Severe Thunderstorm Warning 55, NWS Des Moines, IA

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-211200-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
935 PM CDT FRI JUN 20 1997

HAZARD -- NUMEROUS THUNDERSTORMS WITH ISOLATED SEVERE THUNDERSTORMS
CAPABLE OF PRODUCING WIND GUSTS IN EXCESS OF 70 MPH...HAIL UP TO TWO
INCHES IN DIAMETER...HEAVY RAIN AND ISOLATED TORNADOES.

TIMING AND AREA OF CONCERN -- FROM 1100 PM UNTIL 300 AM OVER THE WEST
PART OF THE FORECAST AREA AND SOUTH OF U.S. HIGHWAY 20...AFTER 100 AM
EAST OF INTERSTATE 35...SOUTH OF U.S. HIGHWAY 20.  THE THREAT WILL END
OVER WESTERN IOWA BY 300 AM AND OVER THE EAST BY 600 AM.

METEOROLOGICAL COMMENTS -- A BOUNDARY LEFT FROM CONVECTION LAST NIGHT
EXTENDED FROM SOUTHERN NEBRASKA EAST THROUGH CENTRAL INTO EAST CENTRAL
IOWA.  IN ADDITION A COLD FRONT EXTENDED FROM THE NORTHEAST CORNER OF
THE STATE...SOUTHWEST INTO THE WEST CENTRAL COUNTIES NEAR ONAWA.  THE
AIRMASS OVER IOWA IS VERY UNSTABLE WITH LIFTED INDICES IN THE -10 TO
-15 DEGREE C RANGE.  IN ADDITION...CAPE VALUES WERE ON THE ORDER OF
5000 TO 6000 J/KG.  THE LATEST SURFACE ANALYSIS SHOWS DEW POINTS
TEMPERATURES OF AT LEAST 75 DEGREES OVER THE SOUTHEAST HALF OF THE
STATE.  A FEW LOCATION WERE AROUND 80.  IN ADDITION TO THE
MOISTURE...THE LOW LEVEL JET WAS INCREASING THIS EVENING.  SPEEDS WERE
IN THE 35 TO 40 MPH RANGE BY MID EVENING.  INTENSE THUNDERSTORMS WERE
FORMING IN TWO AREAS THIS EVENING.  ONE WAS OVER WESTERN
NEBRASKA...THE SECOND OVER SOUTHEAST AND EAST CENTRAL NEBRASKA.  THE
TWO AREAS ARE LIKELY TO COMBINE AND ADVANCE EAST LATER TONIGHT.  THE
GREATEST THREAT OF SEVERE WEATHER WILL BE OVER THE WEST HALF OF
IOWA...WITH THE THREAT OVER THE EAST BEING MORE FROM HEAVY RAIN.
SPOTTY RAINFALL OF 3 TO 5 INCHES ARE POSSIBLE...ESPECIALLY SOUTH OF A
SIOUX CITY TO OTTUMWA LINE.

PRECAUTIONS -- EMERGENCY MANAGERS SHOULD REMAIN ALERT AS A WATCH IS
LIKELY WITHIN THE NEXT HOUR.  SPOTTER ACTIVATION MAY BE NEEDED THIS
EVENING.  STAY TUNED TO LOCAL TV...CABLE TV OR NOAA WEATHER RADIO FOR
THE LATEST SHORT-TERM FORECAST AND SEVERE WEATHER OUTLOOK.