Flash Flooding and Damaging Winds in Iowa, August 1 to 2, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
310 PM CDT TUE AUG 1 2006

.DISCUSSION...

COMPLICATED SFC CONDITIONS THIS AM WITH STATIONARY BOUNDARY ACROSS
SE COLORADO TO KONL TO KMSP TO KIWD (IRONWOOD MI) LINE. WEAK LOW HAS
DEVELOPED ALONG THE BOUNDARY OVER NW KANSAS WITH SECONDARY WARM
FRONT NOW FORMING OVER SOUTHEAST NEBRASKA IN RESPONSE TO AN OUTFLOW
BOUNDARY OVER SOUTHERN SECTIONS OF IOWA. AS FOR REMAINING HEAT
EVENT...HEAT ADV IN EFFECT FOR SOUTHEAST PORTIONS OF CWA WILL EXPIRE
THIS EVENING AS PLANNED AS NORTHERN PORTIONS TRIMMED SIGNIFICANTLY
THIS MORNING WITH ONSET OF CONVECTION. BREAK IN HEAT IN THE FORECAST
FOR WED AND BEYOND...THOUGH TEMPS CREEP BACK UP BY THE WEEKEND. TDS
REMAIN HIGH OVER THE REGION WITH RELATIVELY DEEP MOISTURE OVER TO
H850MB ON PROGGED SOUNDINGS...THOUGH LAPS SOUNDINGS THIS MORNING
NEARLY SATURATED TO H200 MB FAR NORTH AND CENTRAL SECTIONS. H700
SHOWS WEAK IMPULSE RESPONSIBLE FOR THIS MORNINGS CONVECTION MOVING
THROUGH 40KT FLOW IN FAR WESTERN IA. SECOND MAXIMUM AND MAIN WAVE
BACK IN TX PANHANDLE AND SHOULD MOVE NORTHEAST BY TNT AND TRIGGER
EXPECTED CONVECTIVE EVENT LATER TODAY.

FOCUS OF FCST TURNS NOW FROM HEAT TO POTENTIAL EXCESSIVE RAINFALL.
CONVECTION CONTINUES TO DIMINISH EAST WITH LLJ STILL FIRING ALONG
WESTERN EDGES OF CWA ATTM. WITH SLOWLY MOVING FRONT TNT AND
POTENTIAL FOR BACKBUILDING CELLS TOWARD 06Z WITH HIGH PWATS. LAST
NIGHTS SPECIAL 00Z RUN OF THE WRF FROM HAS CONVECTION DEVELOPING
NORTH/WEST THIS AFTERNOON AND CONTINUING INTO THE OVN HOURS. MODELS
IN GENERAL AGREEMENT WITH HIGHEST MOISTURE TRANSPORT OVER FAR NC
IOWA THEN SHIFTING INTO SOUTHERN MN BY AM HOURS. QPF AMTS AND
PLACEMENT DIFFER WITH GFS BEING THE MOST EXCESSIVE SOLN WITH 3-5
INCH AMTS NORTH. NAM/WRF RUNS SHOWING LESS...BUT STILL IMPRESSIVE
1-3 INCH AMTS. AM LEANING TOWARD 1-3 INCH AS PER CURRENT FCST.
CURRENTLY THE GFS MOST RESEMBLES THE SYNOPTIC SITUATION.
COMPLICATING THE FORECAST IS THE MESO BOUNDARY SET UP OVER THE SOUTH
CENTRAL COUNTIES. ACCAS VERY PREVALENT AS OF 130 PM AT THE WFO THIS
AFTERNOON. IF CONVECTION WORKS ALONG THE BOUNDARY THIS EVENING... A
MORE SOUTHERLY PLACEMENT OF HIGHEST QPF MAY BE NEEDED AS AN UPDATE
THIS EVENING. WED STILL IN QUESTION AS GFS CONTINUES TO HINT AT
MOISTURE DIVERGENCE ACROSS THE CWA DURING THE DAYTIME HOURS AS FRONT
STRETCHED OUT AND DROPS SOUTH...THEN STORMS REFIRING ALONG BOUNDARY
FAR SOUTH AND INTO MISSOURI. NAM NOT AS STRONG WITH OVERALL DYNAMICS
TONIGHT OR AGGRESSIVE WITH TIME AND HAS PM REDEVELOPMENT OVER THE
SOUTHERN REGIONS DURING THE DAYTIME HOURS. PREFER THE NAM SOLN WHICH
IS SIMILAR TO THE EURO/GEM...WITH GEM EVEN SLOWER FOR THE PM HOURS
WED INTO THURS AFTERNOON. NAM DEVELOPS A NICE DEF ZONE THURSDAY
WHICH MAY PROLONG THE PRECIP OVER SOUTHERN SECTIONS FOR THE DAY.

