Severe Thunderstorm Warning 73, NWS Des Moines, IA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1247 PM CDT WED MAY 12 2010

.UPDATE AVIATION 12/18Z...

.SHORT TERM /TODAY/...
UPDATED ZONES TO REFLECT CONTINUED REGENERATION OF SHOWERS/SCT
THUNDER ACROSS THE SOUTH.  FORCING LOOKS TO REMAIN FAIRLY UNIFORM
THIS AFTERNOON OVER THE SOUTH HALF.  SEVERE POTENTIAL MAY INCREASE
FAR SOUTH THIS EVENING AS MAIN SHORT WAVE LIFTS NORTHEAST. ATTM...
LOOKS LIKE HAIL WOULD BE THE MAIN THREAT AS LATEST GFS GUIDANCE NOW
HAS 1200-1600 J/KG MLCAPE OVER FAR SOUTH THIS EVENING. WILL BE
MONITORING TRENDS FOR THE DAY TODAY/THIS EVENING.  HEAVY RAIN THREAT
STILL VERY LIKELY SOUTH/SOUTHEAST THIS EVENING AND TNT WITH
POTENTIAL OF 2-3 INCH RAINFALL IN HEAVIER STORMS./REV

.PREVIOUS SHORT TERM /TODAY/...
BROAD THETA-E/WARM ADVECTION REGIME HAS DEVELOPED CONVECTION ACROSS
NE...KS AND MO AIDED BY SHORT WAVE WHICH LIFTED INTO HIGH PLAINS
DURING THE EVENING.  HOWEVER...UNFORTUNATELY...NONE OF THE MODELS
WITH EITHER EXPLICIT OR PARAMETERIZED CONVECTIVE SCHEMES SEEM TO BE
HANDLING REALITY TOO WELL AT THE MOMENT LEADING TO REDUCED
CONFIDENCE.  THUS WILL LEAN TOWARD EXTRAPOLATION SOMEWHAT FOR THE
FORECAST...ESPECIALLY THIS MORNING.  SEEMS TO BE A DECENT DVN/UVM
COUPLET WITH WAVE LIFTING ACROSS KS/NE AND EXTRAPOLATION SUGGESTS A
SEVERAL HOUR WINDOW OF SHOWERS AND STORMS LIFTING ACROSS NWRN 2/3RDS
OF IA THIS MORNING.  ALTHOUGH THE WAVE MAY PRODUCE A BREAK...BELIEVE
STRONG LIFT NOTED ON 300/305K SFCS WILL EVENTUALLY DEVELOP
ADDITIONAL CONVECTION LATER THIS AFTERNOON AS INFLUENCE OF CURRENT
KS/NE WAVE WANES.  ONGOING KS/MO CONVECTION CLOSER TO SFC WARM FRONT
APPEARS TO BE MOVING MORE EAST THAN NORTH...SO SERN IA IN ELEVATED
MOISTURE CONVERGENCE MIN MAY NOT SEE MUCH CONVECTION UNTIL
ADDITIONAL SFC BASED DEVELOPMENT OCCURS.  NAM/GFS MLCAPES/CINS SEEM
TO HOLD THIS POTENTIAL OFF UNTIL AFTER 00Z WHEN UPSTREAM DEVELOPMENT
OVER MO MAY FINALLY REACH SERN IA.

NELY WINDS WITH PLENTY OF CLOUDS AND PRECIP SHOULD KEEP TEMPS FROM
RISING MUCH AT ALL TODAY.  RAW LOW LEVEL MODEL TEMPS SUGGEST AT OR
BELOW THE COOLER END OF GUIDANCE IS BEST.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
BULK OF THE FORECAST REMAINS FORECAST ON HEAVY RAIN AND SEVERE
WEATHER POTENTIAL FOR THIS EVENING INTO EARLY THURSDAY MORNING.
MODELS IN DISAGREEMENT WITH THE AMOUNT OF QPF AND PLACEMENT TONIGHT
INTO THURSDAY...BUT THERE IS AGREEMENT WITH LOCATION OF 500MB LOW
AND TIMING OF COLD FRONT THROUGH THE STATE PAST 06Z THURSDAY.
LEANED TOWARDS THE ECMWF FOR QPF AND POPS AS IT HAS BEEN THE MOST
CONSISTENT WITH THIS SYSTEM THE PAST COUPLE OF MODEL RUNS.

TONIGHT INTO THURSDAY...IMPRESSIVE ISENTROPIC LIFT AND MOISTURE
TRANSPORT CONTINUES ACROSS THE STATE TONIGHT ALONG AND NORTH OF THE
WARM FRONT...AND THEN CONFINES MAINLY TO THE SOUTHEAST CWA PAST 06Z
THURSDAY AS FRONTAL BOUNDARY BEGINS TO PUSH ACROSS AREA.
FRONTOGENETICAL FORCING AND MOISTURE AVAILABLE STILL PREVALENT
ENOUGH TO KEEP CHANCE POPS ACROSS THE NORTHWEST PAST 06Z. BEST
ELEVATED INSTABILITY COVERS MUCH OF THE SOUTHERN AND EASTERN HALF
OF THE CWA TONIGHT. 0-1KM SHEAR VALUES RANGES FROM 30-35KTS
TONIGHT...WITH HELICITY VALUES WELL IN THE 300-400 M2/S2 RANGE
ACROSS THE SOUTH. HOWEVER...BUFR SOUNDINGS STILL SHOWING STRONG
INVERSION WITHIN THE SAME AREA SO TORNADIC DEVELOPMENT LOOKS TO BE
DIFFICULT. BETTER SHOT AT RECEIVING SOME ELEVATED LARGE HAILERS
TONIGHT...BUT CANNOT RULE OUT THE POTENTIAL FOR AN ISOLATED
TORNADO ACROSS THE FAR SOUTH ALONG THE BORDER. PW VALUES IN THE
RANGE OF 1.5 TO NEAR 2 INCHES WITH WARM CLOUD TOPS NEARING 12000
FEET TONIGHT OVER THE SOUTHEAST. AREA IS STILL PRIMED FROM RECENT
RAINFALL. AS A RESULT...ISSUED A FFA FOR THE SOUTH AND EASTERN
PORTIONS OF THE CWA WHERE QPF AMOUNTS RANGE IN THE 1-1.5 INCHES
THROUGH TOMORROW MORNING WITH THE BULK OF THAT COMING B/T 00-06Z
TONIGHT.

