Flash Flood Warning 19, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
248 PM CDT SAT JUN 26 2010

.DISCUSSION...

MAIN CONCERNS IN THE FORECAST ARE TONIGHT WITH THE THREAT OF
STORMS AND CURRENT HEAT. MANY SITES MEETING HEAT ADVSRY CRITERIA
AND THIS SHLD CONT SO NO CHANGES PLANNED ATTM. OTHERWISE...LEAD
SHRTWV TROF /NW OVR THE NEB PANHANDLE AT 19Z/ WL CONT TO MOV NEWD
OVR THE RIDGE. STORMS ARE EXPECTED TO INCREASE IN COVERAGE OVR
THE UPPER MO RVR VALLEY AS THIS WAVE APPROACHES THIS AFTN...BUT
AMOUNT AND TIMING OF COVERAGE IN THE OAX CWA IS NOT CERTAIN ATTM.
18Z SNDG INDCD STG CAP IN PLACE...BUT UPSTREAM MID LVL COOLING AND
FORCING FOR LARGE-SCALE ASCENT SHLD ALLOW THE CAP TO BE BROKEN
OVR THE NW CWA...ALNG THE CDFNT...BY LATE AFTN. SUFFICIENT
INSTABILITY AND WEAK TO MARGINAL SHEAR /25 KT EFF BULK SHEAR/ SHLD
ALLOW FOR A FEW SVR STORMS IN THE NW FA. STEEP MID LVL LAPSE RATES
OF 8 C/KM IN THE H7 TO H5 LAYER AND STG INSTABILITY SHLD ALLOW
HAIL TO BE THE MAIN THREAT. WEAK LO LVL SHEAR SHLD ALSO ALLOW FOR
SOME DECENT OUTFLOW FM THE STORMS...AND MAYBE A COUPLE OF SVR
WIND GUSTS. TOR THREAT STILL LOOKS VERY SMALL GIVEN THE LO LVL
VEERED AND WEAK SHEAR. STORMS SHLD TEND TO BUILD SEWD THRU THE
FA....BUT WEAKEN WITH SWD EXTENT DO TO WEAKENING SHEAR WITH A
FARTHER S LATITUDE. WILL MAINTAIN HIGH POPS THRU THE OVERNIGHT
HOURS WITH CAT POPS OUT EAST.

SFC FNT THEN SHIFTS S OF THE FA ON SUN WITH DRIER AND COOLER AIR
MOVING IN. REINFORCING SHOT OF COOLER AIR AGAIN ARRIVES ON MON
BEFORE UPPR LVL RIDGE BUILDS IN AND TMPS WARM TOWARD MID WEEK.
SOME AGREEMENT IN THE MODELS IN W/SW FLOW DVLPG TOWARD NEXT
WEEKEND WHICH MAY LEAD TO A CHC OF TSRA...BUT WILL WAIT FOR
FURTHER AGREEMENT ON TIMING BEFORE INCLUDING IN THE FORECAST.

&&

.AVIATION...

TAF SITES KOFK/KOMA/KLNK

18Z TAFS

VFR CONDITIONS ARE EXPECTED TO PREVAIL FOR MUCH OF THE TAF CYCLE.
SHRA/TSRA WILL DEVELOP IN THE AREA...AND THESE MAY AFFECT TAF
SITES...TEMPORARILY LOWERING VIS/CIGS AS THEY MOVE THROUGH.  HAVE
INCLUDED TEMPO GROUPS TO HEDGE TOWARD THUNDER MENTION...BUT WITH
JUST SHRA/CB COMBO FOR NOW UNTIL CONFIDENCE IN TIMING AT EACH SITE
INCREASES.  ONCE STORMS MOVE THROUGH...TAF SITES WILL REMAIN VFR.
COLD FRONTAL PASSAGE WILL SHIFT SRLY WINDS TO NWLY TNGT.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR NEZ012-015-017-018-
     031>034-042>045-050>053-065>068-078-088>093.

IA...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR IAZ043-055-056-069-
     079-080-090-091.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
430 PM CDT SAT JUN 26 2010

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-271130-
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-
430 PM CDT SAT JUN 26 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 SUNDAY

THERE IS A MODERATE RISK FOR SEVERE THUNDERSTORMS TO THE NORTH OF
A LINE FROM NELIGH TO WAYNE. THERE IS A SLIGHT RISK FOR SEVERE
THUNDERSTORMS ACROSS THE REST OF THE OUTLOOK AREA. THE MAIN THREAT
TIME FOR SEVERE THUNDERSTORMS IS AFTER 6 PM IN NORTHEAST
NEBRASKA...AND AFTER 9 PM ACROSS THE REST OF THE OUTLOOK AREA. THE
MAIN THREAT FROM THUNDERSTORMS TONIGHT IS VERY LARGE HAIL AND
DAMAGING WINDS.

THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS NORTH CENTRAL AND
NORTHEAST NEBRASKA LATER THIS AFTERNOON. THUNDERSTORMS WILL THEN
MOVE EAST AND SOUTHEAST ACROSS THE AREA THROUGH THE EVENING HOURS.
EXTREME INSTABILITY AND SUFFICIENT VERTICAL WIND SHEAR WILL ALLOW
A FEW OF THESE STORMS TO BECOME SEVERE. DUE TO THE EXTREME
INSTABILITY...VERY LARGE HAIL...POSSIBLY TO BASEBALL SIZE...WILL
BE POSSIBLE WITH THESE STORMS...AS WELL AS STRONG STRAIGHT LINE
WINDS. THE THREAT FOR STRAIGHT LINE WINDS IS GREATEST NEAR THE
MISSOURI RIVER IN NORTHEAST NEBRASKA AND INTO WESTERN IOWA. THE
SEVERE WEATHER THREAT WILL DIMINISH EARLY THIS MORNING AS
INSTABILITY WEAKENS.

A FEW THUNDERSTORMS COULD LINGER INTO SUNDAY MORNING...MAINLY SOUTH
OF INTERSTATE 80. SEVERE STORMS ARE NOT EXPECTED BY SUNDAY
MORNING.

ALSO...HEAT INDICES WILL CONTINUE AROUND 105 DEGREES ACROSS A
LARGE PART OF EASTERN NEBRASKA AND SOUTHWEST IOWA. A HEAT ADVISORY
REMAINS IN EFFECT THROUGH EARLY THIS EVENING.

FLOODING WILL CONTINUE ACROSS PORTIONS OF THE BIG BLUE RIVER AND
ITS TRIBUTARIES...AND ALSO ALONG THE MISSOURI DOWNSTREAM FROM
PLATTSMOUTH.

.DAYS TWO THROUGH SEVEN...SUNDAY NIGHT THROUGH FRIDAY

FLOODING ALONG THE MISSOURI RIVER IS EXPECTED TO CONTINUE
THROUGHOUT NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING...PARTICULARLY IN
NORTHEAST NEBRASKA AND NORTHWEST IOWA.

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