Severe Thunderstorm Warning 36, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
417 PM CDT FRI MAY 23 2008

.DISCUSSION...
THE MAIN CONCERN EARLY IN THE FORECAST WAS POTENTIAL FLASH FLOODING
TONIGHT. 12Z NAM AND GFS QPF APPEAR TO SERIOUSLY UNDERESTIMATE
HEAVY RAINFALL POTENTIAL. LOW LEVEL MOISTURE REMAINS ABUNDANT...
AND WILL BE SHOVELED NORTH OVER A QUASI STATIONARY FRONT IN CENTRAL
KS BY AN INCREASING AND VEERING LLJ. EXPECT A REPEAT OF LAST NIGHT
WHEN MAIN TSTM AREA DEVELOPS TO OUR WEST THIS EVE THEN TRANSLATES
EAST OVERNIGHT. MUCH OF THE AREA HAS RECEIVED 2/3 TO 1 1/2 INCHES
OF RAIN IN THE PAST 24 HRS...LOWERING 3 HOUR FLASH FLOOD RAINFALL
TO THE 1 TO 1.6 RANGE IN THE FLASH FLOOD WATCH AREA.  FAR EASTERN
NEB AND WESTERN IA HAVE LESS POTENTIAL AS BEST MOISTURE AXIS WILL
BE FARTHER WEST MOST OF THE NIGHT.

FORECAST CONFIDENCE IS OVERALL MODEST DESPITE EXCELLENT MODEL AGREEMENT
ON MAIN FEATURES...AS THE AREA WILL REMAIN IN SOME STRONG GRADIENTS
FOR AT LEAST SEVERAL DAYS. PLACEMENT OF SFC FRONT WILL DEPEND QUITE
A BIT ON CONVECTIVE ACTIVITY. BEST ESTIMATE IS THAT WARM FRONT WILL
LIFT NORTH THROUGH MUCH OF THE AREA SAT AFTERNOON BUT MAY NOT PENETRATE
NORTHEAST. EXPECT SUBSTANTIAL CLOUD COVER EVEN SOUTH OF THE FRONT...
LIKE ERN KS TODAY.  THIS WILL SUPPRESS MAX TEMPS SOMEWHAT.  SEE LATEST
SWO FOR DISCUSSION OF SEVERE POTENTIAL...WHICH COULD BE STRONG BY LATE
TOMORROW AFTN AND EVE.

AFTER MORE THUNDERSTORMS SAT NIGHT...FRONT APPEARS TO MAKE MORE PROGRESS
ON SUNDAY. DRY LINE TROUGH MOVES EAST INTO THE AREA BY LATE AFTN AND
WILL LIKELY ACT AS A FOCUS FOR MORE TSTMS AND SEVERE WX.  MODELS HAVE
BEEN SHOWING UNUSUAL AGREEMENT FOR THE PAST 24 HRS THAT THIS WILL
EVOLVE INTO AN MCS SOMEWHERE IN THE AREA SUNDAY NIGHT...SO MORE
HEAVY RAIN AND FLOODING ARE POSSIBLE.

MONDAY THROUGH THURSDAY THE AREA WILL BE SANDWICHED BETWEEN A COOL
DRY AIRMASS PUSHING INTO THE NORTHERN PLAINS...AND HOT MOIST AIR
SOUTH OF A SLOW MOVING COLD FRONT.  UPPER RIDGING WILL TEND TO SLOW
THE SOUTHWARD FRONTAL PROGRESS AND KEEP THE AREA IN A CHC OF PRECIP.
WENT CLOSE TO HPC GUIDANCE DURING THIS PERIOD.

ANOTHER SHORT WAVE IN SW FLOW MAY BE APPROACHING THE AREA NEXT FRIDAY...
BUT CONFIDENCE ON TIMING IS LOW.

&&

.AVIATION...
FOR TAF SITES KOMA...KLNK AND KOFK THRU 24/06Z.

AT 09Z...LINE OF TSRA QUICKLY MOVING THRU WRN IA WITH CB TOPS
GENERALLY FL400. STRONGEST ACTIVITY HAS PASSED ALL TAF SITES...BUT
EXPECT LINGERING -SHRA/SHRA WITH EMBEDDED VCTS THRU ABOUT 11Z AND
MVFR CIGS. AFT 12Z...MVFR CONDITIONS PREVAILING ALL TAF SITES
THEREAFTER. STRONG SFC LOW SITUATED OVR SRN HIGH PLAINS WITH TIGHT
PRESSURE GRADIENT ACROSS THE REGION WILL TRANSLATE TO  SFC WINDS
G20-30KT PREVAILING FROM THE SE ALL SITES...SO NO CROSS WIND
CONCERNS THRU THE PD.
&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH FROM 11 PM CDT THIS EVENING THROUGH SATURDAY
     MORNING FOR NEZ016-030>032-042-043-050-051-065-066-078-
     088>090-092.