IN THE LATER PERIODS...WILL BE LOOKING AT A MORE ZONAL FLOW
WITH SUB-TROPICAL RIDGE JUST TO THE SOUTH AND WESTERLY ENERGY
TRANSLATING EAST IN THE FLOW. TIMING OF FEATURES WILL BE MOST
CHALLENGING. AT PRESENT...WEAK WAVE SUGGESTED AS EARLY AS SAT NIGHT
OVER REGION WITH MORE UPSTREAM WAVES THROUGH EARLY NEXT WEEK. THIS
WOULD SUGGEST AT LEAST 20 POPS GOING FORWARD WITH CHANCE UPDATES
POSSIBLE OVER THE NEXT DAY OR TWO. LONGER OUT...GEM/GFS HINTING AT
RETURN OF BUILDING RIDGE AS WEEK PROGRESSES...JUST IN TIME FOR THE
FAIR.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...FLASH FLOOD WATCH TONIGHT ALONG
AND N OF MASON CITY-FORT DODGE-SAC CITY LINE. HEAT ADV LEFT TO
EXPIRE SE AT 00Z.

&&

REV/MYERS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
531 PM CDT TUE AUG 1 2006

IAZ004>007-015>017-023>025-033>035-021100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-SAC-CALHOUN-WEBSTER-
531 PM CDT TUE AUG 1 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHERN IOWA.

.DAY ONE...TONIGHT

SHOWERS AND THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL ARE EXPECTED
THIS EVENING AND THROUGH THE OVERNIGHT HOURS. MOST LOCATIONS WILL
RECEIVE AMOUNTS OF ONE TO THREE INCHES. LOCALIZED AMOUNTS OF UP
TO 5 INCHES ARE POSSIBLE. WITH THE POTENTIAL FOR THE HEAVY RAIN TO
FALL WITHIN A SHORT PERIOD OF TIME...FLASH FLOODING MAY OCCUR
ACROSS THE AREA. A FEW STORMS MAY ALSO BE SEVERE WITH THE PRIMARY
THREAT BEING DAMAGING STRAIGHT LINE WINDS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

ADDITIONAL NON SEVERE THUNDERSTORMS ARE POSSIBLE WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING AND OVERNIGHT FOR
SEVERE WEATHER POTENTIAL...INCLUDING HEAVY RAINFALL AND POSSIBLE
FLASH FLOODING.

IAZ026>028-036>039-044>050-057>062-070>075-081>086-092>097-021100-
FRANKLIN-BUTLER-BREMER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-
CARROLL-GREENE-BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-
POLK-JASPER-POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-
ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-
WAYNE-APPANOOSE-DAVIS-
531 PM CDT TUE AUG 1 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND
SOUTHERN IOWA.

.DAY ONE...TONIGHT

SCATTERED THUNDERSTORMS ARE POSSIBLE OVERNIGHT...MAINLY ALONG AND
NORTH OF A CRESTON TO MONTEZUMA LINE. A FEW SEVERE STORMS WITH
DAMAGING WINDS ARE POSSIBLE.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

AREAS OF SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS THE AREA
ON WEDNESDAY AS A FRONTAL SYSTEM DROPS SOUTHWARD OVER CENTRAL AND
SOUTHEAST IOWA. SOME STORMS WEDNESDAY AFTERNOON AND NIGHT MAY BE SEVERE
WITH THE PRIMARY THREAT BEING DAMAGING THUNDERSTORM WINDS. LOCALLY
HEAVY RAINFALL WILL ALSO BE POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE...BUT NOT LIKELY OVERNIGHT. SPOTTER
ACTIVATION MAY BE NEEDED WEDNESDAY AFTERNOON AND NIGHT FOR SEVERE
WEATHER INCLUDING LOCALLY HEAVY RAIN AND POSSIBLE FLASH FLOODING.