Severe Thunderstorm Warning 69, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
251 PM CDT MON JUN 1 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY. MAIN SHORT TERM FORECAST
CONCERNS ARE THE POTENTIAL FOR SEVERE CONVECTION ALONG THE FRONTAL
BOUNDARY NEAR THE NEBRASKA/KANSAS BORDER THIS EVENING...THEN
POTENTIAL FOR HEAVY AND POTENTIALLY FLOODING RAINS A LITTLE
FURTHER NORTH INTO THE CWFA BY MIDNIGHT AND BEYOND.

THE SURFACE FRONT AT 19Z WAS LOCATED BETWEEN KLNK AND KBIE...AND
BETWEEN KRDK AND KICL. BELIEVE THAT CONTINUED WEAK CONVECTION JUST
NORTH OF THE FRONT SHOULD CONTINUE TO PUSH THIS SOUTHWARD TOWARD THE
NE/KS AND IA/MO BORDER REGIONS THROUGH 00Z...ALLOWING THE FRONT TO
BECOME COLLOCATED ALONG AN OUTFLOW BOUNDARY THAT WAS NOTED ON VIS
SATELLITE IMAGERY IN THE SAME AREA. THIS IS ALSO WHERE THE STORMS
SHOULD POP THIS AFTERNOON...MOST LIKELY AFTER 21Z BASED ON CU
FIELD THAT IS DEVELOPING ACROSS THE QUAD-STATE REGION...AND
CONTINUING THROUGH 03Z. GIVEN SYNOPTIC PARAMETERS...DEFINITELY
LOOKS MULTICELLULAR WITH A WIND/HAIL THREAT...BUT ALSO A SMALL
WINDOW FOR TORNADOES AS WELL WITH ANY STORM DIRECTLY ON/OR
CROSSING THE BOUNDARY. LOCALIZED HEAVY RAIN WILL ALSO OCCUR WITHIN
THESE THUNDERSTORMS WITH MOISTURE POOLING ALONG THE FRONT AS H7
DEWPOINTS ARE FORECAST TO INCREASE TO AROUND +4 AND H85 DEWPOINTS
RISE TO +14.

FURTHER NORTH OF THE STALLED FRONT...AM NOT EXPECTING MUCH EARLY
THIS EVENING OTHER THAN A FEW SPOTTY SHOWERS AND ISOLATED
RUMBLES OF THUNDER WITH NO SIGNIFICANT SEVERE WEATHER. THE FOCUS
FOR HEAVY RAIN DOES SHIFT NORTH THOUGH OVERNIGHT AS THE LOW LEVEL
JET INCREASES...AND EMPHASIS SHIFTS TO ALONG/NORTH OF THE H85
BOUNDARY IN THE CENTRAL PART OF THE CWFA. BY MID TO LATE EVENING...
THE PLATTE RIVER VALLEY REALLY SHOULD LIGHT UP...WITH TORRENTIAL
RAINERS ON THE NOSE OF THE LOW LEVEL JET. THE CONCERN IS THAT A FEW
OF THESE AREAS DID PICK UP VERY HEAVY RAINS LAST NIGHT...MAINLY
FROM YORK COUNTY EASTWARD THROUGH SEWARD AND NORTHERN LANCASTER
COUNTIES LAST NIGHT. OTHER SPOTTY ISOLATED HEAVY DOWNPOURS IN THE
KOLU AREA ALSO OCCURRED. THUS...IN THESE COUNTIES THE 6HR FFG
VALUES HAVE DROPPED TO 2-2.5 INCHES...AND FEEL ITS BEST TO ISSUE A
FLASH FLOOD WATCH OVERNIGHT...WHERE ANOTHER DELUGE CAN BE EXPECTED
WITH ANOTHER 3 INCHES OR MORE. I DO EXPECT THUNDERSTORMS WITH
HEAVY RAIN EXTENDING EAST/NORTHEAST TOWARD THE FREMONT/OMAHA
AREA...THEN TOWARD BLAIR/TEKAMAH/ONAWA CORRIDORS LATER. ITS ALSO
WITHIN THIS SAME AXIS WHERE HEAVY RAINS WILL LIKELY CONTINUE ON
TUESDAY MORNING. FFG VALUES ARE HIGHER IN THIS SECONDARY AREA OF
HEAVY RAINFALL DUE TO NOT AS MUCH RAIN FALLING LAST NIGHT. AND
EVEN THOUGH WEVE BEEN DRY...3 INCHES OF RAINFALL COULD CAUSE SOME
MINOR SMALL/STREAM FLOODING...ESPECIALLY IN LNK/OMA/CBF METRO AREAS.
THUS...WILL EXTEND THE FLASH FLOOD WATCH TO COVER THESE AREAS
ALSO...WHICH LINES UP REALLY WELL WITH THE MOST RECENT EXCESSIVE
RAINFALL OUTLOOK ISSUED BY HPC.

