Severe Thunderstorm Warning 135, NWS Milwaukee, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
330 AM CDT FRI SEP 1 2000

FORECAST CHALLENGES ARE POTENTIAL FOR SEVERE WEATHER ACROSS SOUTHERN
WISCONSIN...POSITION OF FRONTAL BOUNDARY...HEAVY RAIN POTENTIAL AND RESULTING
TEMPERATURE FORECASTS.

MODELS HAVE NOT REALLY HANDLED THE POTION OF THE FRONTAL BOUNDARY
WELL.  THEY HAVE TENDED TO BE TO FAST ON THE SOUTHWARD SAG.  THIS
AFTERNOON APRROACHING WEAK SHORTWAVE OVER W IA/SW MN HAS RESULTED IN
KEEPING THE TROF A BIT MORE PRONOUNCED.  INSTABILITY AXIS HAS LI'S
OF AROUND -10..LATEST RUC SOUNDINGS SHOW LOW LEVEL CAP WEAKENING.
AS RESULT MAIN PROBLEM IS WHEN CONVECTION WILL CHANGE FROM ACCAS
ABOVE CAP...TO MORE SURFACE BASED.  WHEN/IF THIS HAPPENS CAPES OF
AROUND 3000 J/KG ARE INDICATED WITH THE RISING PARCELS.  WIND FIELDS
ARE WEAK..SO EVEN THOUGH ACTUAL WIND DIRECTIONS ARE FAVORABLE FOR
SUPERCELLS..THE ACTUAL SHEAR VALUES ARE QUITE LOW.  THIS MEANS HEAVY
RAINS ARE ANTICIPATED WITH ANY DEVELOPING THUNDERSTORMS. LOW LEVEL
MOISTURE CONVERGENCE HAS BEEN INCREASING IN THE INSTABILITY
AXIS...SO CAP MAY BE BROKEN SOON...ESPECIALLY WITH APPROACHING WEAK
SHORTWAVE.

HEAVY RAIN POTENTIAL WILL BE DUE TO TRAINING.  WILL MENTION HEAVY
RAINS...BUT NO FLASH FLOOD WATCH SINCE FFG VALUES ARE FAIRLY
HIGH...AND MAIN EFFECT OF UPPER SHORTWAVE APPEARS HEADED JUST NW OF
OUR FORECAST AREA THIS AFTERNOON.

AFTER SHORTWAVE PASSES BOUNDARY SHOULD SAG SOUTH MORE...BUT AVN
STILL HAS BOUNDARY JUST N OF THE WI/IL BORDER INTO NOON TIME
SATURDAY.  HOWEVER FORCING IS WEAK.  COOL AIR WILL BE SHALLOW WITH
MID LEVEL INSTABILITY AND 2000 G/KG CAPES CONTINUING EVEN SATURDAY
JUST NORTH OF THE SRUFACE BOUNDARY.

NEXT SHORTWAVE MOVING INTO THE N PLAINS SATURDAY SHOULD INTENSIFY
SURFACE LOW OVER THE CENTRAL/N PLAINS...THAT WOULD BRING THE
BOUNDARY FARTHER N ON SUNDAY.

OBVIOUSLY POSTION OF BOUNDARY...AND LOW CLOUD COVER N OF IT WILL
DICATATE MAX TEMPS THIS WEEKEND.  DIFFERENCES IN AVN AND NGM BASED
MOS BEAR THIS OUT WITH 10 DEGREE DIFFERENCES BETWEEN THEM.  WILL
LEAN MORE TOWARD THE AVN.

.UWNMS...NOT AVAILABLE.

.MKX...NONE.

$$h
HENTZ

WIZ046-047-051-052-056>060-062>072-022300-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
1100 AM CDT FRI SEP 1 2000

...HAZARDOUS WEATHER OUTLOOK...
...FOR SOUTH CENTRAL AND SOUTHEAST WISCONSIN...

THREAT...
SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND THIS EVENING.
THE THREATS WILL BE LARGE HAIL...DAMAGING WINDS AND LOCALLY HEAVY
RAINFALL.

DISCUSSION...
A WARM AND HUMID AIRMASS WILL INTERACT WITH A FRONTAL BOUNDARY
SAGGING IN FROM THE NORTH...AND AN APPROACHING UPPER LEVEL
DISTURBANCE...TO GENERATE THUNDERSTORMS THIS AFTERNOON AND THIS
EVENING. HEAVY RAIN IS THE BIGGEST THREAT...BUT SOME OF THE STORMS
MAY BE SEVERE WITH LARGE HAIL AND DAMAGING WINDS.  THE CHANCE OF
THUNDERSTORMS IS EXPECTED TO CONTINUE TONIGHT...BUT WITH THE LOSS OF
SURFACE HEATING THE RISK OF SEVERE WILL DIMINISH SOMEWHAT...WHILE
THE THREAT OF HEAVY RAIN CONTINUES.

SPOTTER ACTIVATION...
STORM SPOTTER GROUPS MAY BE NEEDED THIS AFTERNOON AND INTO THE
EVENING HOURS.

HENTZ