423
FXUS02 KWBC 301848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
248 PM EDT WED SEP 30 2009
VALID 12Z SAT OCT 03 2009 - 12Z WED OCT 07 2009
A RATHER UNUSUAL AND BLOCKY PATTERN STARTS OFF THE MEDIUM RANGE
PERIOD THIS WEEKEND AS A PAIR OF UPPER LOWS SIT ACROSS THE
NORTHWEST AND GREAT LAKES REGIONS. NEARLY THE ENTIRE LOWER 48
STATES IS FORECAST TO HAVE BELOW NORMAL HEIGHTS AS UPPER RIDGING
IS CONFINED TO CANADA AND ALASKA. THE EASTERN CLOSED LOW SHOULD
MOVE INTO ONTARIO/QUEBEC AS ITS ATTENDANT COLD FRONT MOVES OFF
MOST OF THE EAST COAST LATE SATURDAY. THE 00Z UKMET IS /AND HAS
BEEN/ AN OUTLIER SOLUTION... SLOWER THAN THE CONSENSUS. 00Z/06Z
GFS AND 00Z CANADIAN MAY BE A TAD ON THE SLOW/WESTERN SIDE OF THE
RECENT ECMWF AND ENSEMBLE CONSENSUS AS THE SFC LOW MOVES ACROSS
THE GREAT LAKES BY SUN/D4. HIGH PRESSURE SHOULD RULE MUCH OF THE
EAST AFTER THE WEEKEND AS HEIGHTS BUILD. THE NEXT SHORTWAVE MAY
WORK ITS WAY TOWARD THE ARROWHEAD OF MINNESOTA BY WED/D7 AS
NORTHERN STREAM ENERGY SLIDES DOWN OVER THE RIDGE ACROSS WESTERN
CANADA. TIMING AGREEMENT IS FAIR BUT ITS STRENGTH IS QUESTIONABLE.
ENSEMBLE SPREAD AT 500MB SHOWS A RELATIVE MAXIMUM IN THIS AREA.
UPSTREAM FLOW HAS A LARGE IMPACT ON THIS AREA AND SHOWS DIFFERING
SCENARIOS AMONG THE MODELS.
THE WESTERN US APPEARS TO BE IN STORE FOR SEVERAL DAYS OF BELOW
NORMAL UPPER HEIGHTS AS A CLOSED LOW DROPS DOWN THE WEST COAST OF
CANADA INTO THE PAC NW. 500MB HEIGHTS ARE FORECAST TO BE TWO TO
THREE STANDARD DEVIATIONS BELOW NORMAL BY THE 00Z ECMWF ENSEMBLE
MEAN. HOWEVER... THIS EVENT COINCIDES WITH A CLIMATOLOGICAL
MAXIMUM IN CLOSED LOW FREQUENCY IN THE VICINITY OF COASTAL
CALIFORNIA /FIRST WEEK OF OCTOBER/. WHAT WAS PRETTY GOOD AGREEMENT
BETWEEN THE GFS AND ECMWF 24 HRS AGO HAS BEEN LOST IN REGARD TO
THE EVOLUTION OF THIS CUTOFF LOW. THE 00Z/06Z GFS RUNS HAVE NOW
DROPPED THE IDEA OF CLOSING OFF THE LOW NEAR COASTAL CALIFORNIA IN
FAVOR OF A DEEP SSW TO NNE TROUGH. THE ECMWF HAS REMAINED
STEADFAST IN SEPARATING THE ENERGY AND BRINGING THE NORTHERN
PORTION EASTWARD TOWARD THE WESTERN LAKES BY WED/D7. THE 00Z
CANADIAN ALSO SUPPORTS THE ECMWF IDEA IN THE WEST. THE PAST 36HRS
OF ENSEMBLES SHOW MORE ECMWF/CANADIAN MEMBERS IN FAVOR OF CLOSING
OFF A SECOND UPPER LOW WHILE THE GFS MEMBERS HAVE VARIED. GIVEN A
CLIMATOLOGICAL PREFERENCE TO DEPOSIT A CLOSED LOW OFF THE CA COAST
IN EARLY OCTOBER AND THE TREND SEEN IN THE ECMWF... FELT IT WAS
REASONABLE TO LEAN TOWARD THE ECMWF SOLUTION. INCLUDED MORE OF THE
00Z ECMWF ENSEMBLE MEAN RATHER THAN THE GEFS MEAN BY WED/D7 GIVEN
ITS BETTER FIT WITH THE CANADIAN/NAEFS ENSEMBLE MEANS AND HIGHER
RESOLUTION. THE MANUAL GRAPHICS ULTIMATELY DEPICT A COMPROMISE
BETWEEN THE 00Z/29 AND 12Z/29 ECMWF RUNS BY WAY OF THE 00Z ECMWF
ENSEMBLE MEAN.
12Z MODEL UPDATE... GFS HAS COME BACK TOWARD ITS EARLIER SOLUTIONS
AND BRIEFLY CLOSES OFF THE SEPARATING WESTERN UPPER LOW AT
00Z/07... BUT FARTHER EAST THAN THE 00Z ECMWF. THE UKMET/CANADIAN
ARE FASTER THAN THE ECMWF TO BRING THE INITIAL CLOSED LOW DOWN THE
WEST COAST BUT BECOME LESS DETACHED THAN THE ECMWF BY TUE/D6 AT
THE END OF THEIR RUNS AND BECOME MUCH SLOWER WITH THE SFC
LOW/FRONT IN THE PLAINS. THE 12Z GEFS MEAN PROVIDES A SHARPER
RIDGE/TROUGH ORIENTATION ACROSS THE NE PAC AND W COAST THAT IS
MORE LIKE THE OTHER 00Z ENSEMBLE MEANS. THE 12Z ECMWF IS MUCH
QUICKER TO EJECT THE INITIAL CLOSED LOW OUT OF THE GREAT BASIN AND
INTO THE GREAT LAKES ABOUT 24 HRS FASTER THAN ITS 00Z RUN AND
UNLIKE ITS ENSEMBLE MEAN. IT DOES... HOWEVER... CONTINUE TO
SEPARATE ENERGY OVER CALIFORNIA BUT NOT AS FAR WEST AS ITS 00Z
RUN. ALL THINGS CONSIDERED... NO CHANGES WERE MADE FOR THE FINAL
GRAPHICS.
FRACASSO
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