Flash Flood and Hail in Nebraska, June 14, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
556 PM CDT FRI JUN 14 2013

.AVIATION...
00Z TAFS FOR KOFK...KOMA AND KLNK.

UNSETTLED AND LOW CONFIDENCE AVIATION FORECAST THROUGH SATURDAY
AFTERNOON WITH SCATTERED CONVECTION POSING AVIATION ISSUES TO
BEGIN PERIOD AT LEAST. CONVECTION WILL THEN IMPACT BOUNDARIES
OVER EASTERN NEBRASKA WITH ADDITIONAL TSTMS POSSIBLE BOTH LATER
TONIGHT AND THEN AGAIN SATURDAY AFTERNOON/EVENING. BEST CONVECTION
CHCS AT TAF SITES APPEARED TO BE THROUGH LATE EVENING AND TEMPO
GROUPS WERE INCLUDED. INSTEAD OF CARRYING TSTM CHCS MANY
PERIODS...ADDITIONAL PERIODS OF CONVECTIVE CHANCES WILL BE
ASSESSED AND INCLUDED AS NECESSARY. THERE IS ALSO SOME RISK OF
LOWER CIGS DEVELOPING BEHIND CONVECTION LATE TONIGHT WHICH COULD
PERSIST INTO SATURDAY AFTERNOON...ESPECIALLY IN NERN NEBRASKA.
THESE TRENDS WILL ALSO BE ASSESSED IN LATER FORECASTS.

CHERMOK
&&

.PREV DISCUSSION... /ISSUED 237 PM CDT FRI JUN 14 2013/

DISCUSSION...

SYNOPSIS...12Z UPPER AIR ANALYSIS INDICATED A SEASONABLY STRONG
UPPER LEVEL TROUGH OVER THE NORTHERN ROCKIES ASSOCIATED WITH 50 M
H5 HEIGHT FALLS AND A 80 KT H25 JET. DOWNSTREAM FROM THE TROUGH A
SHORTWAVE RIDGE COVERED THE CENTRAL AND NORTHERN PLAINS. STEEP MID
LEVEL LAPSE RATES ASSOCIATED WITH EML EXTENDED ACROSS THE HIGH
PLAINS FROM CNTRL/WRN SD INTO CNTRL/WRN KS WITH H7 TO H5 DELTA-T
VALUES OF +22 OR BETTER. THIS WAS CAPPING A FAIRLY MOIST LOWER
LEVEL AIRMASS CHARACTERIZED BY H85 DEWPOINTS OF +15 OR BETTER
/+19C AT KTOP/ FROM SE NEB INTO SRN KS. 19Z SFC ANALYSIS INDCD THE
CDFNT ASSOCIATED WITH THE UPPER TROUGH FROM ERN SD INTO CNTRL NEB.
A WARM FRONT EXTNDD FM AROUND OLU TO BIE.

FORECAST...MAIN FORECAST CONCERN IS FOR SEVERE THUNDERSTORM
CHANCES THIS EVENING. GIVEN THE UPSTREAM LAPSE RATES...MOIST
BOUNDARY LAYER AND PLENTY OF SUN IN THE WRN CWA THIS AFTERNOON THE
ATMOSPHERE IS EXPECTED TO BECOME STRONGLY UNSTABLE WITH MLCAPE OF
3000-4000 J/KG. LITTLE IN THE WAY OF LARGE-SCALE FORCING FOR
ASCENT IS INDICATED IN MODELS AND THIS SEEMS REASONABLE GIVEN
LITTLE UPSTREAM HEIGHT FALLS AT 12Z. THUS FORCING FOR SURFACE-
BASED CONVECTIVE INITIATION WILL GENERALLY RELY ON MESOSCALE
EFFECTS. THIS APPEARS TO LIKELY HAPPEN AS DEEP BOUNDARY LAYER
MIXING IN CENTRAL NEB INTO NRN KS REDUCES THE CIN BY LATE AFTN.
THUS OUR CURRENT FEELING IS THAT STORMS WILL INITIALLY DEVELOP
FROM NW KS INTO CENTRAL NEB...AND THEN INTO NE NEB. THESE STORMS
WILL THEN TRY AND MOVE OFF THE INITIATING BOUNDARY INTO ERN NEB.
THIS WILL BECOME INCREASINGLY DIFFICULT THE FARTHER SOUTH INTO THE
STRONGER CAP IN THE SRN FA. THUS WE WILL HAVE THE HIGHEST POPS
THIS EVENING IN THE CENTRAL AND NRN CWA AND THEN INTO WEST CENTRAL
IA LATER THIS EVENING. THE SEVERE WEATHER THREAT IS THERE THIS
EVENING FOR THE STORMS THAT GET GOING GIVEN THE INSTABILITY.
COVERAGE WILL NOT BE GREAT HOWEVER GIVEN THE LACK OF LARGER-SCALE
FORCING AND STORMS WILL TREND TO DECREASE IN COVERAGE/INTENSITY BY
LATE EVENING. DEEP LAYER SHEAR IS SUFFICIENT FOR SUPERCELLS WITH
AROUND 30-40 KT OF EFFECTIVE SHEAR...BUT MID AND UPPER LEVEL
STORM-RELATIVE FLOW IS WEAK...AND THUS A TENDENCY TOWARD HP
SUPERCELL MODE IS MORE LIKELY. LOW LEVEL SHEAR ALONG THE SYNOPTIC
WARM FRONT IS ALSO SUFFICIENT FOR AN ISO TORNADO THREAT BUT THE
WEAK RELATIVE FLOW WILL LIKELY LIMIT A MORE ROBUST TORNADO THREAT.
LATER TONIGHT WE MAY SEE ADDITIONAL ACTIVITY /NON SEVERE/ MOVE OUT
OF THE HIGH PLAINS BEHIND THE FRONTAL BOUNDARY ACROSS NORTHERN NEB
AND INTO NW IA BY SAT MORNING.

