Severe Thunderstorm Warning 361, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
225 PM CDT SUN SEP 30 2007

.DISCUSSION...
POTENT UPPER LEVEL SYSTEM SWINGING THROUGH THE REGION TODAY INTO
THIS EVENING...WITH THE SFC LOW CURRENTLY ANALYZED NEAR EAST CENTRAL
NEBRASKA. STILL ANTICIPATING DEVELOPING CONVECTION ACROSS THE CWA BY
LATE THIS AFTERNOON INTO EARLY EVENING SITUATED ALONG A MERGING COLD
FRONT/DRYLINE EXTENDING SOUTH OUT OF THE LOW INTO SE NEBRASKA AND
ERN KANSAS. MOISTURE CONTINUES TO POOL AHEAD OF THE FRONT WITH LOWER
TO MID 60S DEWPOINTS ADVECTING INTO WESTERN/CENTRAL IOWA. DAMAGING
WIND POTENTIAL STILL POSES THE GREATEST SEVERE THREAT WITH THE
ACTIVITY EXPECTED ACROSS IOWA DUE TO STRONG LOW LEVEL FLOW...AND
GREATER THAN 60-70KT 0-6KM BULK SHEAR. DIRECTIONAL SHEAR STILL NOT
THE BEST...BUT AS SFC LOW TRACKS THROUGH NORTHWEST IOWA...AREA
NEAREST THE SFC LOW MAY SEE ENOUGH BACKING OF THE SURFACE WIND TO
ENHANCE THE WIND PROFILE IN THE LOWEST LEVELS. OTHERWISE SYSTEM
EXPECTED TO MAIN THUNDERSTORM THREAT TO BE EAST OF CWA BY MID
EVENING...AS COLD FRONT QUICKLY SLIDES INTO EASTERN IOWA. STILL MAY
SEE SOME LINGERING PRECIPITATION DUE TO SOME WRAP-AROUND SHOWERS
THROUGH LATE EVENING. STRONG GUSTY WINDS ALSO NOTED IN DRY SLOT AREA
ACROSS SE NE INTO ERN KS...AND WILL HAVE TO MONITOR FOR POSSIBILITY
OF NON-CONVECTIVE ADVISORY CRITERIA WINDS ON THE BACKSIDE OF THIS
SYSTEM.

SFC HIGH PRESSURE THEN BRIEFLY BUILDS INTO THE CWA MONDAY...WITH
RETURN FLOW SETTING UP ACROSS THE PLAINS AND IOWA INTO MONDAY NIGHT
AHEAD OF THE NEXT SHORTWAVE EJECTING OUT OF THE CENTRAL/SOUTHERN
ROCKIES. THIS SYSTEM NOT LOOKING AS DYNAMIC AS CURRENT SYSTEM...BUT
STILL LOOKING STRONG ENOUGH FOR A GOOD SHOT OF PRECIPITATION. TIMING
AND TRACK FROM THE LATEST MODEL RUNS SHOWING GOOD CONTINUITY WITH
SOME WAA -TRW EXPECTED TO PUSH INTO THE WESTERN CWA LATE MONDAY
NIGHT...THEN PUSHING THROUGH THE REMAINDER OF THE CWA TUESDAY.
LATEST TIMING BRINGS FRONTAL BOUNDARY THROUGH MID MORNING TO MID
AFTERNOON TIMEFRAME WHICH SHOULD LIMIT THE SEVERE/THUNDERSTORM
POTENTIAL SOME. HOWEVER LOW LEVEL FLOW STILL FAIRLY STRONG WITH
DECENT SHEAR SO CANNOT COMPLETELY RULE OUT SEVERE ACTIVITY ATTM.
PROGRESSIVE UPPER LEVEL FLOW CONTINUES THROUGH THE REST OF THE WEEK
INTO NEXT WEEKEND...WITH SFC HIGH PRESSURE BUILDING INTO THE AREA
WEDNESDAY. MODELS INDICATING SLIGHTLY COOLER H85 TEMPS SINKING DOWN
INTO THE AREA BEHIND THE SYSTEM TUESDAY SO DID LOWER TUESDAY NIGHT
LOWS A FEW DEGREES. WAA PATTERN AHEAD OF SFC LOW PRESSURE ASSOCIATED
WITH UPPER LEVEL TROUGH DIGGING INTO THE INTERMOUNTAIN WEST THURSDAY
NIGHT INTO FRIDAY WILL BRING ANOTHER CHANCE FOR SOME SHOWERS AND
THUNDERSTORMS ACROSS THE AREA. BEST FRONTAL POSITION/LIFT SHOWING UP
ACROSS THE AREA THURSDAY NIGHT...AND MAY PUSH NORTH OF THE AREA INTO
FRIDAY. AS SFC BOUNDARY GETS HUNG UP ACROSS THE AREA INTO THE
WEEKEND...BETTER CHANCES OF PRECIPITATION EXPECTED INTO SATURDAY AND
SATURDAY NIGHT. UPPER RIDGING EXPECTED TO BUILD ACROSS THE AREA INTO
SUNDAY. AS FOR TEMPERATURES...SEASONAL CONDITIONS ARE EXPECTED
THROUGHOUT THE FORECAST PERIOD...WITH H85 TEMPS HOVERING IN THE
TEENS CELSIUS FOR THE MOST PART.