THE WHOLE SYSTEM EVENTUALLY BEGINS TO SHIFT EAST TUESDAY AFTERNOON
AND EVENING WITH ALL PRECIP ENDING BY DAYBREAK WEDNESDAY. WEDNESDAY
DOES APPEAR DRY AND SLIGHTLY COOL...WITH DRY WEATHER EXTENDING INTO
THURSDAY WITH WARMER...BUT STILL SLIGHTLY BELOW NORMAL TEMPS.

.LONG TERM...THURSDAY NIGHT THROUGH. THIS PERIOD WILL BE DOMINATED BY
A SOMEWHAT ACTIVE WEATHER PATTERN AS A SERIES OF IMPULSES MOVE
THROUGH THE PLAINS.  THE FIRST IMPULSE IS STILL EXPECTED THURSDAY
NIGHT AND EARLY FRIDAY...WHICH DRIVES A COLD FRONT INTO THE REGION.
THE NEXT IMPULSE MOVES IN FRIDAY NIGHT THROUGH EARLY SATURDAY...AND
YET ANOTHER SUNDAY NIGHT THROUGH MONDAY. HATE TO BLANKET POPS OVER A
3 OR 4 DAY PERIOD LIKE THAT...BUT THATS WHAT THE MODELS ARE NOW
SUGGESTING...WITH RELATIVELY GOOD AGREEMENT BETWEEN THE GFS/ECMWF.
NO REMARKABLE TEMPERATURE SWINGS EITHER WAY...AND IF ANYTHING SHOULD
BE A LITTLE COOLER THAN NORMAL DUE TO PERSISTENT CLOUDS/PRECIP
HANGING AROUND.

&&

.AVIATION...
FOR TAF SITES KOFK/KOMA/KLNK FORECAST VALID THROUGH 02/18Z.

FRONTAL BOUNDARY ALONG THE NEBRASKA KANSAS BORDER EXTENDING INTO
SOUTHWEST IOWA WILL CONTINUE TO BE THE FOCUS FOR THUNDERSTORM
DEVELOPMENT BETWEEN 21Z AND 00Z.  ALL THREE TAF SITES TO REMAIN VFR
THROUGH 00Z.  THUNDERSTORM DEVELOPMENT WILL SPREAD NORTH TOWARD KOMA
AND KLNK AFTER 00Z AND THESE TWO LOCATIONS MAY SEE SOME IFR CEILINGS
LESS THAN 1000 FEET IN THUNDERSTORMS AFTER 00Z.  KOFK WILL ALSO SEE
THUNDERSTORM DEVELOPMENT AND LOWER CEILINGS BUT NOT UNTIL AFTER
06Z.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH FROM 10 PM CDT THIS EVENING THROUGH TUESDAY
     MORNING FOR NEZ015-032>034-042>045-050>053-065>067-078.

IA...FLASH FLOOD WATCH FROM 10 PM CDT THIS EVENING THROUGH TUESDAY
     MORNING FOR IAZ043-055-056-069.

&&

DEWALD/MEYER

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