Hail and Damaging Winds in Iowa, August 4 to 5, 2008

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1030 PM CDT MON AUG 4 2008

.UPDATED AVIATION DISCUSSION FOR 05/06Z

.SHORT TERM UPDATE...TONIGHT.

WEAK BOUNDARY LIES OVER SOUTHERN IA AT 00Z. SOME THUNDER
REDEVELOPMENT STILL POSSIBLE ALOFT AS LOW LEVEL JET BEGINS TO
IMPINGE ON THE BOUNDARY AND ELEVATED STORMS INCREASE IN COVERAGE
FROM I80 SOUTH TO THE BORDER...MAINLY AFT 06Z. AT 00Z THE JET
APPEARS TO BE TURNING SLIGHTLY MORE WEST-EAST WHICH WILL KEEP BEST
LIFT SOUTH. HAVE AGAIN TRIMMED POPS...WX...AND QPF FOR THE REGION
FOR OVERNIGHT. CAPES REMAIN HIGH SOUTH BUT CAP OF +12C STILL
HOVERING OVER THE AREA AT 00Z. HAVE RAISED MINS A DEGREE MOST AREAS
AND HAVE RAISED DEW POINTS. LITTLE PUSH BEHIND BOUNDARY FOR NOW AND
EXPECT THAT INSTEAD OF AIRMASS BEING REPLACED WITH DRIER AIR BY
MORNING...WILL MORE LIKELY SEE PATCHY FOG TOWARD PRE-DAWN AND DAWN
HOURS./REV

.PREVIOUS SHORT TERM...TONIGHT THROUGH THU
FORECAST ISSUE IS POTENTIAL SEVERE WEATHER TONIGHT ACROSS THE
MAJORITY OF THE CWA. FRONTAL BOUNDARY DRAPED ACROSS CENTRAL IOWA
WITH FEW SHOWERS AND THUNDERSTORMS ALREADY DEVELOPING ALONG THE
FRONT THIS AFTERNOON AND POTENTIALLY BECOMING MORE SFC BASED WITH
TIME.  ABUNDANT INSTABILITY AND MOISTURE AVAILABLE ALONG THE I80
CORRIDOR THIS AFTERNOON/TONIGHT...WITH CAP SLOWLY ERODING.  HOWEVER
THE RUC MAY BE A BIT TOO AGGRESSIVE IN THIS REGARD...AT LEAST FOR
THE TIME BEING...DUE TO OVERDONE AWOS DEWPOINTS.  HAVE INCREASED
POPS ALONG CENTRAL PORTIONS OF CWA THROUGH 06Z...AND MAINLY EASTERN
PORTIONS OF CWA OVERNIGHT.  IF ANY STORMS DUE TAP THIS EXTREME
INSTABILITY THEY WOULD QUICKLY BECOME SEVERE WITH ALL MODES
POSSIBLE. PWS RANGE ABOVE 1.5 INCHES TO NEAR 2.5 INCHES ACROSS
SOUTHEAST PORTIONS OF CWA BY 03Z MONDAY...SO SOME LOCALLY HEAVY RAIN
IS LIKELY...AND SHIFTED QPF MAX FURTHER SOUTH TONIGHT. SHARP
TEMPERATURE GRADIENT ACROSS THE STATE THIS EVENING...MAINLY TWEAKED
LOWS DOWN IN THE NORTH OVERNIGHT.

BY TUESDAY...FRONTAL CONVERGENCE AND SURFACE BASED POTENTIAL
DIMINISHES SOMEWHAT.  HOWEVER GFS/SREF BOTH SUGGEST ELEVATED FORCING
IN RIGHT ENTRANCE REGION OF JET SEGMENT AS IT CROSSES MN TOWARD THE
GREAT LAKES SO CONTINUE TO HAVE CHANCE POPS SRN TWO-THIRDS DRIFTING
FROM WEST TO EAST WITH TIME.  SIMILAR FORCING MAY ALSO LINGER OVER
SOUTHERN IOWA TUE EVE.  BY WED AND THU...SFC HIGH PRESSURE SETTLES
INTO IA WITH FAIR AND COOLER WEATHER.

