Severe Thunderstorm Warning 496, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
317 PM CDT WED AUG 13 2008

.SHORT TERM...
SCATTERED THUNDERSTORMS HAVE DEVELOPED OVER SOUTHERN MINNESOTA THIS
AFTERNOON AND A FEW HAVE TRIED TO TRICKLE INTO NORTHERN IA. STORMS
FIRING ALONG 700 MB TROUGH AND WEAK SFC BOUNDARY. SYSTEM NOT QUITE
IN PHASE AND HAVING DIFFICULTY BECOMING ORGANIZED THROUGH A FEW
SEVERE STORMS HAVE BEEN REPORTED IN MINNESOTA. SFC HEATING IN CNTRL
IOWA HAS ALLOWED SUBSIDENCE AND MIXING OF DRIER AIR TO THE SFC AND
HAS DIMINISHED INSTABILITY. A FEW STORMS WILL REMAIN POSSIBLE
TONIGHT ALONG WITH AREAS OF FOG LATE. BEST LANDSPOUT ENVIRONMENT IS
ALONG THE UPPER MISSISSIPPI RIVER VALLEY AND JUST TO THE EAST OF
HERE SO HOPEFULLY WILL ESCAPE THAT FUN TONIGHT.

.LONG TERM /THU-WED/...
FORECAST REMAINS IN FLUX DURING PERIOD AS FAIR AMOUNT OF UNCERTAINTY
REMAINS WITH UPPER LEVEL LOW TRACK THIS WEEKEND THROUGH MID NEXT
WEEK. A BACKDOOR COLD FRONT MOVES IN FROM THE NORTHEAST ON THURSDAY
AND REACHES CENTRAL IOWA AROUND 21Z. SHOULD HOLD HIGHS IN THE 70S
ACROSS THE NORTHEAST HALF WITH 80S TO THE SW. A FEW THUNDERSTORMS
WILL LIKELY DEVELOP ALONG THE BOUNDARY THOUGH CLIMATOLOGICALLY THIS
IS NOT A FAVORED SETUP FOR WIDESPREAD DEVELOPMENT. THE BOUNDARY WILL
CONTINUE TO THE SOUTHWEST INTO THURSDAY EVENING. UPPER LEVEL SYSTEM
DROPPING THROUGH NEBRASKA ALONG WITH ATTENDANT SFC FEATURES WILL
INTERACT WITH GRADUALLY STALLING BOUNDARY OVER ERN NEBRASKA THROUGH
SW IA AND NRN MO AND THIS WILL REMAIN THE PRIMARY FOCUS FOR
PRECIPITATION POTENTIAL THROUGH FRIDAY.

HIGH PRESSURE WILL SETTLE SOUTH INTO THE UPPER MIDWEST AND UPPER
MISSOURI BASIN FRIDAY NIGHT BRINGING DRIER SFC AIR TO THE AREA.
UNCERTAINTY REMAINS WITH CLOSE UPPER LEVEL LOW TREKKING SOUTH ALONG
THE ROCKY MOUNTAIN WEST THEN EVENTUALLY SPINNING INTO THE PLAINS.
UNCERTAINTY REMAINS ON HOW FAR SOUTH IT WILL DIG AND WITH LACK OF
MID LEVEL FLOW...WHAT WILL GIVE IT A NUDGE TO FINALLY MOVE.
CURRENTLY LACK OF A KICKER SEEMS TO POINT TO A PROLONGED STAY OVER
THE SOUTHERN PLAINS BEFORE LIFTING OUT SOMETIME NEXT WEEK. LARGE
SYSTEM MOVING THROUGH THE GULF OF ALASKA WILL EVENTUALLY PUSH RIDGE
UP OVER THE INTERMOUNTAIN WEST. CANADIAN AND ECMWF SUGGESTING A
HURRICANE AROUND THE GULF OF MEXICO WHICH COULD ALSO BECOME A
FACTOR. HAVE MADE LITTLE CHANGES TO PRECIP CHANCES DURING THE
EXTENDED DUE TO INCONSISTENCIES AND MANY FACTORS INVOLVED. ONCE
SYSTEM DOES ARRIVE...EXPECT A COOL AND RAINY PERIOD.

