460
FXUS02 KWBC 081930
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
330 PM EDT SAT AUG 08 2009
VALID 12Z TUE AUG 11 2009 - 12Z SAT AUG 15 2009
THE LONGWAVE PATTERN IS SHOWING SIGNS OF RETURNING TO A MORE
NORMAL AUGUST PATTERN. AS THE CURRENT DEEP TROF LIFTS OUT OF THE
WRN STATES...THE POLAR WESTERLIES WILL RETREAT TO A MORE NORMAL
SUMMER LOCATION NEAR OR JUST N OF THE US/CANADIAN BORDER. IN FACT
HEIGHTS ACROSS THE ENTIRE NRN TIER OF STATES MAY AVERAGE OUT A BIT
ABOVE NORMAL DURING THE MEDIUM RANGE...SOMETHING THAT HAS NOT
HAPPENED ON THAT LARGE A SCALE SO FAR THIS SUMMER. THE
DETERMINISTIC 00Z/08 ECMWF MADE ANOTHER ATTEMPT A BRINGING IN AN
ANOMALOUSLY DEEP TROF INTO THE PACIFIC NW STATES AROUND FRI DAY 6.
THOUGH NOT AS FAR S AS THE PREVIOUS DEEP WRN TROF...IT IS STILL
ANOMALOUSLY INTENSE COMPARED TO CLIMO...AND WE THINK THAT THE
00Z/08 ENSEMBLE MEANS OF THE NAEFS AND ECMWF DO A PRETTY
REASONABLE JOB AT KEEPING MOST OF THE HEIGHT FALL WITH THAT
FEATURE ALONG AND OFFSHORE THE PACIFIC NW COAST.
THE 12Z GFS HAS TRENDED A LITTLE DEEPER/FASTER WITH THE NEXT
IMPORTANT TROF TO ENTER THE PACIFIC NW COAST...THOUGH NOT AS DEEP
OR PROGRESSIVE AS THE 00Z/08 ECMWF RUN. THE NEW 12Z/08 GEFS MEAN
IS WEAKER STILL...AND SUPPORTS OUR EARLIER PRELIM REASONING. THE
NEW 12Z/08 ECMWF IS IN FACT TRENDING TOWARDS THE 12Z/08 GFS WITH
THE FRI DAY 6 PACIFIC NW TROF...REINFORCING THE TRUTH THAT THE
LAW OF AVERAGES WORKS OUT WELL OVER THE LONG RUN.
FINAL PROGS UPHOLD THE EARLIER RATIONALE. WE KEPT OUR BLEND OF 40%
OF THE NEW 00Z/08 ECMWF ENSEMBLE MEAN WITH 30% EACH OF THE 00Z/08
GFS AND ECMWF. THIS BLEND MAINTAINED THE REASONABLE 00Z/08 AND
12Z/08 DETERMINISTIC GFS/ECMWF AVERAGE OF THE NEW UPPER TROF
EXPECTED ALONG THE PACIFIC NW COAST FOR LATE NEXT WEEK. THE 00Z/08
ECMWF ENSEMBLE MEAN WAS ALSO QUITE COMPATIBLE WITH THE
CORRESPONDING ENSEMBLE MEANS OF THE CANADIAN AND GEFS IN DEPICTING
THIS NEW TROF NEAR THE PACIFIC NW COAST. ENSEMBLE SPAGHETTI PLOTS
CLEARLY SHOWED THE DETERMINISTIC 00Z/08 ECMWF TO BE AN OUTLIER
NEAR THE SRN EDGE OF THE ENVELOPE OF SOLUTIONS WITH ITS DEEP TROF
OVER THE PACIFIC NW FOR FRI DAY 6. THE 00Z/08 GEFS AND NAEFS MEANS
WERE MORE CLIMATOLOGICAL IN KEEPING A BROADER LESS INTENSE TROF
MORE ALONG/OFFSHORE THE PACIFIC NW COAST EARLY NEXT WEEKEND.
ANOTHER POTENTIAL PROBLEM AREA LATE IN THE PERIOD WILL BE OVER ERN
NOAM...WHERE THE ECMWF MEAN SHOWS FLAT ANTICYCLONIC FLOW ACROSS SE
CANADA...IN CONTRAST TO THE GEFS MEAN SHOWING A WEAK BROAD TROF
OVER THE NERN STATES. AT THIS TIME I PREFER A PATTERN A BIT LESS
RIDGY THAN THE 00Z/08 ECMWF MEAN IN SE CANADA....BUT HIGHER
HEIGHTS OVER THE NE STATES NEXT WEEKEND THAN SHOWN BY THE 00Z/08
GEFS MEAN. THE NEW 12Z/08 GFS/ECMWF CONTINUE TO SUPPORT THIS
REASONING. ONE PROBLEM LATE IN THE PERIOD MIGHT BE THE NWD EXTENT
OF MOISTURE INTO THE MID ATLANTIC STATES AS A WEAK SHEAR AXIS OR
UPPER LOW DEVELOPS OVER THE TN VLY/GULF STATES. ABOVE NORMAL
HEIGHTS WILL KEEP CONVECTION GENERALLY SPARSE ACROSS THE NRN TIER
OF STATES. HOWEVER HIGHER PWS ALONG WITH A GOOD CHANCE OF OF
DIURNAL CONVECTIVE ACTIVITY MAY WORK SLOWLY NWD INTO THE OH
VLY/MID ATLANTIC STATES DAYS 5-7 ALONG AND TO THE RIGHT OF A SHEAR
AXIS ALOFT.
FLOOD
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