090
FXUS02 KWBC 281836
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
236 PM EDT MON SEP 28 2009
VALID 12Z THU OCT 01 2009 - 12Z MON OCT 05 2009
THE FULL ARRAY OF MODEL AND ENSEMBLE GUIDANCE DISPLAYS BETTER THAN
AVERAGE AGREEMENT REGARDING THE ACTIVE PATTERN EXPECTED ACROSS THE
CONUS DURING THE MEDIUM RANGE PERIOD. FOR THE FIRST HALF OF THE
FCST... THU INTO SAT... A CLOSED UPPER LOW MOVING ACROSS THE CNTRL
CONUS SHOULD GRADUALLY PUSH AWAY A LEADING SYSTEM OVER THE NERN
CONUS/SERN CANADA. CONSENSUS CLUSTER OF THE 00Z
ECMWF/UKMET/CANADIAN INDICATES THAT RECENT GFS RUNS AND IN
PARTICULAR THE 06Z VERSION MAY BE A LITTLE TOO FAST WITH THE SFC
REFLECTION ASSOC WITH THE CNTRL CONUS UPPER LOW. 12Z GUIDANCE
DOES LITTLE TO CHANGE EARLIER THINKING WITH THE GFS STILL FASTER
THAN MOST OTHER SOLNS WITH PORTIONS OF THIS SYSTEM DURING THE
SHORT RANGE AND EARLY MEDIUM RANGE FCST.
DURING THE SECOND HALF OF THE FCST... SAT THRU MON...
MODELS/ENSEMBLES AGREE THAT ANOTHER VIGOROUS TROF SHOULD AMPLIFY
INTO THE WEST BUT WITH SOME DIFFS OVER TROF AMPLITUDE AND TRACK OF
THE EMBEDDED UPPER LOW. THE 00Z ECMWF LEANS TOWARD THE EXTREME
END OF THE 00Z GEFS/ECMWF ENSEMBLE ENVELOPE WITH RESPECT TO THE
SWWD EXTENT OF THE TROF... AND PREVIOUS ECMWF RUNS AS REPRESENTED
BY THE FOUR-CYCLE LAGGED AVG FCST /LAF/ COMPARE BETTER TO THE
ENSEMBLE MEANS THAT SHOW THE CORE OF THE WRN TROF SOMEWHAT FARTHER
INLAND THAN THE 00Z ECMWF. THE 00Z ECMWF ALSO DOES NOT COMPARED
WELL TO ENSEMBLE GUIDANCE WITH UPSTREAM FLOW BY DAYS 6-7.
MEANWHILE THE 12Z GFS WRN CONUS UPPER LOW IS SOMEWHAT S/SE VERSUS
OTHER SOLNS BY DAY 6 SUN... WITH THE 12Z UKMET/CMC REACHING A DAY
6 POSN CLOSER TO BUT NOT QUITE AS FAR N/NW AS THE 00Z ECMWF. A
COMPROMISE APPROACH SEEMS REASONABLE FOR RESOLVING THESE DIFFS.
DOWNSTREAM BY NEXT MON THE 00Z ECMWF IS MORE AMPLIFIED WITH THE
ERN TROF THAN MOST OTHER 00Z/06Z/12Z GUIDANCE. BY D+8
TELECONNECTIONS RELATIVE TO BOTH THE POSITIVE HGT ANOMALY CENTER
FCST OVER THE NERN PAC AND NEGATIVE CENTER OVER THE WRN CONUS ALSO
FAVOR HIGHER HGTS OVER THE EAST COMPARED TO THE 00Z ECMWF FCST.
