207
FXUS02 KWBC 261837
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
236 PM EDT MON OCT 26 2009
VALID 12Z THU OCT 29 2009 - 12Z MON NOV 02 2009
MOST MODEL/ENSEMBLE SOLNS AGREE UPON EJECTION OF A STRONG
ROCKIES/PLAINS SYSTEM AS NWLY FLOW PROGRESSES INTO THE WRN CONUS
BY DAY 4 FRI. THE 00Z/12Z UKMET RUNS WHICH MAINTAIN A RIDGE OVER
THE WEST FOR A LONGER TIME THAN OTHER GUIDANCE ARE DISCOUNTED AS
LOW PROBABILITY OUTLIERS. DURING THE LATTER HALF OF THE PERIOD
THERE IS A REASONABLE CONSENSUS THAT LARGE SCALE FLOW SHOULD
DECREASE IN AMPLITUDE... ACHIEVING A WEAK WRN RIDGE/E-CNTRL CONUS
TROF CONFIGURATION BY NEXT MON. CURRENT GUIDANCE SPREAD AND SOME
INCONSISTENCIES AMONG OPERATIONAL GFS/ECMWF RUNS OVER THE PAST 1-2
DAYS REGARDING THE VIGOROUS PLAINS SYSTEM AND EVOLUTION OF
UPSTREAM FLOW RESULT IN MODERATE TO LOW CONFIDENCE IN ANY
PARTICULAR SOLN DURING THE FIRST HALF OF THE PERIOD. HOWEVER THE
12Z GFS/GEFS MEAN/CANADIAN ALL SUGGEST THE SYSTEM MAY BE FASTER
THAN THE 00Z ECMWF. THE 00Z ECMWF ENSEMBLE MEAN ALSO INDICATES
FASTER TIMING BUT SHOWS A FARTHER NWD TRACK THAN CONSENSUS. THE
12Z GFS LIKELY BECOMES TOO DEEP SFC/ALOFT OVER THE NRN CONUS/SRN
CANADA... WHICH BY SUN LEADS TO AN ERN CONUS SHRTWV TROF THAT IS
MORE AMPLIFIED THAN MOST OTHER SOLNS. OTHERWISE LATER IN THE
PERIOD CONFIDENCE IS ABOVE AVERAGE WITH LARGE SCALE FLOW AND THE
ASSOC MEAN SFC PATTERN... BUT OF COURSE MUCH UNCERTAINTY EXISTS
WITH THE DAILY PROGRESSION OF ERN PAC SYSTEMS EXPECTED TO WEAKEN
AS THEY REACH THE WRN CONUS. THE DAYS 3-6 THU-SUN FCST
INCORPORATES VARIOUS COMPONENTS OF THE 12Z GFS/GEFS MEAN/CMC AND
00Z ECMWF/ECMWF ENSEMBLE MEAN... WITH DAY 7 EXCLUDING THE CMC
SINCE IT TERMINATES AT DAY 6. THIS APPROACH PROVIDES A REASONABLE
CONSENSUS-WEIGHTED COMPROMISE FOR THE VIGOROUS SYSTEM TRACKING
NEWD FROM THE PLAINS AND APPROACHING UPSTREAM FLOW HEADING
INTO/THRU THE WEST... AND CAPTURES THE MOST AGREEABLE ASPECTS OF
THE LATE-PERIOD FCST.
REGIONAL HIGHLIGHTS...
..WEST
EXPECT BELOW TO MUCH BELOW NORMAL DAYTIME TEMPS OVER MUCH OF THE
WEST ON THU... WITH STEADY MODERATION THEREAFTER SUCH THAT BY
SUN-MON NRN AREAS SHOULD BE WITHIN A FEW DEGREES ON EITHER SIDE OF
NORMAL WHILE SRN AREAS SHOULD AVERAGE A FEW DEGREES ABOVE NORMAL.
CNTRL ROCKIES SNOW SHOULD TAPER OFF AFTER THU AS THE
ROCKIES/PLAINS SYSTEM TRACKS NEWD. MEANWHILE A STEADY FLOW OF
PACIFIC MSTR SHOULD SUPPORT PERSISTENT PCPN FROM THE NRN HALF OF
THE WEST COAST INTO THE NRN ROCKIES WITH HIGHEST TOTALS OVER
FAVORED TERRAIN.
..CENTRAL/EAST
VIGOROUS SYSTEM TRACKING NEWD FROM THE PLAINS WILL SPREAD A BROAD
PCPN SHIELD ACROSS THE PLAINS/MS VALLEY INTO THE GRTLKS THU INTO
FRI NIGHT. FARTHER EWD/SEWD EXPECT LIGHTER AND LESS ORGANIZED
ACTIVITY DURING NEXT WEEKEND AS DYNAMICS LIFT NEWD INTO CANADA.
PORTIONS OF THE CNTRL-NRN HIGH PLAINS MAY SEE SOME SNOW AND WELL
BELOW NORMAL TEMPS WITH THIS SYSTEM. MEANWHILE STRONG GULF INFLOW
AHEAD OF THE TRAILING COLD FRONT SHOULD SUPPORT AREAS OF HVY RNFL
OVER PORTIONS OF THE ERN PLAINS AND LOWER-MID MS VALLEY REGION
FROM THU INTO FRI NIGHT. THE EXTENT OF HIGH PLAINS SNOWFALL AND
HOW MUCH MSTR REACHES THE UPR MS VLY/GRTLKS WILL DEPEND ON YET TO
BE RESOLVED DETAILS OF SYSTEM EVOLUTION. CONSULT LATEST SPC
CONVECTIVE OUTLOOKS FOR FURTHER INFO REGARDING THE SEVERE WEATHER
THREAT ASSOC WITH THIS SYSTEM.
RAUSCH
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