Severe Thunderstorm Warning 28, NWS Des Moines, IA

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-180310-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
408 PM CDT FRI MAY 17 1996

HAZARD...SEVERE THUNDERSTORMS WITH DAMAGING WINDS UP TO OR GREATER
THAN 60 MPH...LARGE HAIL GREATER THAN 3/4 INCH DIAMETER...AND
ISOLATED TORNADOES ESPECIALLY TOWARD THE MINNESOTA BORDER.  HEAVY
RAIN IS ALSO A THREAT WITH UP TO 2 INCHES POSSIBLE ACROSS NORTHERN
PORTIONS.

AREA OF CONCERN...THE ENTIRE DES MOINES COUNTY WARNING AREA...WITH
THE HIGHEST RISK ALONG AND NORTH OF A FORT DODGE...TO WATERLOO
TO CEDAR RAPIDS LINE.

TIMING DETAILS...DEVELOPMENT SHOULD START AFTER 6PM ACROSS
NORTHWEST IOWA...AND THEN PROGRESS EASTWARD EARLY THIS EVENING.  AS
THE STORMS MOVE EAST THEY SHOULD BUILD SLIGHTLY TO THE SOUTH
ALIGNING WITH INTERSTATE 35 BY 9PM AND REACH WATERLOO TOWARDS 10PM.

METEOROLOGICAL COMMENTS...A VERY UNSTABLE AIRMASS WAS IN PLACE
ACROSS CENTRAL IOWA THIS AFTERNOON WITH TEMPERATURES WELL INTO THE
80S AND DEWPOINTS AROUND 70 DEGREES.  LIFTED INDICES WERE AS
LOW AS -12 BUT WARMER TEMPERATURES ALOFT WERE "CAPPING" THE
INSTABILITY AND PREVENTING THUNDERSTORMS FROM DEVELOPING AT THIS
TIME.  HOWEVER AN APPROACHING UPPER LEVEL DISTURBANCE ACROSS THE
CENTRAL PLAINS WILL TRAVERSE THE STATE THIS EVENING PROVIDING A
SOURCE OF UPWARD VERTICAL MOTION ALLOWING SEVERE THUNDERSTORMS TO
FORM.  THE CAP IS THE WEAKEST OVER NORTHERN SECTIONS OF THE STATE SO
THIS IS THE MOST LIKELY AREA FOR STORMS TO FORM.

AT THIS TIME UPPER LEVEL WINDS WERE FAIRLY UNIFORM WITH SOUTHERLY
WINDS AT THE SURFACE THEN BECOMING SOUTHWESTERLY AROUND 10000 FEET.
WITH THIS WIND STRUCTURE...DAMAGING WINDS AND LARGE HAIL WILL BE THE
PRIMARY THREAT EARLY WITH PREDICTED STORM MOTION NORTHEAST AT 30
MPH.  HOWEVER THE ENVIRONMENT MAY BECOME MORE FAVORABLE FOR
ISOLATED TORNADOES AS THE EVENING PROGRESSES. UPPER LEVEL
WINDS SHOULD BECOME MORE WESTERLY AS THE DISTURBANCE APPROACHES.
STORM MOVEMENT MAY BECOME MORE WESTERLY INCREASING THE LIKELIHOOD OF
TORNADIC DEVELOPMENT.

PRECAUTIONS...EMERGENCY MANAGERS MAY WISH TO HEIGHTEN THEIR
AWARENESS OF NATIONAL WEATHER SERVICE PRODUCTS AS SPOTTERS WILL MORE
THAN LIKELY NEED TO BE ACTIVATED LATER THIS EVENING.  THE STORM
PREDICTION CENTER INDICATES THAT A SEVERE WEATHER OUTBREAK IS
EXPECTED TONIGHT SO SEVERE THUNDERSTORMS OR TORNADO WATCHES WILL
LIKELY BE ISSUED.

SMALL

IAZALL-180330-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
824 PM CDT FRI MAY 17 1996

HAZARD...SEVERE THUNDERSTORMS WITH DAMAGING WINDS OF 60 MPH OT
GREATER AND LARGE HAIL - UP TO THREE DIAMETER.  ISOLATED TORNADOES
ARE POSSIBLE.

AREA OF CONCERN...GREATEST AREA OF CONCERN UNTIL 11 PM CDT IS WEST
OF A LINE FROM SHENANDOAH TO FORT DODGE TO MASON CITY.  CENTRAL
PORTION OF THE STATE COULD RECEIVE ISOLATED DAMAGING WINDS AFTER 9
PM CDT.

TIMING DETAILS...STORMS IN WEST CENTRAL IOWA WILL MOVE NORTHEAST
THROUGH THE AREA OF GREAT CONCERN AND INTO NORTH CENTRAL IOWA BEFORE
MIDNIGHT.  STORMS IN CENTRAL IOWA ARE NOT EXPECTED UNTIL AFTER 9 PM
CDT OR LATER.

METEOROLOGICAL COMMENTS...VERY UNSTABLE AIR REMAINS OVER THE STATE
HOWEVER VERY WARM AIR ALOFT IS KEEPING MUCH OF THE AREAS CAPPED AND
INHIBITING DEVELOPMENT.  HOWEVER AS A COLD FRONT PUSHES INTO FARTHER
INTO THE STATE THIS CAP WILL BE OVERCOME AND DEVELOPMENT IS LIKELY.
AT THE SAME TIME A FAIRLY STRONG JET WILL TRACK OVER THE AREA AND
FURTHER ENHANCE THE LIKELIHOOD OF DEVELOPMENT DESPITE THE TIME OF
DAY.  UPPER LEVEL WINDS CONTINUE TO SHOW WEAK DYNAMICS FAVORABLE
FOR TORNADIC DEVELOPMENT.  INSTEAD THE WIND PROFILE FAVORS DAMGING
STRAIGHT LINE WINDS.

PRECAUTIONS...EMERGENCY MANAGERS MAY CONTINUE TO MONITOR THE LATEST
FORECASTS AND STATEMENTS OUTSIDE THE WATCH AREA.  INSIDE THE WATCH
AREA COUNTIES IN WEST CENTRAL IOWA CAN EXPECT STORMS OVER THE NEXT
FEW HOURS.