Severe Thunderstorm Warning 25, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
626 AM CDT WED APR 17 2013

.AVIATION...

12Z TAFS FOR KOMA...KLNK...KOFK.

SHRA AND TSRA HAVE INCREASED OVER THE AREA SINCE 06Z...AND SOME
MVFR CEILINGS DEVELOPED. THERE SHOULD CONTINUE TO BE A DECREASE
IN CEILINGS THIS MORNING WITH SOME IFR CONDITIONS POSSIBLE INTO
THE EARLY AFTERNOON. CEILINGS SHOULD BE MOSTLY IFR LATER THIS
AFTERNOON AND INTO THE OVERNIGHT. NORTH WINDS ARE ALSO EXPECTED
TO INCREASE TONIGHT AND A RAIN/SNOW MIX MAY OCUR AT KOFK.

MILLER

&&

.PREV DISCUSSION... /ISSUED 355 AM CDT WED APR 17 2013/

DISCUSSION...
MAIN FORECAST CONCERN IS PRECIPITATION EVENT THAT IS BEGINNING IN
THE EARLY MORNING HOURS.  SUBJECTIVE 00Z UPPER AIR ANALYSIS
INDICATES UPPER LOW CENTERED IN SOUTHWEST MT/EASTERN ID...WITH ONLY
WEAK 500MB HEIGHT FALLS OF 30M IN NV AND HEIGHT RISES ELSEWHERE
ACROSS THE WESTERN AND CENTRAL CONUS.  115KT UPPER-LEVEL JET STREAK
EXTENDED FROM SOUTHERN CA INTO NORTHEAST SD...WITH 100KT JET BEHIND
THE LOW ALONG THE NORTH PACIFIC COAST.  850MB/MID-LEVEL LOW WAS
CENTERED IN THE 4 CORNERS REGION...WITH BOUNDARY EXTENDING FROM
THERE ACROSS NORTHERN KS TO THE MO/IA BORDER. WARM SECTOR SOUTH OF
THE FRONT WAS MOISTENING FROM THE TX BIG BEND TO NORTH CENTRAL OK TO
NORTHEAST KS...WITH 850MB DEWPOINTS 8C OR GREATER IN THAT AREA AND
12C OR HIGHER IN MUCH OF THAT AREA.  700-500MB LAPSE RATES WERE
STEEPENING ACROSS THE SOUTHERN TO CENTRAL PLAINS...WITH 20C TEMP
DIFFERENCES AS FAR NORTH AS CENTRAL KS/SOUTHWEST MO.  SURFACE LOW AT
08Z WAS CENTERED IN NORTHEAST NM...WITH NORTHEAST WINDS ACROSS MUCH
OF THE CENTRAL PLAINS AS SURFACE WARM FRONT REMAINED WELL
SOUTH...NEAR THE TX/OK BORDER INTO CENTRAL AR.

MAIN FORECAST CONCERNS INCLUDE HOW MUCH PRECIPITATION WILL
FALL...WHERE AND WHEN FROZEN PRECIPITATION MAY FALL...AND POTENTIAL
FOR THUNDERSTORMS TODAY AND THIS EVENING.  STORMS SHOULD OVERSPREAD
MUCH OF THE CWA BEFORE 12Z...AND CONTINUE TO OVERSPREAD ALL BUT THE
NORTHWESTERNMOST CWA THROUGH THE MORNING.  WITH SKINNY PROFILE OF
MUCAPE...AND WEAK SHEAR IN THE ELEVATED LAYER...SEVERE WEATHER IS
NOT A THREAT THIS MORNING...THOUGH A FEW OF THE STRONGER PULSES
COULD PRODUCE SMALL HAIL.  RAIN IN THE EXTREME NORTHWEST CWA MAY MIX
WITH SNOW THIS MORNING...BUT EXPECT NO ACCUMULATION AS TEMPERATURES
HOLD ABOVE FREEZING.  IN THE 850MB WARM SECTOR...EFFECTIVE SHEAR
WILL INCREASE THROUGH THE AFTERNOON TO AROUND 25-35KT...AND MUCAPE
SHOULD REACH 500-1000 J/KG IN THE WARM SECTOR /PER FORECAST
SOUNDINGS NEAR KFNB/.  STORMS WILL REMAIN WELL ELEVATED ABOVE ABOUT
900-850MB...BUT A FEW HAILERS ARE POSSIBLE IN THAT ENVIRONMENT THIS
AFTERNOON INTO THE EVENING.

