739
FXUS02 KWBC 091802
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
201 PM EDT FRI OCT 09 2009
VALID 12Z MON OCT 12 2009 - 12Z FRI OCT 16 2009
THE MEDIUM RANGE FCST STARTS WITH A COMPLEX PATTERN OVER THE ERN
PAC AND NRN NOAM AS OF EARLY MON. THIS PATTERN CONSISTS OF AN
ANOMALOUSLY STRONG CLOSED HIGH OVER/NEAR NERN ALASKA WITH A NEARLY
E-W TROF ACROSS SRN/S-CNTRL CANADA AND AN EVOLVING MEAN TROF OVER
THE ERN PAC. OVER THE FOLLOWING DAYS MODELS AND ENSEMBLES VARY
WIDELY WITH THE EXACT DETAILS OF WRN CANADA ENERGY FCST TO
RETROGRADE INTO THE PAC... AND ENERGY INITIALLY WITHIN THE ERN PAC
TROF. GEFS/ECMWF/CANADIAN ENSEMBLES ARE DIVERSE ENOUGH TO YIELD
SOMEWHAT ILL-DEFINED MEANS BUT DO HINT THAT THE 00Z ECMWF MAY BE A
LITTLE OVERDONE WITH THE AMOUNT OF WRN CANADA ENERGY THAT RETURNS
TO THE PAC NW BY THU. HOWEVER THE ENERGY OVER THE ERN PAC
EVOLVES... THERE IS AT LEAST A MODERATE CONSENSUS THAT THE ERN PAC
MEAN TROF SHOULD COME ASHORE AROUND MIDWEEK WITH CONTINUED EWD
PROGRESSION THEREAFTER. BY NEXT THU-FRI THE 00 GEFS AND 12Z
ECMWF/CANADIAN ENSEMBLE MEANS SHOW REMARKABLY GOOD AGREEMENT WITH
A MID LVL TROF AXIS CROSSING THE CNTRL CONUS. EVEN WITH SOME
QUESTIONABLE DETAILS THE 00Z ECMWF MID LVL FCST GENERALLY COMPARES
MUCH BETTER TO ENSEMBLES THAN THE GFS BY LATE WEEK... WITH THE
LATTER MODEL BECOMING EXTREMELY AMPLIFIED EVEN COMPARED TO GEFS
MEMBERS FROM WED ONWARD. THE ENSEMBLE MEAN SCENARIO APPEARS
REASONABLE BASED ON D+8 TELECONNECTIONS RELATIVE TO A CORE OF
NEGATIVE HGT ANOMALIES FCST TO BE BETWEEN ALASKA AND HAWAII... AND
STRONG POSITIVE ANOMALIES NEAR GREAT BRITAIN. FARTHER EWD... THE
GFS/UKMET ARE MUCH STRONGER THAN OTHER SOLNS WITH THE SYSTEM
EXPECTED TO REACH THE NORTHEAST BY TUE. GIVEN THAT THE SYSTEM
EVOLVES WELL INTO THE COOL AIR... PREFER THE ECMWF/GEFS MEAN WHICH
KEEP THE SYSTEM FAIRLY WEAK UNTIL IT TRACKS INTO THE ATLC.
DAYS 3-4 MON-TUE START WITH THE 00Z ECMWF DUE TO ITS PREFERRED
HANDLING OF THE SYSTEM CROSSING THE NERN QUADRANT OF THE CONUS
DURING THAT TIME FRAME... AND AN ACCEPTABLE SOLN WITH THE PORTION
OF ERN PAC EVOLUTION THAT IS NEAREST TO THE WEST COAST. FUTURE
GUIDANCE MAY PROVIDE SOME CONFIDENT ADJUSTMENTS WITH FINER
DETAILS. DAYS 5-7 WED-FRI EMPHASIZE THE COMMON IDEAS OF THE
TELECONNECTION-FAVORED 00Z GEFS/00Z ECMWF ENSEMBLE MEANS WITH A
SMALL MINORITY OF THE 00Z ECMWF ADDED TO INCREASE DETAIL SLIGHTLY.
IN SPITE OF OP MODEL GUIDANCE SPREAD A REASONABLE CONSENSUS STILL
GIVES A STRONG THREAT OF VERY HEAVY/EXCESSIVE RAINFALL INTO NRN
AND CENTRAL CA AND EWD INTO THE SIERRA TUES-THURS AS THE MORE SRN
STREAM PAC WESTERLIES BECOME DOMINANT AND A WELL AGREED UPON
STRONG EPAC STORM WINDS UP OFF THE OR/WA COAST TUES-WED. THIS
SYSTEM APPEARS LIKELY TO BRING IN VERY STRONG ONSHORE WINDS AND
HIGH TIDES WITH THE HVY RAINS AS FAR SOUTH AS PT CONCEPTION.
WIDESPREAD TWO DAY RAINFALL IN THIS AREA MAY EXCEED 6 INCHES WITH
LOCALLY HEAVIER AMOUNTS. MODERATE TO HEAVY RAINS WILL ALSO SPREAD
INTO COASTAL OR AND WA.
SECOND AREA OF POTENTIAL HVY RAINS MAY AFFECT THE ARKLATEX REGION
AND EWD ACROSS THE TN VALLEY INTO THE SRN APPLCHNS ALONG THE SRN
EDGE OF THE WESTERLIES. A WIDE SPREAD OF SFC REFLECTION SOLUTIONS
HERE WITH CYCLOGENSIS MAKE THIS AN UNCERTAIN AREA AT THIS TIME AS
TO AMOUNTS. BY LATE IN THE PERIOD AN AGREED UPON ENS MEAN TROF OF
GFS/ECMWF IN THE MS VALLEY MAY YIELD A LARGE AREA OF RAINFALL FROM
THE GREAT LAKES REGION SWD TO THE GULF COAST AND EWD FOR NEXT FRI
AND SAT.
RAUSCH/ROSENSTEIN
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