Severe Thunderstorm Warning 151, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
323 PM CDT SUN JUL 21 2013

.DISCUSSION...
QUIET WEATHER HAS RETURNED TO - OR CONTINUES IN - THE AREA.
SUBJECTIVE 12Z UPPER AIR ANALYSIS INDICATES DECENT UPPER-LEVEL WAVE
CENTERED IN EASTERN KS...AND ANOTHER WAVE FROM THE SD/MN BORER
THROUGH CENTRAL NEB.  THE SD/NEB WAVE HELPED SHOWERS AND
THUNDERSTORMS DEVELOP IN SOUTHWEST IA EARLIER TODAY AND HAS SINCE
MOVED EAST...WITH A MID-LEVEL HIGH IN ITS WAKE.  12C+ MOISTURE AXIS
AT 850MB EXTENDED ACROSS THE SOUTHERN TIER OF THE US...NOSING
NORTHWARD IN EASTERN NEB/WESTERN IA AND ON INTO ND.  700MB MOISTURE
AXIS HAD SAGGED SOUTHWARD INTO KS/OK...WITH 700-500MB TEMPERATURE
DIFFERENCE OF 20C+ ACROSS NEB/SOUTHERN SD AND WESTWARD INDICATING
FAIRLY STEEP MID-LEVEL LAPSE RATES.  WEAK SURFACE PRESSURE GRADIENT
WAS EVIDENT AT 19Z...WITH A WEAK WIND SHIFT/WARM FRONT EXTENDING
ACROSS CENTRAL TO EASTERN NEB.

MAIN FORECAST CONCERNS INCLUDE CHANCE FOR STORMS MONDAY
AFTERNOON/EVENING...THEN PERIODIC CHANCES THROUGH THE WEEK.  SURFACE
FRONT IS PROGGED TO DEVELOP AS SHORTWAVE DROPS ACROSS SD/MN...WITH
INCREASING INSTABILITY AHEAD OF THE FRONT AND SHEAR INCREASING
DURING THE DAY.  ATMOSPHERE ALONG AND AHEAD OF THE FRONT SHOULD
DESTABILIZE BY MID-AFTERNOON...WITH STORMS STARTING TO BREAK OUT
LIKELY NEAR THE I-80 CORRIDOR.  STORMS SHOULD THEN DROP SOUTHEAST
THROUGH THE EVENING INTO THE SOUTHEASTERN CWA.  A FEW MODELS ALSO
POKE UP SOME CONVECTION LATE TONIGHT/MONDAY MORNING...BUT 850MB FLOW
NEVER REALLY GETS ORGANIZED TONIGHT AS IT VEERS QUICKLY IN RESPONSE
TO UPPER-LEVEL WAVE...AND THUS THINK ANY OVERNIGHT/EARLY MORNING
CONVECTION WILL REMAIN CLOSER TO THE UPPER-LEVEL WAVE IN MN/MAYBE
SD.  AFTERNOON/EVENING STORMS WILL CERTAINLY FIND A STRONGLY
UNSTABLE ENVIRONMENT...WITH 2000-3000 J/KG CAPE...AND MODEST DEEP-
LAYER SHEAR...WITH AROUND 30-35KT 0-6KM BULK SHEAR /AND VIRTUALLY NO
LOW-LEVEL SHEAR/.  COULD SEE A COUPLE OF STORMS IN THE LATE
AFTERNOON/EARLY EVENING BECOME SEVERE...WITH HAIL AND WIND THREATS.
STORMS SHOULD EXIT THE CWA BY MID TO LATE EVENING...WITH A QUIET
NIGHT ON MONDAY NIGHT INTO TUESDAY AS HIGH PRESSURE MOVES ACROSS THE
MISSOURI VALLEY.

RETURN FLOW WILL POKE INTO WESTERN NEBRASKA BY AROUND TUESDAY
AFTERNOON...AND LIKELY WILL SPARK CONVECTION WEST AND NORTHWEST OF
THE AREA LATER TUESDAY.  AM NOT BUYING ECMWF DEPICTION OF A LARGE
MCS DROPPING OUT OF CENTRAL SD AND ACROSS EASTERN NEB ON TUESDAY
NIGHT...AS CONVECTION WOULD LIKELY BE WELL WEST TO START AND WOULD
MOVE SOUTH-SOUTHEAST...REMAINING WELL WEST OF THE AREA.  HAVE
REMOVED POPS ON TUESDAY AND SCALED BACK TUESDAY NIGHT
SUBSTANTIALLY...MORE IN LINE WITH NAM/GFS DEPICTION.  QUIET WEATHER
SHOULD THEN CONTINUE ON WEDNESDAY.  HAVE NUDGED UP TEMPERATURES A
TOUCH ON TUESDAY/WEDNESDAY AS WELL...WITH LESS CLOUD/PRECIP IN THE
FORECAST.

