Severe Thunderstorm Warning 56, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
300 PM CDT THU MAY 8 2003

MAIN CONCERN IS EARLY THREAT OF SVR WX OVR SRN/WRN IA.  SECOND THO
MAIN CONCERN IS HVY RAINS CNTRL AND S.  IN LONG TERM AGN RAINFL
COULD PLAY INTO FLOODING PIX.

IN EARLY PERIODS FAVOR COMBO RUC/MESOETA WHICH APPEAR TO BE HANDLING
CURRENT SITUATION WELL.  BIG QUESTION RELATES TO MOVEMENT OF WARM
FNT AND WHETHER MOISTURE AND ASSOCIATED DYNAMICS CAN PUSH FAR ENOUGH
NORTH.  MODELS HINT AT THIS WITH SWRN IA BEST AREA FOR SVR WX.  IF
FNT STALLS INVOF SRN IA XPCT ISOLD HAIL LARGEST THREAT WITH THOSE
STORMS TURNING INTO HVY RAINS.  ATMOSPHERE TURNS VERY UNSTABLE WITH
-8 TO -12 SHOWWLTR AND CAPES ARND 3500. ON FRIDAY STILL LEANING WITH
MESOETA WITH SHWRS ERY MRNG THEN REDVELOPMENT LT IN DAY AS S/W MOVES
INTO THE AREA WITH LEAN TWD GFS.  GUID TEMPS ACCEPTED.

IN LONG TERM GFS MODEL OF CHOICE AS MORE CONSISTENT RUNS.  SOLUTION
APPEARS MOST REASONABLE.  WL HIT SATURDAY AFTN LKLY HWVR WILL CUTOFF
PCPN BY SUN AFTN IN LINE WITH GFS MODEL.  SHIFT IN CURRENT PATTERN
LEAVES AREA DRY AT LEAST TWO DAYS MAYBE INTO THURSDAY.  AT END OF
EFP WAA BEGINS WITH CHC SWRB HALF OF STATE.  GUID TEMPS LOOK
REASOANBLE WITH LEAN TWD AVN.

FLOOD WATCH EXPANDED AS GFS SOLUTION BOUGHT FOR MODEL OF CHOICE WITH
SHIFT MAX PCPN N.  HWVR ANTECEDENTS LOW THERE BUT WITH HEAVIER RAINS
RESPONSE COULD BE RAPID.  OVRALL EXPECT MORE FLOODING TYPE SITUATION
WITH ISOLD FLASH FLOODING ON LOCAL FF PRONE STREAMS.

.DSM...FLOOD WATCH TONIGHT ENITRE CWA TONIGHT AND FRIDAY.
FORSTER

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-091100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1232 PM CDT THU MAY 8 2003

...SEVERE WEATHER AND HEAVY RAINS POSSIBLE LATE THIS AFTERNOON AND
TONIGHT...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

SHOWERS AND A FEW THUNDERSTORMS WILL CONTINUE ACROSS THE SOUTHWEST
THIRD OF IOWA...AND EXPAND NORTHWARD INTO CENTRAL IOWA DURING THE
AFTERNOON.  SOME OF THESE STORMS MAY PRODUCE WIND GUSTS OVER 40 MPH.
HOWEVER THE THREAT OF SEVERE WEATHER WILL INCREASE SHARPLY BY LATE
AFTERNOON AND NIGHT.  LOW PRESSURE SHOULD MOVE ACROSS KANSAS
THIS AFTERNOON REACHING THE LOWER MISSOURI RIVER VALLEY DURING THE
EARLY EVENING HOURS.  THIS WILL ALLOW WARM...MOIST AND UNSTABLE AIR
TO SURGE NORTHWARD INTO IOWA...ESPECIALLY SOUTHWEST PORTIONS OF THE
STATE.  HIGH WIND SHEAR VALUES WILL COMBINE WITH THE INSTABILITY TO
PRODUCE SEVERE STORMS WHICH ARE EXPECTED TO INTENSIFY SOMETIME AFTER
400 PM ACROSS SOUTHWEST IOWA...AND THEN QUICKLY SPREAD NORTHEASTWARD
OVER THE REMAINDER OF THE STATE.  LARGE HAIL AND DAMAGING WINDS MAY
OCCUR OVER MUCH OF IOWA...WITH TORNADOES POSSIBLE PRIMARILY OVER
SOUTHWEST SECTIONS.

HEAVY RAINS WILL BE POSSIBLE TOO WITH THIS SURGE OF WARM AND VERY
MOIST AIR.  DUE TO THE RELATIVELY FAST MOVEMENT OF THE SYSTEM...THE
PERIOD OF RAINFALL WILL NOT BE EXTENDED...ONLY LASTING SEVERAL
HOURS...BUT RAINS MAY BE QUITE HEAVY FOR A SHORT TIME.  RAINFALL
AMOUNTS BY FRIDAY MORNING COULD REACH OR EXCEED AN INCH IN MANY
LOCATIONS.  WITH THE GROUND NEARLY SATURATED ACROSS MUCH OF CENTRAL
AND SOUTHERN IOWA FROM PREVIOUS RAINS...NEW FLOODING MAY OCCUR...OR
ONGOING FLOODING AGGRAVATED.  A FLOOD WATCH REMAINS IN EFFECT FOR
ALL BUT THE NORTHWEST CORNER OF THE DES MOINES NATIONAL WEATHER
SERVICE FORECAST AREA TONIGHT WHEN HEAVY RAINS MAY OCCUR...AND INTO
FRIDAY WHEN FLOODING MAY BE IN PROGRESS EVEN AFTER THE RAINS HAVE
DIMINISHED.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

ANOTHER WARM FRONT WILL PUSH INTO NORTHERN MISSOURI OVERNIGHT FRIDAY
INTO EARLY SATURDAY. THUNDERSTORMS WITH LARGE HAIL ARE POSSIBLE OVER
SOUTHERN IOWA. DURING THE DAY ON SATURDAY...ANOTHER SURFACE LOW WILL
TRACK THROUGH THE STATE WITH THE POTENTIAL FOR ADDITIONAL SEVERE
WEATHER AND HEAVY RAIN. AT THIS TIME...AREAS SOUTH OF HIGHWAY 30
APPEAR TO BE MOST AT RISK SATURDAY. THE CUMULATIVE EFFECT OF RAINS
THURSDAY THROUGH SUNDAY COULD AGGRAVATE THE CURRENT MINOR FLOODING
IN CENTRAL IOWA...AND CREATE ADDITIONAL RIVER FLOODING CONCERNS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED ACROSS SOUTHERN IOWA LATE
THIS AFTERNOON AND TONIGHT...AND MAY BE NEEDED OVER THE REMAINDER OF
THE STATE TONIGHT.

&&

MORE INFORMATION CAN BE OBTAINED AT WWW.CRH.NOAA.GOV/DMX (ALL LOWER
CASE).

SMALL