Severe Thunderstorm Warning 138, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
342 PM CDT WED MAY 23 2007

.DISCUSSION...

FOR THE SHORT TERM PERIODS TONIGHT THROUGH SATURDAY...MAIN CONCERN
IS FLASH FLOOD POTENTIAL TONIGHT OVER MOST OF CWA. HPC HAS PORTIONS
OF THE CWA COVERED WITH A MODERATE RISK FOR EXCESSIVE RAINFALL
THROUGH THURSDAY AFTERNOON...AND THE POTENTIAL FOR UP TO 5 INCHES
LOCALLY WITH STRONGER THUNDERSTORMS. AMPLE MOISTURE IN PLACE WITH AN
AXIS OF HIGH PWS FROM THE GULF STATES TO THE UPPER MIDWEST. AN 18Z
SOUNDING HERE SHOWED PWS VALUE OF 1.33...A BIT OVER 150% OF NORMAL.
ACTIVITY WILL DEVELOP AS STRONG DYNAMICS FROM APPROACHING UPPER LEVEL
VORT MAX CURRENTLY ROUNDING THE BASE OF MAIN UPPER TROF OVER THE
ROCKIES ENVELOPS THE PLAINS. MEANWHILE A NEARLY STAGNANT SURFACE
BOUNDARY EXTENDED FROM ABOUT SRN MN THROUGH ERN NEB AND NRN KS. A
SECOND...STRONGER BOUNDARY WAS UPSTREAM AND WAS PUSHING ACROSS THE
WRN DAKOTAS. LARGE SCALE LIFT INCREASES DRAMATICALLY THIS EVENING AS
UPPER DYNAMICS INCREASE VIA FAVORABLE JET POSITION/RRQ DIVG AND
INCREASING DPVA COMBINES WITH STOUT BOUNDARY LAYER CONVERGENCE
ASSOCIATED WITH SECONDARY SURFACE FRONT PUSHING THROUGH. PCPN
EFFICIENCY ALSO FAVORABLE FOR HEAVY RAIN WITH DEEP WARM CLOUD DEPTH
FROM CLOUD BASE TO 3KM. THEREFORE WILL POST FLASH FLOOD WATCH AREAS
SOUTHEAST OF A LINE FROM ABOUT PLATTE COUNTY TO WAYNE COUNTY
THROUGH 12Z THURSDAY. THROUGH THURSDAY AFTERNOON MODELS QUICKLY SHIFT
BEST FORCING/MOISTURE WELL EAST OF THE CWA. HOWEVER...WILL GO WITH
TOKEN SLGT POPS DURING THE AFTERNOON IN CASE OF POST-FRONTAL
ACTIVITY. OTHERWISE...DRY FORECAST IN PLACE UNTIL FRIDAY NIGHT WHEN
LOW LEVEL JET KICKS IN AND ADVECTS MORE GULF MOISTURE INTO THE
PLAINS...POSSIBLY POPPING OFF SOME WARM SECTOR ELEVATED CONVECTION.
WILL CONTINUE POPS INTO SATURDAY AS ANOTHER NORTHERN PLAINS WAVE
PUSHES THE NEXT COLD FRONT ACROSS THE CWA.

IN THE EXTENDED PERIODS SUNDAY THROUGH WEDNESDAY...ACTIVE WEATHER
ANTICIPATED WITH AMPLE GULF MOISTURE AVAILABLE COINCIDING WITH A
SERIES OF FROPAS. ON SUNDAY MODELS DEPICT SURFACE HIGH PRESSURE
CENTERED NEAR THE DAKOTAS EXTENDING INTO PORTIONS OF THE CENTRAL
PLAINS AND PUSHING THE SURFACE COLD FRONT INTO KS/MO. MODELS SUGGEST
THE BOUNDARY LIFTING NORTHWARD BY LATE AFTERNOON SUNDAY AND ACROSS
THE CWA SUNDAY NIGHT. IT APPEARS HPC IS FAVORING THE ECMWF/CMC
SOLUTION OF PLACING SURFACE LOW OVER CENTRAL HIGH PLAINS MOVING THE
BOUNDARY NORTHWARD WHILE THE GFS SEEMS TO DELAY IT NORTHWARD TILL
MONDAY. ALL THIS IN PART TO DIFFERING LARGE SCALE PATTERN ACROSS THE
CONUS. ECMWF/CMC PROG SHARPER PACIFIC NW TROF WHILE GFS FLOW IS
FLATTER...THUS THE MORE PROGRESSIVE SOLUTION BY THE ECMWF/CMC. WILL
THEREFORE COVER THE CWA WITH SMALL POPS THROUGH SUNDAY NIGHT. MAY
SEE SOME LINGERING PCPN MAINLY NE CWA ON MONDAY AS WELL AS SURFACE
LOW SLIDES FROM ERN WY TO THE DAKOTAS BY LATE AFTERNOON AND
BOUNDARY EXITS. FROM MONDAY NIGHT ON UNCERTAINTIES ARE ABOUND AS
LONG RANGE MODELS CONTINUE TO DIVERGE. HPC STILL THOUGH STRONGLY
FAVORING THE ECMWF/CMC SOLUTIONS AS THEY WERE SUPPORTED BY
NCEP/EURO ENSEMBLES. THIS SUGGESTS STRONG UPPER LOW WILL SLIDE
EASTWARD ACROSS SOUTHERN CANADA DAY 6/7 WITH A PRE-FRONTAL TROF
MOVING THRU THE PLAINS WITH THE NEXT COLD FRONT FOLLOWING ALONG.
FROPA ACROSS THE CWA WOULD APPEAR TO BE TUES NIGHT/WED MORNING
TIME FRAME...THUS SUGGESTING SMALL POPS REASONABLE FOR NOW.

AVIATION...

FOR KOFK/KOMA/KLNK...HEAVY TO EXTREME RAINFALL LIKELY BEGINNING
AFTER 01Z FOR ALL TAF SITES. CIGS GENERALLY MVFR WITH OCCASIONAL IFR
CONDITIONS INVOF STRONG/SEVERE THUNDERSTORMS MAINLY FOR KOMA &
KLNK. SEVERE THREAT SHOULD DIMINISH SOMETIME AFTER O6Z...BUT HEAVY
RAIN POTENTIAL WILL CONTINUE THRU 12Z THURSDAY.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR NEZ015-033-034-
     043>045-050>053-065>068-078-088>093.

IA...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR IAZ043-055-056-
     069-079-080-090-091.

&&

DEE

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
251 PM CDT WED MAY 23 2007

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

0243 PM     HAIL             4 SW SIDNEY             40.71N 95.70W
05/23/2007  E0.75 INCH       FREMONT            IA   TRAINED SPOTTER

&&

DNIETFEL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
316 PM CDT WED MAY 23 2007

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

0311 PM     HAIL             RED OAK                 41.01N 95.22W
05/23/2007  M0.88 INCH       MONTGOMERY         IA   LAW ENFORCEMENT

0314 PM     HAIL             RED OAK                 41.01N 95.22W
05/23/2007  E1.00 INCH       MONTGOMERY         IA   LAW ENFORCEMENT

&&

MILLER