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FXUS02 KWBC 211830
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
230 PM EDT WED OCT 21 2009
VALID 12Z SAT OCT 24 2009 - 12Z WED OCT 28 2009
OPERATIONAL MODELS AND ENSEMBLES CONTINUE TO DISPLAY A SERIES OF
THREE SYSTEMS TRACKING THRU A BROAD MEAN TROF OVER THE CONUS.
TAKING INTO ACCOUNT THE COMBINATION OF GUIDANCE SPREAD AND
VERIFYING TIME FRAME... THE MOST UNCERTAINTY APPEARS TO EXIST WITH
THE EVENTUAL EVOLUTION OF THE MIDDLE SHRTWV TROF WHICH THE AVERAGE
OF SOLNS WOULD PLACE OVER THE PLAINS ON SUN. THE CANADIAN GLBL IS
ALREADY A SLOW OUTLIER VERSUS CONSENSUS INCLUDING THE 12Z CANADIAN
ENSEMBLE MEAN AS OF SUN SO ITS SOLN IS DISCOUNTED. HOWEVER EVEN
AMONG OTHER MODELS THERE IS RAPID DIVERGENCE OF SOLNS AS THIS
PLAINS ENERGY EJECTS NEWD. THE 00Z GFS BECOMES SLOWEST DUE TO THE
TROF INCORPORATING SOME UPSTREAM ENERGY BEFORE CONTINUING ALONG.
THE 00Z ECMWF HAS ADJUSTED SLOWER TO A COMPROMISE BETWEEN THE
12Z/20 RUN AND THE GFS... WHILE THE UKMET/NOGAPS ARE FASTER THAN
THE 12Z/20 ECMWF. PREFER AN AVERAGE OF LATEST GUIDANCE CLOSEST TO
THE 12Z/20 ECMWF WITH THIS FEATURE.
FARTHER WWD... THERE IS DECENT AGREEMENT UPON AN INCREASINGLY
DEEP/AMPLIFIED TROF THAT SHOULD EXTEND FROM THE NRN PLAINS INTO
NWRN MEXICO BY DAY 7 WED. MODELS/ENSEMBLES SHOW TYPICAL SPREAD
WITH EXACT AMPLITUDE AND ORIENTATION OF THE TROF. THE SIMILARLY
DEEP 00Z ECMWF/CMC SOLNS ARE POSSIBLE GIVEN THE
AMPLIFICATION/SHARPENING UPSTREAM... BUT FOR NOW PREFER A
COMPROMISE WITH SOMEWHAT FLATTER ENSEMBLE MEANS TO ACCOMMODATE
TYPICAL UNCERTAINTY BY THAT TIME FRAME. THE 00Z GFS IS CLOSER TO
THIS COMPROMISE ALOFT BUT COMPARED TO REMAINING GUIDANCE MAY BE
SOMEWHAT EXTREME WITH ITS LOW PRESSURE CENTER REACHING THE MID MS
VALLEY BY EARLY NEXT WED.
WITH THE SYSTEM FCST TO TRACK FROM THE GRTLKS NEWD SAT-SUN... LATE
IN THE SHORT RANGE PERIOD THE 00Z ECMWF STRAYS TO THE FAST EDGE OF
MODEL/ENSEMBLE CONSENSUS DUE TO FLATTER UPSTREAM FLOW. THE 00Z
GFS MAY BE SLIGHTLY STRONG DUE TO ITS OWN QUESTIONABLE MID LVL
DETAILS LATE IN THE SHORT RANGE... BUT ITS OVERALL FCST COMPARES
MORE FAVORABLY TO CURRENT CONSENSUS AND PRIOR ECMWF CONTINUITY.
COMBINED WITH PREFERENCES UPSTREAM... THE 12Z/20 ECMWF RUN SEEMS
TO PROVIDE THE BEST STARTING POINT FOR THE EVOLUTION OF THIS
SYSTEM. DUE TO THE PERSISTENT MEAN PATTERN... THE FRONT TRAILING
FROM THE SFC LOW SHOULD STALL FROM JUST OFF THE SERN COAST SWWD
INTO THE GULF OF MEXICO FOR A MAJORITY OF THE PERIOD.
OVER THE TROPICS THE 00Z ECMWF EXHIBITS ANOTHER CONTINUITY CHANGE
IN DOWNPLAYING ANY POTENTIAL NWRN CARIBBEAN TROPICAL DEVELOPMENT
THAT PRIOR RUNS HAD ADVERTISED. THE 00Z GFS NOW DEPICTS A WEAK
SYSTEM WHILE REMAINING GUIDANCE IS RATHER ILL DEFINED. THE FINAL
HPC FCST BRINGS A WEAK FEATURE TOWARD WRN CUBA BY DAY 7 WED. THIS
IS ABOUT A DAY SLOWER THAN YESTERDAY BASED UPON LATEST AND LESS
ORGANIZED SATELLITE TRENDS AFTER COORDINATION WITH TPC.
MULTIPLE QUESTION MARKS PRESENT IN THE 00Z ECMWF/GFS RESULT IN
PREFERRING THE 12Z/20 ECMWF AS THE BASIS FOR THE DAYS 3-5 SAT-MON
FCST WITH ONLY MINOR ADJUSTMENTS. THE 00Z GEFS/ECMWF ENSEMBLE
MEANS ARE ADDED TO THE 12Z/20 ECMWF FOR DAYS 6-7 TO EMPHASIZE WHAT
CONSENSUS EXISTS WITH THE LARGER SCALE PATTERN. WE SEE NO
COMPELLING REASON TO CHANGE CONTINUITY MUCH AT THIS TIME FOR THE
FINAL HPC PROGS AFTER CONSIDERATION OF STILL QUITE VARIED 12 UTC
GUIDANCE.
RAUSCH/SCHICHTEL
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