Severe Thunderstorm Warning 118, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
330 PM CDT THU MAY 10 2001

IN THE SHORT TERM...EAST TO WEST OUTFLOW BOUNDARY ALONG HIGHWAY 20
NOW BEGINNING TO LIGHT UP WHILE ADDITIONAL DEVELOPMENT EXPECTED
FURTHER WEST ALONG COLD FRONT. ATMOSPHERE OVER SOUTHWEST IOWA SHOULD
HAVE WARMED ENOUGH TO ELIMINATE WEAK CAP SHOWN ON 18Z OMA SOUNDING.
LCL HAVE LOWERED CONSIDERABLY FROM YESTERDAY...THROUGH THEY STILL
REMAIN FAIRLY HIGH AT AROUND 5.5K FT. SURFACE WINDS IN WARM SECTOR
HAVE VEERED SO IT APPEARS MAIN THREAT FROM STORMS WILL CONTINUE TO
BE HAIL/WIND. SOME ROTATING STORMS MAY BE A LITTLE MORE LIKELY ALONG
THE OUTFLOW BOUNDARY TO THE NORTH OR NEAR OUTFLOW/FRONTAL
INTERSECTION. AS SHORT WAVE TROUGH MOVES THROUGH CWA THIS EVENING...
CONVECTION SHOULD BE SHUNTED OFF INTO N MO AND SE IA BY OR AROUND
MIDNIGHT.

MOST OF THE FRONTAL CONVECTION SHOULD BE S OF THE CWA FRIDAY SO WILL
MAINTAIN A DRY FORECAST.

MODELS SHOWING SOME POSSIBILITY OF WARM AIR ADVECTION SHOWERS/STORMS
SATURDAY. WILL HOLD OFF ON ADDITION OF POPS ACROSS THE NORTH FOR NOW
AND LET ANOTHER MODEL RUN OR TWO PASS TO GET A BETTER HANDLE ON
THAT. HAVE LEFT EXTENDEDQ UNCHANGED.

MOS TEMPS LOOK PRETTY GOOD AND ARE IN LINE WITH CURRENT FORECASTS.

.DSM...NONE

JAW

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1245 PM CDT THU MAY 10 2001

...MORE SEVERE THUNDERSTORM DEVELOPMENT LIKELY AFTER 3 PM IN CENTRAL
AND WEST CENTRAL IOWA...

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.  MONITOR SHORT
TERM FORECASTS FOR ADDITIONAL FORECAST INFORMATION AS THESE
THUNDERSTORMS EVOLVE AND SPREAD SOUTHEAST THROUGH THE STATE.

SCATTERED MODERATE THUNDERSTORMS IN NORTH CENTRAL IOWA HAVE BEEN
WEAKENING OVER THE LAST ONE HOUR.  HOWEVER...A STRENGTHENING FRONTAL
BOUNDARY FROM NEAR WATERLOO THROUGH FORT DODGE TO BETWEEN SIOUX
CITY AND OMAHA...WILL BE THE FOCUS FOR ADDITIONAL DEVELOPMENT OF
THUNDERSTORMS AROUND MID AFTERNOON INTO THE EVENING HOURS.
CONVERGENCE OF MOISTURE WAS INCREASING OVER WESTERN IOWA AND EASTERN
NEBRASKA NEAR THIS FRONT...WITH STRONG SURFACE HEATING TAKING PLACE
SOUTH OF THE FRONT.  AN UPPER LEVEL DISTURBANCE AND JET STREAM OF
WINDS OVER NEBRASKA AND SOUTH DAKOTA WILL AID IN THUNDERSTORM
DEVELOPMENT AS WELL.  WIND AND INSTABILITY PARAMETERS INDICATE THAT
A FEW SUPERCELL THUNDERSTORMS ARE POSSIBLE...EVOLVING INTO A LINE OF
STORMS BY THIS EVENING.

IAZ004>007-015>017-023>026-033>037-044>048-111100-
BOONE-CALHOUN-CARROLL-CERRO
GORDO-CRAWFORD-EMMET-FRANKLIN-GREENE-HAMILTON-HANCOCK-HARDIN-
HUMBOLDT-KOSSUTH-PALO
ALTO-POCAHONTAS-SAC-STORY-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...BOONE...CARROLL...
DENISON...ESTHERVILLE...FORT DODGE...IOWA FALLS...MASON CITY AND
WEBSTER CITY
1245 PM CDT THU MAY 10 2001

* EVENT TIMING... NOW THROUGH 6 PM.

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE

IAZ027-028-038-039-049-050-057>062-070>075-111100-
ADAIR-AUDUBON-BLACK
HAWK-BREMER-BUTLER-CASS-DALLAS-GRUNDY-GUTHRIE-JASPER-MADISON-MAHASKA-
MARION-MARSHALL-POLK-POWESHIEK-TAMA-WARREN-
INCLUDING THE CITIES OF...ATLANTIC...DES MOINES...GRINNELL...
INDIANOLA...KNOXVILLE...MARSHALLTOWN...NEWTON...OSKALOOSA...PELLA...
PERRY...WATERLOO AND WAVERLY
1245 PM CDT THU MAY 10 2001

* EVENT TIMING... 3 PM TO 8 PM.

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

* SPOTTER ACTIVATION OUTLOOK...  MODERATE

IAZ081>086-092>097-111100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MONROE-RINGGOLD-TAYLOR-
UNION-WAPELLO-WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...LAMONI
AND OTTUMWA
1245 PM CDT THU MAY 10 2001

* EVENT TIMING... 3 PM TO MIDNIGHT

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - THE RISK OF FLASH FLOODING WILL ALSO
INCREASE THIS EVENING AS POTENTIAL THUNDERSTORM TRAINING
OCCURS OVER ALREADY SATURATED GROUND.

KULA

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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 .

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