Damaging Winds in Iowa, April 11, 2001

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