467
FXUS02 KWBC 291836
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
235 PM EDT TUE SEP 29 2009
VALID 12Z FRI OCT 02 2009 - 12Z TUE OCT 06 2009
00Z MODEL AND ENSEMBLE GUIDANCE CONTINUES TO SHOW BETTER THAN
AVERAGE AGREEMENT WITH THE EXPECTED LARGE SCALE FLOW THRU THE
MEDIUM RANGE PERIOD... ALBEIT WITH SOME DETAIL UNCERTAINTIES
CREEPING INTO THE FCST BY THE FIRST HALF OF NEXT WEEK. THRU DAY 5
SUN THERE IS VERY GOOD CLUSTERING OF MODEL/ENSEMBLE SOLNS
REGARDING THE DEEP TROF AND EMBEDDED CLOSED LOW EVOLVING OVER THE
WEST. BY THE LATTER HALF OF THE PERIOD THERE IS INCREASED SPREAD
WITH THE ULTIMATE EVOLUTION OF ENERGY WITHIN A MEAN TROF FROM THE
ERN BERING SEA/WRN ALASKA SWD... IMPACTING THE EXACT SHAPE OF THE
NERN PAC/WRN CANADA RIDGE AND DOWNSTREAM FLOW. A MINORITY OF 00Z
ECMWF/GEFS/CANADIAN ENSEMBLE MEMBERS STILL REFLECT THE IDEA FROM
SOME EARLIER OPERATIONAL ECMWF RUNS THAT THE ENERGY ROUNDING THE
NERN PAC RIDGE MAY SERVE TO RELOAD THE WRN CONUS TROF... BUT MOST
ENSEMBLES LEAN CLOSER TO THE GENERAL 00Z ECMWF AND 00Z/06Z GFS
SCENARIO OF NRN STREAM FLOW HEADING INTO A CNTRL CANADA/NRN PLAINS
MEAN TROF BY DAY 7 TUE. TELECONNECTIONS RELATIVE TO THE POSITIVE
HGT ANOMALY CENTER OVER THE NERN PAC AND NEGATIVE CENTER OVER THE
WRN CONUS APPEAR TO PROVIDE REASONABLE SUPPORT FOR THE MAJORITY
SOLN WHICH WOULD CORRESPOND TO A SFC WAVE REACHING THE UPR MS
VALLEY/GRTLKS REGION NEAR OR SLIGHTLY BEYOND THE END OF THE FCST
PERIOD.
TO THE EAST OF THIS EVOLUTION THERE ARE STILL SOME DETAIL ISSUES
TO BE WORKED OUT WITH THE SYSTEM FCST TO TRACK ACROSS THE ERN HALF
OF THE CONUS AND ERN CANADA DURING THE PERIOD. THE 00Z UKMET IS A
SLOW OUTLIER AND IS DISCOUNTED AS UKMET RUNS OVER THE PAST DAY OR
SO HAVE NOT COMPARED WELL TO THE OVERWHELMING CONSENSUS OF
MODELS/ENSEMBLES IN VARYING WAYS. TELECONNECTIONS RELATIVE TO THE
EVOLVING WRN CONUS TROF HAVE FAVORED RISING HGTS IN THE EAST...
SUPPORTING OPERATIONAL ECMWF TRENDS OVER THE PAST DAY TOWARD A
FASTER DEPARTURE OF THIS SYSTEM FROM THE EAST AS HAS BEEN FCST BY
GFS RUNS AND MOST ENSEMBLE GUIDANCE. STILL THE 00Z GFS MAY BE A
LITTLE TOO FAST DURING THE FIRST HALF OF THE PERIOD AND THE 06Z
GFS MAY LEAN A TAD FAST BY SUN. THESE ISSUES FAVOR A BLEND OF 00Z
AND 12Z/28 ECMWF RUNS FOR RESOLVING REMAINING DETAILS OF THIS
SYSTEM.
OVER THE TROPICAL ERN PACIFIC MOST GUIDANCE IS SUGGESTING SOME
DEVELOPMENT FROM A BROAD AREA OF CONVECTION INITIALLY NEAR 110W
LONGITUDE... WITH A GRADUAL RECURVING TOWARD BAJA CALIF AS THE
FEATURE WEAKENS. FINAL FCST REFLECTS TPC/HPC COORDINATED
EVOLUTION. ASSOC MOISTURE MAY EVENTUALLY CROSS NRN MEXICO/SRN
AZ-NM AND CONTINUE INTO THE PLAINS.
