Flooding in Iowa, April 18 to 21, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1240 AM CDT FRI APR 18 2008

...UPDATED FOR AVIATION DISCUSSION...

.SHORT TERM...TODAY
SHORT TERM ISSUE FOCUS SQUARELY ON SYSTEM PASSING THOUGH THE STATE
TODAY.  SFC LOW PRESSURE CURRENTLY NEAR KMCI AND MOVING GRADUALLY
NORTHEAST.  HAVE HAD WIDESPREAD MODERATE TO HEAVY RAINS ACROSS
PORTIONS OF THE SOUTHERN CWA WHERE ONE TO ONE AND THREE QUARTERS OF
AN INCH HAS ALREADY FALLEN.  RIVERS IN THE AREA HAVE RISEN RAPIDLY
IN RESPONSE AND EXPECT THIS TO PERSIST INTO TODAY.  APPEARS TRAIN OF
SHOWERS AND ISOLD CONVECTION WL CONTINUE ACRS THE SOUTHEAST THROUGH
MID MORNING BEFORE SOME BREAK.  WL ALSO WATCH FOR BRIEF PERIODS OF
HEAVIER DOWNPOURS WITH ANY POSSIBLE CONVECTION AS FLASH FLOODING
WOULD BE EASY TO PRODUCE GIVEN THE MOIST CONDITIONS. BREAK LATER
THIS MORNING AND EARLY AFTERNOON MAY BE SHORT IN DURATION AS MODELS
SUGGESTING THAT SOME DEFORMATION PCPN WL SLIDE BACK OVER THOSE AREAS
WITH ADDITIONAL RAINFALL.  FARTHER NORTHWEST...EXPECT DEFORMATION
PCPN TO DEVELOP OVER THE NEXT FEW HOURS WITH A DECENT BAND OF PCPN
BY MID MORNING.  THIS AREA WL GRADUALLY SLIDE EAST NORTHEAST DURING
THE DAY AS THE UPPER LOW AND ASSOCIATED FORCING PUSH INTO THE LOWER
MISSOURI AND MID MISSISSIPPI RIVER VALLEYS.  SEE NO REASON TO CANCEL
WATCH AT THIS POINT AND WL CONTINUE THROUGH 6 PM THIS EVENING.
GIVEN EXTENSIVE CLOUDINESS AND PCPN...HAVE UNDERCUT GUIDANCE IN MOST
LOCATIONS. EXCEPTION MAY BE IN THE SOUTHEAST WHERE WARM SECTOR
REMAINS IN PLACE.

&&

LONG TERM...TONIGHT THROUGH THURSDAY
THE STORM SYSTEM AFFECTING IOWA TODAY WILL BE SLOW TO
DEPART...DRIFTING INTO WESTERN ILLINOIS LATER TONIGHT AND AROUND
NORTHERN INDIANA SATURDAY. THIS WILL LEAD TO DIMINISHING RAIN
CHANCES IN THE WEST LATE TONIGHT...HOWEVER POPS WILL REMAIN HIGH IN
THE EAST THROUGH SATURDAY. AS THE LOW FINALLY EXITS EASTWARD
SATURDAY NIGHT SOME RIDGING WILL BRING A BRIEF PERIOD OF DRY AND
QUIET WEATHER SUNDAY AND SUNDAY NIGHT. CONCURRENTLY A LARGE
MID-LEVEL CYCLONE WILL SPIN UP OVER WESTERN MONTANA...WITH A SURFACE
TROUGH MOVING OVER THE GREAT PLAINS AND APPROACHING WESTERN IOWA BY
MONDAY MORNING. IT IS BEYOND THIS POINT THAT LONG-RANGE FORECAST
MODELS DIFFER IN THEIR SOLUTIONS FOR RAINFALL AND SURFACE
FIELDS...AS BOTH THE GFS AND ECMWF MAINTAIN THE MID-LEVEL TROUGH
OVER THE NORTHERN ROCKIES THROUGH THE END OF THE WEEK. BY THUS
PLACING OUR AREA BENEATH PERSISTENT SOUTHWESTERLY 500 MB FLOW...THE
MODELS ARE SPINNING UP SURFACE LOW PRESSURE SYSTEMS WHICH MOVE
RAPIDLY NORTHEASTWARD THROUGH THE MIDWEST. THE DEVELOPMENT AND
TIMING OF SUCH SYSTEMS IS VERY DIFFICULT TO PREDICT...AND THIS IS
LEADING TO A LOT OF VARIATION IN SURFACE SOLUTIONS FROM MODEL TO
MODEL AND FROM RUN TO RUN. THERE IS SOME GENERAL AGREEMENT IN
PARTICULARLY HIGH RAIN CHANCES MONDAY NIGHT AND TUESDAY
MORNING...AND AGAIN TOWARD THE END OF THE FORECAST PERIOD. WITH GOOD
MID-LEVEL ENERGY AT LEAST ISOLATED THUNDERSTORMS ARE LIKELY DURING
THE PERIODS OF HIGHER RAIN CHANCES.

