Severe Thunderstorm Warning 451, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
159 PM CDT SUN SEP 28 2008

.SHORT TERM...
CONVECTIVE COMPLEX STRENGTHENING THIS AFTERNOON ALONG PRE-FRONTAL SFC
TROF INVOF 30KT EFFECTIVE SHEAR...ISENTROPIC UPGLIDE/MAX LIFT OVER
NRN NEB. RADAR TRENDS THOUGH SHOW ACTIVITY WEAKENING AS IT
DRIFTS FARTHER SE THRU THE CWA. OTHERWISE LARGER PICTURE FROM SATL
PIX WAS SHOWING MAIN UPPER LEVEL TROF MOVING ACROSS THE DAKOTAS WITH
ATTENDANT SFC FRONT EXTENDING FROM ERN ND TO ABOUT SWRN. REGIONAL 88D
MOSAIC SHOWED PCPN ACTIVITY WAS DEVELOPING ALONG THE SFC FRONT...
WHICH WILL EVENTUALLY BE FOCUS FOR ADDITIONAL CONVECTIVE ACTIVITY
TONIGHT OVER THE CWA. MODELS IN DECENT AGREEMENT FROPA WILL BEGIN
AROUND 00Z TONIGHT WITH AN UNSTABLE ENVIRONMENT IN PLACE TO INTERACT
WITH. PWS PLOT SHOWED WELL ABOVE NORM VALUES FOR THE SEASON FROM
MORNING UAA. MODELS GRABBING ONTO THIS AND PROG KI VALUES AOA 35
OVERNIGHT SUGGESTING INCREASED POTENTIAL FOR HVY PCPN ACCOMPANYING
CONVECTIVE ACTIVITY. APPEARS TO BE MARGINAL CHANCE FOR SEVERE STORMS
AS WELL. FAVORABLE SHEAR/MID LVL LAPSE RATES ATOP RICH LLVL MOISTURE
SOURCE POINT TO HAIL THREAT WITH A FEW STORMS. HOWEVER...WIDESPREAD
SEVERE ACTIVITY DOES NOT APPEAR PROBABLE. SFC FRONT WILL EVENTUALLY
CLEAR THE CWA EARLY MONDAY MORNING WITH LINGERING PCPN COMING TO A
CLOSE. OTHERWISE DRY AND COOL CONDITIONS ON TAP TUESDAY THRU
THURSDAY. MODELS DEPICT DEEPENING ERN CONUS TROF WITH SECONDARY CAA
SURGE THRU THE GREAT LAKES AND INTO THE OH/TN VLY. ANTICIPATE THAT
WESTWARD ADVANCE OF SIGNIFICANT CAA SHOULD BE HELD AT BAY AS UPPER
LEVEL RIDGING SLOWLY BUILDS EAST...BUT WILL STILL SEE NOTICEABLE
COOLING TREND RELATIVE TO TEMPS THE LAST SEVERAL DAYS.

.LONG TERM...
IN THE EXTENDED PERIOD...THERE ARE SOME MAJOR DIFFERENCES BETWEEN
THE ECMWF AND GFS HANDLE THE STRENGTH OF LONGWAVE TROUGHS ACROSS
NORTH AMERICA.  THE ECMWF IS MUCH DEEPER IN THE UPPER LOW OVER
ONTARIO AND DIVES SOUTHWARD INTO THE GREAT LAKES.  IT IS ALSO DEEPER
IN THE TROUGH THAT ROTATES OUT INTO THE PLAINS ON SUNDAY. EVEN
THOUGH THERE ARE THESE DIFFERENCES...THE UPPER AIR PATTERN BEGINS AS
NORTHWEST FLOW ON THURSDAY AND THEN TRANSITIONS TO AN UPPER RIDGE
OVER THE AREA ON FRIDAY TO INCREASING SOUTHWEST FLOW ON SATURDAY AND
SUNDAY. DRY FORECAST THROUGHOUT THE EXTENDED UNTIL SUNDAY WHEN A
SLIGHT CHANCE OF THUNDERSTORMS IS POSSIBLE OUT OVER WESTERN PORTIONS
OF THE CWA.

&&

.AVIATION...
FOR TAF SITES KOMA/KLNK/KOFK THROUGH 29/18Z.

VFR CONDITIONS EXPECTED AT KOMA AND KLNK THROUGH 00Z.  THEN EXPECT
MVFR CONDITIONS WITH THUNDERSTORMS IN VICINITY IN ADVANCE OF COLD
FRONT.  ACTUAL COLD FRONT PASSAGE WILL OCCUR AFTER 03Z WITH
ADDITIONAL SHOWERS AND THUNDERSTORMS.  AT KOFK...VICINITY
THUNDERSTORMS TIL 22Z TO 23Z...THEN REDEVELOPMENT OF ADDITIONAL
SHOWERS AND THUNDERSTORMS WITH COLD FRONT PASSAGE AFTER 03Z.
SHOWERS AND THUNDERSTORMS WILL MOVE SOUTHEAST AND CLEAR ALL THREE
TAF SITES BETWEEN 12Z AND 15Z FOLLOWED WITH VFR BUT BREEZY NORTH
WINDS OF 10 TO 20 KTS.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&

DEE/SMITH/MEYER

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
514 PM CDT SUN SEP 28 2008

IAZ043-055-056-069-079-080-090-091-NEZ015-018-030>034-042>045-
050>053-065>068-078-088>093-290400-
BOONE-BURT-BUTLER-CASS-COLFAX-CUMING-DODGE-DOUGLAS-FREMONT IA-GAGE-
HARRISON IA-JEFFERSON-JOHNSON-LANCASTER-MADISON-MILLS IA-MONONA IA-
MONTGOMERY IA-NEMAHA-OTOE-PAGE IA-PAWNEE-PLATTE-POTTAWATTAMIE IA-
RICHARDSON-SALINE-SARPY-SAUNDERS-SEWARD-SHELBY IA-STANTON-THURSTON-
WASHINGTON-WAYNE-
514 PM CDT SUN SEP 28 2008

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 MONDAY

THUNDERSTORMS WILL LIKELY MOVE ACROSS THE OUTLOOK AREA TONIGHT.
LOCALLY HEAVY RAIN WILL BE POSSIBLE...ALONG WITH GUSTY WINDS AND
POSSIBLY SMALL HAIL. A FEW THUNDERSTORMS MAY LINGER OVER SOUTHWEST
IOWA AND THE SOUTHEAST CORNER OF NEBRASKA INTO MONDAY MORNING.

.DAYS TWO THROUGH SEVEN...MONDAY NIGHT THROUGH SUNDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTER ACTIVATION IS NOT ANTICIPATED TONIGHT OR MONDAY.

NEZ011-012-016-017-290400-
ANTELOPE-CEDAR-KNOX-PIERCE-
514 PM CDT SUN SEP 28 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST
NEBRASKA.

.DAY ONE...TONIGHT AND MONDAY

SEVERE THUNDERSTORM WATCH IN EFFECT UNTIL 11 PM.

THUNDERSTORMS WILL PUSH ACROSS NORTHEAST NEBRASKA THIS EVENING...WITH
SOME STORMS BECOMING SEVERE MAINLY OVER AREAS NORTH OF A LINE FROM
ABOUT LAUREL TO ELGIN. LARGE HAIL APPEARS TO BE THE MAIN THREAT...
WITH DAMAGING WIND GUSTS AND LOCALLY HEAVY RAINFALL POSSIBLE AS
WELL.

.DAYS TWO THROUGH SEVEN...MONDAY NIGHT THROUGH SUNDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING.

DEE

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