Severe Thunderstorm Warning 336, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1245 PM CDT MON SEP 13 2010

.SHORT TERM /TODAY/...
WEAK SFC TROUGH AXIS IN PLACE ACROSS THE CENTRAL/SOUTHERN CWA...WITH
SOME MID LEVEL CLOUDS STRETCHING ACROSS CENTRAL NEBRASKA/IOWA IN
VICINITY OF WEAK FRONTAL BOUNDARY ALOFT. ANOTHER WEAK SHORTWAVE TO
MOVE THROUGH THE NEARLY ZONAL FLOW ALOFT...AND MOVE INTO IOWA BY
TONIGHT. SOUTHERLY FLOW ALOFT WILL INCREASE AHEAD OF THIS
WAVE...SENDING MOISTURE NORTHWARD INTO NEBRASKA/WESTERN IOWA BY LATE
THIS AFTERNOON. SURFACE WINDS BEGIN TO SHIFT BACK AROUND TO THE
SOUTH/SOUTHEAST BY LATE AFTERNOON ACROSS THE WESTERN CWA AS WELL.
NOSE OF THETA-E RIDGE ALOFT TO MOVE NORTHWARD AND EASTERN EDGE OF
MOISTURE ADVECTION TO BE SITUATED ACROSS EXTREME
WESTERN/SOUTHWESTERN CWA BY LATE AFTERNOON. HAVE SOME ELEVATED
INSTABILITY...BUT ATMOSPHERE TO REMAIN CAPPED WITH LOWER LEVEL
TEMPERATURES IN THE MID TO UPPER TEENS. LOOKS LIKE ANY THUNDERSTORM
ACTIVITY WILL LIKELY BE JUST BEYOND THE TODAY PERIOD AS THE
SHORTWAVE APPROACHES THE AREA ALOFT AT THIS TIME. H85 TEMPS JUST
SLIGHTLY COOLER THAN YESTERDAY...WITH SFC WINDS LIGHTER AND MORE OF
AN EASTERLY DIRECTION. WITH THAT SAID...KEPT MAX TEMPS SLIGHTLY
COOLER THAN HIGHS FROM THE PREVIOUS DAY.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
ACTIVE WEATHER APPEARS IN STORE FOR IOWA STARTING TONIGHT AND
PERSISTING THROUGH THURSDAY MORNING.  STRONG THETA-E AND THERMAL
ADVECTION IS EXPECTED TONIGHT AS A SHORTWAVE PASSES THROUGH THE
PLAINS.  CONVECTION IS FORECAST TO DEVELOP WEST OF THE STATE THIS
AFTERNOON AND SPREAD EAST INTO IA OVERNIGHT.  THIS CONVECTION WILL
BE FED BY A DECENT LLJ AND ASSOCIATED MOISTURE...THEREFORE LOCALIZED
HEAVY RAIN WILL BE POSSIBLE TONIGHT.  STORMS WILL PROGRESS SOUTHEAST
ON TUESDAY WITH PCPN COMING TO AN END BY MIDDAY ACRS THE AREA.
ANTICIPATE A LULL IN THE WEATHER FROM THIS TIME INTO EARLY WEDNESDAY
AS WEAK SFC RIDGING NUDGES INTO THE STATE.  HOWEVER...A MORE
VIGOROUS WAVE WILL CROSS THE INTERMOUNTAIN WEST AND PASS INTO THE
PLAINS BY WEDNESDAY.  THIS WILL INDUCE CYCLOGENESIS IN THE PLAINS ON
WEDNESDAY WITH MOISTURE STREAMING NORTHWARD AHEAD OF THE SYSTEM.
ANTICIPATE SHOWERS AND THUNDERSTORMS TO DEVELOP AND SPREAD INTO IA
DURING THE DAY ON WEDNESDAY AHEAD OF THE SFC LOW.  THE THREAT OF
PCPN WILL PERSIST INTO WEDNESDAY NIGHT AND EARLY THURSDAY AS
MOISTURE TRANSPORT REMAIN STRONG INTO THE STATE.  WITH RELATIVELY
HIGH PWATS AND DECENT THERMAL GRADIENT ACRS THE STATE...ANTICIPATE
STAGE WILL BE SET FOR ANOTHER ROUND OF HEAVY RAINS DURING THIS
TIME.  INSTABILITY NEVER GETS OUT OF HAND ACRS THE AREA WITH MAIN
AXIS OF HIGHER CAPES REMAINING TO THE WEST...THEREFORE DONT
ANTICIPATE A LARGE SEVERE THREAT AT THIS TIME BUT WILL CONTINUE TO
MONITOR.  AS WAVE PASSES LATE WEDNESDAY NIGHT...SUBSIDENCE WILL
INCREASE QUICKLY WITH PCPN CUTTING OFF RAPIDLY FROM WEST TO EAST BY
THURSDAY MORNING.  THEN DRY CONDITIONS WITH WEAK SFC RIDGING WILL
HOLD ON THROUGH THE DAY ON FRIDAY PRIOR TO THE ARRIVAL OF ANOTHER
FRONT.  BOTH GFS AND ECMWF INDICATE SOME ACTIVE WEATHER INTO THE
WEEKEND BUT PLENTY CAN CHANGE BETWEEN NOW AND THEN WITH NO CHANGE TO
THE GRIDS IN THAT TIME FRAME.