&&

.AVIATION...18/18Z
SURFACE AND UPPER LOW STILL ROTATING AROUND SOUTHERN IOWA AND MOVING
VERY SLOWLY EAST.  NO CHANGE TO CONDITIONS EXPECTED UNTIL LATE IN
THE FORECAST PERIOD.  THIS MEANS IFR CONDITIONS DUE TO CEILINGS AND
OCCASIONALLY VSBYS IN HEAVIER SHOWERS AND FOG.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...FLOOD WATCH GENERALLY ALONG AND
SE OF BLACK HAWK-POLK-DECATUR COUNTIES TODAY.

&&

LONG TERM...LEE
SHORT TERM/AVIATION...COGIL

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1023 PM CDT THU APR 17 2008

IAZ038-039-049-050-060>062-073>075-083>086-094>097-190330-
GRUNDY-BLACK HAWK-MARSHALL-TAMA-POLK-JASPER-POWESHIEK-WARREN-
MARION-MAHASKA-CLARKE-LUCAS-MONROE-WAPELLO-DECATUR-WAYNE-
APPANOOSE-DAVIS-
1023 PM CDT THU APR 17 2008

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

.DAY ONE...TONIGHT

ISOLATED NON SEVERE THUNDERSTORMS ARE POSSIBLE TONIGHT.

A FLOOD WATCH REMAINS IN EFFECT TONIGHT FOR PERIODS OF MODERATE
TO LOCALLY HEAVY RAINFALL RESULTING IN PONDING WATER IN FIELDS AND
RISES ON AREA STREAMS AND RIVERS LATE TONIGHT OR FRIDAY AND
POSSIBLE RIVER FLOODING. IN FACT FLOOD WARNINGS HAVE BEEN ISSUED
FOR THE SOUTH FORK CHARITON AND CHARITON RIVERS. PLEASE REFER TO
THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR
FURTHER DETAILS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

NON SEVERE THUNDERSTORMS WILL CONTINUE THROUGH FRIDAY. THERE WILL
BE PERIODS OF MODERATE RAINFALL WHICH MAY RESULT IN FURTHER PONDING
OF WATER IN FIELDS AND RISES IN AREA STREAMS AND RIVERS LATE
FRIDAY AND POSSIBLE RIVER FLOODING THROUGH THE WEEKEND. A FLOOD
WATCH AND RIVER FLOOD WARNINGS ARE IN EFFECT THROUGH AT LEAST FRIDAY
AFTERNOON.

ADDITIONAL CHANCES FOR THUNDERSTORMS WILL ARRIVE MONDAY AND TUESDAY
WITH THE POSSIBILITY OF A FEW SEVERE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED HOWEVER RAINFALL REPORTS AND
ANY REPORTS OF FLOODING WOULD BE GREATLY APPRECIATED.

IAZ004>007-015>017-023>028-033>037-044>048-057>059-070>072-081-
082-092-093-190330-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-CRAWFORD-CARROLL-GREENE-BOONE-STORY-
AUDUBON-GUTHRIE-DALLAS-CASS-ADAIR-MADISON-ADAMS-UNION-TAYLOR-
RINGGOLD-
1023 PM CDT THU APR 17 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

ISOLATED NON SEVERE THUNDERSTORMS ARE POSSIBLE TONIGHT.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

ISOLATED NON SEVERE THUNDERSTORMS WILL CONTINUE THROUGH FRIDAY.

ADDITIONAL CHANCES FOR THUNDERSTORMS WILL ARRIVE MONDAY
AND TUESDAY. THERE IS THE POTENTIAL FOR STORMS TO BE STRONG TO
SEVERE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED HOWEVER RAINFALL REPORTS WOULD
BE GREATLY APPRECIATED.

MOYER