THE FRONTAL BOUNDARY REMAINS IN THE AREA FOR SAT...BUT THE
CONVECTIVE EVOLUTION REMAINS A BIT MUDDY AT THIS POINT DUE TO
EFFECTS FROM CONVECTION LATE TONIGHT. NEVERTHELESS WITH STRONG
INSTABILITY IN THE AREA AND A FRONTAL BOUNDARY...THERE IS SOME
THREAT OF A FEW AFTN STORMS IN THE CWA SAT AFTERNOON...ESPECIALLY
IN THE CNTRL AND SRN FA. AS THE UPPER LEVEL ENERGY FROM THE
SOUTHERN PLAINS MOVES INTO THE LOWER MO RIVER VALLEY LATE
SAT...THE 850 MB FLOW VEERS AND THIS SHOULD ALLOW FOR MUCH OF SAT
NIGHT TO BE DRY WITH MOST OF THE ACTIVITY SOUTH AND EAST OF OUR
FA. WE HAVE LIMITED POPS TO THE EVENING AND REMOVED MOST MENTION
AFTER MIDNIGHT. SUN ALSO IS A BIT UNCLEAR WITH THE FRONT STILL IN
THE AREA. HEIGHTS WILL BE LOWERING TOWARD THE END OF THE WEEKEND
THOUGH...AND PROVIDING A BETTER FOCUS FOR CONVECTION TO THE SOUTH.
WE WILL CONTINUE SOME POPS THROUGH THE DAY ON SUN...BUT THE BEST
COVERAGE MAY BE WEST AND SOUTH OF OUR FA. A STRONGER PUSH OF DRY
AIR AND COOLER TEMPERATURES WILL MOVE IN ON SUNDAY NIGHT LEADING
TO A DRY STRETCH FOR MON-WED ACROSS THE FA.

BOUSTEAD

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
509 PM CDT FRI JUN 14 2013

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-151215-
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-
509 PM CDT FRI JUN 14 2013

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

.DAY ONE...TONIGHT AND SATURDAY

THUNDERSTORMS ARE EXPECTED TO DEVELOP OR MOVE INTO THE REGION
THROUGH THIS EVENING. ANY STORM THIS EVENING WOULD HAVE THE
POTENTIAL TO DROP LARGE HAIL AND CONTAIN DAMAGING WINDS. IN
ADDITION...THE STRONGER STORMS POSE THE THREAT FOR PRODUCING A
TORNADO AND A TORNADO WATCH IS IN EFFECT FOR MUCH OF THE AREA
UNTIL 10 PM.

VERY UNSTABLE CONDITIONS HAVE DEVELOPED OVER THE REGION AND A
WARM FRONT EXTENDED FROM NORTHEAST NEBRASKA INTO SOUTHWEST IOWA.
IN ADDITION...A WEAK COOL FRONT WILL BE PUSHING INTO EASTERN
NEBRASKA THIS EVENING. THE STORM INTENSITY AND COVERAGE IS
FORECAST TO DECREASE BY AROUND MIDNIGHT AS STORMS MOVE SOUTH AND
EAST...WITH A FEW LINGERING THUNDERSTORMS POSSIBLE OVERNIGHT.

ADDITIONAL THUNDERSTORMS COULD DEVELOP ACROSS THE AREA SATURDAY
AFTERNOON AS A FRONT WILL LIKELY REMAIN IN THE AREA. STRONG AND
EVEN A FEW SEVERE STORMS ARE AGAIN POSSIBLE. HOWEVER...A LOT WILL
DEPEND ON THE IMPACT THE ACTIVITY TONIGHT AND SATURDAY MORNING HAS
ON THE FRONTAL POSITION AND AMOUNT OF INSTABILITY RECOVERY THAT CAN
OCCUR. LATER OUTLOOKS WILL ASSESS THIS POSSIBILITY.

.DAYS TWO THROUGH SEVEN...SATURDAY NIGHT THROUGH FRIDAY

PERIODS OF THUNDERSTORMS ARE EXPECTED THROUGH SUNDAY NIGHT AS A
FRONT SLOWLY MOVES SOUTHEAST...THE THREAT OF SEVERE WEATHER
PERSISTS THROUGH SUNDAY NIGHT.

ADDITIONAL THUNDERSTORMS ARE POSSIBLE LATER NEXT WEEK AS WARMTH
AND INSTABILITY RETURN TO THE PLAINS AHEAD OF A LARGE WEST COAST
UPPER LOW THAT WILL BE MOVING INLAND.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTERS SHOULD BE PREPARED FOR ACTIVATION THROUGH MID
EVENING.

CHERMOK