128
FXUS02 KWBC 241816
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
215 PM EDT SAT OCT 24 2009
VALID 12Z TUE OCT 27 2009 - 12Z SAT OCT 31 2009
WITH THE EXPECTATION OF POSITIVE ANOMALY CENTERS AT 500 HPA IN THE
NORTHEAST PACIFIC AND NORTHWEST ATLANTIC...A MEAN TROUGH SHOULD
PERSIST MID-CONTINENT THROUGH THE MEDIUM RANGE PERIOD. WHILE THE
FLOW PATTERN ACROSS THE PACIFIC SHOWS GOOD AGREEMENT...EVEN WITH
EMBEDDED DETAILS...THE SAME CANNOT BE SAID IN AND NEAR NORTH
AMERICA. THE 00Z UKMET DEPARTS FROM THIS IDEA WITH ITS CLOSED LOW
SETTLING INTO THE SOUTHWEST...SO IT WAS NOT PREFERRED. WITH A
POLAR LOW RETURNING TO THE NORTH POLE...AND A POSSIBLE CLOSED
CYCLONE MOVING DOWN THE WESTERN CANADIAN COAST...SYSTEMS SHOULD
REMAIN PROGRESSIVE WITHIN NORTH AMERICA...WHICH WAS ANOTHER REASON
TO SCRAP THE SLOWER UKMET. THE 00Z CANADIAN HAS MINIMAL ENSEMBLE
SUPPORT FROM THE 00Z MULTI-MODEL ENSEMBLE GUIDANCE SURFACE LOW
SPREAD...SO DECIDED AGAINST ITS USE. THE 00Z CANADIAN/GEFS/ECMWF
ENSEMBLE MEMBERS WERE CLOSER TO THE 06Z GFS/00Z OR 06Z GEFS MEAN
THAN THE OTHER GUIDANCE...SO USED A BLEND OF THOSE PIECES OF
GUIDANCE TO START WITH...MAKING ADJUSTMENTS IN THE MIDWEST AND
NEAR THE EAST COAST TO KEEP OUR PROGS WITHIN THE MIDDLE OF THE
OVERALL ENSEMBLE SPREAD AND TO ACCOUNT FOR TRENDS SEEN IN THE 12Z
GUIDANCE. THIS KEPT REASONABLE CONTINUITY. DAY-TO-DAY CHANGES IN
THE GUIDANCE MAKES THIS FORECAST LESS CERTAIN THAN USUAL. THIS
PATTERN SHOULD BE WET ACROSS THE SOUTHERN AND EASTERN STATES TO
THE EAST OF THE MEAN TROUGH AXIS.
SHORTWAVE/SURFACE LOW MOVING FROM THE SOUTHERN PLAINS INTO THE
MIDWEST...
SURFACE LOW FORMING NEAR CAROLINA COAST LATE WEDNESDAY...
THE 00Z ECMWF WAS ON THE SLOW SIDE OF THE GUIDANCE WITH THIS
SYSTEM...WHILE THE 12Z NAM/12Z GFS ARE STRONGER AND QUICKER. THE
00Z CANADIAN DOES NOT APPEAR TO CARRY THIS SYSTEM AT ALL. THE 12Z
RUNS OF THE GFS/CANADIAN/UKMET SIGNIFICANTLY TRENDED IN THE
DIRECTION OF THE 00Z ECMWF WITH THIS SHORTWAVE...THOUGH BY
THURSDAY MORNING THE 12Z GFS DEPARTS SIGNIFICANTLY FROM THE OTHER
GUIDANCE/ENSEMBLE MEANS WITH ITS QUICKER/DEEPER SOLUTION AND
CANNOT BE USED. THERE IS ENOUGH SEPARATION IN THE FLOW PATTERN TO
ALLOW FOR A SEPARATE SHORTWAVE. PER THE TREND SEEN IN THE 12Z
GUIDANCE...TRENDED THE PRESSURES AND 500 HPA HEIGHTS TOWARDS THE
INTERMEDIATE 12Z GFS SOLUTION FOR TUESDAY AND WEDNESDAY...WHICH
NOW HAVE A LOW MOVING FROM THE NORTHWEST GULF OF MEXICO INTO THE
MID-MISSISSIPPI VALLEY MID WEEK BEFORE THE SURFACE CYCLONE BECOMES
ABSORBED BY THE PROGRESSIVE SYSTEM MOVING ACROSS SOUTHERN CANADA.
THIS MID-LEVEL SHORTWAVE SHOULD HELP SPUR A NEW LOW OFFSHORE NORTH
CAROLINA...WHICH IS ADVERTISED BY THE 06Z GFS/12Z CANADIAN/12Z
UKMET AND HALF OF THE 00Z ECMWF ENSEMBLE MEMBERS...WHICH SHOULD
KEEP THE CAROLINAS WEDGED UNDERNEATH COOL HIGH PRESSURE UNTIL
THURSDAY.
WESTERN CANADA/NORTHERN ROCKIES/NORTHERN PLAINS LATE NEXT WEEK...
THE MODELS SHOW DISAGREEMENT CONCERNING HOW THE REMAINS OF
TROPICAL STORM NEKI IN THE CENTRAL PACIFIC MAY /06Z GFS AND 00Z
ECMWF/ AND OR MAY NOT /12Z CANADIAN AND 12Z UKMET/ INTERACT WITH A
SYSTEM IN THE NORTHERN STREAM. IF IT DOES...NEKI WOULD THEN
STRENGTHEN AS AN EXTRATROPICAL CYCLONE /POSSIBLY BOMBING OUT/ ONCE
THE SYSTEM MOVES PAST THE APEX OF THE RIDGING IN THE EASTERN
PACIFIC. DID NOT WANT TO GO WITH A SOLUTION AS AMPLIFIED AS THE
00Z ECMWF HERE...WHICH SIGNIFICANTLY BROKE CONTINUITY WITH THIS
SYSTEM. HOWEVER...DID RESPECT THE 15Z CPHC TROPICAL CYCLONE
FORECAST AND FORECAST A CYCLONE OF SOME DEPTH. A 06Z GFS/06Z GEFS
MEAN COMPROMISE APPEARS BEST HERE...UNTIL THE MODELS COME INTO
BETTER AGREEMENT.
ROTH
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page