Severe Thunderstorm Warning 84, NWS Detroit, MI

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
228 PM EDT THU SEP 19 2002

A DEEP SOUTHERN BRANCH TROUGH IS LOCATED NEAR THE TEXAS PANHANDLE
WITH A WEAKER NORTHERN BRANCH TROUGH JUST NORTH OF MINNESOTA PER
CURRENT WATER VAPOR LOOP. THE WATER LOOP ALSO SHOWS A PLUME OF DEEP
MOISTURE ACROSS THE MISSISSIPPI VALLEY AND WESTERN GREAT LAKES
AHEAD OF THESE TROUGHS. AT THE SURFACE...A COLD FRONT EXTENDS FROM
FAR WESTERN LAKE SUPERIOR TO NORTHERN TEXAS. WIDESPREAD CONVECTION
CURRENTLY EXTENDS FROM EASTERN TEXAS ALL THE WAY TO SOUTHWEST LOWER
MICHIGAN. ONCE AGAIN...PRECIPITATION CHANCES WILL BE THE MAIN
CONCERN THIS FORECAST PERIOD AS THIS SLOW MOVING FRONT APPROACHES
THE AREA.

THE 12Z MODEL SOLUTIONS ARE IN GOOD AGREEMENT IN LIFTING THE UPPER
TROUGH OVER THE SOUTHERN PLAINS NORTHEAST INTO WESTERN GREAT LAKES
BY FRIDAY EVENING AND DEAMPLIFYING THE TROUGH. THE ETA SOLUTION HAS
BEEN TRENDING TOWARD THE MORE CONSISTENT AVN THE LAST SEVERAL RUNS.
I WILL THUS BE FOLLOWING THE AVN TIMING ON THE FRONTAL
BOUNDARY...WHICH BRINGS IT ACROSS SE MICHIGAN FRIDAY EVENING.

AREA RADAR DATA IS SHOWING CONVECTION PUSHING ACROSS SOUTHWEST LOWER
MICHIGAN ATTM. THIS AREA OF CONVECTION IS OCCURRING AHEAD OF A WEAK
SHORT WAVE IN NORTHERN ILLINOIS. SOME MODEST SURFACE MOISTURE
CONVERGENCE AHEAD OF THIS WAVE IS AIDING THE CONVECTIVE DEVELOPMENT.
WITH SURFACE TEMPS HAVING CLIMBED WELL INTO THE 80S THIS AFTERNOON
AND SFC DEWPOINTS AROUND 70...LAPS DATA HAS INDICATED CAPE VALUES
RANGING FROM 2200 TO 2400 J/KG ACROSS THE FORECAST AREA.  THIS WEAK
WAVE AND LOW LEVEL MOISTURE CONVERGENCE IS POISED TO WORK ACROSS SE
MICHIGAN THIS EVENING. BASED ON COVERAGE OF PRECIP AND PROJECTED
MOVEMENT OF THE WAVE AND MOISTURE ADVECTION...I WILL CARRY LIKELY
WORDING FOR SHOWERS AND THUNDERSTORMS ACROSS THE NORTH AND SCATTERED
NEAR DETROIT. PRECIP LOADING WITH AMPLE MOISTURE MAY ALLOW A FEW OF
THESE STORMS TO PRODUCE SOME LOCALLY HEAVY WIND GUSTS. I EXPECT SOME
MCS DEVELOPMENT OVER THE MID MISSISSIPPI VALLEY AND WESTERN OHIO
VALLEYS LATER TONIGHT AS A 35 TO 40KT NOCTURNAL JET DEVELOPS AHEAD
OF THE SURFACE FRONTAL BOUNDARY. CONVECTIVE DEBRIS MOVING INTO THE
SOUTHERN LAKES REGION FROM THIS SYSTEM ALONG WITH ADDITIONAL 850MB
THETA E ADVECTION OVERNIGHT SHOULD SPELL MORE NUMEROUS SHOWERS AND
THUNDERSTORMS. SOME OF THE STRONGER CONVECTION SHOULD PRODUCE SOME
LOCALLY HEAVY RAINFALL AS PRECIPITABLE WATER VALUES APPROACH 1.8
INCHES OVERNIGHT.

FRIDAY AND FRIDAY NIGHT...THE UPPER LEVEL WAVE WILL SHEAR OUT AS IT
MOVES INTO THE WESTERN GREAT LAKES. CONVERGENCE ALONG THE FRONTAL
BOUNDARY IS ALSO PROGGED TO WEAKEN. THE BEST UPPER LEVEL DIVERGENCE
IS ALSO PROGGED TO RESIDE JUST SOUTHEAST OF THE FORECAST AREA.
NONETHELESS...VERY HIGH MOISTURE CONTENT IN THE ATMOSPHERE AND SOME
MODEST LIFT SHOULD SPELL AT LEAST LIKELY POPS ACROSS THE FORECAST
AREA. SPC HAS PLACED SE MICHIGAN IN A SLIGHT RISK. DEEP LAYER SHEAR
WILL INCREASE AS MID LEVEL JET OF 50KTS MOVES OVER LOWER
MICHIGAN...SUGGESTING GOOD POTENTIAL FOR SOME ORGANIZED STORMS. A
LIMITING FACTOR TO ORGANIZED SEVERE CONVECTION WILL BE POTENTIAL
CONVECTIVE DEBRIS CLOUDS AND PRECIP DURING THE MORNING LIMITING THE
INSTABILITY. IF WE ARE ABLE TO REACH GUIDANCE HIGHS OF NEAR
80...WHICH WILL LIKELY HAPPEN IF A FEW BREAKS IN THE OVERCAST
DEVELOP...MODIFIED SOUNDINGS SUGGEST CAPE NEAR 1900 J/KG. THIS
COMBINED WITH THE DYNAMIC WIND FIELDS WOULD SUPPORT A SLIGHT RISK
FOR SEVERE STORMS. THE FRONT AND LOW LEVEL MOISTURE AXIS IS STILL
PROGGED TO EXIT EAST OF THE FORECAST AREA DURING THE OVERNIGHT
HOURS.

