Severe Thunderstorm Warning 47, NWS Des Moines, IA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
625 PM CDT THU APR 29 2010

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
SURFACE CDFNT ENTERED NW IA BY 20Z. STRONG SOUTHERLY FLOW EXTENDED
ACROSS CENTRAL IOWA WITH MANY LOCATIONS MEETING WIND ADVRY
CRITERIA.  WILL KEEP ADVISORY GOING UNTIL 5 PM. AT THAT POINT...IT
WILL BE ALLOWED EXPIRE IF THE WINDS ARE STARTING TO COME DOWN.
FORECAST PROBLEM TONIGHT IS THUNDERSTORM POTENTIAL TONIGHT.  RETURN
FLOW MOISTURE COMING INTO IA ATTM WITH SURFACE DEWPOINTS IN THE
50S.  MIXED LAYER CAPES NEAR 1000 J/KG OVR WRN IA ATTM BUT
INSTABILITY APPEARS CAPPED. MOISTURE CNVG LOOKS BEST SOUTHWEST OF
IOWA AND ANOTHER MAXIMUM IN NW IA.  THINKING NOW IS THAT DEVELOPMENT
WILL OCCUR SOUTHWEST OF DMX FA THIS EVENING AND THEN MOVE NORTHEAST
ACROSS CENTRAL IA TONIGHT.  ALSO...BECOMING A LITTLE CONCERNED ABOUT
AREA OF MOISTURE CNVG OVR NW IA WHERE THERE IS DECENT SURFACE
CONFLUENCE.  BASED ON THIS...WILL FORECAST CHANCE OF THUNDERSTORMS
ALL EVENING INSTEAD OF DELAYING ONSET UNTIL AFTER 03Z.  GOOD DEEP
SHEAR FOR ROTATION...BUT HIGH TEMP/DEWPOINT SPREADS SHOULD RESULT IN
HIGH BASED TSTMS SO TORNADO THREAT LOOKS LOW.  BETTER THREAT FOR
THAT MIGHT BE TONIGHT DUE TO DECENT LOW-LVL SHEAR.  MAIN THREAT IN
WRN IA SHOULD BE LARGE HAIL WITH ISOLD SVR WIND. PW VALUES
RELATIVELY LOW AND FAST MOVEMENT SHOULD MINIMIZE HEAVY RAIN THREAT.
BY 12Z...EXPECT SURFACE BNDRY OVER CENTRAL IA WITH DECAYING
CONVECTION.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
SHOWERS AND THUNDERSTORMS LIKELY ONGOING A THE START OF THE PERIOD
OVER NORTHWEST IOWA. LOW PRESSURE WILL LIFT NORTH LIFT OUT OF KANSAS
DURING THE DAY WITH THE SFC FRONTAL BOUNDARY RETROGRADING BACK TO
THE WEST DURING MORNING. SOME UNCERTAINTY TONIGHT ABOUT EXACT
BOUNDARY LOCATION ON FRIDAY DUE TO OVERNIGHT CONVECTION HOWEVER THE
BOUNDARY SHOULD BE NEAR INTERSTATE 35 BY LATE MORNING INTO THE EARLY
AFTERNOON. STRONG SHORT WAVE AND UPPER JET WILL ARRIVE TOWARD 18Z
AND SHOULD FORCE CONVECTION INITIATION BY EARLY TO MID AFTERNOON.
SUPERCELL POTENTIAL LOOKS HIGH AND DOMINATED BY RIGHT MOVERS. STRONG
SHEAR AND MID TO UPPER LEVEL FLOW SHOULD ENHANCE TORNADO POTENTIAL
ALONG WITH LOWERING LCL LEVELS AS DEWPOINTS INCREASE INTO THE LOWER
TO MID 60S. WITH DRY MID LEVEL AIR...COULD HAVE DISCRETE SUPERCELLS
INITIALLY EVENTUALLY TRANSLATING INTO A LINEAR LINE WITH EMBEDDED HP
SUPERCELLS. BUNKER RIGHT MOVING SUPERCELL MOTIONS OF 55-65 KTS AND
850-300 MB MEAN WINDS OF 75 KTS ENSURE THAT ANY STORMS WILL BE
RACING TO THE NORTHEAST.