&&

.AVIATION...13/18Z
FOG HAS LIFTED WITH VSBYS NOW P6SM. CONVECTION CONTINUES TO MOVE
OUT OF MN INTO NW IA ATTM AND HOLDING TOGETHER WITH UPPER LEVEL
SUPPORT AND WEAK SFC BOUNDARY. INSTABILITY AXIS OF TD GREATER THAN
60F WILL CONTINUE TO SUPPORT SOUTH MOVEMENT THRU AFTERNOON.   MID
LEVEL CONVECTION ALREADY DEVELOPING IN ERN SD. SCATTERED
THUNDERSTORMS...POSSIBLY A LINE FOR A FEW HOURS...WILL MOVE SWD
LOWERING CONDITIONS FOR A FEW HOURS WITH POTENTIAL FOR GUSTY OUTFLOW
AND SOME HAIL. LINE MOVING A BIT FASTER THAN EARLIER EXPECTED SO
HAVE HASTENED TIMING OF CONVECTION ACROSS MOST OF THE REGION. MAY
SEE SOME LINGERING ACTIVITY INTO THE EVENING HOURS. THINGS SHOULD
QUIET DOWN AFTER MIDNIGHT WITH MVFR FOG EXPECTED...THOUGH WILL HAVE
TO WATCH TYPICAL TROUBLE AREAS SUCH AS KOTM AND KMCW FOR POSSIBLE
IFR OR LIFR FOG. /REV

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SHORT TERM...REV
AVIATION...REV
LONG TERM...DONAVON

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1100 AM CDT WED AUG 13 2008

IAZ004>007-015>017-023>026-033>037-044>047-057>059-070-071-081-
092-141015-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-SAC-CALHOUN-WEBSTER-HAMILTON-
HARDIN-CRAWFORD-CARROLL-GREENE-BOONE-AUDUBON-GUTHRIE-DALLAS-CASS-
ADAIR-ADAMS-TAYLOR-
1100 AM CDT WED AUG 13 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS BY MID AFTERNOON AND CONTINUING
INTO THE OVERNIGHT HOURS. ISOLATED SEVERE THUNDERSTORMS ARE
POSSIBLE MAINLY THROUGH EARLY TONIGHT...WITH HAIL UP TO THE SIZE
OF QUARTERS...DAMAGING WIND GUSTS UP TO 60 MPH...AND SMALL
TORNADOES ALL POSSIBLE.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE ARE INTERMITTENT CHANCES OF THUNDERSTORMS FROM THURSDAY
THROUGH MONDAY...THOUGH THE CHANCES WILL BE QUITE LOW FRIDAY
THROUGH SUNDAY. THE SEVERE WEATHER THREAT APPEARS FAIRLY LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND TONIGHT.

IAZ027-028-038-039-048>050-060>062-072>075-082>086-093>097-141015-
BUTLER-BREMER-GRUNDY-BLACK HAWK-STORY-MARSHALL-TAMA-POLK-JASPER-
POWESHIEK-MADISON-WARREN-MARION-MAHASKA-UNION-CLARKE-LUCAS-MONROE-
WAPELLO-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
1100 AM CDT WED AUG 13 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

THERE IS A SLIGHT CHANCE OF THUNDERSTORMS THIS AFTERNOON...MAINLY
NORTH OF INTERSTATE 80. THE CHANCE OF THUNDERSTORMS WILL INCREASE
AND EXPAND SOUTHWARD TONIGHT. ISOLATED SEVERE THUNDERSTORMS ARE
POSSIBLE MAINLY LATE THIS AFTERNOON AND EARLY TONIGHT...WITH HAIL
UP TO THE SIZE OF QUARTERS AND DAMAGING WIND GUSTS UP TO 60
MPH THE MAIN THREATS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE ARE INTERMITTENT CHANCES OF THUNDERSTORMS FROM THURSDAY
THROUGH MONDAY...THOUGH THE CHANCES WILL BE QUITE LOW FRIDAY
THROUGH SUNDAY. THE SEVERE WEATHER THREAT APPEARS FAIRLY LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND TONIGHT.

MOYER/REV