River Flood Warning 28, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
311 AM CDT FRI MAY 30 2008

.DISCUSSION...
...MAIN FORECAST PROBLEM IS THE NEAR TERM WEATHER AND POPS NEXT
WEEK...

THE ON-GOING SEVERE CONVECTION AND BROAD PRECIPITATION AREA IS BEING
ASSISTED BY STRONG VERTICAL MOTION AS A RESULT OF THE PHASING OF A
NORTHERN STREAM SHORTWAVE OVER THE DAKOTAS WITH A SOUTHERN STREAM
SHORTWAVE MOVING OUT OF COLORADO PER WATER VAPOR LOOP.  THIS PHASING
IS PROVIDING TWO SOURCES OF DPVA FOR THE CENTRAL PLAINS.  IN
ADDITION...STRONG UPPER LEVEL JET DIVERGENCE WAS NOTED OVER
NEBRASKA.

SURFACE ANALYSIS SHOWS THE ASSOCIATED CYCLOGENESIS IS TAKING PLACE
OVER SOUTHEAST COLORADO AND THE DAKOTAS... WITH A DISTINCT FRONTAL
BOUNDARY BETWEEN THE TWO.  POSITION OF THE SYNOPTIC FRONT IS DILUTED
BY THE ONGOING CONVECTION...HOWEVER IT APPEARS TO EXTEND FROM NEAR
SIOUX FALLS TO YORK TO NEAR HILL CITY.

BOUNDARY LAYER INGREDIENTS CONSIST OF SIGNIFICANT MOISTURE...SUCH AS
SURFACE DEWPOINTS IN THE 60S IN THE WARM SECTOR... WITH A 50-60 KNOT
LLJ NEAR THE TOP OF THE BOUNDARY PER 88DS AND WIND PROFILERS.
THEREFORE THE SHEAR AND INSTABILITY PARAMETERS CONTINUE TO SUPPORT
SEVERE CONVECTION UNTIL THE VERTICAL MOTION SHUTS OFF AS JET MAX
AND SHORTWAVES MOVE EAST.  TIMING OF THE END OF CONVECTION SHOULD BE
NO LATER THAN 18Z...WHICH IS ALSO WHEN THE FRONT IS PROGGED TO HAVE
CLEARED THE FORECAST AREA.  THUS WILL CONTINUE TO MENTION THE
ONGOING SEVERE CONVECTION THROUGH THE MORNING HOURS AND WILL CHECK
RADAR TRENDS BEFORE MAKING FINAL DECISIONS.

LINGERING MORNING CONVECTION WILL CONTINUE TO EXACERBATE ON-GOING
FLOODING PROBLEMS ESPECIALLY FROM PLATTE COUNTY EAST...BUT THESE
AREAS ARE ALREADY COVERED WITH FLOOD WARNINGS AND STATEMENTS.
THEREFORE WILL CANCEL THE FLOOD WATCH AT 4 AM WITH MORE APPROPRIATE
PRODUCTS PROVIDING INFORMATION ON THE HYDROLOGICAL CONDITIONS.
NUMEROUS FLASH FLOOD WARNINGS AND STATEMENTS ARE IN AFFECT FOR
PORTIONS OF THE FORECAST AREA.

300 MB ANALYSIS HAD A 100 METER HEIGHT RISE OVER LAS VEGAS AT 00Z
THURSDAY INDICATIVE OF THE BUILDING WESTERN US UPPER RIDGE.  THIS
RIDGE IS PROGGED TO MOVE EAST OVER THE WEEKEND AND BE POSITIONED
JUST TO OUR WEST SUNDAY AND OVERHEAD BY MONDAY NIGHT.  SURFACE HIGH
DOMINATES THE BOUNDARY LAYER THROUGH MONDAY...THEN NEXT WAVE BEGINS
TO PUSH THROUGH THE RIDGE AND BREAK IT DOWN BY MONDAY NIGHT.  DECENT
MODEL AGREEMENT EXISTS WITH THESE FEATURES.  GFS AND ECMWF AGREE ON
SHOWING A SHARP EVOLUTION OF THE WAVE INTO A HIGH AMPLITUDE CUTOFF
UPPER LOW IN THE OKLAHOMA PANHANDLE BY THURSDAY NIGHT.

THIS TRANSLATES TO A DRY AND WARM WEEKEND WITH OUR NEXT SIGNIFICANT
CHANCES FOR RAIN SUNDAY NIGHT INTO MUCH OF NEXT WEEK.  SUNDAY NIGHT
RAIN CHANCES WILL BE A FUNCTION OF HOW THE WARM FRONT SURGES NORTH
AND HOW MUCH MOISTURE CAN RETURN.  HAVE ADJUSTED POPS BY TRIMMING
THEM A BIT LATER TOWARDS MONDAY MORNING.  THEN FOR THE REMAINDER OF
THE WEEK THE TROF TO OUR WEST SHOULD PROVIDE FOR AN ACTIVE PERIOD.

&&

.AVIATION...
FOR TAF SITES KOMA...KLNK AND KOFK THRU 31/06Z.

TAF SITES WILL AGAIN BE MAINLY AFFECTED BY THE ON-GOING COMPLEX
CONVECTION... BUT EXPECT THIS TO GRADUALLY END BY 12Z FOR MOST
AREAS.  THEN A RAPID IMPROVEMENT TO VFR CONDITIONS IS EXPECTED FOR
MOST OF THE DAY AS THE AIRMASS DRIES OUT AND SUBSIDENCE DOMINATES.
SKIES MAY CLEAR OR BECOME SCATTERED BY THE EVENING HOURS.

&&

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

&&

NIETFELD

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