PRECIPITATION IN THE NORTHWEST CWA SHOULD START TO MIX WITH SNOW
AGAIN LATER IN THE EVENING...CHANGING TO ALL SNOW LATE TONIGHT AS
THE RAIN/SNOW MIX LINE ADVANCES TO ROUGHLY SIOUX CITY TO YORK.
ACCUMULATIONS OVERNIGHT MAY REACH 1-2 INCHES...BUT WITH WARM
SURFACES...EXPECT SOME COMPACTION AND MELTING OF THE SNOW THAT
FALLS.  COLD AIR ADVECTION WILLL CONTINUE THROUGH THE DAY AS THE
COLDER AIR SPILLS IN BEHIND THE EXITING UPPER LOW...CHANGING
PRECIPITATION SLOWLY TO A RAIN/SNOW MIX BY THURSDAY EVENING ACROSS
THE REST OF THE AREA.  STILL THINK THAT DAYTIME APRIL INSOLATION
WILL LIMIT ACCUMULATION POTENTIAL...EVEN IN THE COLDER
NORTHWEST...AND MAY SEE JUST AN ADDITIONAL INCH OR SO OF
ACCUMULATION THROUGH THE DAY.  SYSTEM WILL EXIT THE AREA THROUGH
THURSDAY NIGHT...WITH A FINAL DUSTING OF LIGHT SNOW LIKELY ACROSS
THE AREA.

CURRENT FORECAST IS FOR A STORM TOTAL OF 2-4 INCHES IN THE NORTHWEST
CWA...AND LESS THAN AN INCH ELSEWHERE.  SNOW WILL FALL OVER 48
HRS...LIKELY ACCUMULATING MAINLY IN THE OVERNIGHT/EARLY MORNING
PERIODS TONIGHT AND THURSDAY NIGHT.  WINDS WILL BE GUSTY...BUT WET
NATURE OF SNOW SHOULD PREVENT MUCH IN THE WAY OF BLOWING/DRIFTING
CONCERNS. GIVEN ALL THESE FACTORS...AS WELL AS LATER SECOND PERIOD
ONSET OF ACCUMULATING SNOW...HAVE OPTED TO ISSUE NO HEADLINES FOR
THE AREA AT THIS TIME.

FOLLOWING THE UPPER LOW...WARM AIR ADVECTION RETURNS TO THE AREA BY
FRIDAY MORNING...AND TEMPERATURES SHOULD RECOVER RATHER QUICKLY FOR
THE WEEKEND.  BEGINNING SATURDAY NIGHT...UNSETTLED WEATHER IS
PROGGED TO BEGIN AGAIN...WITH A WEAK WAVE ON SATURDAY NIGHT/SUNDAY
BRINGING PRECIP POTENTIAL...FOLLOWED BY A STRONGER WAVE AROUND
MONDAY/MONDAY NIGHT THAT WILL ALSO DRAG COLDER AIR BACK INTO THE
AREA.

MAYES

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
410 AM CDT WED APR 17 2013

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-172315-
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-
410 AM CDT WED APR 17 2013

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

.DAY ONE...TODAY AND TONIGHT

PERIODS OF THUNDERSTORMS WILL CONTINUE ACROSS MOST OF EASTERN
NEBRASKA AND WESTERN IOWA TODAY. STORMS THIS MORNING ARE NOT
EXPECTED TO BE SEVERE...THOUGH A FEW STORMS MAY CONTAIN SMALL
HAIL. THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS THIS
AFTERNOON AND EVENING IN SOUTHEAST NEBRASKA AND SOUTHWEST
IOWA...WITH LARGE HAIL THE PRIMARY HAZARD.

AS COLDER AIR REACHES NORTHEAST NEBRASKA...RAIN IS EXPECTED TO
CHANGE TO A RAIN-SNOW MIX PERIODICALLY TODAY...THEN CHANGE TO SNOW
LATER TONIGHT. AN INCH OR TWO OF SNOW ACCUMULATION IS POSSIBLE
THROUGH TONIGHT...WEST OF A LINE FROM WAYNE TO COLUMBUS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE POTENTIAL FOR PERIODS OF ACCUMULATING SNOW WILL CONTINUE IN
NORTHEAST NEBRASKA THROUGH THURSDAY AND THURSDAY NIGHT...WITH SNOW
POSSIBLY MIXING WITH RAIN AT TIMES ON THURSDAY. PRECIPITATION
WILL CHANGE FROM RAIN TO SNOW ELSEWHERE ACROSS THE AREA BY
THURSDAY EVENING. STORM TOTAL ACCUMULATIONS OF 2 TO 4 INCHES OF
SNOW ARE POSSIBLE NORTHWEST OF A LINE FROM WAYNE TO
COLUMBUS...WITH AN INCH OR LESS ELSEWHERE. GUSTY NORTHWEST WINDS
ALSO ARE LIKELY ON THURSDAY...WITH GUSTS UP TO 25 TO 35 MPH
POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY OR TONIGHT.

MAYES

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