749
FXUS02 KWBC 191718
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
117 PM EDT MON OCT 19 2009
VALID 12Z THU OCT 22 2009 - 12Z MON OCT 26 2009
THE LATEST MODELS AND ENSEMBLE GUIDANCE CONTINUE THE THEME OF A
BROAD MEAN TROF OVER THE CONUS WITH FAST PACIFIC FLOW CARRYING
MULTIPLE SHRTWVS INTO/THRU THIS FEATURE. WHILE CONTINUITY WITH
THE EXPECTED LARGE SCALE PATTERN HAS BEEN FAIRLY GOOD... SOLNS
STILL DISPLAY SIGNIFICANT DIFFS AND IN SOME CASES CONTINUITY
CHANGES WITH THE DETAILS OF INDIVIDUAL SYSTEMS.
COMPARED TO REMAINING MODEL/ENSEMBLE GUIDANCE THE GFS/UKMET APPEAR
TOO STRONG WITH MID LVL ENERGY FCST TO CROSS THE NORTHEAST THU-THU
NIGHT... AND THUS TOO STRONG WITH ASSOC LOW PRESSURE EXPECTED TO
TRACK INTO THE CANADIAN MARITIMES. UPSTREAM MOST 00Z GUIDANCE
INCLUDING THE GFS/ECMWF/CMC HAS MADE A NOTICEABLE SLOWER
ADJUSTMENT WITH THE PLAINS/MS VALLEY SYSTEM AS OF DAY 3 THU.
FOLLOWING THIS TREND TO SOME DEGREE SEEMS REASONABLE IN LIGHT OF
THE NUMBER OF MDLS MAKING THIS CHANGE... BUT THE ABRUPT NATURE OF
THIS CHANGE LOWERS CONFIDENCE SOMEWHAT. BY FRI-SAT THERE IS FAIR
AGREEMENT THAT INCOMING ERN PAC/WRN NOAM ENERGY SHOULD INTERACT
WITH THIS LEADING SYSTEM TO HELP DEEPEN LOW PRESSURE OVER THE MS
VALLEY/GRTLKS. HOWEVER THE GFS IS EXTREME COMPARED TO OTHER
MODEL/ENSEMBLE SOLNS WITH THE SEWD AMPLITUDE OF THE OVERALL TROF
BY DAY 5 SAT... SO ITS DEEP GRTLKS SYSTEM IS LIKELY OVERDONE.
ANOTHER WILD CARD EARLY-MID PERIOD INVOLVES THE ULTIMATE TRACK OF
ERN PAC HURCN RICK. THE ECMWF IS FASTER/MORE DEFINED THAN OTHER
SOLNS OR TPC TRACK... SO ASPECTS OF ITS PLAINS/MS VLY EVOLUTION
ARE QUITE QUESTIONABLE.
BY DAYS 6-7 SUN-MON... THERE IS LOOSE CLUSTERING OF GUIDANCE
TOWARD LOW PRESSURE TRACKING OVER/NEAR THE NERN STATES INTO THE
CANADIAN MARITIMES. BEHIND THIS SYSTEM THE PREVAILING CONSENSUS
OF SOLNS SUGGESTS THE GFS MAY BE TOO FAST WITH ITS TROF REACHING
THE GRTLKS/MS VALLEY BY DAY 7 MON AND TOO STRONG/SLOW WITH ITS
SYSTEM NEARING THE WEST COAST AT THAT TIME. ALBEIT WITH SOME
DETAIL DIFFS... THE ECMWF/CMC AND GEFS/ECMWF ENSEMBLE MEANS
PROVIDE MUCH BETTER AGREEMENT AND ARE PREFERRED FOR THE HANDLING
OF ERN PAC AND CONUS FLOW BY LATE IN THE FCST.
IN ORDER TO MAINTAIN AS MUCH OPERATIONAL MODEL DETAIL AS POSSIBLE
WHILE ACCOUNTING FOR UNCERTAINTY THAT CONTINUES FROM LATE IN THE
SHORT RANGE...A DAYS 3-7 SOLUTION INCORPORATING 60% 00 UTC
CANADIAN AND 40% OF GENERALLY SUPPORTIVE 00 UTC ECMWF ENSEMBLE
MEAN FITS THE BILL. PREFER TO KEEP THIS BLEND FOR OUR FINAL PROGS
AND MAINTAIN CLOSE HPC CONTINUITY INSTEAD OF CHASING VARIED TRENDS
FROM 12 UTC GUIDANCE IN AN UNCERTAIN PATTERN.
RAUSCH/SCHICHTEL
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