TRACK OF THE PLAINS/MS VALLEY UPPER LOW IS STILL A QUESTION MARK
THOUGH... AS MODELS DIFFER IN HOW QUICKLY THEY ERODE THE RIDGE
OVER HUDSON BAY AND VICINITY. ECMWF LAF INDICATES THE RIDGE MAY
HOLD ON LONGER THAN THE 00Z ECMWF MEAN AND THUS KEEP LOW PRESSURE
OVER THE NORTHEAST MORE SUPPRESSED THAN FCST BY MOST OTHER
MODEL/ENSEMBLE MEAN SOLNS. THE 12Z UKMET IS THE LONE MODEL TO
KEEP ERN NOAM FLOW SUFFICIENTLY BLOCKED TO SHEAR THE PLAINS/MS
VALLEY ENERGY. CONTINUITY OF NON-ECMWF GUIDANCE ASIDE FROM THE
UKMET TOWARD LIFTING OUT THE ERN TROF FASTER THAN THE ECMWF HAS
SOME SUPPORT FROM TELECONNECTIONS RELATIVE TO UPSTREAM FLOW BY
LATE IN THE PERIOD... SO WOULD LIKE TO TREND A LITTLE FASTER WITH
THE NERN CONUS SYSTEM BY DAY 7 MON.
DAYS 3-4 THU-FRI MAINTAIN A 00Z ECMWF SOLN BASED ON OPERATIONAL
CONSENSUS THAT IS SLOWER THAN THE GFS WITH THE CNTRL CONUS SYSTEM.
DAYS 5-7 SAT-MON START OUT WITH A NEARLY EVEN BLEND OF THE 00Z
ECMWF... 12Z/27 ECMWF... AND 00Z ECMWF ENSEMBLE MEAN TO YIELD A
WRN TROF THAT IS SOMEWHAT LESS EXTREME/WWD VERSUS THE 00Z ECMWF
BUT SFC DETAILS THAT ARE BETTER DEFINED THAN THE ENSEMBLE MEAN.
OVER THE EAST THIS BLEND REFLECTS CONSENSUS THAT THE FRONT
REACHING THE GULF OF MEXICO AND VICINITY SHOULD NOT EXTEND AS FAR
SWD AS FCST BY THE 00Z ECMWF. OVER THE NORTHEAST MODEST
ADJUSTMENTS WERE MADE TO TREND A FRACTION FASTER WITH LOW PRESSURE
BY EARLY NEXT WEEK.
REGIONAL HIGHLIGHTS...
..WEST
SYSTEM DEPARTING FROM THE WEST ON THU WILL LEAVE BEHIND A DAY OR
TWO OF BELOW TO WELL BELOW NORMAL TEMPS LATE THIS WEEK WITH SOME
MODERATION THEREAFTER. THEN A STRONG SYSTEM AMPLIFYING INTO THE
WEST DURING THE WEEKEND WILL BRING UNSEASONABLY COOL DAYTIME TEMPS
TO NRN/WRN PARTS OF THE WEST. EXACT DETAILS THAT HAVE AT BEST
MODERATE CONFIDENCE AT THIS TIME WILL DETERMINE FAVORED LOCATIONS
FOR PCPN... SOME POSSIBLY IN THE FORM OF SNOW AT HIGH ELEVS...
OVER THE NRN HALF OF THE WEST. EXTREME SRN AREAS INCLUDING AZ/NM
MAY SEE SOME ENHANCED MOISTURE FROM LOWER LATITUDES OF THE ERN
PACIFIC.
..CENTRAL/EAST
THE DOMINANT SYSTEM OVER THE MEDIUM RANGE PERIOD WILL TRACK
GRADUALLY EWD FROM THE PLAINS. HEAVIEST RNFL SHOULD BE OVER THE
NRN AND ERN PLAINS LATE THIS WEEK WITH VIGOROUS DYNAMICS... AND
OVER THE NORTHEAST SAT-MON DUE IN PART TO A FAVORABLE FLOW OF
MOISTURE FROM THE ATLC. CONSULT SPC OUTLOOKS FOR FURTHER INFO
REGARDING SEVERE POTENTIAL. BY SUN-MON... COMBINATION OF LOW LVL
GULF INFLOW AND SWLY FLOW OF MOISTURE FROM THE ERN PAC MAY ENHANCE
RNFL AT SOME LOCATIONS OVER THE SRN PLAINS. DAYTIME TEMPS SHOULD
AVERAGE BELOW NORMAL FROM THE PLAINS INTO THE GRTLKS WITH NEAR
NORMAL READINGS ELSEWHERE. COOLEST TEMPS RELATIVE TO NORMAL
SHOULD BE OVER PARTS OF THE NRN/CNTRL PLAINS LATE THIS WEEK.
RAUSCH
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page