&&

.AVIATION...
13/18Z...CONVECTIVE TRENDS WILL BE THE PRIMARY FOCUS THROUGH THIS
PERIOD.  EXPECT SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS...THE
FIRST OF WHICH IS QUITE ELEVATED...9KFT OR ABOVE...AND JUST CROSSING
THE MO RIVER INTO IA NEAR KSUX/KTQE RIGHT NOW.  HAVE CARRIED SEVERAL
HOURS OF VCSH/CB WORDING AT KFOD TO ACCOUNT FOR THIS...AND MAY HAVE
TO INTRODUCE SIMILAR WORDING AT KDSM LATER THIS AFTERNOON.  LATER
TONIGHT ADDITIONAL AND LIKELY STRONGER CONVECTION SHOULD DEVELOP
WEST OF THE MO RIVER REACHING IA EARLY TUE MORNING.  THIS SHOULD BE
RELATIVELY HIGH BASED AS WELL SO HAVE CARRIED VFR THROUGHOUT THE
NIGHT AND TUE MORNING.  LOWER CONDITIONS ARE POSSIBLE...BUT
CONFIDENCE IN LOCATION AND TIMING NOT GREAT ENOUGH TO CARRY AT THE
MOMENT.  SIMILAR CONFIDENCE IN CONVECTION...SO NOTHING MORE THAN CB
RIGHT NOW.

&&

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

&&

SHORT TERM...BEERENDS/SMALL
LONG TERM...COGIL
AVIATION...SMALL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
555 AM CDT MON SEP 13 2010

IAZ005>007-016-017-024>028-035>039-046>050-058>062-071>075-081>086-
092>097-141100-
KOSSUTH-WINNEBAGO-WORTH-HANCOCK-CERRO GORDO-HUMBOLDT-WRIGHT-FRANKLIN-
BUTLER-BREMER-WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-GREENE-BOONE-
STORY-MARSHALL-TAMA-GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK-ADAIR-
MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS-MONROE-
WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
555 AM CDT MON SEP 13 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED NON SEVERE THUNDERSTORMS WILL BE POSSIBLE LATE TONIGHT
WITH HEAVY DOWNPOURS AND LOCALIZED HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

NON SEVERE STORMS WILL REMAIN ON TUESDAY MORNING WITH A HEAVY
RAIN THREAT...BEFORE ENDING BY MIDDAY. THUNDERSTORM CHANCES WILL
RETURN ON WEDNESDAY INTO EARLY THURSDAY. AT THIS POINT...SEVERE
WEATHER APPEARS LIMITED...HOWEVER THE STORMS WILL BE CAPABLE OF
PRODUCING HEAVY DOWNPOURS AND LOCALIZED FLOODING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

IAZ004-015-023-033-034-044-045-057-070-141100-
EMMET-PALO ALTO-POCAHONTAS-SAC-CALHOUN-CRAWFORD-CARROLL-AUDUBON-CASS-
555 AM CDT MON SEP 13 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL BE POSSIBLE LATE TONIGHT WITH A FEW
SEVERE STORMS POSSIBLE. LARGE HAIL WILL BE THE MAIN THREAT ALONG
WITH HEAVY DOWNPOURS WHICH COULD LEAD TO LOCALIZED FLOODING.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

NON SEVERE STORMS WILL REMAIN ON TUESDAY MORNING WITH A HEAVY
RAIN THREAT...BEFORE ENDING BY MIDDAY. THUNDERSTORM CHANCES WILL
RETURN ON WEDNESDAY INTO EARLY THURSDAY. AT THIS POINT...SEVERE
WEATHER APPEARS LIMITED...HOWEVER THE STORMS WILL BE CAPABLE OF
PRODUCING HEAVY DOWNPOURS AND LOCALIZED FLOODING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
210 PM CDT MON SEP 13 2010

IAZ044-132015-
CRAWFORD-
210 PM CDT MON SEP 13 2010

...STRONG THUNDERSTORMS ENTERING WEST CENTRAL IOWA...

AT 207 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM OVER EAST CENTRAL MONONA COUNTY...MOVING EAST AT
30 MPH.

UP TO PENNY SIZE HAIL...OCCASIONAL CLOUD TO GROUND LIGHTNING AND
BRIEF MODERATE DOWNPOURS...ARE POSSIBLE WITH THIS STORM.

* THE THUNDERSTORM WILL BE NEAR...
  CHARTER OAK BY 215 PM CDT...
  ARION AND DOW CITY BY 230 PM CDT...
  DENISON AIRPORT AND BUCK GROVE BY 240 PM CDT...
  9 MILES SOUTH OF VAIL BY 250 PM CDT...
  MANILLA BY 255 PM CDT...
  ASPINWALL BY 305 PM CDT...

STAY AWAY FROM HIGH OBJECTS OUTDOORS SUCH AS TREES. SEEK SHELTER IN A
STURDY STRUCTURE UNTIL THIS STORM HAS PASSED.

SMALL