMBINING WITH FRONTAL
BOUNDARY DRAPED ACROSS THE CWA COULD PROVE TO BE VERY INTERESTING.
EHI/S CLIMB OVER 2 WITH HELICITIES IN EXCESS OF 200
M2/S2...PRIMARILY ALONG AND NORTH OF INTERSTATE 69 WITH CAPES AROUND
2K J/KG.  OF COURSE, WITH ALL OF THIS CONVECTION IN THE MODELS, IT
WILL BE VERY DIFFICULT TO PIN DOWN FRONTAL PLACEMENT AND SEVERE
POTENTIAL.  WE ARE CERTAIN THAT WE WILL REMAIN IN THE MCS TRACK FOR
HEAVY RAINFALL AND FLOODING INTO THE WEEKEND.

LOOKS LIKE A BREAK ARRIVES FOR EARLY NEXT WEEK AS UPSTREAM TROF
RELOADS ACROSS THE PLAINS.  THIS WILL SEND ANOTHER COLD FRONT ACROSS
THE LAKES NEXT WEEK AS IT STILL LOOKS COOL AND WET FOR LATE WEEK
INTO THE HOLIDAY WEEKEND.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...FLOOD WATCH...THROUGH 6 PM
SATURDAY...ALL OF SOUTHEAST LOWER MICHIGAN.

&&

BGM

EXPERIMENTAL GRAPHICAL FORECASTS ARE AVAILABLE ONLINE AT
HTTP://WWW.CRH.NOAA.GOV/DTX  (ALL LOWER CASE)

HAZARDOUS WEATHER OUTLOOK FOR SOUTHEAST MICHIGAN
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
937 PM EDT FRI MAY 21 2004

MIZ047>049-053>055-221200-
BAY-HURON-MIDLAND-SAGINAW-SANILAC-TUSCOLA-
937 PM EDT FRI MAY 21 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE SAGINAW VALLEY AND THUMB

.DAY ONE...TONIGHT

A FLOOD WATCH IS IN EFFECT TONIGHT AS ADDITIONAL HEAVY RAINFALL IS
ANTICIPATED.  PLEASE REFER TO THE LATEST FLOOD WATCH STATEMENTS
ISSUED BY YOUR NATIONAL WEATHER SERVICE.

ANOTHER COMPLEX OF THUNDERSTORMS IS EXPECTED TO TRACK ACROSS THE
REGION TOWARD SUNRISE.  THE MAIN HAZARD WILL BE ADDITIONAL HEAVY
RAINFALL ON ALREADY SATURATED GROUND.  THESE THUNDERSTORMS ARE
DEVELOPING ALONG AND AHEAD OF WARM FRONT WHICH STRETCHES FROM THE
OHIO VALLEY INTO THE NORTHERN PLAINS. THUNDERSTORMS TONIGHT WILL
TRACK TO THE EAST AROUND 40 MPH.  WITHIN THE STRONGEST CELLS...HALF
INCH SIZED HAIL AND WIND GUSTS TO 50 MPH WILL BE POSSIBLE.

.DAY TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THUNDERSTORMS...POSSIBLY SEVERE...WILL LINGER THROUGH THE WEEKEND
ALONG WITH HEAVY RAINFALL POTENTIAL.  A FLOOD WATCH REMAINS IN
EFFECT THROUGH SATURDAY...BUT MAY NEED TO BE EXTENDED THROUGH SUNDAY
IF CONDITIONS WARRANT.

A PERSISTENT NEARLY STATIONARY FRONT WILL LINGER ACROSS THE STATE
THROUGH THE WEEKEND.  ADDITIONAL THUNDERSTORMS ARE EXPECTED ALONG
THE FRONTAL BOUNDARY AND SOME MAY BECOME SEVERE WITH LARGE
HAIL...DAMAGING WIND GUSTS...FLOODING RAINFALL ALONG WITH A
POSSIBLE TORNADO.  EXACT TIMING AND PLACEMENT OF THUNDERSTORMS WILL
BE DIFFICULT TO ASCERTAIN AND WILL LIKELY CHANGE THROUGH THE
WEEKEND.  YOUR NATIONAL WEATHER SERVICE WILL CONTINUE TO MONITOR THE
SITUATION CLOSELY.

.SPOTTER INFORMATION STATEMENT...

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION MAY ONCE AGAIN BE NEEDED TONIGHT AND INTO THE
WEEKEND.

MIZ060>063-068>070-075-076-082-083-221200-
GENESEE-LAPEER-LENAWEE-LIVINGSTON-MACOMB-MONROE-OAKLAND-SHIAWASSEE-
ST. CLAIR-WASHTENAW-WAYNE-
937 PM EDT FRI MAY 21 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST MICHIGAN

.DAY ONE...TONIGHT

ANOTHER LINE OF THUNDERSTORMS WILL MOVE THROUGH THE AREA TONIGHT AND
BRING A CHANCE OF SEVERE WEATHER ALONG AND SOUTH OF INTERSTATE 69.
THE BEST CHANCE OF SEVERE WEATHER WILL BE FROM 10 PM TO 2 AM. THE
STRONGEST STORMS WILL BE CAPABLE OF WIND GUSTS AROUND 60 MPH AND HAIL
AROUND 1 INCH...AS THEY MOVE EAST AT 50 MPH.

A FLOOD WATCH IS IN EFFECT TONIGHT AS ADDITIONAL HEAVY RAINFALL IS
ANTICIPATED.  PLEASE REFER TO THE LATEST FLOOD WATCH STATEMENTS
ISSUED BY YOUR NATIONAL WEATHER SERVICE.

ANOTHER COMPLEX OF THUNDERSTORMS IS EXPECTED TO TRACK ACROSS THE
REGION TOWARD SUNRISE.  THE MAIN HAZARD WILL BE ADDITIONAL HEAVY
RAINFALL ON ALREADY SATURATED GROUND.  THESE THUNDERSTORMS ARE
DEVELOPING ALONG AND AHEAD OF WARM FRONT WHICH STRETCHES FROM THE
OHIO VALLEY INTO THE NORTHERN PLAINS.

.DAY TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THUNDERSTORMS...POSSIBLY SEVERE...WILL LINGER THROUGH THE WEEKEND
ALONG WITH HEAVY RAINFALL POTENTIAL.  A FLOOD WATCH REMAINS IN
EFFECT THROUGH SATURDAY...BUT MAY NEED TO BE EXTENDED THROUGH SUNDAY
IF CONDITIONS WARRANT.

A PERSISTENT NEARLY STATIONARY FRONT WILL LINGER ACROSS THE STATE
THROUGH THE WEEKEND.  ADDITIONAL THUNDERSTORMS ARE EXPECTED ALONG
THE FRONTAL BOUNDARY AND SOME MAY BECOME SEVERE WITH LARGE
HAIL...DAMAGING WIND GUSTS...FLOODING RAINFALL ALONG WITH A
POSSIBLE TORNADO.  EXACT TIMING AND PLACEMENT OF THUNDERSTORMS WILL
BE DIFFICULT TO ASCERTAIN AND WILL LIKELY CHANGE THROUGH THE
WEEKEND.  YOUR NATIONAL WEATHER SERVICE WILL CONTINUE TO MONITOR THE
SITUATION CLOSELY.

.SPOTTER INFORMATION STATEMENT...

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.
SPOTTER ACTIVATION MAY ONCE AGAIN BE NEEDED TONIGHT AND INTO THE
WEEKEND.

BT