Severe Thunderstorm Warning 86, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
310 PM CDT FRI JUL 30 1999

MAIN FORECAST CONCERNS ARE IN THE SHORT-TERM...WITH SHOWER AND
THUNDERSTORM CHANCES TONIGHT...FLASH FLOODING AND SEVERE. THEN IN THE
LONG-TERM...DRIER AND MORE SEASONABLE AIR FOR THE WEEKEND.

LATEST WATER VAPOR SATELITE IMAGERY INDICATES TWO SHORTWAVES...ONE OVER
FAR NORTHWEST MO...AND ANOTHER HELPING TO SPAWN SOME THUNDERSTORMS OVER
CENTRAL SOUTH DAKOTA. THE 17Z SURFACE ANALYSIS HAS AN AREA OF LOW
PRESSURE OVER EASTERN SD WITH A COLD FRONT STRETCHING SOUTH AND NORTH
OF THERE. DEWPOINTS BEHIND THE FRONT DROP INTO THE 60S AND 50S.
FORECAST AREA VERY HOT AND HUMID...WITH TEMPERATURES IN THE 90S AND
DEWPOINTS IN THE MIDDLE TO UPPER 70S. HEAT INDICES AVERAGED AROUND
110.

12Z MODEL RUNS CONTINUE SOME DIFFERENCES. THE ETA DEVELOPS CONVECTION
ALONG THE FRONTAL BOUNDARY...WITH THE HEAVIEST RAINS MOVING ACROSS
SOUTHEAST MN INTO WESTERN WI. NGM DEVELOPS MORE PCPN TO THE
SOUTH...OVER IOWA...WITH NOT AS MUCH TO THE NORTH. SEEMS MAINLY DUE TO
THE SURFACE LOW POSITIONING...WHICH THE NGM HAS TOO FAR SOUTH. CURRENT
SATELITE TRENDS AND MORNING ANAYLSIS SUPPORT THE ETA AND WILL GO WITH
THAT SOLUTION.

ATMOSPHERE PRIMED FOR THUNDERSTORMS TONIGHT...WITH THE CHANCE FOR SOME
GOING SEVERE. SURFACE BASED CAPES RANGED FROM 6000-10000 J/KG LATE THIS
AFTERNOON...AND LI/S FROM -12 TO -16. A SOMEWHAT INVERTED-V SOUNDING
WOULD INDICATE THE POSSIBILITY OF DAMAGING DOWNBURST WINDS...BUT THERE
IS LITTLE SHEAR. HAIL PROBABLY THE BIGGER THREAT. PW/S ARE ALSO QUITE
HIGH...IN THE 1.5 TO 2 INCH RANGE FROM 00Z TONIGHT THROUGH 12Z
SATURDAY. GRIDDED DATA INDICATES FROM 1/2 INCH OF ACCUMULATION ACROSS
THE SOUTHERN PART OF THE CWA...TO UP TO 1 1/2 INCHES TO THE NORTH. FEEL
THAT MIGHT BE UNDERDONE FOR THE SOUTH. FFG CLOSE TO 1.5 INCHES FOR MOST
AREAS...ALTHOUGH CLOSER TO AN INCH ACROSS NE IA. STORMS WILL LIKELY BE
SLOW MOVERS WITH SOME TRAINING. WILL ALL THE RECENT PROBLEMS ACROSS THE
WESTERN CWA...AND THE LIKELIHOOD OF HEAVY RAIN...WILL ISSUE A FLASH
FLOOD WATCH FOR WEST OF THE MISSISSIPPI RIVER TONIGHT.

THE COLD FRONT MOVES INTO SOUTHEAST MN BY 06Z...WHILE THE SECONDARY
WAVE CATCHES UP TO THE FRONT AND SPINS ACROSS THE SAME AREA AT THAT
TIME. THE ETA STRENGTHENS THIS WAVE A BIT...BUT FEEL THAT IS PROBABLY
CONVECTIVELY ENDUCED. THE AREA IS ALSO UNDER SOME FAVORABLE JET
DYNAMICS AND THE 850 MB MOISTURE TRANSPORT HAS A GOOD SURGE ACROSS THE
FORECAST AREA THROUGH 06Z.

FRONT PUSHES OUT OF WI BY SATURDAY NIGHT...WITH DRIER AND MORE
SEASONABLE AIR FOLLOWING IN ITS WAKE. 850 MB TEMPERATURES DROP OFF INTO
THE MIDDLE TEENS BY 00Z SUNDAY...WITH SURFACE DEWPOINTS BEHIND THE FRONT
FALLING INTO THE 50S. WITH NORTHWEST FLOW ALOFT AND CANADIAN HIGH
PRESSURE SINKING OVER THE DAKOTAS...AFTER THE SHOWERS SATURDAY MORNING
THE REST OF THE WEEKEND SHOULD ROUNDOUT ON A PLEASANT NOTE.

TEMPERATURE-WISE...RETURNING TO MORE NORMAL CONDITIONS FOR THE NEXT
COUPLE DAYS...AND THEN SOME COOLER THEN NORMAL FOR THE BEGINNING OF THE
NEW WORK WEEK. FAN/FMR/FWC GUIDANCE ALL COMPARIABLE...BUT LIKE ETA
2-METER TEMPERATURES FOR TONIGHT. WITH RAIN COOLED AIR BEING THE MAJOR
FACTOR FOR THE COOLING //FRONT NOT MOVING THROUGH UNTIL AFTER
12Z//...THE OTHER GUIDANCE IS A BIT TOO COOL.

DANGEROUS HEAT INDICES...ESPECIALLY ACROSS NORTHEAST IOWA...WILL
CONTINUE THROUGH ABOUT 8 OR 9 PM...SO WILL CONTINUE THE WARNING AND
ADVISORY FOR THIS EVENING. WITH COOLER AND MORE SEASONABLE CONDITIONS
FINALLY RETURNING FOR THE WEEKEND...NO ADDITIONAL HEAT ADVISORIES OR
EXTENTIONS WILL BE NEEDED.

COORDINATED WITH DMX...MPX...DVN.

.LSE...FLASH FLOOD WATCH TONIGHT FOR NORTHEAST IA AND SOUTHEAST MN.
       IAZ008>011...018...019...029...030.
       MNZ079...086>088...094>096.

       EXCESSIVE HEAT WARNING THIS EVENING FOR NORTHEAST IA.
       IAZ008>011...018...019...029...030.

       HEAT ADVISORY THIS EVENING FOR SOUTHWEST AND CENTRAL WI.
       WIfZ017-029-032>034...041>044...053>055...061.
       MNZ079...086>088...094>096.

RIECK

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LA CROSSE WI
533 PM CDT FRI JUL 30 1999

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

0504 PM    WHITEHALL                 WI   WIND DAMAGE
07/30/99   TREMPEALEAU                    TREES DOWN ESTIMATED WINDS
                                          TO 60 MPH

NELSON