TEMP WISE...HAVE TRIMMED HEAT ADVY SOMEWHAT TO FIT CURRENT
CONDITIONS BUT STILL PLAN ON HAVING IT EXPIRE AT 00Z.  NO REAL
DEVIATIONS FROM GUIDANCE BLEND THROUGH PERIOD BASED ON SUGGESTIONS
FROM FORECAST SOUNDINGS.  HAVE LOWERED DEWPOINTS SOMEWHAT HOWEVER
BUT CONFIDENCE NOT THE GREATEST AS MIXING AND EVAPOTRANSPIRATION
BATTLE FOR HOW DRY WE CAN GET DURING PEAK HEATING.

.LONG TERM...THU THROUGH MON
LITTLE OF CONCERN IN THIS PERIOD.  MODELS IN GOOD AGREEMENT WITH
BROAD GREAT LAKES TROUGH KEEPING IA IN NWLY FLOW ALOFT AND
INFLUENCED BY SFC HIGH PRESSURE.  HAVE LEFT FORECAST UNCHANGED FOR
THE MOST PART WITH LITTLE OR NO CHANCES FOR PRECIP.  NO SIGNIFICANT
ISENT LIFT IN PLACE AND LACK OF CONVERGENCE AND INSTABILITY SHOULD
KEEP SFC BASED DEVELOPMENT AT BAY.  PREFERRED SOLUTION IS A BLEND OF
ECMWF/GEFS WHICH SUGGESTS MO VALLEY MAY BE ACTIVE BUT GENERALLY
ALONG AND SOUTH OF THE RIVER SO WILL LEAVE SLIGHT CHANCES IN PLACE
SW THU-SUN.  CHANCES MAY HAVE TO BE INTRODUCED BEYOND DAY 7 AS SFC
HIGH RETREATS.

DID NOT CHANGE TEMPS TOO MUCH EITHER OUTSIDE OF LOWERING A FEW
DEGREES IN SPOTS.  STATE FAIR SHOULD KICK OFF WITH BELOW NORMAL
TEMPS AND HUMIDITIES DUE TO INFLUENCE OF HIGH PRESSURE AND NLY TO
SELY TRAJECTORIES.

&&

.AVIATION...05/06Z
FRONT NOW ALONG THE IA/MO BORDER WITH WEAKENING CAP IN PLACE ALOFT.
LOW LEVEL JET NOW BEGINNING TO OVERRUN THE UPPER LEVEL FRONT WITH A
THIN LINE OF ELEVATED CONVECTION BREAKING OUT ACROSS CENTRAL IA. FOR
NOW...BEST CONVERGENCE TO REMAIN SOUTH OF THE REGION UNTIL LATE.
SOME MVFR CIGS AND BR EXPECTED TOWARD MORNING AS RH INCREASES AND
SOME THUNDER CONTINUES.  HAVE INCREASED -TSRA CHANCES IN THE SHORT
TERM FOR TAF SITES ALONG/SOUTH OF I80 INCLUDING KDSM AND KOTM FOR
THROUGH 12Z. ACTIVITY SHOULD BEGIN TO WIND DOWN AFT 13Z SOUTH. -REV

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE

&&

KLP/BSS/REV

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
747 PM CDT MON AUG 4 2008

IAZ057>062-070>075-081>086-092>097-051900-
AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK-CASS-ADAIR-MADISON-
WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-
TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
747 PM CDT MON AUG 4 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL IOWA.

.DAY ONE...TONIGHT
SCATTERED THUNDERSTORMS ARE EXPECTED TO REDEVELOP AFTER MIDNIGHT
ACROSS THE OUTLOOK AREA...WITH AREAS SOUTH OF HIGHWAY 92 FAVORED. A
FEW OF THE STORMS MAY BE SEVERE WITH QUARTER SIZED HAIL AND WINDS TO
60 MPH BEING THE MAIN THREATS.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

SCATTERED NON SEVERE THUNDERSTORMS ARE EXPECTED ON TUESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED OVER FAR SOUTHERN IOWA AFTER
MIDNIGHT TONIGHT.

IAZ004>007-015>017-023>028-033>039-044>050-051900-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE-
BOONE-STORY-MARSHALL-TAMA-
747 PM CDT MON AUG 4 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL TO NORTH
CENTRAL IOWA.

.DAY ONE...TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

SCATTERED NON SEVERE THUNDERSTORMS ARE EXPECTED TO END ON TUESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED.

PODRAZIK/REV