Flash Flood Warning 5, NWS Des Moines, IA

IAZ044-045-057-070-081-092-232150-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
443 AM CDT WED JUL 23 1997

HAZARD--ISOLATED THUNDERSTORMS WITH HEAVY RAINFALL.  THERE IS A SMALL
THREAT OF SEVERE WEATHER.

AREA OF CONCERN--ALONG AND WEST OF A DENISON--ATLANTIC--BEDFORD LINE.

TIMING DETAILS--THROUGH 900 AM.

METEOROLOGICAL COMMENTS--A STRONG WARM ADVECTION ZONE HAS SET UP ALONG
THE WESTERN PART OF IOWA.  SOUTHWESTERLY INFLOW OF 20 TO 25 KTS
THROUGH THE LOWEST 5000 FT HAS INCREASED CONVERGENCE ALONG THIS
BOUNDARY.  STORM RELATIVE MOVEMENT WAS BETWEEN 330 AND 360 AT 25 KTS
WHICH DRAMATICALLY INCREASES THE WIND SHEAR PROFILE AND HELICITY
VALUES FOR INDIVIDUAL STORMS.  THE ATMOSPHERE IS QUITE UNSTABLE ABOVE
THE BOUNDARY LAYER...BUT MID-LEVEL TEMPERATURES ARE QUITE WARM.  THE
THREAT FOR LARGE HAIL IS MINIMAL DUE TO THIS FACTOR...BUT THE MAGNITUDE
OF THE SHEAR PROFILE IS FAVORABLE FOR ISOLATED SUPERCELL
STORMS...ESPECIALLY ALONG THE MISSOURI RIVER.

PRECAUTIONS--SPOTTER ACTIVATION MAY BE NEEDED EARLY THIS MORNING WITHIN
THE AREA OF CONCERN.  STAY TUNED TO FURTHER SHORT TERM FORECASTS FOR
ADDITIONAL INFORMATION.

KULA

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-240020-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
731 AM CDT WED JUL 23 1997

HAZARD--THUNDERSTORMS WITH A SLIGHT THREAT OF SEVERE WEATHER INCLUDING
DAMAGING WINDS.  THE THREAT FOR LARGE HAIL WILL BE LOCALIZED.  HEAVY
RAINS UP TO 3 INCHES WITH INDIVIDUAL STORMS.

AREA OF CONCERN AND TIMING DETAILS--

THROUGH 1000 AM...ALONG AND WEST OF A CARROLL--MOUNT AYR LINE.

REDEVELOPMENT TIME AROUND 800 PM NORTHWEST OF AN ALGONA-DENISON
LINE...SPREADING SOUTHEAST INTO CENTRAL AND SOUTH CENTRAL IOWA THROUGH
THE NIGHT.  THUNDERSTORM ACTIVITY IS NOT EXPECTED TO REACH THE
WATERLOO...TAMA AND OTTUMWA AREAS AT THIS TIME.

METEOROLOGICAL COMMENTS--THE WARM ADVECTION ZONE CURRENTLY IN PLACE
OVER WESTERN IOWA WILL BEGIN TO SHIFT NORTH AND NORTHEAST TODAY.
THUNDERSTORMS CURRENTLY IN PROGRESS ARE BEING DRIVEN BY THE NIGHTTIME
MAXIMUM OF THE LOW-LEVEL JET OF 25 KNOTS WHICH HAS ENHANCED CONVERGENCE
IN THIS ZONE.  STORMS WILL LIKELY DIMINISH IN INTENSITY BY 1000 AM AS
THIS CONVERGENCE WEAKENS.

A STATIONARY FRONT OVER EASTERN NEBRASKA THROUGH WESTERN MISSOURI WILL
LIFT NORTH INTO NORTHERN IOWA BY THIS EVENING.  IT WILL BE ATTACHED TO
A SURFACE LOW IN CENTRAL SOUTH DAKOTA.  THUNDERSTORMS ARE FORECAST TO
REDEVELOP NEAR THIS LOW WHERE MOISTURE CONVERGENCE WILL MAXIMIZE.  THE
AIRMASS OVER NEBRASKA AND KANSAS WILL BECOME RATHER UNSTABLE...BUT
CAPPED AS WARM AIR ALOFT CREATES AND INVERSION LAYER. STORMS OVER
EASTERN SOUTH DAKOTA WILL MOVE SOUTHEAST INTO IOWA WITH A STRONG
STEERING FLOW FROM THE NORTHWEST.  THEY ARE EXPECTED TO REMAIN
SCATTERED IN NATURE SIMILAR TO THE ONES CURRENTLY IN PROGRESS THIS
MORNING.  A FEW SUPERCELLS ARE POSSIBLE DUE TO THE STRONG DIRECTIONALLY
SHEARED WIND PROFILE EXPECTED WITH SOUTHEASTERLY LOW-LEVEL WINDS
VEERING TO THE NORTHWEST THROUGH THE MID-LEVELS RATHER SHARPLY. STORM
RELATIVE INFLOW WILL BE ENHANCED WITH THIS SETUP MAINTAINING STRONG
UPDRAFTS.  THE THREAT FOR HEAVY RAINS WILL EXIST AGAIN IN A LOCAL
FASHION WITH PRECIPITABLE WATERS INCREASING TO NEAR 2 INCHES OVER THE
FORECAST AREA.  FLOOD PROBLEMS WOULD BE HIGHLY LOCALIZED WITH ONLY A
FEW COUNTIES IN NORTH CENTRAL IOWA WITH SATURATED GROUND.

PRECAUTIONS--SPOTTER ACTIVATION MAY BE REQUIRED WITHIN BOTH FORECAST
TIME FRAMES.  PLEASE UTILIZE SHORT TERM FORECASTS FOR ADDITIONAL
INFORMATION.

KULA