Severe Thunderstorm Warning 47, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
345 AM CDT WED APR 11 2001

MAIN FORECAST CONCERNS WILL FLOOD POTENTIAL THIS MORNING WITH SOME
SOME SEVERE WX AND THEN INCREASING SEVERE WEATHER THREAT THIS
AFTERNOON AS DRY LINE CUTS ACROSS THE CWA. LOW LEVEL JET THIS
MORNING AND THE WARM FRONT ACROSS CENTRAL IOWA POSE THE THREAT OF
SOME FLOODING ACROSS CENTRAL SECTIONS OF THE FORECAST AREA. MODEL
QPF SUPPORTS THIS AS WELL. FIRST ROUND OF PRECIPITATION THIS MORNING
AS AN MCS OVER EASTERN NEBRASKA TAKES SHAPE AND ROLLS EAST ACROSS
CENTRAL IOWA. INVERTED TROUGH RUNNING NORTHEAST FROM LOW INTO
NORTHWEST IOWA ...WARM FRONT DRAPED ACROSS CENTRAL IOWA IN VICINITY
OF LINE OF TSRA FROM NEAR KSUX TO JUST NORTH OF MOLINE....WILL LIFT
NORTH LATER THIS MORNING...TAKING FLOOD POTENTIAL NORTH OF THE AREA.
THEN SECOND ROUND OF PRECIPITATION ASSOCIATED WITH DRY LINE THIS
AFTERNOON...WITH EMPHASIS ON SURFACE BASED CONVECTION AND THE
MODERATE THREAT OF SUPERCELL THUNDERSTORMS THIS AFTERNOON. LOW LEVEL
SHEAR AND INSTABILITY SUPPORT THIS THREAT. MODELS IN GOOD AGREEMENT
IN HAVING THE DRY LINE PUSHING INTO EASTERN SECTIONS OF IOWA BY
AROUND 00Z...WITH THE SEVERE WEATHER THREAT ALMOST OUT OF THE AREA.
DRY SLOT WILL HAVE PUSHED BEST MOISTURE TO THE EAST SO FLOOD THREAT
WILL BE OVER BY AFTERNOON WESTERN HALF OF THE FORECAST AREA...THEN
LATE AFTERNOON EASTERN HALF.

SECONDARY CONCERN IS SPEED OF THE DRYLINE. MESO-ETA AT 300 AM IS A
LITTLE SLOWER THAN CURRENT OBSERVATIONS. THE AVN HAS BEEN THE
QUICKEST ON BRINGING THIS FEATURE THROUGH. IF THE DRY LINE COMES
THROUGH EARLIER INSTABILITY WILL NOT BE AS GREAT PER MODEL FORECAST
LAPSE RATES. SO SEVERE WX THREAT WILL BE REDUCED. WILL HAVE TO
MONITOR THIS TREND...AS IT COULD BE A FACTOR LATER THIS MORNING AND
INTO THE EARLY AFTERNOON HOURS.

TONIGHT INTO THURSDAY...WEATHER CONCERNS WILL SHIFT TO STRONG WINDS
SOUTHWEST OF THE LOW PRESSURE SYSTEM. MAY NEED TO ISSUE A WIND
ADVISORY FOR LATE AFTERNOON AND OVERNIGHT TIME FRAME...THIS WILL
POSSIBLE BE ISSUED LATER THIS AFTERNOON. WINDY CONDITIONS
WILL CONTINUE THE FIRST HALF OF THE DAY THURSDAY BEFORE
DECREASING.

.DSM...FLOOD WATCH CONTINUES FOR ENTIRE FA THRU THIS AFTERNOON.

TC

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1014 PM CDT TUE APR 10 2001

A STRONG LOW PRESSURE AREA OVER SOUTHEAST COLORADO TONIGHT SHOULD
REACH NORTHWEST IOWA BY WEDNESDAY AFTERNOON.  A WARM FRONT AHEAD OF
THE LOW IS EXPECTED TO PUSH NORTHWARD ACROSS IOWA OVERNIGHT WITH
HEAVY RAIN...LARGE HAIL AND DAMAGING WIND PRIMARY THREATS.  BY
WEDNESDAY AFTERNOON...A DRY LINE OVER TEXAS MAY REACH IOWA DURING
PEAK HEATING OF THE AFTERNOON.  HIGH AMOUNTS OF INSTABILITY AND
SHEAR WILL BE IN PLACE...SO ALL FORMS OF SEVERE WEATHER...INCLUDING
TORNADOES...WILL BE POSSIBLE.

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-111100-
ADAIR-ADAMS-APPANOOSE-AUDUBON-BLACK
HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CASS-CERRO
GORDO-CLARKE-CRAWFORD-DALLAS-DAVIS-DECATUR-EMMET-FRANKLIN-GREENE-
GRUNDY-GUTHRIE-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-JASPER-KOSSUTH-LUCAS-
MADISON-MAHASKA-MARION-MARSHALL-MONROE-PALO
ALTO-POCAHONTAS-POLK-POWESHIEK-RINGGOLD-SAC-STORY-TAMA-TAYLOR-UNION-
WAPELLO-WARREN-WAYNE-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...ATLANTIC...BOONE...
CARROLL...CENTERVILLE...CHARITON...CRESTON...DENISON...DES MOINES...
ESTHERVILLE...FORT DODGE...GRINNELL...INDIANOLA...IOWA FALLS...
KNOXVILLE...LAMONI...MARSHALLTOWN...MASON CITY...NEWTON...
OSKALOOSA...OTTUMWA...PELLA...PERRY...WATERLOO...WAVERLY AND WEBSTER
CITY
1004 PM CDT TUE APR 10 2001

* EVENT TIMING... THUNDERSTORMS WILL BE POSSIBLE ANYTIME TONIGHT AND
  WEDNESDAY

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

* SPOTTER ACTIVATION OUTLOOK... LOW TONIGHT...MODERATE WEDNESDAY

* THIS IS A POTENTIALLY DANGEROUS SEVERE WEATHER SITUATION...
  ESPECIALLY FOR WEDNESDAY AFTERNOON.  MONITOR LATER NATIONAL
  WEATHER SERVICE STATEMENTS AND FORECASTS FOR UPDATED INFORMATION
  DURING THIS EVENT.  SEVERE THUNDERSTORM OR TORNADO WATCHES WILL
  LIKELY BE ISSUED LATER TONIGHT OR WEDNESDAY.

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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 .

SMALL