839
FXUS02 KWBC 121732
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
131 PM EDT SAT JUL 12 2008
VALID 12Z TUE JUL 15 2008 - 12Z SAT JUL 19 2008
FINAL MANUAL GRAPHICS WILL BE UNCHANGED FROM THE UPDATED PRELIM
MADE THIS MORNING. THE NEW 12Z/12 GFS IS MOSTLY SIMILAR TO ITS 00Z
RUN BUT HAS TRENDED A BIT SLOWER WITH ITS SHORTWAVE MOVING INTO
THE LAKES REGION THU-FRI DAYS 5-6...OR ALMOST HALFWAY TOWARDS THE
ECMWF TIMING OF THAT FEATURE. THE 12Z/11 CANADIAN FAVORS MORE TROF
OVER THE NW STATES DAYS 5-6 THAT THE 12Z GFS...AND KEEPS MORE
RIDGE OVER THE ERN STATES DAY 6 THAN THE CORRESPONDING GFS. IN
MANY WAYS THE NEW 12Z/12 UKMET IS LIKE AN AVERAGE OF THE
GFS/CANADIAN...BUT IS MUCH FLATTER DAYS 5-6 WITH THE AMPLITUDE OF
SYS MOVING ACROSS THE NRN US/CANADIAN BORDER.
SIMILAR TO YESTERDAY...THE MAIN MODEL/ENSEMBLE BONE OF CONTENTION
WILL BE THE POTENTIAL UPPER TROF ALONG/JUST OFF THE PAC
NW/VANCOUVER BC COAST...AND SHORTWAVE ENERGY SHEARING OUT OF IT
INTO VERY SLIGHTLY CYCLONIC...ALMOST ZONAL FLOW NEAR THE
US/CANADIAN BORDER. EXPECT LOWER THAN AVERAGE PREDICTABILITY ALONG
50N FROM THE NE PACIFIC ACROSS THE US/CANADIAN BORDER. UPDATED
PRELIM PROGS BLENDED 60% OF THE 00Z ECMWF WITH 40% OF THE 00Z GFS
FOR DAYS 3-4...AND 60% OF THE 00Z ECMWF WITH 40% OF THE 00Z GEFS
ENSEMBLE MEAN THE REMAINDER OF THE PERIOD. THIS BLEND WAS CHOSEN
TO PRESERVE SOME OF THE CHARACTER OF THE ECMWF WITHOUT WASHING THE
SURFACE PATTERN OUT TOO MUCH AS WOULD THE GEFS MEAN. WE ARE NOT AS
SOLD TODAY AS YESTERDAY ON A PROMINENT PACIFIC NW TROF.
TODAY...HPC CHOOSES THE CENTER OF THE ENVELOPE DEFINED BY THE
SOMEWHAT MORE AMPLIFIED GFS FAMILY OF SOLUTIONS...WITH TROFS NEAR
125W AND THE GRT LAKES DAYS 5-6...AND A FLATTER ECMWF FAMILY
PATTERN WITH SOMEWHAT MORE SPREAD OVER THE WRN STATES.
..REGIONAL HIGHLIGHTS
..SOUTHEAST
RESIDUAL MOISTURE AND INSTABILITY FROM A FRONTAL BOUNDARY WILL
FUEL DIURNAL CONVECTION EACH DAY WITH SOME LOCALLY HEAVY RAINFALL.
..SW MONSOON AREA
MONSOONAL MOISTURE NOW IN PLACE SHOULD CONTINUE TO SUPPORT DIURNAL
ACTIVITY EACH DAY IN FAVORED AREAS. MORE WESTERLY MID-LEVEL FLOW
ABOVE LATITUDE 40N WILL KEEP THE NWRN STATES DRIER.
...NRN PLAINS/MS VLY
THE PROXIMITY OF FRONTS AND THEIR MESO-GENERATED ACTIVITY FOR
SEVERAL DAYS SUPPORTS THE THREAT OF LOCALLY EXCESSIVE RAINFALL IN
AREAS THAT HAVE SEEN SEVERE FLOODING OVER THE PAST MONTH.
..TROPICS
HURCN BERTHA SHOULD REMAIN NO THREAT TO ANY LAND AREAS...AS IT MAY
CONTINUE TO ERRATICALLY DRIFT IN THE AMBIENT FLOW FOR SOME TIME. A
CLOSING OFF SYS TO ITS ENE MAY EVENTUALLY GET CLOSE ENOUGH TO
STEER BERTHA ESE BEYOND DAY 5. SEE BULLETINS FROM THE TPC.
FLOOD
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