Severe Thunderstorm Warning 9, NWS Des Moines, IA

IAZ070>075-081>086-092>097-181825-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1019 AM CDT THU APR 18 1996

HAZARD...SEVERE WEATHER IS NOT ANTICIPATED OVER MOST OF CENTRAL
IOWA...HOWEVER ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE OVER
SOUTHEAST SECTIONS. IF SEVERE THUNDERSTORMS DO DEVELOP...THE MAIN
THREAT WOULD BE DAMAGING WIND AND MOSTLY LIKELY SMALL HAIL.

AREA OF CONCERN...SOUTH CENTRAL IOWA...MAINLY EAST OF A
NEWTON...CORYDON LINE...INCLUDING OSKALOOSA AND OTTUMWA.
THE AREA OF CONCERN IS EAST OF DES MOINES AND AMES.

TIMING DETAILS...SCATTERED LIGHT SHOWERS DOT PARTS OF NORTHWEST AND
NORTH CENTRAL IOWA AS OF 10AM.  IF SEVERE WEATHER DOES DEVELOP...IT
WILL NOT BE UNTIL AFTER 2 PM. THE RAPID MOVEMENT OF THE STORMS WOULD
KEEP IT FROM LASTING PAST 6 PM.

METEOROLOGICAL COMMENTS...LOW PRESSURE WAS LOCATED NEAR OMAHA WITH A
FRONTAL BOUNDRY EXTENDING FROM NORTH CENTRAL IOWA TO THE SW TIP. DEW
POINTS ARE GENERALLY IN THE 40S EXCEPT FOR A FEW LOWER 50S IN THE
FAR SOUTHWEST. POSITIVE FACTORS FOR THIS EVENT INCLUDE A STRONG
LOW-LEVEL JET PASSING OVER THE EASTERN HALF OF IOWA. IT IS
LIKELY THAT STRONG HEATING WILL OCCUR THIS AFTERNOON COINCIDING WITH
A FRONTAL PASSAGE AND POTENT UPPER DYNAMICS.  ON THE NEGATIVE
SIDE/LIMITING FACTORS...WE SEE VERY SHALLOW MOISTURE AHEAD OF THE
APPROACHING COLD FRONT. THERE IS A NARROW PUSH OF 50 DEGREE DEWPOINTS
IMMEDIATELY AHEAD OF THE FRONT. THE LOW LEVEL JET WILL CONTINUE TO
PUSH THE 50 DEGREE DEWPOINTS INTO THE STATE JUST AHEAD OF THIS
FRONT. AS THE LOW PUSHES NORTHEAST...WINDS COULD BECOME MORE
SOUTHEAST WITH SOME LIMITED POOLING OF MOISTURE IN THE VICINITY OF
SOUTH CENTRAL IOWA BY AFTERNOON. ALSO...A SIGNIFICANT CAP/MID-LEVEL
TEMPERATURE INVERSION OVER THE STATE WILL KEEP THINGS QUIET WELL INTO
THE AFTERNOON.

PRECAUTIONS...NO SPECIAL ACTIONS AT THIS TIME. EMERGENCY MANAGERS
AND THE MEDIA SHOULD LOOK FOR FURTHER CENTRAL IOWA THUNDERSTORM
OUTLOOKS AS THIS SITUATION DEVELOPS. THE NEXT OUTLOOK WILL BE
ISSUED AROUND NOON.

FELDT/KULA

IAZALL-182005-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1202 PM CDT THU APR 18 1996

HAZARD...
ISOLATED SEVERE THUNDERSTORMS WITH LARGE HAIL...MOST LIKELY AROUND 1
INCH IN DIAMETER...WIND GUSTS IN EXCESS OF 60 MPH AND FREQUENT CLOUD
TO GROUND LIGHTNING.

AREA OF CONCERN...
THE EASTERN HALF OF IOWA...MAINLY EAST OF INTERSTATE 35...OR EAST OF
A MASON CITY TO DES MOINES TO LAMONI LINE. THE GREATEST THREAT WILL
BE EAST OF A WATERLOO TO CENTERVILLE LINE AFTER 2 PM.

TIMING DETAILS...
THROUGH 2 PM...MORE GENERAL THUNDERSTORM ACTIVITY IS EXPECTED WITH
BRIEF HEAVY DOWNPOURS OF UP TO ONE-HALF INCH AND ISOLATED HAIL UP TO
ONE-HALF INCH IN DIAMETER. AFTER 2 PM...IN THE GREATER AREA OF
CONCERN...HAIL SIZE MAY LIKELY BE LARGER AND THE POTENTIAL FOR
HIGHER WIND GUSTS WILL BE REALIZED.

METEOROLOGICAL COMMENTS...
AT 1130 AM...LOW PRESSURE WAS LOCATED OVER NORTH CENTRAL
MINNESOTA AND ANOTHER NEAR ATLANTIC, IOWA. A COLD FRONT CONNECTED
THE AREAS OF LOW PRESSURE...AND CONTINUED INTO EASTERN KANSAS.
SOUTHERLY FLOW CONTINUED TO BRING SHALLOW LOW-LEVEL MOISTURE THROUGH
MISSOURI AND WAS JUST BEGINNING TO ENTER SOUTHERN IOWA. DEW POINTS
IN THIS AIR MASS WERE IN THE LOW TO MID 50S. THE MORE GENERAL
THUNDERSTORM ACTIVITY DEVELOPING IN CENTRAL AND NORTHEAST IOWA WAS
ORIGINATING AT AROUND 5000 FT AND WAS DUE MAINLY TO THE UPPER
LEVEL CIRCULATION CENTER ENTERING SOUTHEAST SOUTH DAKOTA. THE WIND
SHEAR PROFILE OVER THE EASTERN HALF OF IOWA...PARTICULARLY THE
EASTERN ONE-QUARTER OF THE STATE WAS FAVORABLE TO SUSTAIN UPDRAFTS
NECESSARY FOR SEVERE THUNDERSTORMS.  THE KEY ITEM TO WATCH FOR THIS
AFTERNOON WILL BE THE MAXIMUM HEATING THAT WILL OCCUR AFTER 2 PM AS
TEMPERATURES WARM TO AROUND 80 DEGREES AND MOISTURE BEGINS NOSING
INTO THE EASTERN HALF OF THE STATE. THE ATMOSPHERE WILL THEN HAVE
THE BEST POTENTIAL TO EQUALIZE THE UNSTABLE CONDITIONS AND PRODUCE
SEVERE THUNDERSTORMS. THE COLD FRONT WILL BE NEAR THE I-35 CORRIDOR
BY 2 PM...SO THE THREAT FOR THUNDERSTORMS WILL BE MINIMAL OVER THE
WESTERN HALF OF THE STATE.

PRECAUTIONS...
EMERGENCY MANAGERS...NWS SPOTTER GROUPS AND THE MEDIA SHOULD
MAINTAIN AWARENESS TO NWS SHORT TERM FORECASTS AND bADDITIONAL
CENTRAL IOWA THUNDERSTORM OUTLOOKS TO BE ISSUED THIS AFTERNOON.