Severe Thunderstorm Warning 99, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
330 PM CDT WED MAY 9 2001

MODELS STILL OFFERING DIFFERENT SOLUTIONS AS TO CONVECTIVE
INITIATION THIS AFTERNOON AND EVENING. AVN STILL THE MOST BEARISH ON
QPF...ESPECIALLY OVER THE WESTERN CWA WHILE NGM AND META FAIRLY
SIMILAR. TOUGH CALL AS TO AREAL COVERAGE OF PRECIPITATION TONIGHT.

NARROW BAND OF LOWER MID 60 DEW PT AIR WORKING NORTH INTO THE MO
RIVER VALLEY. A FEW STATIONS IN NW IA NOW MIXING OUT WITH TDS
DROPPING INTO THE UPPER 40S. LOOKS LIKE WARM FRONT SET UP ALONG THE
NORTH BORDER OF THE CWA. BEST LOW LEVEL THETA-E CONVERGENCE HAS BEEN
OVER E NEBRASKA INTO SE SD WHILE PRESSURE FALL MAX NOW EDGING E INTO
SW MN ALONG AND JUST NORTH OF WARM FRONT. AIRMASS STILL CAPPED WITH
CINS STRONGER OVER S MN. CURRENT THINKING IS THAT LOW LEVEL
CONVERGENCE ALONG WARM FRONT WILL NOT BE ENOUGH FOR THUNDERSTORM
DEVELOPMENT OVER NE PORTION OF CWA. BEST AREA FOR INITIATION APPEARS
TO BE ALONG BAND OF GREATEST INSTABILITY ALONG BAND OF CONVERGENCE
ASSOCIATED WITH SURFACE TROUGH OVER FAR NW IA INTO EXTREME SW MN.
THE STORMS MOVING INTO THE NW CWA WILL BE QUITE HIGH BASED WITH HAIL
AND WIND BY FAR THE GREATER THREAT. AT LEAST A SCATTERED LINE OF
CONVECTION SHOULD SAG SE WITH BETTER TENDENCIES FOR HIGHER QPFS TO
OUR NORTH AND PERHAPS TO OUR WEST AND SW LATER TONIGHT AS 50 KT LOW
LEVEL JET INCREASES OVER KS AND PROVIDES ADDED CONVERGENCE OVER
NEBRASKA.

THE MAIN COLD FRONT THEN DROPS INTO THE CWA THURSDAY MORNING WITH
ATMOSPHERE PRIMED OVER THE CENTRAL AND SOUTH FOR STRONG CONVECTION.
STEEP MID LEVEL LAPSE RATES AND PERHAPS A LITTLE BETTER LOW LEVEL
MOISTURE POOLING SHOULD SUPPORT LIKELY POPS OVER MOST OF THE CWA
DURING THE DAY. WILL DIMINISH POPS IN THE NORTH DURING THE EVENING.

FRONT SHOULD BE FAR ENOUGH TO THE SOUTH THAT I WILL ELIMINATE
MORNING POPS IN THE SOUTH ON FRIDAY.

.DSM...NONE

JAW

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
330 PM CDT WED MAY 9 2001

...SEVERE WEATHER THREAT WILL INCREASE AFTER 5 PM IN NORTHWEST
IOWA...

A TROUGH OF LOW PRESSURE FROM JUST EAST OF SIOUX FALLS AND SIOUX
CITY INTO EASTERN NEBRASKA IS SHOWING SIGNS OF TOWERING CUMULUS
DEVELOPMENT THAT MAY BUILD INTO THUNDERSTORMS BETWEEN 4 AND 6 PM.
THESE STORMS WILL ENCOUNTER INCREASING MOISTURE IN NORTHWEST IOWA AS
DEW POINTS INCREASE INTO THE LOWER 60S.  STRONG INSTABILITY AND WIND
SHEAR EXIST WHICH FAVOR THE FORMATION OF SUPERCELL THUNDERSTORMS
CAPABLE OF LARGE HAIL...DAMAGING WINDS AND ISOLATED TORNADOES.  THE
TORNADO THREAT IS GREATEST NEAR A WARM FRONT ALONG THE IOWA
MINNESOTA BORDER.  DAMAGING WINDS WILL BECOME THE MAIN THREAT LATE
THIS EVENING AND OVERNIGHT IN THE REST OF CENTRAL AND SOUTHWEST IOWA
AS THUNDERSTORMS BUILD SOUTHWEST INTO INCREASING SOUTHERLY WIND FLOW.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ004>007-015>017-023>025-100420-
CERRO GORDO-EMMET-HANCOCK-HUMBOLDT-KOSSUTH-PALO
ALTO-POCAHONTAS-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...ESTHERVILLE AND MASON CITY
330 PM CDT WED MAY 9 2001

* EVENT TIMING... 5 PM TO 10 PM.

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE.

* MISCELLANEOUS INFORMATION - THUNDERSTORMS WILL LIKELY BEGIN AS
  SUPERCELL THUNDERSTORMS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND
  TORNADOES...EVOLVING INTO A LINEAR STORM MODE WITH DAMAGING WINDS.

IAZ026>028-033>039-044>050-101100-
BLACK
HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CRAWFORD-FRANKLIN-GREENE-
GRUNDY-HAMILTON-HARDIN-MARSHALL-SAC-STORY-TAMA-WEBSTER-
INCLUDING THE CITIES OF...AMES...BOONE...CARROLL...DENISON...FORT
DODGE...IOWA FALLS...MARSHALLTOWN...WATERLOO...WAVERLY AND WEBSTER
CITY
330 PM CDT WED MAY 9 2001

* EVENT TIMING... 7 PM TO 2 AM.

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE

IAZ057>062-070>075-081>086-092>097-101100-
ADAIR-ADAMS-APPANOOSE-AUDUBON-CASS-CLARKE-DALLAS-DAVIS-DECATUR-
GUTHRIE-JASPER-LUCAS-MADISON-MAHASKA-MARION-MONROE-POLK-POWESHIEK-
RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-
INCLUDING THE CITIES OF...ATLANTIC...CENTERVILLE...CHARITON...
CRESTON...DES MOINES...GRINNELL...INDIANOLA...KNOXVILLE...LAMONI...
NEWTON...OSKALOOSA...OTTUMWA...PELLA AND PERRY
330 PM CDT WED MAY 9 2001

* EVENT TIMING... 9 PM TO 5 AM.

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE.

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

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 PREDIxCTION CENTER WEBSITE AT
WWW.SPC.NOAA.GOV/PRODUCTS/OUTLOOK/PROBINFO.HTML .

KULA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
746 PM CDT WED MAY 09 2001

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

0733 PM    LAURENS                   IA   1 INCH HAIL
05/09/01   POCAHONTAS                     REPORTED BY LAW
                                          ENFORCEMENT OFFICIAL.

0735 PM    2 NE LAURENS              IA   1 INCH HAIL
05/09/01   POCAHONTAS                     REPORTED BY STORM
                                          SPOTTER.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
824 PM CDT WED MAY 09 2001

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

0754 PM    5 SW CURLEW               IA   1 INCH HAIL
05/09/01   PALOALTO                       REPORTED BY MEDIA.

0757 PM    HAVELOCK                  IA   1 INCH HAIL
05/09/01   POCAHONTAS                     REPORTED BY STORM
        D                                  SPOTTER.

0800 PM    HAVELOCK                  IA   1.75 INCH HAIL
05/09/01   POCAHONTAS                     REPORTED BY STORM
                                          SPOTTER.