Severe Thunderstorm Warning 224, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
937 PM CDT SUN JUL 10 2011

.UPDATE...

UPDATED TO INCREASE OVERNIGHT LOWS AND ADJUST POPS.

&&

.DISCUSSION...

02Z SFC ANALYSIS INDCS WEAK SURFACE LOW OVER SOUTHEAST SOUTH
DAKOTA WITH A WEAK COOL FRONT/SURFACE TROUGH TO THE SOUTHWEST INTO
SOUTHWEST NEB. THUNDERSTORMS HAVE FORMED BOTH ALONG THE SURFACE
TROUGH AND IN THE DEEPLY MIXED BOUNDARY LAYER AIR OVER NORTHWEST
KS LATE THIS AFTERNOON. THE MAIN ISSUE FOR THE OVERNIGHT PERIOD IS
WHETHER ANY OF THESE STORMS WILL AFFECT THE CWA AND COVERAGE IF
THEY DO.

THE 00Z KOAX SOUNDING INDICATED AN EXTREMELY UNSTABLE...BUT
CAPPED ATMOSPHERE OVER THE FA TO SURFACED-BASED CONVECTION.
UPSTREAM...THE KTOP SOUNDING INDICATED EVEN WARMER MID LEVEL AIR.
MODIFICATION OF THE OAX SOUNDING AND LIFTING A PARCEL FROM NEAR
850 MB INDICATES AROUND 3800 J/KG OF MUCAPE AND CIN OF NEAR -70
J/KG. THUS IT APPEARS THAT THE SOUTHERN CWA WILL LIKELY REMAINED
CAPPED THROUGH THE NIGHT...AND HAVE LOWERED OR REMOVED GOING POPS
THERE. OUR CURRENT THINKING IS THAT FARTHER NORTH /GENERALLY NORTH
OF HIGHWAY 30/ THE COMBINATION OF THE INCREASING LOW LEVEL JET
AND LIFT FROM THE OUTFLOW OF THE ONGOING STORMS WILL LIKELY BE
ENOUGH TO KEEP SOME CONVECTION GOING INTO OUR FA. THUS GOING MID
TO HIGH CHANCE POPS IN NORTHEAST NEB AND WEST CENTRAL IOWA APPEARS
ON TRACK AFTER MIDNIGHT...AND MAKE LITTLE CHANGE HERE. GIVEN THE
INSTABILITY AND MID LEVEL FLOW AROUND 40 KT...SOME ORGANIZATION
WILL BE POSSIBLE WITH THE CONVECTION LEADING TO ISOLATED SEVERE
POSSIBLE. LAPSE RATES ON THE 00Z SOUNDING WERE NOT OVERLY
IMPRESSIVE...BUT SOME MARGINALLY SEVERE HAIL WILL BE POSSIBLE.
MAIN THREAT WILL LIKELY BE WIND GIVEN THE THETA-E PROFILE. IN
ADDITION TO CHANGES IN POPS...DID INCREASE OVERNIGHT LOWS TO THE
SOUTH OF WHERE WE EXPECT ANY PRECIP.

BOUSTEAD

&&

.PREV DISCUSSION... /ISSUED 230 PM CDT SUN JUL 10 2011/

SHORT TERM...TONIGHT THROUGH WEDNESDAY.

LOOKS LIKE A PRETTY ACTIVE WEATHER PATTERN FOR THE AREA DURING
THIS TIME WITH A PERSISTENT SURFACE BOUNDARY SETTING UP NEAR THE
SOUTHERN NEBRASKA BORDER. 12Z GFS AND NAM VERY SIMILAR IN HANDLING
THIS FEATURE WHICH ACTS AS A FOCUS FOR PERIODS OF CONVECTION NORTH
OF THE BOUNDARY. MAIN UNCERTAINTY WILL DEAL WITH TIMING AND
STRENGTH OF SHORT WAVE ENERGY MOVING ALONG PERIPHERY OF THE BROAD
UPPER HIGH OVER THE SOUTHEAST PART OF THE NATION.

PLENTY OF MOISTURE AVAILABLE FOR SOME SIGNIFICANT RAINFALL WITH
AREAS ALONG THE SOUTH DAKOTA NEBRASKA BORDER INTO NORTHWEST IOWA
APPEARING TO HAVE THE BEST CHANCE TO EXPERIENCE NOCTERNAL HEAVY
RAIN EVENTS WHICH WOULD COMPOUND CURRENT FLOODING ON THE MISSOURI
RIVER.

TEMPERATURES ALSO WILL BE PROBLEMATIC WITH HOT AND HUMID
CONDITIONS CONTINUING ALONG AND SOUTH OF THE SURFACE BOUNDARY
WHILE CLOUDS AND RAIN WILL PROVIDE COOLER TEMPERATURES IN
NORTHERN PARTS OF THE AREA. WILL LIKELY HAVE TO WATCH HOW
CONVECTION IMPACTS THE BOUNDARY ON DAY TO DAY BASIS WITH REGARDS
TO LOCATION OF THE SULTRY AIR AND ANY ADDITIONAL HEAT HEADLINES
BEYOND MONDAY.