&&

.AVIATION...30/18Z

CLASSIC NEG TILT TROF AND DRY LINE FEAT MOVG INTO THE STATE AND
TRIED TO TIME LINE OF SIG TSRA THRU THE TAFS.  FOLLOWING FROPA,
SHOULD SEE A PD OF A FEW HRS OF MVFR CIGS IN WNWLY FLOW WITH VFR
CONDS SPRDG OVR SITES BY SNRS.

&&

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

&&

SHORT TERM...MS SEP 07
LONG TERM...ALBRECHT
AVIATION...MS SEP 07

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1251 PM CDT SUN SEP 30 2007

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-011030-
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-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-
APPANOOSE-DAVIS-
1251 PM CDT SUN SEP 30 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

A LINE OF THUNDERSTORMS WILL DEVELOP RAPIDLY TO THE WEST AND MOVE
INTO WESTERN IOWA AFTER 200 PM.  THE STORMS WILL ADVANCE EAST INTO
CENTRAL IOWA BY THE LATE AFTERNOON AND TO THE EASTERN PART OF
CENTRAL IOWA BY LATE AFTERNOON.  THUNDERSTORMS WILL END FROM WEST TO
EAST DURING THE EARLY EVENING HOURS.  SOME OF THE THUNDERSTORMS ARE
LIKELY TO BE SEVERE THIS AFTERNOON OVER THE WEST HALF...AND INTO THE
EVENING HOURS EAST OF INTERSTATE 35.  SUPERCELL THUNDERSTORMS WILL
LIKELY BE THE INITIAL MODE DURING THE EARLY TO MID AFTERNOON
HOURS...WITH ALL TYPES OF SEVERE WEATHER POSSIBLE...INCLUDING
ISOLATED TORNADOES. THE STORMS WILL FORM INTO A LINE RATHER
QUICKLY.  AFTER THE LINE BECOMES WELL ORGANIZED...THE PRIMARY SEVERE
WEATHER THREAT WILL BE DAMAGING STRAIGHT LINE WINDS OF 60 TO 80 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THUNDERSTORMS WILL AGAIN AFFECT THE REGION ON TUESDAY AND SOME OF
THOSE STORMS COULD BE SEVERE AS WELL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY THIS AFTERNOON INTO THE EARLY
EVENING...AND MAY BE NEEDED TUESDAY.

MS SEP 07

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
447 PM CDT SUN SEP 30 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0430 PM     TSTM WND DMG     4 ESE DELPHOS           40.64N 94.28W
09/30/2007                   RINGGOLD           IA   TRAINED SPOTTER

            6 INCH TREE BRANCHES DOWN

&&

ALBRECHT