FRIDAY THROUGH SUNDAY...SURFACE HIGH PRESSURE BUILDS INTO THE REGION
FRIDAY AND SATURDAY AND IT WILL BE A WELCOMING DRY AND WARMER
PERIOD.  GFS/ECMWF DEPICTING A WEAK SHORTWAVE TO CUT ACROSS THE
STATE SATURDAY NIGHT INTO SUNDAY. KEPT WITH LOW POPS OVER THE SOUTH
DURING THIS TIME FRAME. TOOK OUT POPS SATURDAY MORNING WITH VERY DRY
AIRMASS IN PLACE AND TWEAKED HIGH TEMPS UP SLIGHTLY.

&&

.AVIATION...
12/18Z...RATHER COMPLEX FCST FOR THE NEXT 18 HOURS. H850 FRONT
CONTINUES TO FIRE CONVECTION OVER THE AREA NOW...WITH EXPECTED WAVE
AND STRONG H850 JET MAX TO INTERACT WITH THE H850 FRONT
TONIGHT...BRINGING MOD/HEAVY RAIN OVER THE NORTHEAST THROUGH 07Z.
FARTHER SOUTHEAST...LINE OF STORMS/HEAVY RAINFALL EXPECTED TO
DEVELOP ACROSS SOUTH CENTRAL IA THIS EVENING AND AFFECT KOTM FOR
MUCH OF THE EVENING/EARLY OVN HOURS THROUGH 08Z. BOTTOM LINE IS THAT
CIGS WILL DROP TO IFR MOST AREAS BY 00Z WITH ONLY SOME IMPROVEMENT
TO LOW MVFR BY 13Z THURS. VSBYS WILL AGAIN BE MVFR WITH OCCASIONAL
IFR IN HEAVIER STORMS. HAVE NOT TRIED TO TIME WORST VSBYS FOR NOW...
BUT EXPECT THE 00-06Z TIMEFRAME TO PRESENT THE MOST DIFFICULT
CONDITIONS. SYSTEM WILL LIFT AWAY AFT 15Z THURS WITH GRADUAL
IMPROVEMENT TOWARD END OF PERIOD. CONCENTRATED ON CONDITIONS THROUGH
13/11Z THIS FCST DUE TO COMPLEXITY./REV

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM THIS EVENING THROUGH THURSDAY MORNING FOR
APPANOOSE-CLARKE-DAVIS-DECATUR-JASPER-LUCAS-MAHASKA-MARION-
MONROE-POWESHIEK-RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-WAYNE.

&&

SHORT TERM SMALL/REV
AVIATION...SMALL
LONG TERM...PODRAZIK

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
428 AM CDT WED MAY 12 2010

IAZ061-062-073>075-082>086-092>097-130930-
JASPER-POWESHIEK-WARREN-MARION-MAHASKA-UNION-CLARKE-LUCAS-MONROE-
WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
428 AM CDT WED MAY 12 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

A FLASH FLOOD WATCH IS IN EFFECT FOR THE AREA. PLEASE REFER TO
THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR
FURTHER DETAILS.

STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS
AFTERNOON AND CONTINUE ACROSS THE AREA TONIGHT. LARGE HAIL AND
DAMAGING WINDS WILL BE THE MAIN THREAT WITH THE SEVERE WEATHER.
HOWEVER...AN ISOLATED TORNADO CANNOT BE RULED OUT ALONG THE
MISSOURI BORDER. IN ADDITION TO THE SEVERE WEATHER
POTENTIAL...AREAS OF FLASH FLOODING ARE POSSIBLE AS THE GROUND IS
STILL VERY SATURATED FROM THE RAIN EARLIER IN THE WEEK AND THE
RAINFALL AMOUNTS FORECAST FOR TONIGHT RANGE FROM 1 TO 2 INCHES
AND LOCALLY HIGHER AMOUNTS. RIVER FLOODING MAY ALSO POSE A PROBLEM
IN SOME AREAS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS AFTERNOON AND
TONIGHT.

KLP

IAZ004>007-015>017-023>028-033>039-044>050-057>060-070>072-081-
130930-
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-CASS-ADAIR-
MADISON-ADAMS-
428 AM CDT WED MAY 12 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

ISOLATED TO SCATTERED THUNDERSTORMS ARE POSSIBLE LATE THIS
MORNING INTO TONIGHT. THE SEVERE THREAT IS LOW...BUT AN ISOLATED
STRONG THUNDERSTORM COULD PRODUCE HAIL AT TIMES. LOCALLY HEAVY
RAIN IS ALSO EXPECTED WERE UP TO AN INCH OF NEW RAINFALL MAY
ACCUMULATE BY LATE TONIGHT.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAYBE NEEDED TODAY AND TONIGHT.

KLP

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