982
FXUS02 KWBC 081852
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
251 PM EDT THU OCT 08 2009
VALID 12Z SUN OCT 11 2009 - 12Z THU OCT 15 2009
THE FINAL HPC PRELIMINARY MEDIUM RANGE SURFACE FRONTS/PRESSURES
AND 500 MB PROGS REMAIN FOR THE MOST PART PRIMARILY DERIVED FROM A
50-50 BLEND OF THE 00Z ECMWF/UKMET SUN-TUE AND 50-50 00Z ECMWF
ENSEMBLE MEAN AND 00Z GEFS MEAN BLEND BY NEXT WED/THU...AFTER
SEEING OVERALL FAVORABLE TRENDS FROM MOST 12 UTC MODEL AND
ENSEMBLE GUIDANCE.
MODEL RUNS OVER THE PAST 24 HOURS HAVE MADE A FEW CHANGES
REGARDING THE EVOLUTION OF A DEEP LAYER SHRTWV MOVING EAST ACROSS
THE OH VALLEY/APPALACHIANS DAY FOUR/EAST COAST DAY 5/TUE...WITH
LOW PRESSURE FORECAST BY THE 00Z ECMWF/UKMET SLIGHTLY FURTHER WEST
THAN YESTERDAYS FORECASTS. THE 00Z GFS HAS SURFACE DEVELOPMENT
MORE OUT FROM THE OH VALLEY IN RESPONSE TO AN INITIALLY CLOSED 700
MB LOW ON DAY THREE WHICH IS FURTHER SOUTHWEST THAN THE
ECMWF/UKMET/CANADIAN GLOBAL MODELS/RESPECTIVE NCEP/ECMWF MEANS.
THE 00 UTC CANADIAN OFFERS A MORE SUPPRESSED SOLUTION. THE 00 UTC
ECMWF/UKMET ARE IN GOOD AGREEMENT AND OFFER BETTER HPC
CONTINUITY...SO A BLEND OF THESE SOLUTIONS WAS USED FOR THE PRELIM
PROGS. HOWEVER...PREFER HOWEVER TO BACK-AWAY SLIGHTLY AFTER
CONSIDERATION OF A COMPOSITE OF 12 UTC MODEL AND ENSEMBLE GUIDANCE
THAT IS A BIT MORE SUPPRESSED. THE HPC FINAL SOLUTION STILL
HIGHLIGHTS A POTENT EARLY SEASON SURGE OF COLD HIGH PRESSURE
SETTLING DOWN ACROSS THE W-CENTRAL THEN ERN US NEXT WEEK.
UPSTREAM...PROBLEMS SEEM TO BEGIN TO DEVELOP IN THE ECMWF AROUND
00Z TUE...WHEN IT COMES UP WITH A NEW CYCLONE ALONG THE FRONT IN
THE NORTHEAST PACIFIC NEAR 39N 132W. THIS LOW IS FCST TO
INTENSIFY...MOVE ONSHORE..PRODUCING A HEAVY TO EXCESSIVE RAINFALL
EVENT IN NORTHERN TO CENTRAL CA. LOW CONFIDENCE EXISTS IN THE
ECMWF GIVEN ITS BREAK IN CONTINUITY AND GIVEN DIFFERENCES WITH THE
00Z UKMET/GFS AND GFS/ECMWF ENSEMBLE MEANS. VALID 00Z WED THE
UKMET LOW NEAR 50N 135W MATCHES THE ECMWF ENSEMBLE MEAN. THE 00Z
ECMWF STRONGER STORM EVENTUALLY BUILDS A WESTERN CANADA AND THEN
CENTRAL CANADA MID-UPPER LEVEL RIDGE...SO MAJOR PHASING CHANGES
FROM THE MEAN AND PRIOR RUN DEVELOPS IN THE 00Z ECMWF OVER
CANADA/BORDER STATES.
THE 00Z ECMWF SOLUTION IS ALSO OUT OF PHASE WITH TELECONNECTIONS
FROM THE POSITIVE HEIGHT ANOMALY OVER/JUST NORTH OF AK...WHICH
CORRELATE WITH LOWER HEIGHTS OVER CENTRAL TO EASTERN CANADA. A
SIMILAR TELECONNECTION RESULT OCCURRED FROM RUNNING THE NEGATIVE
HEIGHT ANOMALY OVER THE NORTHERN PACIFIC NEAR 39N 160W.
CONSEQUENTLY....WITH BETTER AGREEMENT AMONG THE NCEP/ECMWF MEANS
AND A BETTER MESHING OF THESE SOLUTIONS WITH UPSTREAM
TELECONNECTIONS...A BLEND OF THESE SOLUTIONS WAS USED FOR DAYS
6/7.
PETERSEN/SCHICHTEL
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