LONG TERM...THURSDAY THROUGH SUNDAY.

HOT WEATHER BECOMES MORE ENTRENCHED IN THE EXTENDED PERIOD AS
UPPER HIGH PRESSURE RIDGE BUILDS NORTH WHILE UPPER TROUGH LINGERS
ALONG THE WEST COAST. ADDITIONAL HEAT RELATED HEADLINES POSSIBLE
DURING THIS TIME AS RAIN CHANCES FOR THE AREA DIMINISH WITH THE
HOT AND HUMID CONDITIONS BECOMING THE MAIN WEATHER STORY.

AVIATION...
TAF SITES KOFK/KOMA/KLNK

18Z TAFS

SCATTERED MID AND HIGH CLOUDS WILL BE THE RULE THROUGH MONDAY
AFTERNOON. HOWEVER AN ISOLATED THUNDERSTORM COULD POP UP IN THE LATE
AFTERNOON OR EARLY THIS EVENING AS THE ATMOSPHERE REMAINS VERY
UNSTABLE. THUNDERSTORMS ARE MORE LIKELY LATE THIS EVENING AND AFTER
MIDNIGHT AS STORMS IN THE HIGH PLAINS OR SOUTH DAKOTA MOVE TOWARD
THE AREA. ANY STORMS TO AFFECT EASTERN NEBRASKA TAF SITES WOULD MOST
LIKELY COME IN THE 08Z TO 14Z TIME FRAME WITH ASSOCIATED MVFR/IFR
VSBYS IN STORMS. OTHERWISE VFR CONDITIONS ASIDE FROM SOME MVFR FOG
POSSIBLE BETWEEN 10Z AND 15Z.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...HEAT ADVISORY UNTIL 8 PM CDT MONDAY FOR NEZ050>053-065>068-078-
     088>093.

IA...HEAT ADVISORY UNTIL 8 PM CDT MONDAY FOR IAZ069-079-080-090-091.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
517 PM CDT SUN JUL 10 2011

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-111230-
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-
517 PM CDT SUN JUL 10 2011

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 ARE EXPECTED TO DEVELOP THIS EVENING IN WESTERN
NEBRASKA. SOME OF THESE THUNDERSTORMS MAY MOVE EAST ACROSS PATS OF
THE AREA OVERNIGHT. THESE WOULD MOST LIKELY AFFECT NORTHEAST
NEBRASKA AND WEST CENTRAL IOWA...ALONG AND TO THE NORTH OF A LINE
FROM DAVID CITY TO BLAIR TO ONAWA IOWA. IF THUNDERSTORMS ARE ABLE
TO MOVE INTO THE AREA...THE MOST LIKELY TIME WILL BE AFTER 10 PM
THROUGH THE EARLY MORNING HOURS. DUE TO EXTREME INSTABILITY...SOME
OF THE STORMS MAY REACH NEAR SEVERE LIMITS WITH DAMAGING WINDS
BEING THE MAIN THREAT. IN ADDITION...GIVEN THE HIGH MOISTURE
CONTENT IN THE ATMOSPHERE...ANY THUNDERSTORM WILL HAVE THE
POTENTIAL TO PRODUCE LOCALLY HEAVY RAINFALL.

A HEAT ADVISORY ALSO REMAINS IN EFFECT FOR SOUTHEAST NEBRASKA AND
SOUTHWEST IOWA THROUGH MONDAY EVENING. THE COMBINATION OF VERY
HIGH HUMIDITY AND TEMPERATURES IN THE 90S WILL CREATE HEAT INDEX
VALUES OF 105 TO 110 THIS EVENING AND AGAIN ON MONDAY.

WIDESPREAD MODERATE TO MAJOR FLOODING WILL CONTINUE ALONG THE
MISSOURI RIVER.

.DAYS TWO THROUGH SEVEN...MONDAY NIGHT THROUGH SATURDAY

THUNDERSTORMS ARE POSSIBLE OVER THE REGION MONDAY THROUGH
WEDNESDAY...ESPECIALLY DURING THE EVENING AND OVERNIGHT HOURS...
AS A WEAK COLD FRONT MOVES INTO THE REGION...AND THEN STALLS OR
WEAKENS. ALTHOUGH UPPER LEVEL FORCING APPEARS TO BE MARGINAL
THROUGH THIS PERIOD...HIGH LEVELS OF INSTABILITY AND THE WEAK
BOUNDARY COULD ALLOW STRONG OR SEVERE THUNDERSTORMS TO DEVELOP
OVER THE REGION. LARGE HAIL...DAMAGING WINDS AND HEAVY RAIN ARE
ALL POSSIBLE WITH THE STRONGER STORMS.

MODERATE TO MAJOR FLOODING WILL CONTINUE ALONG THE MISSOURI RIVER
FOR THE NEXT SEVERAL WEEKS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVITY SHOULD NOT BE NEEDED TONIGHT OR ON MONDAY.

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