Severe Thunderstorm Warning 288, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
646 PM CDT TUE AUG 3 2010

...UPDATED FOR 00Z AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
QUASI-STATIONARY FRONTAL BOUNDARY IS SET UP OVER SOUTHERN
IOWA/NORTHERN MISSOURI...BUT CONVERGENCE SEEMS LACKING ALONG THE
BOUNDARY. NAM/GFS CONSISTENT IN BRINGING PRECIP ALONG SOUTHERN IOWA
WHERE ECMWF/SREF BOTH EXPAND PRECIP AREA INTO NORTHERN IOWA. FEEL
THE NAM/GFS TO BE MORE REPRESENTATIVE. MOISTURE TRANSPORT SHOULD BE
FAIRLY WEAK TONIGHT AS WEST-SOUTHWESTERLY LLJ REMAINS UNDER 20 KTS
AS INDICATED BY MODELS...HOWEVER AIRMASS IS ALREADY FAIRLY MOIST
WITH PWATS OF AROUND 2.4 INCHES. FORWARD AND BACKWARD PROPAGATING
CORFIDI VECTORS BOTH INDICATING STORM MOTION SHOULD BE PROGRESSIVE
TONIGHT. HIGH PWATS NOTWITHSTANDING...BELIEVE THE LACK OF ANY STRONG
FORCING AND PROGRESSIVE STORM MOTION WILL PRODUCE LOWER QPF THAN
GUIDANCE.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
HUDSON BAY UPPER TROUGH SHOULD BE STRONG ENOUGH TO PUSH PERSISTENT
QUASI-STATIONARY BOUNDARY WELL SOUTH BY WEDNESDAY NIGHT. LINGERING
THUNDERSTORMS FROM TONIGHT PLUS SOME SHORTWAVE ENERGY MOVING INTO
CENTRAL IA IS ENOUGH TO JUSTIFY SMALL POPS ON WEDNESDAY.  SUBSIDENCE
BEHIND THE WAVE WEDNESDAY NIGHT COUPLED WITH 850 MB DRYING AND WEAK
COLD ADVECTION SUGGEST DRY CONDITIONS SO PCPN WAS REMOVED FROM THE
FORECAST.  RELIEF FROM HIGH HUMIDITY THURSDAY AND THURSDAY NIGHT AS
SURFACE RIDGE BUILDS IN.  BASED TEMPS ON BLEND OF MET/MAV WHICH
APPEARED REASONABLE IN LOWERING TEMPS TO NEAR NORMAL.

IN THE DAY 4-7 RANGE /FRIDAY THROUGH TUESDAY/...BASED FORECAST ON A
COMBINATION OF 00Z GFS ENSEMBLES...00Z ECMWF AND TO A LESSER EXTENT
THE 06Z GFS.  HUDSON BAY UPPER TROUGH FORECAST TO FLATTEN THE UPPER
RIDGE EARLY IN THE PERIOD OVER THE GREAT LAKES AND OHIO VALLEY. IN
TURN...THE RIDGE IS FORECAST TO BUILD NORTH OVER THE PLAINS BY THE
END OF THE WEEK AND INTO THE WEEKEND AND BEYOND.  THE MODELS ARE IN
FAIR AGREEMENT WITH THE OVERALL PATTERN. SURFACE HIGH PRESSURE RIDGE
SHOULD BE NEAR IOWA ON FRIDAY BEFORE IT MOVES EAST ALLOWING RETURN
FLOW DO DEVELOP UNDER RISING 500 MB HEIGHTS.  KEPT WAA THUNDERSTORM
CHANCES GOING AS DEEPER MOISTURE AND WARM AIR RETURN.  BY DAYS
6-7...RIDGE SHOULD BE WELL ESTABLISHED PUSHING THE WESTERLIES NORTH
OF IA. THIS SHOULD DECREASE PRECIPITATION CHANCES. CENTRAL IA SHOULD
BE WELL INTO THE WARM AIR AND EXPECT TO SEE HOT AND HUMID
CONDITIONS.  MADE SOME ADJUSTMENTS COMPARED TO HPC GUIDANCE
INCLUDING SLIGHTLY WARMER TEMPERATURES AND HIGHER DEWPOINT
TEMPERATURES.