FOR THIS WEEKEND...SIGNIFICANT COLD AIR ADVECTION WILL
OCCUR...ESPECIALLY FOLLOWING A WEAK SFC TROUGH SATURDAY AFTERNOON AS
A DEEP UPPER TROUGH DIGS INTO THE GREAT LAKES. THE AVN AND ETA
MODELS ARE NOT SHOWING VERY MUCH DEEP LAYER MOISTURE THROUGH THE
WEEKEND. AT THIS POINT...I WILL CARRY A DRY FORECAST. LATER SHIFTS
WILL HAVE TO MONITOR THIS FOR SUNDAY AS SHORT WAVE TROUGHS MAY
INTERACT WITH OVER LAKE INSTABILITY TO PUSH SOME SHOWERS WELL
INLAND.

EXTENDED DISCUSSION...THERE IS STILL A FAIR AMOUNT OF AGREEMENT
AMONG THE MEDIUM RANGE MODEL SOLUTIONS SHOWING A HUDSON BAY LOW WITH
A DEEP UPPER TROUGH OVER NORTHERN TIER US NEXT WEEK. THE MAIN
DIFFERENCES ARISE WITH RESPECT TO THE AMOUNT OF COLD AIR FILTERING
DOWN INTO THE SOUTHERN GREAT LAKES...WITH THE AVN AND ETAXX
SOLUTIONS COLDER THAN THE UKMET...ECMWF AND CANADIAN SOLUTIONS.
THERE APPEARS TO BE SOME VARIANCE AMONG AVN ENSEMBLE MEMBERS AS TO
HOW COLD IT WILL GET ACROSS THE SOUTHERN GREAT LAKES REGION AS WELL.
SO...GIVEN THERE IS GOOD AGREEMENT IN SHOWING THE HUDSON BAY LOW
NEXT WEEK...I WILL KEEP TEMPS AT TO A LITTLE BELOW CLIMO. I WILL NOT
HOWEVER SIDE WITH THE VERY COOL MEX NUMBERS GIVEN SOME OF THE WARMER
SOLUTIONS. MAY SEE SOME SHORT WAVES AND WEAK SURFACE TROUGHS ROTATE
AROUND THE UPPER LOW NEXT WEEK. TIMING OF THESE WILL BE DIFFICULT
THOUGH. THE WARMER SOLUTIONS ALSO SUGGEST THAT THESE WAVES MAY BE
MORE OF A PROBLEM ACROSS THE NORTHERN LAKES. SO AT THIS POINT...I
WILL LEAVE THE FORECAST DRY.

.DTX...NONE.

CONSIDINE

MIZ047>049-053>055-060>063-068>070-075-076-082-083-200900-

HAZARDOUS WEATHER OUTLOOK FOR SOUTHEAST MICHIGAN
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
430 PM EDT THU SEP 19 2002

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.

HAZARD...
SCATTERED TO NUMEROUS THUNDERSTORMS WILL OCCUR ACROSS ALL OF
SOUTHEAST MICHIGAN THIS AFTERNOON AND TONIGHT. THERE IS A CHANCE
THAT SOME STORMS WILL REACH SEVERE LIMITS. THE PRIMARY HAZARD WILL
BE DAMAGING WIND GUSTS IN EXCESS OF 60 MPH...WITH HAIL AN INCH OR
LARGER POSSIBLE IN A FEW CASES.

DISCUSSION...
HUMID AIR OVER SOUTHEAST MICHIGAN...COMBINED WITH DAYTIME HEATING...
HAS LED TO NUMEROUS THUNDERSTORMS THIS AFTERNOON. THESE STORMS WILL
CONTINUE TO SPREAD NORTHEAST OVER THE AREA AT AROUND 30 MPH.

THE PRIMARY SEVERE THUNDERSTORM HAZARD WILL BE DAMAGING WIND GUSTS
IN EXCESS OF 60 MPH...WITH HAIL AN INCH OR LARGER POSSIBLE IN A FEW
CASES. THE HIGH MOISTURE CONTENT OF THE AIR WILL MAKE HEAVY RAINFALL
POSSIBLE AS WELL.

THE STRONGEST STORMS WILL EXIT SOUTHEAST MICHIGAN LATER THIS
EVENING...AROUND 10 PM.

SPOTTER ACTIVATION...
SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND THIS EVENING.

OUTLOOK FOR FRIDAY AND SATURDAY...
THUNDERSTORMS ARE LIKELY AGAIN ON FRIDAY.

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)

BT

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
511 PM EDT THU SEP 19 2002

TIME(EDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0438 PM    PERRY                     MI   .88 INCH HAIL
09/19/02   SHIAWASSEE                     REPORTED BY LAW
                                          ENFORCEMENT

0500 PM    MIDLAND                   MI   WIND DAMAGE
09/19/02   MIDLAND                        NUMEROUS TREES DOWN
                                          REPORTED BY LAW ENFORCEMENT

JHB