635
FXUS02 KWBC 201749
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
148 PM EDT TUE OCT 20 2009
VALID 12Z FRI OCT 23 2009 - 12Z TUE OCT 27 2009
TELECONNECTIONS WITH A NEGATIVE ANOMALY BOUNCING AROUND 50N 155W
FAVORS BROAD TROUGHING FROM EASTERN CANADA INTO THE PLAINS...WHICH
IS AGREED UPON BY THE GLOBAL GUIDANCE AND ENSEMBLE MEAN SOLUTIONS
FROM THE GEFS/ECMWF. DETAIL ISSUES REMAIN...AS USUAL. A
COMPROMISE OF THE 06Z GFS AND 00Z ECMWF APPEARS BEST CONCERNING
THESE ISSUES. CHANGES IN THIS BLEND WERE MADE PER THE ENSEMBLE
CLUSTERING/SPREAD SEEN IN THE 00Z MULTI-MODEL ENSEMBLE GUIDANCE TO
TRY TO KEEP OUR PRESSURES WITHIN THE MIDDLE OF THE OVERALL
ENVELOPE OF POSSIBILITIES. THIS SOLUTION KEPT REASONABLE
CONTINUITY.
SYSTEM MOVING FROM THE MISSISSIPPI VALLEY THROUGH NEW ENGLAND THIS
WEEKEND...
THE FIRST SYSTEM IS EXPECTED TO BE NEAR THE MS VALLEY AS OF DAY 3
FRI AND STRENGTHEN AS IT TRACKS NEWD. SOME DETAIL DIFFS ALREADY
BECOME EVIDENT IN THE LATTER HALF OF THE SHORT RANGE PERIOD SO
CONFIDENCE IS STILL MODERATE AT BEST FOR THE FRI-SUN EVOLUTION OF
THIS SYSTEM. AT THE VERY LEAST THE 00Z GEFS MEAN IS LIKELY TOO
WEAK/SWD IN LIGHT OF OPERATIONAL SOLNS. THE PAST COUPLE ECMWF
RUNS APPEAR REASONABLE THRU THE SHORT RANGE AND HAVE GENERAL
SUPPORT FROM THE 00Z CANADIAN AND 12Z ECMWF ENSEMBLE MEAN FOR
TRACK THEREAFTER. SLIGHTLY FARTHER SWD TRACKS OF THE GFS/UKMET
ARE NOT OUT THE QUESTION BUT THEIR SOLNS MAY NOT BE IDEAL LATE IN
THE SHORT RANGE.
SYSTEM CROSSING THE LOWER 48 FROM SATURDAY ONWARD...
THE SECOND SYSTEM SHOULD REACH WESTERN NORTH AMERICA BY SATURDAY
WITH THE ASSOCIATED SURFACE SYSTEM EVENTUALLY WEAKENING AS MID
LEVEL ENERGY REACHES THE CNTRL CONUS. THE COMBINATION OF THIS
ENERGY ALONG WITH SOME SRN STREAM ENERGY THAT MAY CROSS NRN
MEXICO... AND WHICH SO FAR DISPLAYS CONSIDERABLE SPREAD AMONG
MODELS/ENSEMBLES...SUPPORTS ONE OR MORE WAVES ALONG THE FRONT LEFT
BEHIND NEAR THE SOUTHEAST COAST/FLORIDA. THE GFS LEANS FASTER
THAN MOST OTHER GUIDANCE WITH ITS MID LVL TROF CROSSING THE
EASTERN CONUS EARLY NEXT WEEK... WHILE THE ECMWF MAY BECOME TOO
SLOW IN LIGHT OF THE THIRD SYSTEM MOVING INTO THE WEST AT THAT
TIME. WITH THIS LAST SYSTEM ENTERING THE WEST THERE IS NO WELL
DEFINED CONSENSUS BUT STILL DECENT AGREEMENT IN PRINCIPLE. RECENT
ECMWF RUNS AND 12Z ECMWF ENSEMBLE MEAN ARE ON THE FASTER SIDE OF
THE SOLN SPREAD... WITH THE GFS/GEFS MEAN SLOWER AND THE CANADIAN
SLOWEST. THE 12Z CANADIAN ENSEMBLE MEAN IS FASTER THAN THE 00Z
CMC SO A COMPROMISE AMONG 06Z GFS/00Z ECMWF BASED GUIDANCE SEEMS
REASONABLE.
WESTERN CARIBBEAN/FLORIDA...
FOR A NUMBER OF DAYS OPERATIONAL ECMWF RUNS /AS WELL AS MANY
CANADIAN AND ECMWF ENSEMBLE MEMBERS/ HAVE BEEN INDICATING TROPICAL
DEVELOPMENT OVER THE WESTERN CARIBBEAN SEA WITH A WELL-DEFINED
SYSTEM TRACKING OVER OR NEAR FLORIDA. NON-ECMWF GUIDANCE HAS
BEGUN JUMPING ON THE BANDWAGON BUT AT A MUCH SLOWER SPEED THAN
ECMWF RUNS. THE MIDDLE OF THE CANADIAN/ECMWF ENSEMBLE GUIDANCE
SPREAD HAS BEEN QUITE CONSISTENT WITH THIS SYSTEMS TIMING FOR
THREE DAYS NOW...WITH THE MIDDLE OF ITS ENSEMBLE LOW SPREAD MOVING
THE LOW INTO FLORIDA EARLY NEXT WEEK. CONSIDERING YESTERDAYS
CONTINUITY AND COORDINATION WITH NHC...A COMPROMISE OF THE 06Z
GFS/00Z ECMWF WHICH IS WITHIN THE SLOWEST QUARTER OF THE
CANADIAN/ECMWF ENSEMBLE MEMBERS IS PRUDENT AT THIS JUNCTURE...EVEN
THOUGH IT IS AGAINST THE USUAL BIAS SEEN WITH RECURVING SYSTEMS
WITHIN THE ECMWF ENSEMBLE SPREAD /THE ECMWF ENSEMBLE MEMBERS TEND
TO BE TOO SLOW TO RECURVE SYSTEMS INTO THE WESTERLIES/. THIS
QUICKENING TREND IN OUR PROGS SHOULD CONTINUE SINCE THERE DOES NOT
APPEAR TO BE ANY REASON FOR THIS SYSTEM TO DAWDLE IN THE WESTERN
CARIBBEAN EARLY NEXT WEEK LOOKING AT THE MEAN STEERING ACROSS THAT
REGION...WHICH SHOWS A DEPRESSION OF THE SUBTROPICAL RIDGES
LATITUDE/IMPINGING OF THE WESTERLIES INTO THE NORTHWEST CARIBBEAN
BY NEXT TUESDAY MORNING DUE TO AN APPROACHING SHORTWAVE TROUGH
MOVING ACROSS THE SOUTHEAST. IF THIS SYSTEM GAINS DEEP CONVECTION
SOONER RATHER THAN LATER...THIS WOULD ALSO CAUSE
ACCELERATION...PARTICULARLY WITH FUTURE GFS SOLUTIONS MAY THEN
OVERSHOOT THE MARK.
ROTH/RAUSCH
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page