SOME CHANCES FOR SHOWERS AGAIN SATURDAY NIGHT OVER THE FAR SOUTHEAST
THEN MAINLY DRY FOR THE REMAINDER OF THE EXTENDED. MAIN FORECAST
CHALLENGE IN THE DAY 4-7 PERIOD IS FRONTAL TIMING MID WEEK.  FAVOR
THE SLOWER ECMWF/GEM SOLUTIONS OVER THE MORE PROGRESSIVE GFS. THE
RESULT IS WARMER THROUGH MUCH OF THE PERIOD.

&&

.AVIATION...
30/00Z...BOUNDARY STRETCHING FROM WEST OF KMCW TO NEAR KFOD INTO
SOUTHEAST NEB WILL BE THE FOCUS FOR THUNDERSTORMS THIS EVENING AND
ACTUALLY RIGHT ON THROUGH THE PERIOD. AM MOST CONCERNED ABOUT TS AT
KMCW AND KFOD EARLY IN THE PERIOD...THEN POSSIBLY AT KDSM LATER
TONIGHT. INSTABILITY WANES OVERNIGHT AND PRECIP SHOULD BECOME MAINLY
SHOWERS. AFTER 18Z THREAT OF TSRA RISES AGAIN...MAINLY ALONG AND
EAST OF I-35. CEILINGS AND VSBY SHOULD INITIALLY REMAIN VFR UNLESS
DIRECTLY UNDER A TSRA...BUT BY MORNING INCREASING LOW LEVEL MOISTURE
SHOULD BRING CEILINGS DOWN BELOW 030.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...WIND ADVISORY FOR THE ENTIRE CWA
FROM 15Z THROUGH 22Z.

&&

SHORT TERM...JOHNSON
LONG TERM...DONAVON
AVIATION...MOYER

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
512 PM CDT THU APR 29 2010

IAZ007-017-025>028-036>039-047>050-059>062-072>074-083>085-094>097-
302215-
WORTH-CERRO GORDO-WRIGHT-FRANKLIN-BUTLER-BREMER-HAMILTON-HARDIN-
GRUNDY-BLACK HAWK-BOONE-STORY-MARSHALL-TAMA-DALLAS-POLK-JASPER-
POWESHIEK-MADISON-WARREN-MARION-CLARKE-LUCAS-MONROE-DECATUR-WAYNE-
APPANOOSE-DAVIS-
512 PM CDT THU APR 29 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

SCATTERED THUNDERSTORMS MAY DEVELOP THIS EVENING IN SOUTHWEST
IOWA. ADDITIONAL THUNDERSTORMS ARE EXPECTED TO MOVE INTO WESTERN
IOWA THIS EVENING AND ACROSS CENTRAL IOWA TONIGHT. A FEW STORMS
MAY PRODUCE LARGE HAIL AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS CENTRAL IOWA MIDDAY
FRIDAY OR FRIDAY AFTERNOON. THE STORMS MAY BE SEVERE WITH
DAMAGING THUNDERSTORM WINDS...LARGE HAIL AND POSSIBLE TORNADOES.
THE RISK OF SEVERE WILL LIKELY SHIFT EAST INTO EASTERN IOWA BY
FRIDAY EVENING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT AND WILL LIKELY BE NEEDED
ON FRIDAY.

IAZ075-086-302215-
MAHASKA-WAPELLO-
512 PM CDT THU APR 29 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

SCATTERED THUNDERSTORMS MAY DEVELOP THIS EVENING IN SOUTHWEST
IOWA. ADDITIONAL THUNDERSTORMS ARE EXPECTED TO MOVE INTO WESTERN
IOWA THIS EVENING AND ACROSS CENTRAL IOWA TONIGHT. A FEW STORMS
MAY PRODUCE LARGE HAIL AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS CENTRAL IOWA MIDDAY
FRIDAY OR FRIDAY AFTERNOON. SOME OF THE STORMS MAY BE SEVERE WITH
DAMAGING THUNDERSTORM WINDS...LARGE HAIL AND POSSIBLE TORNADOES.
THE RISK OF SEVERE WILL LIKELY SHIFT EAST INTO EASTERN IOWA BY
FRIDAY EVENING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT AND WILL LIKELY BE NEEDED
FRIDAY.

