Severe Thunderstorm Warning 156, NWS Des Moines, IA

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-310130-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1032 AM CDT SAT MAY 30 1998

HAZARD--THUNDERSTORMS WITH LARGE HAIL...DAMAGING WINDS...VERY HEAVY
RAINFALL AND ISOLATED TORNADOES.

TIMING AND AREA OF CONCERN--THE PRIMARY THREAT FOR SEVERE WEATHER WILL
BE ALONG AND NORTH OF INTERSTATE 80 FROM NOON THROUGH EARLY EVENING.
A LESSER THREAT FOR SEVERE WEATHER WILL OCCUR SOUTH OF INTERSTATE 80
SOUTH TO THE IOWA/MISSOURI BORDER.

METEOROLOGICAL COMMENTS--A VERY UNSTABLE AIRMASS IS IN PLACE OVER IOWA
TODAY.  IN ADDITION...THERE IS A RICH SUPPLY OF MOISTURE ORIGINATING
FROM THE PACIFIC...KNOWN AS THE PINEAPPLE CONNECTION.  AS A SOUTHERLY
WIND INCREASES ACROSS THE STATE THEY WILL INTERACT WITH A NEARLY
STATIONARY FRONT EXTENDING ACROSS THE STATE FROM A DAVENPORT TO SIOUX
FALLS LINE.

LIFTED INDICES OF -8 TO -12 ARE FORECAST OVER THE STATE WITH CAPES
INCREASING TO ALMOST 5000 J/KG AND HELICITY VALUES IN THE 400 TO 500
RANGE.

PRECAUTIONS--EMERGENCY MANAGERS FOR COUNTIES ALONG AND NORTH OF
INTERSTATE 80 SHOULD PREPARE THEIR SPOTTER NETWORKS FOR DEPLOYMENT
AROUND OR JUST AFTER THE NOON HOUR.  EMERGENCY MANAGERS FOR COUNTIES
TO THE SOUTH OF INTERSTATE 80 SHOULD ALERT THEIR SPOTTERS FOR POSSIBLE
DEPLOYMENT LATER THIS AFTERNOON OR EVENING.

FAB