Flash Flood Warning 9, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
347 PM CDT SUN JUN 20 2010

.DISCUSSION...

...MAIN FORECAST CHALLENGE IS PLACEMENT OF EVENING/OVERNIGHT MCS
ACTIVITY AND RESULTANT QPF...

SCATTERED ELEVATED CONVECTION CONTINUES ALONG A FEW WEAK E-W
BOUNDARIES LOCATED ACROSS EASTERN NEB/SW IA. WIDESPREAD LOW CLOUDS
HAS LEFT AREA QUITE STABLE THIS AFTERNOON SO WE ARE NOT EXPECTING
FURTHER SFC BASED TSTM DEVELOPMENT UNTIL MUCH LATER...MORE ON THAT
BELOW.

CURRENT SUBJECTIVE SFC ANALYSIS SHOWS LOW PRESSURE CENTERED OVR FAR
SOUTHEAST COLORADO WITH MAIN FRONTAL BOUNDARY EXTENDING NORTHEAST
ACROSS WESTERN KANSAS AND ACROSS I-70 CORRIDOR. CONVECTIVE
INITIATION IS ONGOING ALONG THIS FRONT AND WILL CONTINUE TO BE THE
FOCUS FOR TSTM DEVELOPMENT THROUGH THIS AFTERNOON. AS STRONG AND
VEERED LLVL JET BEGINS TO DEVELOP THIS EVENING...STORMS ARE LIKELY
TO PUSH NORTH INTO NEBRASKA AND DEVELOP INTO AN ORGANIZED MCS WITH
WIND AS THE PRIMARY HAZARD ALONG WITH HAIL AND HEAVY RAIN.

SPEAKING OF HEAVY RAIN...WE HAVE SHIFTED THE HEAVIEST QPF SLIGHTLY
FARTHER SOUTH THAN ORIGINALLY FORECAST DUE TO THE INABILITY OF THE
FRONTAL BOUNDARY TO PUSH NORTH AS THE FORECAST MODELS HAVE LED US TO
BELIEVE IN RECENT RUNS. THIS PUTS ABOUT 1-2" ACROSS MUCH OF THE CWA WITH
SOME ISOLATED 3" AMOUNTS LIKELY...ESPECIALLY ACROSS EAST CENTRAL
NEBRASKA AND WEST CENTRAL IOWA. THE UPPER REACHES OF THE ELKHORN
RIVER AND AREAS ALONG THE PLATTE IN EASTERN NEBRASKA CONTINUE TO
RECEDE AS FORECAST. IF OVERNIGHT RAINFALL AMOUNTS OF AN INCH OR SO
WERE TO OCCUR...WE WOULD SEE A SLOWING OF THE RECESSION OF THE FALL.
HOWEVER IF HEAVIER AMOUNTS OF 3 OR MORE INCHES WERE TO
OCCUR...ADDITIONAL RISES COULD OCCUR...AREA WIDE.

TOMORROW WE EXPECT A SIMILAR SET UP...AND WHERE EXACTLY THE SFC
FRONT RESIDES WILL BE KEY ON TSTM INITIATION. MOISTURE WILL REMAIN
IN PLACE WHICH WILL BE SUPPORTIVE OF HEAVY RAIN...MAINLY NOCTURNAL.
WE HAVE ISSUED A FLASH FLOOD WATCH IN EFFECT UNTIL 12Z MONDAY.

HAVE FAIRLY LOW CONFIDENCE WITH THE EXTENDED FORECAST AND BASICALLY
WENT WITH HPC'S GUIDANCE.

&&

.AVIATION...

