055
FXUS02 KWBC 111802
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
202 PM EDT SUN OCT 11 2009
VALID 12Z WED OCT 14 2009 - 12Z SUN OCT 18 2009
00Z GEFS AND 12Z ECMWF/CANADIAN ENSEMBLE GUIDANCE MAINTAINS
UNUSUALLY GOOD CONTINUITY AND AGREEMENT WITH THE EXPECTED LARGE
SCALE FLOW OVER THE NEXT SEVEN DAYS. MID LVL ENERGY ENTERING THE
WEST AS OF EARLY DAY 3 WED SHOULD AMPLIFY AS IT PROGRESSES INTO
THE ERN HALF OF THE CONUS... IN RESPONSE TO THE DEVELOPMENT OF A
FAIRLY AMPLIFIED ERN PAC TROF/WRN NOAM RIDGE PATTERN. THE
RESULTING ERN CONUS TROF SHOULD BE REINFORCED BY INCLUSION OF NRN
STREAM ENERGY BY FRI-SAT AS WELL. THE ERN PAC/WRN NOAM PATTERN
SHOULD BECOME SOMEWHAT FLATTER AND MORE PROGRESSIVE BY THE END OF
THE PERIOD DAY 7 SUN... WITH SOME EXPECTED DIFFS ARISING AS TO
EXACT TIMING OF THE MEAN TROF NEARING THE WEST COAST.
COMPARING THE 00Z MODELS TO EACH OTHER AND THE ENSEMBLE
CONSENSUS... THE 00Z GFS HAS SOMEWHAT OF A FRIEND IN THE UKMET BUT
OTHERWISE THE CONSISTENT ENSEMBLE MEANS AND 00Z ECMWF/CANADIAN
ARGUE FOR TIMING THAT IS SLOWER THAN THE GFS WITH THE WRN ENERGY
THAT AMPLIFIES INTO THE EAST AND SUPPORTS CNTRL-ERN CONUS LOW
PRESSURE. THE GFS MAY ALSO BE TOO AMPLIFIED WITH FLOW AROUND THE
SERN SIDE OF THE ERN PAC MEAN TROF THU INTO FRI... AND IS A LITTLE
FASTER AND/OR DEEPER WITH UPSTREAM ENERGY ARRIVING INTO THE WEST
NEXT WEEKEND. MEANWHILE BY FRI-SAT THE 00Z ECMWF BECOMES
STRONGER/EWD THAN CONSENSUS WITH ITS MID LVL RIDGE THAT BUILDS
INTO WRN-CNTRL NOAM... WHICH LIKELY PLAYS A PART IN THE MODEL
BECOMING MORE AMPLIFIED AND CLOSED THAN MOST OTHER GUIDANCE WITH
ERN CONUS FLOW NEXT WEEKEND. THE CANADIAN ALSO CLOSES OFF A LOW
BUT FARTHER NWD. SOME OF THE DETAILS EXHIBITED IN LATEST GUIDANCE
BY DAYS 5-7 ARE WITHIN THE REALM OF POSSIBILITY BUT FOR NOW WILL
MAINTAIN CONTINUITY THAT FAVORS THE LARGER SCALE AGREEMENT OF THE
ENSEMBLE MEANS.
FOR DAYS 3-4 WED-THU THE 00Z ECMWF IS A GOOD REPRESENTATIVE OF
CONTINUITY/CONSENSUS AND IS THEREFORE FOLLOWED FOR THAT PART OF
THE FCST. DETAIL QUESTIONS BY DAYS 6-7 SAT-SUN LEAD TO GREATER
WEIGHTING OF THE 00Z GEFS/12Z ECMWF ENSEMBLE MEANS THAN THE 00Z
ECMWF... WHILE THE TRANSITIONAL DAY 5 FCST USES 50 PERCENT
WEIGHTING OF THE 00Z ECMWF.
...UPDATED MORNING PRELIMS INCORPORATE THE NEWER 00Z ECMWF MEANS
AND THE 06Z GFS WHICH IS VERY SIMILAR TO THE OP ECMWF THRU THE
PERIOD.