12Z UPDATE... THE UKMET REMAINS AN OUTLIER OVER THE ERN HALF OF
THE CONUS... THE GFS MAY STILL BE A LITTLE FAST OVER PARTS OF THE
EAST... AND THE CANADIAN EITHER MAINTAINS CONTINUITY OR TRENDS
TOWARD CONSENSUS WITH THE ERN SYSTEM. OVER THE WEST NEW GUIDANCE
REMAINS WITHIN THE ESTABLISHED SOLN SPREAD WITH TYPICAL RUN TO RUN
VARIABILITY. THE GEFS MEAN IS STILL ON THE SLOWER SIDE OF
GUIDANCE WITH THE POSSIBLE WAVE REACHING THE UPR MS VLY/GRTLKS BUT
STILL MERITS MINORITY WEIGHTING.
THE FINAL FCST REFLECTS NO CHANGE FROM THE UPDATED PRELIM
ISSUANCE. DAYS 3-5 FRI-SUN START WITH A BLEND OF THE 00Z AND
12Z/28 ECMWF RUNS TO REFLECT PREFERENCES FOR THE ERN SYSTEM
PROVIDE A GOOD REPRESENTATION OF CONSENSUS EVOLUTION OVER THE
WEST. DAYS 6-7 MON-TUE USE A NEARLY EVEN BLEND OF THE 00Z
ECMWF/GEFS MEAN/ECMWF MEAN TO ACCOUNT FOR DETAIL UNCERTAINTIES
WITHIN WHAT SEEMS TO BE AN EMERGING CONSENSUS FOR THE LARGER SCALE
NOAM MEAN FLOW WITH SOME SUPPORT FROM TELECONNECTIONS.
REGIONAL HIGHLIGHTS...
..WEST
DEEP SYSTEM EVOLVING OVER THE WEST WILL SUPPORT BELOW TO MUCH
BELOW NORMAL DAYTIME TEMPS OVER THE NRN TWO THIRDS OF THE WEST AND
A MAJORITY OF CA. A FEW LOCATIONS WITHIN THE NRN ROCKIES/GREAT
BASIN REGION MAY SEE AT LEAST ONE DAY WITH HIGH TEMPS NEAR RECORD
COOL LEVELS. CLOUDS/PCPN WILL KEEP MIN TEMPS MORE MODERATE
RELATIVE TO NORMAL. FAVORED TERRAIN IN THE NRN ROCKIES SHOULD SEE
THE HIGHEST PCPN TOTALS OVER THE 5-DAY PERIOD WITH LIGHTER AMTS
OVER THE REMAINDER OF THE NRN HALF OF THE WEST. SOME PCPN WILL
LIKELY BE IN THE FORM OF SNOW AT HIGHER ELEVS. A SECOND RELATIVE
MAXIMUM OF PCPN MAY OCCUR OVER OR JUST S OF SRN AZ/NM AS MOISTURE
IS FCST TO STREAM NEWD FROM THE LOWER LATITUDES OF THE PACIFIC.
..CENTRAL/EAST
SYSTEM TRACKING THRU THE ERN HALF OF THE CONUS INTO ERN CANADA
FROM FRI INTO EARLY NEXT WEEK WILL BE ACCOMPANIED BY A BROAD
SHIELD OF RNFL. SOME LOCALLY HVY RNFL IS POSSIBLE OVER THE GULF
COAST/SOUTHEAST WITH THE TRAILING COLD FRONT FRI INTO SAT... WHILE
THE PROBABILITY FOR HVY RNFL APPEARS HIGHER OVER THE NORTHEAST
SAT-SUN AS STRONG ATLC INFLOW FEEDS MOISTURE INTO THE REGION.
EXPECT ANOTHER EXPANDING AREA OF RNFL TO MOVE EWD/NEWD FROM THE
PLAINS DURING THE WEEKEND AND EARLY NEXT WEEK... WITH
CONTRIBUTIONS FROM LOW LVL WRN GULF INFLOW... HIGHER LEVEL MSTR
TRANSPORT FROM THE ERN PACIFIC/NRN MEXICO... AND EWD PROGRESSION
MOISTURE CROSSING THE NRN HALF OF THE WEST EARLIER IN THE PERIOD.
EXPECT CONSISTENTLY BELOW NORMAL DAYTIME TEMPS OVER THE NRN PLAINS
AND VICINITY WITH MORE VARIABLE READINGS ON EITHER SIDE OF NORMAL
ELSEWHERE.
RAUSCH
!)
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