TAF SITES KOFK/KOMA/KLNK

18Z TAFS

A NEARLY STATIONARY FRONT EXTENDING OVER CNTRL/ERN NEB WILL RESULT
IN ADDITIONAL CONVECTIVE ACTIVITY FOR ALL TERMINALS THRU ABOUT
21/06Z TONIGHT. IT IS POSSIBLE STORMS INVOF KOMA/KLNK MAY PRODUCE
OCCASIONAL GR...BUT HAVE OPTED TO NOT INCLUDE DO TO LACK OF
CONFIDENCE OF EXACTLY WHEN THIS MAY OCCUR. ALSO...IS POSSIBLE THAT
STRONGER +TSRA PASSING THRU MAY PUSH CONDITIONS TO IFR AT TIMES.
THIS NOT INCLUDED IN ANY TAFS EITHER...BUT WILL REEVALUATE FOR
BETTER DETERMINATION OF SPECIFICS AT UPCOMING 21/00Z TAF ISSUANCE.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH THROUGH MONDAY MORNING FOR NEZ011-012-015>018-
     030>034-042>045-050>053-065>068-078-088>093.

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

&&

KERN/DEE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
532 PM CDT SUN JUN 20 2010

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-211245-
MONONA-HARRISON-SHELBY-POTTAWATTAMIE-MILLS-MONTGOMERY-FREMONT-
PAGE-KNOX-CEDAR-THURSTON-ANTELOPE-PIERCE-WAYNE-BOONE-MADISON-
STANTON-CUMING-BURT-PLATTE-COLFAX-DODGE-WASHINGTON-BUTLER-
SAUNDERS-DOUGLAS-SARPY-SEWARD-LANCASTER-CASS-OTOE-SALINE-
JEFFERSON-GAGE-JOHNSON-NEMAHA-PAWNEE-RICHARDSON-
532 PM CDT SUN JUN 20 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
IOWA...WEST CENTRAL IOWA...EAST CENTRAL NEBRASKA...NORTHEAST
NEBRASKA AND SOUTHEAST NEBRASKA.

.DAY ONE...TONIGHT

THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS EVENING ACROSS SOUTHERN
NEBRASKA...WITH STORMS SPREADING ACROSS EASTERN NEBRASKA AND
WESTERN IOWA THROUGH THE OVERNIGHT HOURS. THE PRIMARY THREATS
WILL BE DAMAGING WINDS AND LARGE HAIL...AS WELL AS HEAVY RAIN.
BECAUSE ADDITIONAL HEAVY RAINFALL IS ANTICIPATED THROUGH
TONIGHT...A FLASH FLOOD WATCH IS IN EFFECT FOR THE ENTIRE OUTLOOK
AREA THROUGH MONDAY MORNING.

ANY HEAVY RAIN WILL EXACERBATE FLOODING PROBLEMS ALONG PORTIONS
OF THE ELKHORN...PLATTE...NISHNABOTNA...AND MISSOURI RIVERS AS
WELL AS THEIR TRIBUTARIES.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS OVER THE OUTLOOK AREA
MONDAY AND TUESDAY. A STALLED FRONTAL BOUNDARY IN THE REGION THROUGH
TUESDAY WILL CONTINUE TO BRING A CHANCE OF THUNDERSTORMS TO THE AREA.
ALTHOUGH EXACT TIMING AND LOCATION ARE UNCERTAIN AT THIS TIME...DUE
TO FAVORABLE SHEAR AND STRONG INSTABILITY...SOME OF THE STORMS COULD
BE SEVERE MONDAY AND TUESDAY. TYPICALLY THIS WEATHER PATTERN RESULTS
IN STRONG TO SEVERE STORMS IN THE LATE AFTERNOON AND EVENING HOURS...
WHICH EVOLVE INTO CLUSTERS OF STORMS THAT MOVE SLOWLY DURING THE
NIGHT AND PRODUCE HEAVY RAIN.

ONGOING RIVER FLOODING IN THE ELKHORN...PLATTE...NISHNOBOTNA AND
MISSOURI RIVER BASINS COULD BE AGGRAVATED AS A RESULT OF REPEATED
HEAVY RAINS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THIS EVENING...PARTICULARLY IN
SOUTHEAST NEBRASKA. ALSO...REPORTS OF HEAVY RAINFALL ACROSS THE
AREA WOULD BE USEFUL.

MAYES

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