Tornado Warning 20, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
346 PM CDT TUE JUN 22 2010

.DISCUSSION...

...SEVERE WX THREAT AND FLOODING CONTINUES...

LATEST SUBJECTIVE SFC ANALYSIS SHOWS TWO WARM FRONTS RESIDING
ACROSS THE AREA. THE FIRST OF WHICH EXTENDS FM NORTH CENTRAL
KANSAS AND HUGS THE KS/NE BORDER TO NEAR FALLS CITY. THE SECOND
BOUNDARY RESIDES ALONG THE MISSOURI RIVER VALLEY FROM NEAR YANKTON
DOWN TO SIOUX CITY AND NEAR DENISON IOWA.

SPECIAL 18Z OBSERVED KOAX SOUNDING INDICATED A CAP STILL IN PLACE.
LOOKING AT RUC ANALYSIS...MUCH OF THE AREA STILL REMAINS CAPPED
WITH EXTREME INSTABILITY ACROSS THE FORECAST AREA.

ONCE THE CAP BREAKS...WE ARE EXPECTING RAPID TSTM DEVELOPMENT WITH
AN TORNADO/HAIL THREAT TO BEGIN WITH...MAINLY UNTIL NEAR SUNSET.
0-6KM EFFECTIVE BULK SHEAR REMAINS AROUND 50+ KTS OVER MUCH OF THE
AREA. THREAT LOOKS TO TURN MORE TO A WIND/HEAVY RAIN THREAT AS
THE STORMS DEVELOP INTO A LARGE COMPLEX AND PUSH FROM WEST TO EAST
ACROSS MUCH OF THE AREA ONCE NOCTURNAL LLVL JET KICKS UP.

HEAVY RAIN IS ANOTHER THREAT ON TOP OF ALREADY SATURATED GROUND.
HAVE ISSUED A FLASH FLOOD WATCH TO COVER HEAVY RAIN POTENTIAL
OVERNIGHT. CURRENTLY HAVE QPF AMOUNTS RANGING AROUND 1-2" WITH
SOME ISOLATED 3" AMOUNTS POSSIBLE...ESPECIALLY ACROSS NORTHEAST
NEBRASKA AND MUCH OF WEST CENTRAL IOWA.

COMPLEX SHOULD EXIT THE AREA BY MID WEDNESDAY MORNING.

HIGH PRESSURE BEGINS TO BUILD INTO THE REGION ON WEDNESDAY. THIS
WILL HELP BY GIVING US A FEW DRYING DAYS. SFC DEWPOINTS SHOULD
RETREAT INTO THE UPPER 50S TO LOWER 60S BY WEDNESDAY NIGHT AND
INTO THURSDAY.

WITH A FEW DRY DAYS UNDER OUR BELT BY LATE IN THE WEEK...RETURN FLOW
WILL BE UNDERWAY BY 12Z FRIDAY AS THE SFC HIGH SLIDES EAST. STRONG
MOIST/WAA IS EXECTED OVERNIGHT FRIDAY INTO SATURDAY SOUTH OF A SFC
LOW PUSHING EAST ACROSS THE NORTHERN PLAINS. THIS LOW WILL SLIDE A
COLD FRONT SOUTH INTO THE FORECAST AREA SOMETIME SATURDAY NIGHT INTO
SUNDAY MORNING. WILL INCLUDE A TSTM CHANCE TO COVER THE FRONT SAT
NIGHT INTO SUNDAY MORNING. OTHERWISE...DRIER AND COOLER
DEWPOINTS/TEMPS WILL FOLLOW AS SFC HIGH PRESSURE BUILDS IN.

INDICATIONS CONTINUE TO SHOW THAT A BIG FAT RIDGE WILL TRY TO BUILD
INTO THE NATIONS MID SECTION FOR NEXT WEEK.

&&

.AVIATION...

