Flood in Nebraska, August 3 to 5, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
256 PM CDT FRI AUG 3 2007

.DISCUSSION...
THE CHANCE OF PCPN THE NEXT FEW DAYS IS THE MAIN FORECAST CONCERN.
UPPER AIR CHARTS FROM THE MORNING SHOWED THE FOLLOWING. AT 850 MB...
A BAND OF DEWPOINTS OF 15 C OR HIGHER STRETCHED FROM MEXICO NORTH
ACROSS TX...OK...KS...WRN NE AND INTO SWRN SD. DECENT MOISTURE WAS
ALSO IN PLACE AT 700 MB...BUT JUST A BIT FARTHER WEST. AT 500 MB...
HEIGHT FALLS OF AROUND 30 METERS WERE NOTED FROM WY AND MT INTO
WRN SD. STRONGER FALLS OF UP TO 90 METERS WERE ASSOCIATED WITH THE
SYSTEM OVER THE PACIFIC NW AND SRN BC CANADA. LATEST WATER VAPOR
LOOP SHOWED A BROAD AND RELATIVELY WEAK ANTICYCLONIC CIRCULATION
PATTERN FROM AZ THROUGH UT...CO...SERN WY AND THEN INTO THE CNTRL
PLAINS.

A CONVECTIVE COMPLEX HAS BEEN STEADILY ADVANCING EASTWARD ACROSS
SRN SD SINCE EARLY THIS MORNING. THE MODELS HAVE BEEN ADVERTISING
THIS WARM ADVECTION PATTERN FOR SEVERAL DAYS. CURRENT MID LEVEL
DEWPOINTS AND FORECAST MID LEVEL DEWPOINTS ARE QUITE HIGH AND 12Z
PRECIPITABLE WATER VALUES WERE MOSTLY 130-170 PERCENT OF NORMAL.
RIW AND SLC WERE BOTH OVER 200 PERCENT OF NORMAL. SHORTWAVE TROF
CURRENTLY OVER WY WILL MOVE EAST TONIGHT. INCREASED CHANCE OF PCPN
FOR ALMOST THE WHOLE FORECAST AREA...BUT ESPECIALLY NORTH. THE 12Z
OPERATIONAL MODELS WERE NOT IN GOOD AGREEMENT WITH QPF...BUT THE
NORTH SHOULD SEE THE HEAVIEST AMOUNTS. THERE DOES APPEARS TO BE
A SLIGHT RISK OF SEVERE STORMS IN THE NORTH THROUGH TONIGHT. THE
12Z GFS DOES SEEM TO HAVE A REASONABLE HANDLE ON THE SITUATION...
AS FAR AS THE SURFACE PATTERN AND AREA OF STRONGEST LIFT SATURDAY.
WILL KEEP THE HIGHEST CHANCE GOING ACROSS THE NRN/NERN 1/3 OF THE
AREA...AND GO COOLER THERE. SOUTHERN ZONES COULD REACH THE LOWER
90S IF CLOUD COVER IS NOT EXTENSIVE. KEPT 20-30 PERCENT POPS GOING
INTO SATURDAY NIGHT AND A SLIGHT CHANCE ON SUNDAY.

FARTHER OUT...SURPRISINGLY THE ECMWF AND LATEST GFS ARE IN VERY
GOOD AGREEMENT WITH THE 500 MB PATTERN. THIS WILL FEATURE A TROF
FROM WESTERN CANADA TO JUST OFF THE COAST OF CA...AND A RIDGE
OVER THE SERN CONUS. AGREEMENT STARTS TO BREAK DOWN LATE IN THE
WEEK IN REGARDS TO THE ACTUAL LOCATION OF THE 500 MB ANTICYCLONE
BUT FOR MOST OF NEXT WEEK WE WILL BE IN SOUTHWEST FLOW ALOFT.
THIS MEANS DISTURBANCES WILL BE MOVING OUT OF THE DESERT SW AND
INTO THE PLAINS. TIMING THE DISTURBANCES WILL BE VERY TOUGH...
BUT RIGHT NOW IT APPEARS AT LEAST TWO PERIODS WILL HAVE A HIGHER
CHANCE BASED ON CURRENT MODEL TIMING. THESE TWO PERIODS ARE
MONDAY NIGHT AND WEDNESDAY. FOR MOST OF NEXT WEEK HIGHS EXPECTED
HIGHS ARE AROUND 90-95 WITH LOWS IN THE UPPER 60S TO LOWER 70S.
THIS WOULD BE A LITTLE ABOVE NORMAL.

