Severe Thunderstorm Warning 158, NWS Des Moines, IA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
918 PM CDT WED MAY 16 2001

MAIN FCST CHALLENGE THIS EVENING WILL BE NOT IF BUT HOW MUCH
CONVECTION DEVELOPS IN THE SOUTHERN QUARTER OF THE CWA...HOW FAR
NORTH IT GETS...AND LACK OF CONVECTION IN NORTH.

EVENING RAOB ANALYSIS AT 850 HPA INDICATING QUASI-STATIONARY
BOUNDARY AROUND IA/MO BORDER.  OVER NRN OHIO/ILLINOIS RIVER
VALLEY...ERN EXTENT OF FRONT CONTINUES TO SLOWLY PUSH EAST AS COLD
FRONT.  12 TO 14 DEG C DEWPOINTS FM ARKLATEX REGION...THRU CEN MO
INTO OHIO VALLEY.  A BIT OF LLJ DEVELOPING IN OK REGION AT 00Z...AND
WOULD EXPECT THIS TO STRENGTHEN JUST A BIT.  FARTHER NORTH...SMALL
SCALE RIDGE OVER MN CONT TO PULL EAST.  FALLS OVR PLNS THIS EVENING
COMBINED WITH STRENGTH OF HIGH CAUSED SOME GUSTY NORTH WNDS OVR NRN
CWA EARLIER TONIGHT...THESE HAVE NOW DIMINISHED.  FINALLY STRONG UPR
JET OVR NRN PLNS/ROCKIES CONTINUES TO PUNCH INTO DAKOTAS.  ASSOC 80H
AND SFC FRONT NOW WELL INTO DAKOTAS.  ALTHOUGH LITTLE MOISTURE
AVAILABLE FOR CONVECTION OVER NRN CWA AND POINTS N AND WEST FOR THIS
SYSTEM TO WORK WITH (THUS HAVE LOWERED POPS IN NORTH FOR
TONIGHT)...STILL MAY BE ENUF INFLUENCE FOR FLO TO BACK AND INCREASE
SOUTH OF QS FRONT.  IF THIS IS INDEED THE CASE...AS MSAS AND
CONCEPTIAL MODELS INDICATE...WOULD EXPECT SOME POTENTIAL FOR HEAVY
RAIN IN SRN CWA.  HPC HAS NOW ISSUED ISOLD EXCESS RAINFALL ALONG
IA/MO BORDER.  WOULD EXPECT SOME TRAINING...BUT MAINLY SLOW
MOVEMENT.  IF LLJ DOES INDEED PICK UP...MOST INCR IN ACTIVITY WILL
BE AFT MIDNIGHT.  THUS HAVE HIT CONVECTION AND HEAVY RAIN POTENTIAL
HARDER IN SRN ZONES.  A GROUP ALONG I-80 SHOULD SUFFICE FOR A BUFFER
GIVEN SHARP MOISTURE GRADIENT.

BROUGHT OVRNIGHT LOWS UP A TAD FOR STILL WARM TEMPS AT 02Z AND
CLOUDS.

ZFP OUT BY 930 PM.

.DSM...NONE

SEARCY

CENTRAL IOWA THUNDERSTORM OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
940 PM CDT WED MAY 16 2001

A NEARLY STATIONARY FRONT WILL REMAIN ALONG THE IOWA...MISSOURI
BORDER OVERNIGHT WHILE ABUNDANT MOISTURE IS LIFTED UP AND OVER THE
FRONT BY AN INCREASINGLY STRONG SOUTHERLY LOW LEVEL JET.  AT THIS
TIME...THE LOW LEVEL JET IS NOT EXPECTED TO INCREASE BEYOND A
MODERATE AMOUNT...THUS WIDESPREAD SEVERE THUNDERSTORM ACTIVITY IS
NOT ANTICIPATED OVER SOUTHERN IOWA.  HOWEVER...THERE IS ENOUGH
INSTABILITY FOR THUNDERSTORMS TO DEVELOP...AS HAS ALREADY HAPPENED.
LOOK FOR THUNDERSTORMS TO CONTINUE TO DEVELOP OVER SOUTHWEST IOWA
AND NORTHWEST MISSOURI...AND SPREAD TO THE EAST AFTER MIDNIGHT.
THERE IS THE POTENTIAL FOR THUNDERSTORMS TO BE BOTH SLOW MOVING AND
TRAIN OVER LOCATIONS WHICH MAY HAVE ALREADY SEEN
THUNDERSTORMS...THUS THERE FLASH FLOODING POTENTIAL IS HIGHER THAN
NORMAL OVER SOUTHERN PARTS OF THE STATE.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ081>086-092>097-171100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MONROE-RINGGOLD-TAYLOR-
UNION-WAPELLO-WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...LAMONI
AND OTTUMWA
934 PM CDT WED MAY 16 2001

* EVENT TIMING... THROUGH 6 AM.

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE FOR HAIL...RAINFALL...OR
FLOODING REPORTS.

IAZ057>062-070>075-171100-
ADAIR-AUDUBON-CASS-DALLAS-GUTHRIE-JASPER-MADISON-MAHASKA-MARION-POLK-
POWESHIEK-WARREN-
INCLUDING THE CITIES OF...ATLANTIC...DES MOINES...GRINNELL...
INDIANOLA...KNOXVILLE...NEWTON...OSKALOOSA...PELLA AND PERRY
934 PM CDT WED MAY 16 2001

* EVENT TIMING... MAINLY AFTER MIDNIGHT THROUGH 6 AM.

* THREAT CATEGORIES...
     TORNADO.......... NONE.
     DAMAGING WINDS... NONE.
     LARGE HAIL....... LOW.
     FLASH FLOODING... LOW.

* SPOTTER ACTIVATION OUTLOOK... LOW.

IAZ004>007-015>017-023>028-033>039-044>050-171100-
BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CERRO
GORDO-CRAWFORD-EMMET-FRANKLIN-GREENE-GRUNDY-HAMILTON-HANCOCK-HARDIN-
HUMBOLDT-KOSSUTH-MARSHALL-PALO
ALTO-POCAHONTAS-SAC-STORY-TAMA-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...BOONE...CARROLL...
DENISON...ESTHERVILLE...FORT DODGE...IOWA FALLS...MARSHALLTOWN...
MASON CITY...WATERLOO...WAVERLY AND WEBSTER CITY
934 PM CDT WED MAY 16 2001

* EVENT TIMING... AFTER 3 AM.

* THREAT CATEGORIES...
     TORNADO.......... NONE.
     DAMAGING WINDS... NONE.
     LARGE HAIL....... NONE.
     FLASH FLOODING... NONE.

* SPOTTER ACTIVATION OUTLOOK... NOT EXPECTED.

SEARCY

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

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 .