TAF SITES KOFK/KOMA/KLNK

18Z TAFS

GENERALLY VFR CONDITIONS EXPECTED OUTSIDE OF THUNDERSTORMS.
THUNDERSTORMS ARE EXPECTED TO DEVELOP IN NORTHEAST
NEBRASKA...NORTHEAST OF KOFK...DURING THE LATE AFTERNOON AND
EVENING. THESE STORMS SHOULD REMAIN WELL AWAY FROM TAF SITES.
HOWEVER A COMPLEX OF THUNDERSTORMS DEVELOPING IN WESTERN NEBRASKA
WILL SWEEP INTO EASTERN NEBRASKA BETWEEN 06Z AND 15Z. GENERAL MVFR
CIGS/VSBYS ARE LIKELY AT KOFK WITH KOMA ON THE SOUTHERN FRINGE.
ISOLATED IFR CONDITIONS ARE LIKELY WITHIN THUNDERSTORM COMPLEX. AS
THE SYSTEM RACES EAST AFTER 14Z OR 15Z...SURFACE WINDS WILL SWITCH
FROM SOUTH TO WEST OR NORTHWEST AND INCREASE INTO THE 15 TO 20 KT
RANGE.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH WEDNESDAY
     MORNING FOR NEZ011-012-015>018-030>034-042>045-050>053-
     065>068-078-088>093.

IA...FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH WEDNESDAY
     MORNING FOR IAZ043-055-056-069-079-080-090-091.

&&

KERN/DERGAN

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
456 PM CDT TUE JUN 22 2010

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-230500-
ANTELOPE-BOONE-BURT-BUTLER-CASS-CEDAR-COLFAX-CUMING-DODGE-DOUGLAS-
FREMONT IA-GAGE-HARRISON IA-JEFFERSON-JOHNSON-KNOX-LANCASTER-MADISON-
MILLS IA-MONONA IA-MONTGOMERY IA-NEMAHA-OTOE-PAGE IA-PAWNEE-PIERCE-
PLATTE-POTTAWATTAMIE IA-RICHARDSON-SALINE-SARPY-SAUNDERS-SEWARD-
SHELBY IA-STANTON-THURSTON-WASHINGTON-WAYNE-
456 PM CDT TUE JUN 22 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 AND WEDNESDAY

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS TONIGHT...GENERALLY
NORTH OF A LINE FROM DAVID CITY TO OMAHA AND AVOCA. A SLIGHT RISK OF
SEVERE THUNDERSTORMS THEN EXISTS OVER THE REST OF THE OUTLOOK
AREA.

WITH A VERY MOIST AND UNSTABLE ENVIRONMENT IN PLACE OVER REGION...
CONDITIONS ARE QUITE FAVORABLE FOR THUNDERSTORM DEVELOPMENT. AS OF
NOW...IT APPEARS THAT NORTHEAST NEBRASKA AND WEST CENTRAL IOWA ARE
MOST SUSCEPTIBLE FOR SEVERE STORM ACTIVITY THIS EVENING. VERY
LARGE...DAMAGING HAIL WILL BE THE INITIAL THREAT...THEN DAMAGING
WINDS AS STORMS DEVELOP INTO A LARGE COMPLEX LATER TONIGHT.
WIDESPREAD HEAVY RAIN CAN BE EXPECTED AS WELL AS THE COMPLEX MOVES IN
FROM WESTERN NEBRASKA. OVER AN INCH OF RAIN IS POSSIBLE OVER A WIDE
AREA.

ANY ADDITIONAL 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...WEDNESDAY NIGHT THROUGH TUESDAY

ONGOING RIVER FLOODING IN THE ELKHORN...PLATTE...NISHNOBOTNA AND
MISSOURI RIVER BASINS WILL CONTINUE FOR MUCH OF THE PERIOD.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION LIKELY WILL BE NEEDED THIS EVENING. ALSO...REPORTS
OF HEAVY RAINFALL WOULD BE USEFUL.

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