.AVIATION...04/00Z
VFR CONDITIONS WILL REMAIN THIS EVENING INTO THE OVERNIGHT.  MAIN
CONCERN IS FOR THUNDERSTORMS DEVELOPMENT IN PORTIONS OF CENTRAL IOWA
OVERNIGHT.  THIS WOULD PRODUCE AREAS OF MVFR TO IFR CONDITIONS IN
AND AROUND THE THUNDERSTORMS WITH LOW MVFR CIGS IN PORTIONS OF THE
STATE.  THE THUNDERSTORMS ARE EXPECTED TO SHIFT EAST ON WEDNESDAY
MORNING WITH CLEARING AS WEAK HIGH PRESSURE BUILDS INTO THE STATE.
ANTICIPATE WIDESPREAD VFR CONDITIONS BY 18Z ON WEDNESDAY AND
CONTINUING FOR THE REMAINDER OF THE DAY.

&&

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

&&

SHORT TERM...HINSBERGER
AVIATION...COGIL
LONG TERM...JAJ

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
825 PM CDT TUE AUG 3 2010

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-041100-
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-
825 PM CDT TUE AUG 3 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR ALL OF CENTRAL IOWA.

.DAY ONE...TONIGHT

ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED OVERNIGHT ACROSS
CENTRAL IOWA...WITH THE MAIN THREAT SOUTH OF HIGHWAY 20. SEVERE
WEATHER IS NOT EXPECTED AT THIS TIME. HOWEVER...HEAVY RAINFALL
MAY OCCUR WITH LOCALIZED FLOODING POSSIBLE.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SCATTERED THUNDERSTORMS ARE EXPECTED INTO WEDNESDAY MORNING BEFORE
GRADUALLY ENDING BY AFTERNOON. AT THIS POINT...SEVERE WEATHER IS
NOT EXPECTED. ADDITIONAL THUNDERSTORMS CHANCES ARE EXPECTED BY
THIS WEEKEND...HOWEVER IT IS TOO EARLY TO DETERMINE SEVERE WEATHER
CHANCES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME.

CC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
627 PM CDT TUE AUG 3 2010

IAZ027-028-037>039-048>050-060>062-073>075-040130-
BUTLER-BREMER-HARDIN-GRUNDY-BLACK HAWK-STORY-MARSHALL-TAMA-POLK-
JASPER-POWESHIEK-WARREN-MARION-MAHASKA-
INCLUDING THE CITIES OF...ALLISON...WAVERLY...ELDORA...
GRUNDY CENTER...WATERLOO...AMES...MARSHALLTOWN...TOLEDO...
DES MOINES...NEWTON...GRINNELL...INDIANOLA...KNOXVILLE...
OSKALOOSA
627 PM CDT TUE AUG 3 2010

...CONDITIONS ARE FAVORABLE FOR FUNNEL CLOUDS...

CURRENT ATMOSPHERIC CONDITIONS SUPPORT THE DEVELOPMENT OF FUNNEL
CLOUDS. USUALLY...THESE FUNNEL CLOUDS CAN FORM FROM SHOWERS AND
WEAK THUNDERSTORMS. THESE FUNNELS ARE NORMALLY BRIEF...DROP ONLY
A FEW HUNDRED FEET FROM THE CLOUD BASE...AND RARELY BECOME A
TORNADO OR CAUSE DAMAGE. HOWEVER...IF ONE IS SPOTTED...PLEASE
REPORT IT IMMEDIATELY TO LOCAL LAW ENFORCEMENT FOR RELAY TO THE
NATIONAL WEATHER SERVICE. IF A TORNADO WARNING WOULD BECOME
NECESSARY...TAKE APPROPRIATE ACTION.

COGIL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1130 PM CDT TUE AUG 03 2010

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

1112 PM     TSTM WND GST     WSW FONTANELLE          41.29N 94.57W
08/03/2010  M62 MPH          ADAIR              IA   MESONET

            SCHOOLNET INSTRUMENT MEASURED A WIND GUST TO 54 KT / 62
            MPH.

&&

LEE