312
FXUS02 KWBC 111837
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
237 PM EDT TUE AUG 11 2009
VALID 12Z FRI AUG 14 2009 - 12Z TUE AUG 18 2009
THE MODELS AND ENSEMBLES CONTINUE TO SHOW UNSEASONALLY AMPLIFIED
MID-UPPER LEVEL FLOW FROM THE ERN PAC INLAND ACROSS NORTH AMERICA
FOR MUCH OF THE MEDIUM RANGE FORECAST PERIOD. THIS PATTERN SEEMS
HIGHLIGHTED BY AN ERN PAC RIDGE/WRN US TROUGH COUPLET AND
DOWNSTREAM CENTRAL US RIDGE...WITH LESS DEFINED EMBEDDED IMPULSES
DIGGING/HANGING BACK AND/OR EJECTING OUT FROM THE WRN US TROUGH TO
FLOW OVER THE CENTRAL US RIDGE AND INTO A ERN US WEAKENSS ALOFT.
THIS PATTERN IS SLOWLY PROGRESSIVE/TRANSITIONAL AND COMPLEX WITH
CONSIDERATION OF THESE TYPE OF EMBEDDED LESS PREDICTABLE
IMPULSES/INTERACTIONS WITH VARIED LOWER LEVEL FRONTAL/LOW
STRUCTURE AND SENSIBLE WEATHER FOCUS DETAILS DAYS 4-7.
GUIDANCE SPREAD FOR FLOW BEYOND THESE SMALL SCALES SEEMS MOST
SIGNIFICANT WITH RESPECT TO THE HANDLING AND SEPARTAION OF ENERGY
DIGGING INTO/OUT FROM THE WRN US MID-UPPER LEVEL TROUGH. IN THIS
FLOW...THE 00 UTC CANADIAN AND NOGAPS DIG/HOLD SIGNIFICANTLY
DEEPER CLOSED LOW ENERGY BACK TOWARD THE WEST COAST 4/5 AND
ESPECIALLY DAYS 6/7 THAN THE 00 UTC ECMWF/UKMET OR 00/06 UTC GFS.
THE 06 UTC GFS HAS TRENDED MORE IN LINE WITH THE 00 UTC ECMWF
ALOFT. GFS ENSEMBLES AND TO A LESSER EXTENT CANADIAN AND SOME
ECMWF ENSEMBLE MEMBERS FROM 00 UTC ARE NOT AS POTENT AS THE
DETERMINISTIC CANADIAN/NOGAPS...BUT DO SUPPORT HOLDING MORE ENERGY
BACK INTO THE WEST THAN THE HIGHER RESOLUTION 00 UTC ECMWF...MOST
ECMWF ENSEMBLES...THE 00 UTC UKMET...AND THE 00/06 UTC GFS.
PREFER TO TAKE THIS INTO ACCOUNT TO SOME DEGREE CONSIDERING
UPSTREAM ERN PAC RIDGE AMPLITUDE POTENTIAL...BUT PREFER TO NOT
DOWNPLAY TOO MUCH THE HIGHER RESOLUTION MODEL/TRENDS.
ACCORDINGLY...THE PRELIM HPC MEDIUM RANGE PROGS WERE PRIMARILY
DERIVED FROM A BLEND OF 70% 00 UTC ECMWF AND 30% FROM THE NAEFS
THAT IS A BIASED CORRECTED COMBINATION OF THE 00 UTC GFS AND
CANADIAN ENSEMBLES. WE SEE NO NEW COMPELLING TRENDS FROM LATEST
12 UTC MODEL AND ENSEMBLE GUIDANCE TO CHANGE HPC CONTINUITY FOR
OUR FINAL PROGS.
SCHICHTEL
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