...AFTN 12Z GFS DRAMATICALLY CHANGES OVER ERN CONUS AS IT PLACES
EMPHASIS ON THE FIRST SHORTWAVE COMING THRU THE OH VALLEY LATE
THURS AND MAKES THE FIRST SFC REFLECTION COASTAL WAVE THE PRIMARY
LOW MOVING UP THE EAST COAST. THIS RESULTS IN THE NEWER RUN BEING
OVER 500NM FASTER THAN PRIOR MODEL CONSENSUS. LATEST 12Z UKMET AND
CMC ALSO TREND THIS WAY. HOWEVER LATEST 12Z GFS ENS MEAN GEFS DOES
NOT AND LOOKS VERY MUCH LIKE PRIOR RUNS AND MODEL CONSENSUS USED
EARLIER. PRUDENT TO ACCELERATE THE EAST COAST SFC LOW TOWARDS THE
3 HIGHER RESOLUTIONS MODEL FORECASTS BUT NOT WHOLEY AS THE GEFS
DOES NOT ACCEPT THIS SOLUTION PREFERING PRIOR MODEL CONSENSUS.
ADJUSTED AFTN FINALS REFLECT A TREND CLOSER TO THE 12Z CMC/NOGAPS
SOLUTION FOR DAYS 4.5 TO 6 LATE THURS TO SAT WITH A FASTER LOW
MOVING NEWD OFF THE NORTHEAST ATLC COAST. HPC TEMP/POPS HEDGED
TOWARDS THIS SOLUTION.
THE ATMOSPHERE AND WEATHER IS MUCH MORE LIKE MID TO LATE NOV THAN
MID OCT OVER NOAM WITH ITS DEVELOPMENT OF HIGH AMPLITUDE PATTERN
AND VERY WET CONDITIONS. VERY HEAVY COASTAL AND INLAND RAINS WILL
CONTINUE DAY 3 WED OVER MOST OF CA EXCEPT EXTREME SOUTH PORTION
WITH PLENTY OF MOISTURE SPREADING WELL INLAND INTO THE ROCKIES.
STRONG SWD DISPLACED JET CORE WILL AMPLIFY TO THE LEE OF THE
MOUNTAINS IN RESPONSE TO BUILDING HTS OVER THE INTERMTN REGION AND
ROCKIES MID TO LATE WEEK. THIS INDUCES STRONG SFC CYCLOGENESIS IN
THE SRN PLAINS WHICH MOVES EWD INTO THE TN VALLEY AND SRN/CNTRL
APPLCHNS THURS NIGHT THEN REFORMS OFF THE VA CAPES FRI AND MOVES
NEWD UP THE ATLC COAST SAT AND SUN. THIS WILL PRODUCE A MDT TO HVY
RAINFALL EVENT THU-FRI FROM THE CENTRAL MS/LOWER OH VALLEY EAST
AND SOUTH INTO THE ATLC SEABOARD. HVY RAINS CONT OVER THE MID ATLC
AND UP THE NEW ENG COAST FRI INTO SAT WITH STRONG NE WINDS AND A
COASTAL GALE THREAT FROM ME INTO NJ.
INLAND THIS SYSTEM WILL HAVE A VERY WELL DEVELOPED H850 LOW
TRACKING FROM THE LOWER OH VALLEY TO THE NEW ENG COAST BY SAT
MORNING. THE EASTERN GREAT LAKES REGION EAST AND NORTHEAST THRU
THE ADIRONDAKS/NRN VT/NH AND NRN HALF OF MAINE MAY SEE H850 TEMPS
AT -3C AND COLDER WITH MDT PSBLY HVY PCPN AND MDT TO HIGH SFC
WINDS. THIS IS AN EARLY SEASON HVY SNOWFALL THREAT FOR THE HIGHER
ELEVATION REGIONS OVER AREAS WHERE DECIDUOUS TREES STILL RETAIN
MOST OF THEIR LEAVES. 00Z ECMWF/CMC AND 06Z GFS INDICATE COLD
ENOUGH CONDITIONS FOR A MDT/HVY SNOW POTENTIAL THREAT AT THIS
TIME. LATEST OP 12Z RUNS OF GFS/CMC/UKMET/NOGAPS PROVIDE A LESSER
SNOW THREAT FOR THIS AREA AS THEY EMPHASIS A LEAD SHORT AND FASTER
SFC LOW COMING UP THE COAST BUT THIS WILL STILL NEED TO BE CLOSELY
MONITORED.
WESTWARD THE PAC NORTHWEST ESP WA STATE CONTS TO BE UNDER ONSHORE
MID LVEL FLOW WITH ANOTHER APPROACHING SHORTWAVE COMING TO THE
COAST SAT NIGHT KEEPING UP WET CONDS.
RAUSCH/ROSENSTEIN
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