Severe Thunderstorm Warning 183, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
324 PM CDT SUN AUG 9 2009

.DISCUSSION...
FOCUS OF SEVEN DAY FORECAST IS ON CONVECITVE POTENTIAL REST OF TODAY
AND TONIGHT. IN WAKE OF MORNING SEVERE STORMS GOOD INSTABILITY
REMAINS ACROSS SOUTHERN HALF OR TWO THIRDS OF CWA WITH NEBULOUS
SURFACE FRONT/OUTFLOW BOUNDARY DRAPED NW-SE ACROSS CENTRAL IOWA.
DISORGANIZED STORMS CONTINUE TO FIRE UP WITHN BROAD PSEUDO-FRONTAL
ZONE. SECONDARY MID-LEVEL IMPULSE ASSOCIATED WITH BROAD TROUGH OVER
KS/NE APPROACHING AND SHOULD INITIATE STRONGER CONVECTION LATE THIS
AFTERNOON INTO TONIGHT...WITH THE ENVIRONMENT CONTINUING TO SUPPORT
ADDITIONAL SEVERE WEATHER. HAVE INCLUDED NUMEROUS TS AND SEVERE
WORDING ACROSS ABOUT SOUTHERN HALF/TWO THIRDS OF AREA TONIGHT. IN
ADDITION TO LARGE HAIL/HIGH WIND THREAT...THERE IS THE POTENTIAL FOR
TRAINING STORMS WITH STEERING FLOW TAKING THEM NORTHEAST THIS
EVENING ALONG THE FRONTAL ZONE...RESULTING IN LOCALLY HEAVY RAIN. IN
MOST OF OUR AREA FFG VALUES ARE QUITE HIGH AFTER A DRY MONTH OR
SO...HOWEVER THE SEVERE THUNDERSTORM THAT STRUCK NORTHEASTERN IOWA
THIS MORNING DROPPED A VERY QUICK INCH OR TWO OF RAIN ALONG THE
TRACK FROM EASTERN HARDIN THROUGH BLACK HAWK COUNTY. IN LIGHT OF
THESE FACTORS HAVE OPTED TO ISSUE A FLASH FLOOD WATCH FOR FIVE
COUNTIES AROUND THIS SWATH...TO RUN THROUGH 12Z TOMORROW MORNING.

FROM MONDAY THROUGH SATURDAY THE FORECAST REMAINS QUIET. KEPT A FEW
SLIGHT POPS MONDAY/MONDAY NIGHT WITH A SECONDARY SHORTWAVE MOVING
OVERHEAD IN THE MID-LEVEL FLOW...HOWEVER MOISTURE WILL BE VERY
LIMITED PRECLUDING ANY HIGHER POPS. HIGH PRESSURE WILL DOMINATE
TUESDAY THROUGH THURSDAY PRODUCING DRY...MILD...AND PLEASANT
WEATHER. TOWARD THE WEEKEND LONG-RANGE MODELS CONTINUE TO INDICATE A
MID-LEVEL TROUGH AND SURFACE FRONT TRAVERSING THE AREA. DISAGREEMENT
ON TIMING AND EVOLUTION OF THIS SYSTEM BETWEEN THE MODELS
PERSISTS...HOWEVER IT IS BEGINNING TO APPEAR A BIT MORE LIKELY THAT
A FRONT WILL APPROACH ON SUNDAY OR SUNDAY NIGHT SO HAVE UPPED THE
POPS A BIT TO LOW CHANCE CATEGORY AT THE END OF THE FORECAST PERIOD.

&&

.AVIATION...09/18Z
ELEVATED CONVECTION STILL DEVELOPING BEHIND COLD FRONTAL BOUNDARY
ACROSS STATE. POST-FRONTAL TAF SITES ARE OCCASIONALLY MVFR. CIGS ARE
TRENDING TO VFR THROUGHOUT THE DAY EXCEPT NEAR TS. AS THE FRONTAL
BOUNDARY MOVES SOUTHEAST TONIGHT...SITES SHOULD SEE SOME CLEARING
AND THERE WILL BE A POTENTIAL FOR RADIATIONAL FOG DEVELOPMENT.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...FLASH FLOOD WATCH THROUGH MONDAY
MORNING FOR BACLK HAWK-BREMER-GRUNDY-HARDIN-TAMA.

&&

SHORT TERM/LONG TERM...LEE
AVIATION...HINSBERGER

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
514 PM CDT SUN AUG 9 2009

IAZ037>039-050-101200-
HARDIN-GRUNDY-BLACK HAWK-TAMA-
514 PM CDT SUN AUG 9 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

SCATTERED STRONG THUNDERSTORMS ARE EXPECTED THIS EVENING AS THEY
TRACK TOWARD THE NORTHEAST. SOME STORMS WILL BE SEVERE. LARGE HAIL
OF GOLF BALL SIZE...STRONG DAMAGING WINDS...AND LOCALLY HEAVY RAIN
ARE THE PRIMARY THREATS.

A FLASH FLOOD WATCH IS IN EFFECT FOR THE OUTLOOK AREA THROUGH. PLEASE
REFER TO THE NATIONAL WEATHER SERVICE WEBSITE FOR FURTHER DETAILS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED LATE THIS AFTERNOON INTO TONIGHT.

IAZ046>049-057>062-070>075-081>086-092>097-101200-
GREENE-BOONE-STORY-MARSHALL-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-
DAVIS-
514 PM CDT SUN AUG 9 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED TO MOVE FROM WEST TO EAST
ACROSS CENTRAL AND SOUTHERN IOWA THIS EVENING AND OVERNIGHT. SOME STORMS
WILL PRODUCE HAIL OF GOLF BALL SIZE OR GREATER...STRONG DAMAGING WINDS
IN EXCESS OF 70 MPH...AND LOCALLY HEAVY RAIN. AN ISOLATED TORNADO IS
POSSIBLE...MAINLY SOUTH OF I-80.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED LATE THIS EVENING AND TONIGHT.

REV

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