Severe Thunderstorm Warning 83, NWS Milwaukee, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
245 AM CDT FRI JUL 23 1999

FCST CHALLENGE INVOLVES POTENTIAL HEAT ADVYS AND CHANCES OF TSTMS.

OLD WARM FNT XTNDS FM W OF FLD TO NEAR MKE ATTM.  WIDELY SCT
ELEVATED TSTMS POPPING ALONG BNDRY.  THIS ACTIVITY SHLD EXIT SE WI
BY MID MRNG.  THEN QUESTION SHIFTS TO TSTM POTENIAL AHD OF SHRTWV
PUSHING ACRS MN.  THIS IS PRODUCING AN MCS HEADING INTO NW/WC WI
ATTM.  THIS MAY AFFECT N PTNS OF OUR CWA THIS MRNG.  MODELS ARE
DOING A POOR JOB WITH THIS MCS. ETA KEEPS CWA DRY THRU 48 HRS.  APRS
NGM HAS BEST HANDLE ON THE MN SHRTWV...ALONG WITH GENERATING AT
LEAST SOME QPF.

PRBLM THEN CENTERS ON SECOND SHRTWV LATER TNGT AND SAT.  APRS ETA
AND NGM DRY MID LVLS BEHIND INITIAL MN SHRTWV...WITH LITTLE RESPONSE
IN THE LOW LVL WIND FIELD TO THE SECOND SHRTWV.  HWVR U.W. NMS MODEL
PAINTS A TOTALLY DIFFERENT PICTURE WITH A SUBTLE WIND SHIFT LINE.
IN ADDITION U.W. NMS KEEPS HIGH DEWPNTS ACRS S WI SAT.  THIS IN
CONTRAST TO NGM WHICH UNREALISTICALLY STARTS DRYING DEWPTS INTO THE
UPR 60S THIS AFTN.  AS SUCH U.W. NMS SHOWS MAX CAPE AXIS ACRS S WI
SAT INSTEAD OF ACRS N IL/ N IN ON THE ETA MODEL.

TSTM CHCS WARRANTED TDY AS MORE TSTMS MAY FORM AHD OF 1ST SHRTWV.
QUESTION IS THEN WHAT TO DO TNGT AND SAT.  WL LIKELY EXTEND TSTM CHC
INTO EVE ACRS SE WI AS ETA AND U.W. NMS STILL SHOWS 700 MB TROF AXIS
ACRS SC WI AT 00Z.  NGM APRS TOO FAST.   FOR NOW WL GO WITH ETA/NGM
AND HAVE DRY FCST SAT.  HWVR IS U.W. NMS VERIFIES THERE WLD BE CHC
FOR TSTMS SAT AFTN.  HOPEFULLY NEXT MODEL RUN CLARIFIES THINGS.

ON THE HEAT ADVSRY SITUATION...NGM DEWPNTS ARE TOO LOW.  XPCT AT
LEAST MID 70 DEWPTS ACRS S WI TDY...NOT THE UPPER 60S AS SHOWN ON
NGM.  PRBLM IS WITH UPSTREAM TSTMS.  ONE SENERIO COULD BE THESE JUST
KEEP COMMING...WITH ENOUGH CLD DEBRIS TO KEEP TMPS DOWN A BIT.  HWVR
WITH HIGH DEWPTS THINK THE BEST APRCH WL BE TO GO WITH HEAT ADVSRY
WITH HEAT INDCIES PSBLY REACHING ARND 105.

.UWNMS...ONLY MODEL SHOWING WIDELY SCT TSTMS OVR SE WI ERLY THIS
MRNG.  SEE ABOVE ON OTHER MATTERS.

.MKX...HEAT ADVSRY TDY ZONES 46..47..51..52..56>60..62>66..67>72.
HENTZ

WIZ046-047-051-052-056>060-062>072-240300-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
1140 AM CDT FRI JUL 23 1999

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

THREAT...
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO
TONIGHT...IN SOUTH CENTRAL AND SOUTHEASTERN WISCONSIN. IN
ADDITION...THE COMBINATION OF HEAT AND HUMIDITY OVER THE REGION...
WILL BRING HEAT INDEX VALUES TO 105 TO 110 OVER SOUTHERN WISCONSIN.

DISCUSSION...
A WARM...HUMID AIRMASS IS IN PLACE OVER SOUTHERN WISCONSIN. HIGH
TEMPERATURES THIS AFTERNOON...ARE EXPECTED TO REACH 90 TO 95
DEGREES. THIS COMBINATION OF HEAT AND HUMIDITY WILL BOOST HEAT INDEX
VALUES TO 105 TO 110.

THE HEAT AND HUMIDITY HAD ALREADY COMBINED TO PRODUCE VERY UNSTABLE
CONDITIONS OVER SOUTHERN WISCONSIN LATE THIS MORNING. AS A WEAK FRONT
MOVES IN FROM THE WEST IT WILL ACT AS FOCUSING MECHANISM FOR THE
DEVELOPMENT OF THUNDERSTORMS...SOME OF WHICH MAY PRODUCE DAMAGING
WINDS AND LARGE HAIL.

SPOTTER ACTION...
STORM SPOTTER GROUPS MAY BE NEED TO BE ACTIVATED THIS AFTERNOON
INTO TONIGHT IN SOUTH CENTRAL AND SOUTHEASTERN WISCONSIN.

GARCIA