Damaging Wind in Nebraska, May 23, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
315 PM CDT TUE MAY 23 2006

.DISCUSSION...

AFTERNOON STLT IMAGERY SHOWED UPPER LOW MOVING INTO WRN SD WITH A
LOBE OF DRIER AIR/POSSIBLE WEAK SUBSIDENCE WORKING TOWARD MO RIVER
AS OF 1830Z. JET SEGMENT ROTATING AROUND THE BASE OF THE UPPER
LOW...A LTL BETTER MOISTURE CONVERGENCE/INSTABILITY AND SFC FRONT/TROUGH
HAD COMBINED TO HELP GENERATE FIRST BATCH OF TSTMS OVR NCNTRL
NEBRASKA WEST OF CWA AS OF 1930Z. LCLS/LFCS WERE MODERATELY
HIGH OVER THE NWRN CWA...BUT INSTABILITY COMBINED WITH INCREASING
SHEAR POTENTIAL AS JET SHIFTS FARTHER ENE THROUGH 00Z HAS PROMPTED
ISSUANCE OF TORNADO WATCH THAT HAS INCLUDED NWRN CWA. FARTHER
EAST...CONVECTIVE TEMPS HAVE BEEN REACHED WITH MODERATE CU
WIDESPREAD...BUT 18Z OAX SOUNDING SHOWED A MIXED LAYER WEAK CAP
STILL PRESENT WHICH HAD AIDED IN KEEPING CU FIELD FROM FIRING...AS
OF 1945Z ANYWAY. BEHIND ABOVE MENTIONED LOBE...MIXING AND THE
POSSIBLE SUBSIDENCE HAD DRIED SFC DWPTS OUT INTO THE MID/UPPER 50S
WHICH SHOULD FURTHER LIMIT SVR THREAT FARTHER E/SE OF CURRENT
WATCH TO MAINLY WIND/HAIL AS LCL/LFCS WERE EVEN HIGHER.
NONETHELESS...CATEGORICAL POPS WILL REMAIN IN THE FORECAST AS
PRECIPITABLE WATER VALUES CONTINUE HIGH AND JET IS FORECAST TO
SHIFT TO MO RIVER BY 06Z PUTTING ERN CWA IN FAVORED RIGHT REAR
ENTRANCE REGION LATER THIS EVENING. WILL SHIFT HIGHEST POPS TO
ERN CWA AFT 05Z AND MARKEDLY DECREASE THEM ACROSS THE WEST AS JET
SHIFTS NE OF WRN ZONES.

GFS HAS BACKED ON CLOSING OFF AND DROPPING THE UPR SYSTEM OVER
NERN CWA ON WED...AND NOW DROPS IT THRU IA ON THURSDAY. THIS
SOLUTION BACKED BY NAM.  HOWEVER...A WEAK THERMAL TROF AT H5 DOES
ROTATE ACROSS ERN NEBR AND WILL KEEP SMALL POPS IN ATTM ACROSS
THE NE. STRONGLY DOWNSLOPING WINDS AND MINIMAL COOL ADVCTN SHOULD
ALLOW HIGHS TO REACH WELL INTO THE 80S MOST AREAS...EXCEPT
POSSIBLY THE FAR NERN ZONES.

LEFT FORECAST DRY WED NIGHT/THU FOR NOW...ALTHOUGH ANY FARTHER WSW
TRACK OF THE UPPER LOW COULD CAUSE FUTURE CHANGES IN FORECAST.
THURSDAY APPEARS COOLEST DAY THROUGH MON/TUE AS A MODERATE AMOUNT
OF COOL ADVCTN OVERSPREADS THE FORECAST AREA.

MADE LTL CHANGES TO FRI-MONDAY PERIOD. AS UPR TROF BECOMES
REESTABLISHED OVER THE WRN U.S. RIDGING ACROSS THE PLAINS SHOULD
PUSH TEMPS WELL ABOVE NORMAL. NOCTURNAL TSTMS REMAIN
POSSIBLE...AND LEFT IN FRI NGT AS A STRONG LOW LVL JET RETURNS AND
SOME FRONTOGENESIS NOTED IN 850-700 MB LYR.

