Severe Thunderstorm Warning 18, NWS Des Moines, IA

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-072100-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
138 PM CDT WED MAY 7 1997

HAZARD--A SQUALL LINE MOVING EAST-SOUTHEAST. THE STRONGEST STORMS MAY
CONTAIN HAIL IN EXCESS OF ONE INCH AND WINDS OF UP TO 70 MPH.

AREA OF CONCERN--ALONG AND SOUTH OF HIGHWAY 30 WITH WEAKER STORMS OVER
NORTHERN IOWA.

TIMING DETAILS--A LINE OF STRONG TO SEVERE THUNDERSTORMS IS EXPECTED
TO DEVELOP WEST OF OMAHA AND MOVE EAST AT 35 MPH.  THE STORMS SHOULD
REACH DENISON AROUND 400 PM...JEFFERSON AND ATLANTIC NEAR 500 PM AND
THE AMES...DES MOINES AND SOUTHERN IOWA AREAS AFTER 600 PM.

METEOROLOGICAL COMMENTS--A COMPLEX OF WEAK TO MODERATE THUNDERSTORMS
OVER THE EASTERN HALF OF IOWA WILL CONTINUE TO MOVE EAST-SOUTHEAST AT
35 MPH. NO SEVERE WEATHER IS ANTICIPATED WITH THESE STORMS SINCE THEY
ARE LOCATED IN THE COOLER AIR NORTH OF A WARM FRONT WHICH EXTENDS FROM
SIOUX CITY TO JUST SOUTHWEST OF DES MOINES AND INTO NORTHEAST
MISSOURI.

CONDITIONS ARE DESTABILIZING OVER EASTERN NEBRASKA AND SOUTHWEST IOWA
AS SOUTHERLY FLOW CONTINUES AHEAD OF A LOW PRESSURE SYSTEM NEAR
NORFOLK NEBRASKA.  TEMPERATURES IN THE MIDDLE 70S AND DEW POINTS IN
THE LOWER 60S ARE PRODUCING MODERATE INSTABILITY WITH LIFTED INDICES
NEAR MINUS 6.  NATIONAL WEATHER SERVICE DOPPLER RADAR AND WIND
PROFILERS ALSO SHOW WINDS ALOFT AND VERTICAL WIND SHEAR INCREASING
ALONG THE MISSOURI RIVER INTO CENTRAL IOWA.  AS A RESULT...A SEVERE
THUNDERSTORM WATCH HAS BEEN ISSUED FOR SOUTHWEST AND SOUTH CENTRAL
IOWA...EASTERN NEBRASKA...NORTHEAST KANSAS AND NORTHWEST MISSOURI
UNTIL 700 PM CDT.

CLOUDY CONDITIONS SHOULD LIMIT THE THREAT OF SEVERE WEATHER NORTH OF
HIGHWAY 30...ALTHOUGH THUNDERSTORMS WITH BRIEF HEAVY RAIN AND GUSTY
WINDS CAN BE EXPECTED DURING THE LATE AFTERNOON AND EARLY EVENING
HOURS.

PRECAUTIONS--SPOTTERS ACTIVATION WILL LIKELY BE NEEDED WEST AND
SOUTHWEST OF DES MOINES BETWEEN 300 PM AND 500 PM. SPOTTERS MAY ALSO
BE NEEDED OVER CENTRAL AND SOUTHERN IOWA AFTER 500 PM. PEOPLE SHOULD
MONITOR RADIO AND TELEVISION FOR FORECAST UPDATES AND WARNINGS.

JUNGBLUTH

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-072300-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
307 PM CDT WED MAY 7 1997

HAZARD--A SQUALL LINE DEVELOPING OVER WESTERN IOWA WILL BECOME SEVERE.
THE STRONGER STORMS WILL PRODUCE HAIL IN EXCESS OF ONE INCH IN
DIAMETER AND WINDS OF UP TO 70 MPH.

AREA OF CONCERN--ALONG AND SOUTH OF HIGHWAY 30 WITH WEAKER STORMS OVER
NORTHERN IOWA.

TIMING DETAILS--STRONG THUNDERSTORMS WILL AFFECT WESTERN IOWA DURING
THE REST OF THE AFTERNOON WITH THE LINE REACHING I-35 BY AROUND 600
PM.  AREAS EAST OF I-35 WILL BE AFFECTED BETWEEN 600 PM AND 800 PM
THIS EVENING.

METEOROLOGICAL COMMENTS--A SQUALL LINE DEVELOPING OVER WESTERN IOWA
WILL ADVANCE EAST AND WILL LIKELY BECOME SEVERE QUICKLY.  THE STORMS
ARE AHEAD OF A COLD FRONT WHICH EXTENDS FROM EXTREME NORTHWEST
IOWA...SOUTHWEST OF NEAR LINCOLN.  A WARM FRONT EXTENDS FORM EAST
CENTRAL NEBRASKA TO JUST SOUTHWEST OF DES MOINES INTO NORTHEAST
MISSOURI.

SIGNIFICANT DESTABILIZATION OF THE ATMOSPHERE HAS OCCURRED DURING THE
EARLY AFTERNOON WITH THE COMBINATION OF SUNSHINE AND INCREASING
MOISTURE.  SURFACE DEW POINT TEMPERATURES IN THE LOW TO MID 60S HAVE
REACHED MUCH OF THE AREA SOUTHWEST OF THE WARM FRONT.  LIFTED INDICES
HAVE FALLEN TO NEAR -6 C.  MID LEVEL WINDS WHICH WERE QUITE WEAK THIS
MORNING HAVE STRENGTHENED THROUGH THE DAY.  THE WIND PROFILE HAS
BECOME MORE FAVORABLE FOR SEVERE THUNDERSTORM DEVELOPMENT AS BOTH
VERTICAL SPEED AND DIRECTIONAL SHEAR HAVE INCREASED.

PRECAUTIONS--SPOTTERS ACTIVATION WILL LIKELY BE NEEDED IN THE NEXT
HOUR OVER SOUTHWEST IOWA AND IN THE CENTRAL AND SOUTH CENTRAL COUNTIES
BY 500 OR 600 PM THIS EVENING.  SPOTTERS EAST OF I-35 SHOULD REMAIN
ALERT FOR THE POTENTIAL AFTER 600 PM.  PEOPLE SHOULD MONITOR RADIO AND
TELEVISION FOR FORECAST UPDATES AND WARNINGS.