MODELS INDICATE A DEVELOPING LEE LOW ON THURSDAY...AND ANOTHER ROUND
OF CONVECTION DEVELOPING ON THE HIGH PLAINS AND MOVING INTO THE
CENTRAL PLAINS OVERNIGHT.  ALSO HAVE LESS CONFIDENCE IN THIS
CONVECTION REACHING THE CWA ON THURSDAY AFTERNOON THROUGH THURSDAY
NIGHT...AND HAVE LOWERED POPS QUITE A BIT THERE...AS WELL.  LONG-
RANGE MODELS ARE FAIRLY CONSISTENT IN DEVELOPING A STRONG UPPER-
LEVEL WAVE IN THE NORTHWEST FLOW...WHICH MOVES ACROSS THE CENTRAL
PLAINS SOMETIME AROUND THURSDAY NIGHT/FRIDAY/FRIDAY NIGHT.  WITH
THAT LOW...WOULD EXPECT A BETTER CHANCE OF RAIN...BUT CONSISTENCY IS
LACKING ON TRACK AND TIMING.  HAVE KEPT THE CHANCE POPS IN THE
SOUTHERN CWA FOR THURSDAY NIGHT AND FRIDAY AS THE BEST GUESS ON
TIMING/LOCATION FOR PRECIP ASSOCIATED WITH THIS LOW...BUT
UNCERTAINTY IS HIGH...AND THERE IS A FAIR CHANCE THAT THIS AREA OF
PRECIP COULD MISS US ALTOGETHER.  NEXT SHOT OF RAIN ARRIVES AROUND
SATURDAY...MAINLY IN THE NORTHERN CWA...AS A WEAK WAVE RIPPLES
THROUGH THE NORTHWESTERLY FLOW WELL NORTH.  OVERALL...AFTER
MONDAY...TEMPERATURES SHOULD REMAIN ON THE BELOW NORMAL SIDE...AND
PRECIP CHANCES ARE WEAK.

MAYES

&&

.AVIATION...
18Z TAFS FOR KOMA...KOFK...KLNK

A SCT TO BKN CU FIELD IS EXPECTED AT OMA/LNK THIS AFTERNOON WITH A
FEW CU AT OFK. THESE WILL LIKELY DISSIPATE QUICKLY THIS EVENING
WITH JUST SOME SCT MID AND HIGH LEVEL CLOUDS EXPECTED OVERNIGHT.
GIVEN THE INCREASE IN LOW-LEVEL MOISTURE WE MAY SEE SOME MVFR CIGS
WITH HZ/BR AT OMA AROUND SUNRISE ON MONDAY BUT IF THIS OCCURS IT
WILL BE SHORT LIVED. SFC CDFNT WILL BE MOVG TOWARD THE TAF SITES
ON MONDAY BUT WON'T MAKE IT PRIOR TO 18Z WITH JUST A GENERAL
SRLY/SWRLY SFC WIND EXPECTED THRU THE PERIOD.

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
534 PM CDT SUN JUL 21 2013

IAZ056-069-079-080-090-091-NEZ052-053-066>068-078-088>093-221245-
SHELBY-POTTAWATTAMIE-MILLS-MONTGOMERY-FREMONT-PAGE-DOUGLAS-SARPY-
LANCASTER-CASS-OTOE-SALINE-JEFFERSON-GAGE-JOHNSON-NEMAHA-PAWNEE-
RICHARDSON-
534 PM CDT SUN JUL 21 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
IOWA...EAST CENTRAL NEBRASKA AND SOUTHEAST NEBRASKA.

.DAY ONE...TONIGHT AND MONDAY

AN ISOLATED STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH EARLY
THIS EVENING AND ALSO MONDAY...FOR PARTS OF EASTERN NEBRASKA AND
WESTERN IOWA. THE PRIMARY HAZARDS WITH THE ISOLATED STORMS WILL BE
LARGE HAIL...DAMAGING WINDS...VERY HEAVY RAINS AND LIGHTNING.

SOME DEEPER MOISTURE HAS RETURNED TO THE REGION AND HEATING THIS
AFTERNOON TO THE UPPER 80S HAS RESULTED IN MODERATE INSTABILITY
AND ISOLATED THUNDERSTORMS. MONDAY...A COLD FRONT WILL MOVE INTO
THE AREA.

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

THUNDERSTORMS ARE POSSIBLE ON MONDAY EVENING AS A COLD FRONT
MOVES THROUGH THE AREA. A FEW STORMS MAY BE ABLE TO BECOME
SEVERE...WITH DAMAGING WINDS AND LARGE HAIL THE MAIN THREATS.

A FEW STORMS ARE POSSIBLE ON TUESDAY NIGHT IN SOUTHEAST NEBRASKA.
THESE STORMS ARE NOT LIKELY TO BE SEVERE.

PERIODS OF THUNDERSTORMS ARE POSSIBLE FROM THURSDAY NIGHT THROUGH
SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED ON A LOCAL BASIS DUE TO THE
ISOLATED NATURE OF STORMS THIS EVENING.

IAZ043-055-NEZ011-012-015>018-030>034-042>045-050-051-065-221245-
MONONA-HARRISON-KNOX-CEDAR-THURSTON-ANTELOPE-PIERCE-WAYNE-BOONE-
MADISON-STANTON-CUMING-BURT-PLATTE-COLFAX-DODGE-WASHINGTON-BUTLER-
SAUNDERS-SEWARD-
534 PM CDT SUN JUL 21 2013

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

ISOLATED STRONG THUNDERSTORMS ARE POSSIBLE MONDAY...FOR PARTS OF
EASTERN NEBRASKA AND WESTERN IOWA. THE PRIMARY HAZARDS WITH THE
ISOLATED STORMS WILL BE SMALL HAIL...GUSTY WINDS...BRIEF HEAVY
RAIN AND LIGHTNING.

THE STORMS WOULD DEVELOP ALONG A COLD FRONT MOVING THROUGH THE
AREA.

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

A FEW STORMS ARE POSSIBLE ON TUESDAY NIGHT IN SOUTHEAST NEBRASKA.
THESE STORMS ARE NOT LIKELY TO BE SEVERE.

PERIODS OF THUNDERSTORMS ARE POSSIBLE FROM THURSDAY NIGHT THROUGH
SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TONIGHT OR MONDAY.

ZAPOTOCNY

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