SOME POTENTIAL IN A FRONT PUSHING INTO THE CWA AS EARLY AS MONDAY
IF 12Z GFS IS TO BELIEVED...SUPPORTED A BIT BY THE ECMWF.
HOWEVER...RIDGE THEN SEEMS TO REBUILD WASHING FRONT OUT. MANY
POSSIBLE SCENARIOS COULD DEVELOP...ONE IS THAT CONVECTION ASSOCD
WITH THE MONDAY FRONT COULD REINFORCE BOUNDARY WITH A LOT OF LOW
CLOUDS AND MUCH COOLER TEMPS THAN GUIDANCE AND WHAT WILL BE REFLECTED
IN ZONES. THIS POSSIBLE OUTCOME WILL HAVE TO BE MONITORED...BUT
FOR NOW WILL CONTINUE TO BASE FORECAST ON UPR RIDGE HOLDING FIRM
ENOUGH TO PROVIDE QUITE WARM TEMPS INTO TUE.

&&

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

CHERMOK

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
517 PM CDT TUE MAY 23 2006

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-241100-
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-
517 PM CDT TUE MAY 23 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PARTS OF EASTERN NEBRASKA AND
SOUTHWEST IOWA.

.DAY ONE...TONIGHT AND WEDNESDAY

A TORNADO WATCH AND A SEVERE THUNDERSTORM WATCH ARE IN EFFECT FOR
PARTS OF EASTERN NEBRASKA UNTIL 9 PM.

SEVERE THUNDERSTORMS ARE EXPECTED THIS EVENING WITH DAMAGING WINDS
AND LARGE HAIL THE PRIMARY HAZARDS FOR THE OUTLOOK AREA. AN
ISOLATED TORNADO CANNOT BE RULED OUT. INSTABILITY IS CURRENTLY IN
PLACE. SHEAR WILL CONTINUE TO INCREASE THIS EVENING...FAVORING
DAMAGING WINDS AND LARGE HAIL. SURFACE TEMPERATURE AND DEWPOINT
DEPRESSIONS WILL WORK TO LIMIT THE TORNADO POTENTIAL...DUE TO
HIGH CLOUD BASES. HOWEVER...LOCALIZED LOW LEVEL SHEAR AND BROAD
DEEP LAYER SHEAR WILL BE FAVORABLE FOR TORNADOES THIS EVENING.

A SURFACE TROUGH AND COLD FRONT WILL MOVE EAST TONIGHT. A STRONG
UPPER LEVEL SYSTEM OVER WESTERN SOUTH DAKOTA WILL EVENTUALLY MOVE
INTO MINNESOTA WEDNESDAY.

THE STORMS WILL ALSO BE CAPABLE OF PRODUCING LOCALLY HEAVY RAIN
THIS EVENING AND TONIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY NIGHT THROUGH MONDAY

THERE IS ALSO A SMALL CHANCE FOR THUNDERSTORMS FRIDAY NIGHT...AS
WELL AS SUNDAY AND MONDAY.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTERS WILL PROBABLY BE NEEDED THIS EVENING...AND HAVE
BEEN ACTIVATED IN PARTS OF NORTHEAST NEBRASKA. STORM SPOTTERS
SHOULD NOT BE NEEDED WEDNESDAY.

ZAPOTOCNY/MILLER

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
230 PM CDT TUE MAY 23 2006

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-042>045
-050>053-065>068-078-088>093-242200-
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-
INCLUDING THE CITIES OF...ALBION...AUBURN...BEATRICE...BELLEVUE...
BLAIR...BLOOMFIELD...CLARINDA...COLUMBUS...COUNCIL BLUFFS...CRETE...
DAVID CITY...FAIRBURY...FALLS CITY...FREMONT...GLENWOOD...HARLAN...
HARTINGTON...LINCOLN...LOGAN...NEBRASKA CITY...NELIGH...NORFOLK...
OMAHA...ONAWA...PAWNEE CITY...PENDER...PIERCE...PLATTSMOUTH...
RED OAK...SCHUYLER...SEWARD...SIDNEY...STANTON...TECUMSEH...
TEKAMAH...WAHOO...WAYNE...WEST POINT
230 PM CDT TUE MAY 23 2006

...WARNING DECISION UPDATE FOR NORTHEAST NEBRASKA...

A TORNADO WATCH HAS JUST BEEN ISSUED FROM BUTLER THROUGH WAYNE AND
CEDAR COUNTIES IN NORTHEAST NEBRASKA UNTIL 9PM.

