915
FXUS02 KWBC 111804
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
204 PM EDT FRI SEP 11 2009
VALID 12Z MON SEP 14 2009 - 12Z FRI SEP 18 2009
MULTI-DAY MEANS DISPLAY A VERY STABLE LARGE SCALE PATTERN
CONSISTING OF A STRONG POSITIVE HGT ANOMALY CENTER POSITIONED JUST
W OR SW OF HUDSON BAY AND A NEGATIVE ANOMALY CENTER OVER THE NERN
PACIFIC. THIS REGIME WILL SUPPORT A MEAN TROF OVER ERN CANADA
EXTENDING INTO THE NERN QUADRANT OF THE CONUS. MOST OTHER AREAS
OF THE CONUS...ASIDE FROM THE EXTREME NORTHWEST WHICH MAY SEE THE
PASSAGE OF ONE OR MORE PIECES OF ENERGY ON THE ERN PERIPHERY OF
THE NERN PAC TROF... WILL LIKELY EXPERIENCE RATHER WEAK FLOW THRU
THE PERIOD.
THE MOST SIGNIFICANT QUESTION MARKS INVOLVE THE EVOLUTION OF
ENERGY WITHIN THE ERN CANADA/NERN CONUS MEAN TROF. THE 00Z ECMWF
IS ON THE SLOW EDGE OF THE MODEL/ENSEMBLE SPREAD WITH A LEADING
SHRTWV AROUND MIDWEEK... WHILE THERE IS A FAIR CLUSTERING OF
OPERATIONAL SOLNS THAT ARE SHARPER AND MORE AMPLIFIED THAN MOST
ENSEMBLES WITH TRAILING ENERGY THAT SHOULD BE A COMBINATION OF
UPPER LOW ENERGY INITIALLY NEAR THE US-CANADIAN BORDER AND
UPSTREAM PACIFIC/NRN CANADA FLOW. SHORT RANGE EVOLUTION OF ENERGY
CUTTING OFF OVER THE NRN PLAINS MAY OFFER POTENTIAL FOR UPSTREAM
ENERGY ALSO TO AMPLIFY A LITTLE MORE THAN THE ENSEMBLE MEANS
ALBEIT A LITTLE FARTHER EWD. THUS WOULD RECOMMEND A BLEND AMONG
THE OPERATIONAL/ENSEMBLE GUIDANCE TO DOWNPLAY QUESTIONABLE
INDIVIDUAL MODEL SOLNS WHILE ACCOUNTING FOR THE AGREEABLE LARGE
SCALE PATTERN.
ELSEWHERE... SLOW MOVING WEAKNESS ALOFT OVER THE SRN PLAINS/LOWER
MS VALLEY WILL MAINTAIN LOW PRESSURE NEAR THE GULF COAST. THE GFS
IS DEEPER ALOFT THAN MOST OTHER GUIDANCE... SO SFC LOW PRESSURE
MAY BE A LITTLE MORE SUPPRESSED AS INDICATED BY RECENT ECMWF RUNS.
MEANWHILE BEST CLUSTERING OF GUIDANCE INDICATES THE CLOSED LOW
MOVING INTO THE WEST MAY BE A LITTLE SWD OF THE 00Z ECMWF. MODEL
CONTINUITY HAS NOT BEEN GOOD WITH THIS FEATURE... WITH THE AVERAGE
OF THE PAST TWO ECMWF RUNS PROVIDING A REASONABLE FCST COMPARED TO
OTHER GUIDANCE. PREFERENCE FOR A CONSENSUS/BLEND APPROACH THAT
MAINTAINS SOME CONTINUITY WHERE FEASIBLE LEADS TO A NEARLY EVEN
BLEND OF THE 00Z ECMWF... 12Z/10 ECWMF... AND 12Z/10 ECMWF
ENSEMBLE MEAN THRU THE DAYS 3-7 PERIOD.
UPDATED MORNING PRELIMS OFFER THE AVAILABILITY OF THE 00Z ECMWF
ENS MEAN WHICH LOKS LIKE TEH LAGGED AVERAGE FORECAST OF THE LAST 4
CYCLES OF THE ECMWF. PRIOR NIGHTSHIFT BLEND WASAN ATTEMPT AT THE
LAGGED AVERAGE SOLUTION. VERY OFTEN IF NOT MOST OF THE TIME A
LAGGED AVERAGE FORECAST OF ECMWF OR COMBO LAGGED AVERAGE FORECAST
OF BOTH ECMWF/GFS LOOKS MUCH LIKE THE 00Z ECMWF ENS MEAN. THIS
WILL BE USED IN THIS MORNINGS UPDATED SOLUTION...EQUAL PARTS ECMWF
AND 00Z ECMWF ENS MEAN WITH A STEADY INCREASE TOWARDS THE ECMWF
MEAN LATE PERIOD.
THIS SOLUTION DAMPENS THE OVERLY AGGRESSIVE ERN CANADIAN/NERN U.S.
SHORTWAVE TROF OF THE OP 00Z ECMWF LATE TUES TO FRI. THIS IS
BASICALLY UNDER HIGH PRESSURE AND THIS BLEND SHOULD BE CLOSE TO
THE GFS MOS SOLUTION.
12Z GFS HAS NO SIG CHANGES WITH THE EXCEPTION OF HAVING A MODERATE
EXITING TROF OFF NEW ENG WED NIGHT. THIS IS MUCH LESS AMPLIFIED
THAN TEH ECMWF SOLUTION AND NOT AS RIDGED AS EARLIER GFS. THIS WAS
HANDLED EARLIER BY USING GFS/ECMWF ENS MEANS. NO CHANGES TO AFTN
FINALS
RAUSCH/ROSENSTEIN
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