Severe Thunderstorm Warning 83, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
215 PM CDT TUE MAY 1 2001

EARLY CONCERN WILL BE SVR WX AND DURATION OF IT.  SECOND FOCUS WILL
BE DAILY HIGH POPS AND POSSIBLE FLOODING.

MODELS HAVE BEEN ADVERTISING COLD FRONT WITH SHARP MID LVL TROF IS
NOW ENTERING THE THE STATE WITH ISOLD CELLS DVLPG ON FNT ATTM.
DESPITE LIMITED MOISTURE TO START WITH THIS AFTN POOLING NEAR THE
FNT AND INCRSG MOISTURE CONVERGENCE HAS ENHANCED CAPE AND SVR
POTENTIAL.  EXPECT TIME OF DAY HAS BIG PLAY INT YPE AS DVLPMNT UP
NORTH POINTS TO TORNADOES WHILE SRN POTENTIAL APPEARS BEST TO BE
HAIL/WIND AS SHEAR NOT THAT GREAT AND PROFLIER (SLATER) NOT AS
FAVORABLE IN SOUTH AS NRN IA NEAR WOOD LAKE PROFLIER WHICH HAS MUCH
BETTER VEERING.  LOOK AT Q/G FORCING 850/500 VEYR FAVORABLE FOR TNGT
THO SOME HINT OF SECONDARY SURGE THAT MIGHT BRING ON DVLPMNT OF
SECOND LINE OF PCPN TNGT.  THEN BOUNDARY ORIENTS E/W AND REMAINS IN
THE AREA AS S/W MOVE BY OVER NEXT SEVERAL DAYS.  KNOWING CLIMO WISE
THAT THIS IS PCPN MAX IN MAY HAVE TO KEEP EYE ON HEAVY RAINS HWVR
WILL NOT ISSUE WATCH ATTM SINCE ANTECEDENTS HAVE RISEN LAST SEVERAL
DAYS DUE TO LACK OF WIDESPREAD H.EAVY RAINS.

LOOK INTO EFP PD JUST AS UNSETTLED WITH SATURDAY ONLY DRY DAY ONYL
IF HIGH OVR MI HOLDS OFF PCPN WITH DRY ERLY FLOW OTRW WET THROUGH
THE PERIOD.

.DSM...NONE

FORSTER

CENTRAL IOWA THUNDERSTORM OUTLOOK...ADDED MISSED TIMING 2ND GROUP
NATIONAL WEATHER SERVICE DES MOINES IA
1140 AM CDT TUE MAY 1 2001

...A MODERATE RISK OF SEVERE WEATHER EXISTS LATE THIS AFTERNOON AND
EVENING IN NORTHERN AND WESTERN IOWA...

THE THREAT FOR SEVERE WEATHER AND HEAVY RAIN WILL INCREASE LATER
TODAY AS A FAST MOVING AND STRONG COLD FRONT IN EASTERN SOUTH DAKOTA
MOVES INTO WESTERN AND NORTHERN IOWA.  SOUTHERLY WINDS AHEAD OF THE
FRONT WERE BRINGING INCREASED LOW LEVEL MOISTURE INTO IOWA WITH DEW
POINTS IN THE LOWER 60S.  EXPLOSIVE THUNDERSTORM DEVELOPMENT IS
EXPECTED IN NORTHWEST IOWA ALONG THE FRONT AS TEMPERATURES REACH
INTO THE MID TO UPPER 80S.  ADEQUATE WIND SHEAR AND STRONG
INSTABILITY FAVOR THE DEVELOPMENT OF SUPERCELL THUNDERSTORMS CAPABLE
OF ALL FORMS OF SEVERE WEATHER.  THE STORMS WILL ORGANIZE INTO A
THUNDERSTORM COMPLEX STILL CAPABLE OF DAMAGING WINDS ALONG WITH
HEAVY RAIN IN CENTRAL AND SOUTHWEST IOWA THIS EVENING.  LOCALIZED
FLASH FLOODING WILL BE A THREAT WITH THE INTENSE RAINFALL RATES.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ004>007-015>017-023>028-033>039-044>050-057>059-070-071-021100-
ADAIR-AUDUBON-BLACK
HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CASS-CERRO
GORDO-CRAWFORD-DALLAS-EMMET-FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-
HANCOCK-HARDIN-HUMBOLDT-KOSSUTH-MARSHALL-PALO
ALTO-POCAHONTAS-SAC-STORY-TAMA-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...ATLANTIC...BOONE...
CARROLL...DENISON...ESTHERVILLE...FORT DODGE...IOWA FALLS...
MARSHALLTOWN...MASON CITY...PERRY...WATERLOO...WAVERLY AND WEBSTER
CITY
1117 AM CDT TUE MAY 1 2001

* EVENT TIMING... 3 PM TO 9 PM.

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... LOW

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - HAIL SIZE UP TO BASEBALLS AND DAMAGING
WIND GUSTS TO 80 MPH ARE POSSIBLE.

IAZ060>062-072>075-081>086-092>097-021100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-JASPER-LUCAS-MADISON-MAHASKA-
MARION-MONROE-POLK-POWESHIEK-RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-
WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...DES
MOINES...GRINNELL...INDIANOLA...KNOXVILLE...LAMONI...NEWTON...
OSKALOOSA...OTTUMWA AND PELLA
1117 AM CDT TUE MAY 1 2001

* EVENT TIMING... 5 PM TIL MIDNIGHT

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... MODERATE

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - HAIL SIZE UP TO BASEBALLS AND DAMAGING
WIND GUSTS TO 80 MPH ARE POSSIBLE.

-------------------------------------------------------------------

THREAT KEY:
    TORNADO.......... ANY TORNADO OCCURRENCE
    DAMAGING WINDS... WINDS >= 58 MPH
    LARGE HAIL....... HAIL >= 3/4 INCH DIAMETER
    FLASH FLOODING... FLOODING CAUSED BY HEAVY RAINS WITHIN 6 HOURS
                      OF RAIN EVENT. POSES THREAT TO LIFE OR
                      PROPERTY.

THREAT CATEGORY KEY:  PROBABILITY OF THREAT OCCURRING WITHIN 25
                      MILES OF POINT WITHIN FORECAST AREA
    NONE....... NOT EXPECTED.  LESS THAN 5% ( 2% FOR TORNADOES)
    LOW........ 5-15% (2-15% FOR TORNADOES)
    MODERATE... 25-35%
    HIGH....... 45% OR GREATER

SPOTTER ACTIVATION OUTLOOK KEY:
    NOT EXPECTED
    LOW........ ACTIVATION POSSIBLE BUT NOT LIKELY
    MODERATE... POSSIBILITIES ABOUT 50-50
    HIGH....... ACTIVATION LIKELY

FOR MORE INFORMATION ON PROBABILISTIC SEVERE WEATHER OUTLOOKS...GO
TO THE STORM PREDICTION CENTER WEBSITE AT
WWW.SPC.NOAA.GOV/PRODUCTS/OUTLOOK/PROBINFO.HTML .

KULA