THE LATEST OAX WSR-88D RADAR HAD SOME ELEVATED SHOWERS LIFTING
ACROSS NORTHEAST NEBRASKA AT 220 PM.  MORE ORGANIZED THUNDERSTORMS
WERE DEVELOPING FROM CHAMBERLAIN SOUTH DAKOTA SOUTH TO AINSWORTH AND
NORTH PLATTE.

THE LATEST SUBJECTIVE SURFACE ANALYSIS HAD THE SURFACE MOIST AXIS
ALONG THE MISSOURI RIVER WITH THE COLD FRONT IN WESTERN NEBRASKA.
SURFACE TEMPERATURES WERE IN THE UPPER 80S WITH SURFACE DEWPOINTS IN
THE 60S.  THE OAX 18Z SOUNDING HAD SURFACE BASED CAPE OF 2996 J/KG
WITH NO CONVECTIVE INHIBITION. THE MIXED LAYER INHIBITION WAS
SMALL...BUT THERE IS SOME.  THE ELEVATED SHOWERS APPEARED TO BE ON
THE NOSE OF SOME GREATER MID LEVEL WARM AIR ADVECTION.

THE 18Z SOUNDING HAD A 0-3KM STORM RELATIVE HELICITY OF 42 M2/S2.
0-6KM SHEAR WAS 28KT.  WE HAVE THE INSTABILITY IN PLACE AND ARE
EXPECTING THE SHEAR TO INCREASE WITH TIME.  EXPECT TO LOOSE THE CAP
AND INCREASE AREAL COVERAGE AND INSTENSITY OF STORMS AS THE
AFTERNOON PROGRESSES AND THE MID LEVEL STORM SYSTEM AFFECT THE AREA
MORE.  WILL MONITOR STORM DEVELOPMENT FOR WARNINGS.

ZAPOTOCNY

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
453 PM CDT TUE MAY 23 2006

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-232315-
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-
INCLUDING THE CITIES OF...ALBION...AUBURN...BEATRICE...BELLEVUE...
BLAIR...BLOOMFIELD...CLARINDA...COLUMBUS...COUNCIL BLUFFS...CRETE...
DAVID CITY...FAIRBURY...FALLS CITY...FREMONT...GLENWOOD...HARLAN...
HARTINGTON...LINCOLN...LOGAN...NEBRASKA CITY...NELIGH...NORFOLK...
OMAHA...ONAWA...PAWNEE CITY...PENDER...PIERCE...PLATTSMOUTH...
RED OAK...SCHUYLER...SEWARD...SIDNEY...STANTON...TECUMSEH...
TEKAMAH...WAHOO...WAYNE...WEST POINT
453 PM CDT TUE MAY 23 2006

...WARNING DECISION UPDATE FOR NORTHEAST NEBRASKA...

AT 21Z...SFC LO WAS LOCATED OVR WRN SD.  MAIN SFC MOISTURE AXIS
EXTNDS FM WRN MO INTO WRN IA. LTST SFC RADAR INDCS TWO NORTH SOUTH
BANDS OF STORMS. INDCS ARE THAT THE UPR LVL SYS IS BGNG TO SWING OUT
TO THE NORHTEAST.  SFC FRONT TROF AS INDICATED BY A FINE LINE ON
RADAR IS BGNG TO MOV EWD.  BELIEVE THAT STORMS WILL BGN EWD MOVMENT
ONCE THIS FRONT CATCHES UP WITH PRESENT CONVECTION.

SPC MESOSCALE ANALYSIS SHOWS SHEAR INCRG OVR NERN NEBRASKA.  BEST
BULK RICHARDSON SHEAR AND HELICITY IS IN THIS AREA. LATEST
PROFILER FM NELIGH INDCD A 173 0-1 KM STORM RELATIVE
HELICITY. ALTHOUGH LCL AND LFC VALUES ARE HIGH...SOME SUPERCELLS MAY
OCR AND PRODUCE AN ISOLATED TORNADO FM ALBION NWD.

