777
FXUS02 KWBC 151802
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
201 PM EDT FRI AUG 15 2008
VALID 12Z MON AUG 18 2008 - 12Z FRI AUG 22 2008
GUIDANCE SHOWS AN EWD PROGRESSION OF LARGE SCALE FEATURES NEXT
WEEK... WITH THE ERN PAC/WEST COAST TROF MOVING INTO THE WEST AND
THE STRONG RIDGE OVER THE W-CNTRL STATES EVENTUALLY REACHING INTO
ERN NORTH AMERICA. THE PRIMARY FCST PROBLEMS INVOLVE THE
AMPLITUDE AND TIMING OF THE TROF ENTERING THE WEST... THE
EVOLUTION OF A TROF AFFECTING THE NERN CONUS/EXTREME ERN CANADA
AROUND MIDWEEK... AND SERN CONUS MID LVL DETAILS THAT WILL
INFLUENCE THE TRACK OF A STRONG NRN CARIBBEAN TROPICAL WAVE WHICH
TPC OUTLOOKS INDICATE HAS A HIGH POTENTIAL FOR TROPICAL CYCLONE
FORMATION DURING THE SHORT RANGE PERIOD.
ALREADY IN THE LATTER HALF OF THE SHORT RANGE PERIOD DIFFS ARISE
WITH THE DETAILS OF BERING SEA TO NERN PACIFIC FLOW... AND THIS
UNCERTAINTY CONTINUES DOWNSTREAM INTO NORTH AMERICA DURING THE
MEDIUM RANGE. THE 00Z ECMWF EVOLUTION THAT LEADS TO A CLOSED LOW
NEAR THE CA COAST AND FLAT CANADIAN FLOW IS NOT SUPPORTED BY MOST
00Z GEFS AND 12Z ECMWF/CANADIAN ENSEMBLES. MEANWHILE THE OLD 12Z
ECMWF AND EC/CANADIAN ENSEMBLE MEANS ALL SUPPORT THE IDEA OF A
SLOWER/DEEPER TROF CROSSING THE WEST COMPARED TO THE 00Z GFS OR
GEFS MEAN. ARGUMENTS COULD BE MADE FOR EITHER SCENARIO. STRENGTH
OF THE W-CNTRL NOAM RIDGE EARLY NEXT WEEK WOULD SUPPORT THE SLOWER
GUIDANCE... WHILE TELECONNECTIONS RELATIVE TO THE NEGATIVE
ANOMALIES GENERALLY FCST NEAR THE AK PENINSULA BY D+8 SUGGEST A
FAIRLY RAPID RETURN TO AN ERN NOAM MEAN TROF AFTER THE END OF THE
MEDIUM RANGE PERIOD. THIS WOULD BE MOST EASILY ACCOMPLISHED BY A
MODERATELY FAST WRN TROF PROGRESSION. FAST UPSTREAM FLOW COULD
ALSO LEAD TO FASTER TIMING THAN THE SLOWER CLUSTER. THE RELATIVE
LACK OF SLOW/DEEP WRN TROFS SO FAR THIS SUMMER SEEMS TO FAVOR
LEANING IN THE GFS/GEFS DIRECTION.
MEANWHILE GUIDANCE IS SHOWING SIGNIFICANT AMPLIFICATION OVER THE
NERN CONUS/CANADIAN MARITIMES BY MIDWEEK. THOUGH NOT AS
AGGRESSIVE AS THE CANADIAN OR OLD 12Z ECMWF SOLNS... THE 00Z
UKMET/NOGAPS AND BEST CLUSTERING OF 00Z GEFS AND 12Z
ECMWF/CANADIAN ENSEMBLES ALL INDICATE THAT THE TROF SHOULD BE MORE
PERSISTENT THAN FCST BY THE THE 00Z GFS/ECMWF RUNS.
THE EARLY/UPDATED MORNING PRELIM FCSTS AND 16Z HPC/TPC
COORDINATION MAINTAIN CONTINUITY REGARDING TROPICAL SYSTEM 92L
THAT WILL IMPACT PORTIONS OF THE SOUTHEAST NEXT WEEK ALBEIT WITH
LOW CONFIDENCE...HAVE ADJUSTED/FCST DAY 7 ON A MORE NWD TRACK AS
PER TRENDS OF 00Z ECMWF/06Z GFS/06Z GHM/HWRF AND MOST OTHER HURCN
MODELS SUGGESTING A MORE EAST AND NORTH TRACK. THIS AFFECTS THE
EAST COAST OF FLORIDA AND GA/SC. DIFFICULTIES OCCUR IN
INITIALIZATION DUE TO THE SYSTEMS CURRENT PROXIMITY TO THE GREATER
ANTILLES. 12Z GUIDANCE FROM GFS/CMC/UKMET AND NEWER GHM/HWRF NOW
INDICATE A MUCH MORE SRLY TRACK AND WEST TRACK ALONG OR SOUTH OF
CUBA AND INTO THE WESTERN GLFMEX WITH A WESTWARD ADJUSTMENT/CHANGE
OF GREATER THAN 300 NM. SEE TPC DISCUSSIONS/ADVISORIES.
LOW CONFIDENCE IN ANY PARTICULAR MODEL SOLN... ALONG WITH OVERALL
PREFERENCES WITH RESPECT TO TROFS AFFECTING THE WEST AND
NORTHEAST... LED TO STARTING THE DAYS FOR EARLY PRELIMS 3-7 FCST
WITH A 70/30 BLEND OF THE 00Z GEFS MEAN AND 12Z/14 ECMWF ENSEMBLE
MEAN RESPECTIVELY. ADJUSTMENTS WERE MADE TO ACCOUNT FOR THE
POTENTIAL TROPICAL FEATURE NEAR THE SERN COAST OR CUBA OR THE
EASTERN GULF OF MEXICO AND TO IMPROVE DEFINITION OF SFC LOW
PRESSURE OVER SERN CANADA EARLY IN THE PERIOD.
UPDATED MORNING PRELIMS INCORPORATED AND BLENDED 00Z GFS AND 00Z
ECMWF FOR DAYS 3 AND 4
MON/TUE. BY DAYS 5-7 THE 06Z GFS WAS BLENDED WITH A 00Z ECMWF ENS
MEAN. TROPICAL POINTS A COORDINATION BETWEEN TPC AND HPC. NO
CHANGES TO AFTN FINALS.
RAUSCH/ROSENSTEIN
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