IA...NONE.
&&

POLLACK/MAYES

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
532 PM CDT FRI MAY 23 2008

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015-017-018-033-034-
044-045-052-053-067-068-091-093-241245-
MONONA-HARRISON-SHELBY-POTTAWATTAMIE-MILLS-MONTGOMERY-FREMONT-
PAGE-KNOX-CEDAR-THURSTON-PIERCE-WAYNE-CUMING-BURT-DODGE-
WASHINGTON-DOUGLAS-SARPY-CASS-OTOE-NEMAHA-RICHARDSON-
532 PM CDT FRI MAY 23 2008

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 SATURDAY

THERE IS A CHANCE FOR THUNDERSTORMS THROUGH SATURDAY
MORNING...WITH THE GREATEST CHANCE FOR SOME STRONG STORMS AFTER
MIDNIGHT. SEVERE STORMS ARE NOT EXPECTED...BUT ANY OF THE STORMS
COULD PRODUCE SMALL HAIL AND BRIEF HEAVY RAIN.

ANOTHER ROUND OF POTENTIALLY SEVERE THUNDERSTORMS IS POSSIBLE BY
LATE SATURDAY AFTERNOON...AND WILL CONTINUE INTO SATURDAY EVENING.
LARGE HAIL AND TORNADOES ARE POSSIBLE WITH THESE STORMS. DUE TO
THE EXPECTED THUNDERSTORM ACTIVITY TONIGHT AND HOW THOSE STORMS
AFFECT THE SURFACE WEATHER PATTERN...LATER OUTLOOKS WILL HAVE TO
REFINE THE FORECAST TO PIN POINT WHERE THE STRONGEST STORMS ARE
EXPECTED. SPOTTERS SHOULD STAY AWARE OF THIS POTENTIAL SEVERE
WEATHER SITUATION.

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

SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH SATURDAY NIGHT...BUT
WILL FAVOR LARGE HAIL AND DAMAGING WINDS AFTER MIDNIGHT. THEN
MORE SEVERE STORMS ARE POSSIBLE SUNDAY AFTERNOON AS ANOTHER UPPER
LEVEL IMPULSE ROLLS THROUGH THE PLAINS AND TRIGGERS STORMS ALONG A
COLD FRONT MOVING INTO THE AREA. THOSE STORMS WILL LIKELY PERSIST
THROUGH MONDAY MORNING. BY MONDAY AFTERNOON...MOST OF THE SEVERE
WEATHER POTENTIAL WILL BE SOUTH OF THE AREA.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTER ACTIVATION SHOULD NOT BE NEEDED TONIGHT...BUT WILL
LIKELY BE NEEDED SATURDAY AFTERNOON AND EVENING.

NEZ016-030>032-042-043-050-051-065-066-078-088>090-092-241245-
ANTELOPE-BOONE-MADISON-STANTON-PLATTE-COLFAX-BUTLER-SAUNDERS-
SEWARD-LANCASTER-SALINE-JEFFERSON-GAGE-JOHNSON-PAWNEE-
532 PM CDT FRI MAY 23 2008

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

.DAY ONE...TONIGHT AND SATURDAY

SCATTERED THUNDERSTORMS ARE POSSIBLE THROUGH THE NIGHT. SOME OF
THE STORMS COULD BE SEVERE...WITH LARGE HAIL THE MAIN THREAT...AND
WILL FAVOR AREAS FROM NORFOLK SOUTH THROUGH ALBION...COLUMBUS...
DAVID CITY AND SEWARD DURING THE EVENING. MORE STORMS ARE EXPECTED
TO DEVELOP OVER SOUTHEAST NEBRASKA BY MIDNIGHT.

FLASH FLOODING IS ALSO POSSIBLE WITH ANY OF THE STORMS...AND RIVER
OR STREAM FLOODING COULD ALSO OCCUR. HEAVY RAINS FROM STORMS THE
PAST COUPLE OF DAYS ALONG WITH POTENTIAL HEAVY WITH ANY NEW STORMS
THAT FIRE TONIGHT.

ANOTHER ROUND OF POTENTIALLY SEVERE THUNDERSTORMS IS POSSIBLE BY
LATE SATURDAY AFTERNOON...AND WILL CONTINUE INTO SATURDAY EVENING.
LARGE HAIL AND TORNADOES ARE POSSIBLE WITH THESE STORMS. DUE TO
THE EXPECTED THUNDERSTORM ACTIVITY TONIGHT AND HOW THOSE STORMS
AFFECT THE SURFACE WEATHER PATTERN...LATER OUTLOOKS WILL HAVE TO
REFINE THE FORECAST TO PIN POINT WHERE THE STRONGEST STORMS ARE
EXPECTED. SPOTTERS SHOULD STAY AWARE OF THIS POTENTIAL SEVERE
WEATHER SITUATION.

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

SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH SATURDAY NIGHT...BUT
WILL FAVOR LARGE HAIL AND DAMAGING WINDS AFTER MIDNIGHT. THEN
MORE SEVERE STORMS ARE POSSIBLE SUNDAY AFTERNOON AS ANOTHER UPPER
LEVEL IMPULSE ROLLS THROUGH THE PLAINS AND TRIGGERS STORMS ALONG A
COLD FRONT MOVING INTO THE AREA. THOSE STORMS WILL LIKELY PERSIST
THROUGH MONDAY MORNING. BY MONDAY AFTERNOON...MOST OF THE SEVERE
WEATHER POTENTIAL WILL BE SOUTH OF THE AREA.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTER ACTIVATION MAY BE REQUIRED TONIGHT...BUT WILL LIKELY
BE NEEDED SATURDAY AFTERNOON AND EVENING.

DERGAN