SMITH

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
702 PM CDT TUE MAY 23 2006

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-240130-
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-
INCLUDING THE CITIES OF...ALBION...AUBURN...BEATRICE...BELLEVUE...
BLAIR...BLOOMFIELD...CLARINDA...COLUMBUS...COUNCIL BLUFFS...CRETE...
DAVID CITY...FAIRBURY...FALLS CITY...FREMONT...GLENWOOD...HARLAN...
HARTINGTON...LINCOLN...LOGAN...NEBRASKA CITY...NELIGH...NORFOLK...
OMAHA...ONAWA...PAWNEE CITY...PENDER...PIERCE...PLATTSMOUTH...
RED OAK...SCHUYLER...SEWARD...SIDNEY...STANTON...TECUMSEH...
TEKAMAH...WAHOO...WAYNE...WEST POINT
702 PM CDT TUE MAY 23 2006

...WARNING DECISION UPDATE FOR NORTHEAST NEBRASKA...

BASED ON OBSERVED DATA OF THE SUB CLOUD LAYER OVER NORTHEAST NEBRASKA
FROM THE NORFOLK NEBRASKA METAR AND THE NELIGH PROFILER...WITH
SUPPLEMENTAL DATA FROM LAPS ANALYSIS... THE LAYER IS CHARACTERIZED BY
A NEARLY DRY ADIABATIC LAPSE RATE.  THE LCL IS AROUND 2000 METERS
WITH THE LCL AROUND 3200 METERS.  THE SURFACE TEMPERATURE-DEWPOINT
SPREAD IS 32F... YIELDING A SLIGHT INVERTED-V SOUNDING WITH A
DOWNBURST CAPE VALUE OF 1100 J/KG.  OAX HAS RECEIVED ONE REPORT OF
A 50 MPH OUTFLOW WIND JUST WEST OF VERDIGRE NEAR THE NIOBRARA
RIVER.  GOOD EVAPORATIVE COOLING SHOULD OCCUR WITHIN THE SUB-CLOUD
LAYER.

THE KINEMATIC ENVIRONMENT REFLECTS ONLY SLIGHT VEERING WITH A NEARLY
STEADY 35-45 MPH WIND.  NOTE THAT THE NELIGH PROFILER WINDS ARE
CONTAMINATED BY A LIGHT SURFACE WIND...WHICH APPEARS TO BE AN
ERROR.  THIS ERRONEOUS REPORT IS PRODUCING A FALSE 0-1KM SRH OF OVER
100 M2/S2... HOWEVER IF THIS OB IS THROWN OUT AND THE NORFOLK
SURFACE METAR IS USED... THE 0-1KM SRH VALUE IS CLOSER TO 50
M2/S2...WITH 0-1KM SHEAR OF ONLY 7 M/S... WITH A 0-3KM SRH OF ONLY
130 M2/S2.  THE SPC MESOANALYSIS...WHICH UTILIZES THE RUC OUTPUT...
APPEARS WAY TOO HIGH WITH ITS 0-1KM SRH VALUE OF 150 M2/S2...AND ITS
0-1KM SHEAR VALUE OF 20 M/S. THUS THE OBSERVED KINEMATIC ENVIRONMENT
SEEMS CONDUCIVE FOR MICROBURSTS BUT LESS CONDUCIVE FOR TORNADOES.

THE STEEP LOW LEVEL LAPSE RATES MAY BE SUPPORTIVE OF THE NON-
SUPERCELL TORNADO PROCESSES.  SPC SURFACE VORTICITY ANALYSIS SHOWS A
CONCENTRATED AREA OF HIGHER VALUES IN NORTHEAST NEBRASKA...AND A
COUPLE OF REPORTS OF FUNNELS HAVE BEEN REPORTED UNDER SOME OF THE
UPDRAFTS ALONG THE LINE IN NORTHEAST NEBRASKA.

ENVIRONMENT WILL BE MONITORED CLOSELY AS UPPER SYSTEM CONTINUES TO
MOVE EAST AND CLOSER TO THE WARNING AREA...AND LOW LEVEL JET
INTENSIFIES AFTER DARK. THE OBSERVED 0-3 KM SHEAR VECTOR IS CURRENTLY
ORIENTED ABOUT 35 DEGREES OFF THE CONVECTIVE LINE...WHICH IS ALSO
ONLY MARGINALLY SUPPORTIVE OF THE LINE INCREASING IN INTENSITY.  THIS
COMBINED WITH SLIGHTLY LOWER SURFACE-BASED AND MEAN LAYER CAPE TO THE
EAST OF THE LINE MAY KEEP THE LINE FROM SIGNIFICANTLY INCREASING IN
INTENSITY THROUGHOUT THE EVENING.

NIETFELD