MILLER

&&

.AVIATION...
BKN-OVC DECK ANTICIPATED AT KOFK...KOMA...AND KLNK THRU MUCH OF THE
OVERNIGHT PD AS CONVECTION CONTINUES TO MOVE IN FM THE NW. CHANCES
OF TSTMS TOO LOW TO ADD A TEMPO GROUP INTO TAFS HOWEVER THINK KOFK
HAS BEST CHANCE AND ADDED A PROB30 OVERNIGHT. OTHERWISE...EXPECTING
VFR CONDITIONS ACROSS TAF SITES.

GRIFFIS

&&

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

MILLER/GRIFFIS

HAZARDOUS WEATHER OUTLOOK...COR
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
846 PM CDT FRI AUG 3 2007

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-041100-
ANTELOPE-BOONE-BURT-BUTLER-CASS-CEDAR-COLFAX-CUMING-DODGE-DOUGLAS-
FREMONT IA-GAGE-HARRISON IA-JEFFERSON-JOHNSON-KNOX-LANCASTER-MADISON-
MILLS IA-MONONA IA-MONTGOMERY IA-NEMAHA-OTOE-PAGE IA-PAWNEE-PIERCE-
PLATTE-POTTAWATTAMIE IA-RICHARDSON-SALINE-SARPY-SAUNDERS-SEWARD-
SHELBY IA-STANTON-THURSTON-WASHINGTON-WAYNE-
846 PM CDT FRI AUG 3 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN NEBRASKA AND SOUTHWEST
IOWA.

.DAY ONE...TONIGHT AND SATURDAY

SCATTERED THUNDERSTORMS WILL MOVE ACROSS PORTIONS OF THE OUTLOOK
TONIGHT...MAINLY NORTH OF A LINE FROM COLUMBUS TO HARLAN IOWA...WITH
ISOLATED THUNDERSTORMS SOUTH.  HAIL AND STRONG GUSTY WINDS MAY
ACCOMPANY A FEW STORMS...BUT ORGANIZED SEVERE WEATHER IS NOT
ANTICIPATED AT THIS TIME.

THERE IS A SLIGHT CHANCE FOR SEVERE THUNDERSTORMS THOUGH SATURDAY
AFTERNOON...MAINLY EAST OF A LINE FROM NIOBRARA TO GLENWOOD IOWA...
WITH LARGE HAIL AND DAMAGING WINDS THE MAIN THREATS.

A FRONTAL BOUNDARY EXTENDING FROM THE WESTERN DAKOTAS TO SOUTHERN
IOWA WILL BE THE FOCUS FOR THE THUNDERSTORM ACTIVITY. SATURDAY WILL
BE A MORE LIKELY TIME FRAME FOR SEVERE STORM DEVELOPMENT AS
ENVIRONMENTAL INSTABILITY INCREASES THROUGH THE AFTERNOON.

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

THUNDERSTORM CHANCES CONTINUE SATURDAY EVENING THROUGH THURSDAY
NIGHT OVER MOST OF THE OUTLOOK AREA. WITH AMPLE MOISTURE IN PLACE...
HEAVY RAINFALL IS A DISTINCT POSSIBILITY FOR SOME LOCATIONS.

.SPOTTER INFORMATION STATEMENT...

STORM SPOTTER ACTIVATION IS NOT ANTICIPATED TONIGHT...BUT MAY BE
NEEDED SATURDAY AFTERNOON OVER PORTIONS OF NORTHEAST NEBRASKA AND
WEST CENTRAL IOWA.

DEE