IAZ004>006-015-016-023-024-033>035-044>046-057-058-070-071-081-082-
092-093-302215-
EMMET-KOSSUTH-WINNEBAGO-PALO ALTO-HANCOCK-POCAHONTAS-HUMBOLDT-SAC-
CALHOUN-WEBSTER-CRAWFORD-CARROLL-GREENE-AUDUBON-GUTHRIE-CASS-ADAIR-
ADAMS-UNION-TAYLOR-RINGGOLD-
512 PM CDT THU APR 29 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

SCATTERED THUNDERSTORMS MAY DEVELOP OVER SOUTHWEST IOWA LATE THIS
AFTERNOON. ADDITIONAL THUNDERSTORMS WILL LIKELY MOVE INTO WESTERN
IOWA THIS EVENING. THE STORMS WILL THEN CONTINUE TO MOVE NORTHEAST
INTO CENTRAL IOWA TONIGHT. THERE IS A SLIGHT CHANCE OF SEVERE
WEATHER WITH LARGE HAIL THE PRIMARY THREAT AND STRAIGHT LINE WINDS
THE SECONDARY THREAT. AN ISOLATED TORNADO IS POSSIBLE OVER
SOUTHWEST IOWA EARLY THIS EVENING.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THUNDERSTORMS ARE IN THE FORECAST FOR FRIDAY. THE MAIN THREAT OF
SEVERE WEATHER WILL BE OVER CENTRAL AND EASTERN IOWA EAST OF A
FORT DODGE TO CRESTON LINE. ALL MODES OF SEVERE WEATHER ARE
POSSIBLE ON FRIDAY INCLUDING LARGE HAIL...DAMAGING WINDS AND TORNADOES.

THERE MAY BE ADDITIONAL NON SEVERE THUNDERSTORMS MONDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT AND FRIDAY.

MOYER

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
639 PM CDT THU APR 29 2010

IAZ005>007-016-017-023>025-033>036-044>046-057-058-070-300145-
KOSSUTH-WINNEBAGO-WORTH-HANCOCK-CERRO GORDO-POCAHONTAS-HUMBOLDT-
WRIGHT-SAC-CALHOUN-WEBSTER-HAMILTON-CRAWFORD-CARROLL-GREENE-
AUDUBON-GUTHRIE-CASS-
INCLUDING THE CITIES OF...ALGONA...FOREST CITY...NORTHWOOD...
GARNER...MASON CITY...POCAHONTAS...HUMBOLDT...CLARION...
SAC CITY...ROCKWELL CITY...FORT DODGE...WEBSTER CITY...DENISON...
CARROLL...JEFFERSON...AUDUBON...GUTHRIE CENTER...ATLANTIC
639 PM CDT THU APR 29 2010

...STRONG THUNDERSTORMS POSSIBLE THIS EVENING...

SCATTERED THUNDERSTORMS WILL FORM IN A LINE FROM NEAR FOREST CITY
TO ATLANTIC BY 9 PM. MOST OF THE STORMS WILL MOVE OFF TO THE
NORTHEAST AT OVER 50 MPH. OTHER STORMS MAY MOVE INTO CRAWFORD AND
SAC COUNTIES BY 730 PM. ANY STORMS COULD BECOME STRONG OR POSSIBLY
SEVERE...WITH HAIL UP TO THE SIZE OF GOLF BALLS AND WIND GUSTS
OVER 60 MPH. THESE THUNDERSTORMS WILL LIKELY LAST WELL INTO THE
NIGHTTIME HOURS...THOUGH THEIR INTENSITY SHOULD WANE OVERNIGHT.

MOYER