080
FXUS02 KWBC 221758
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
157 PM EDT THU OCT 22 2009
VALID 12Z SUN OCT 25 2009 - 12Z THU OCT 29 2009
THERE ARE TWO CONSTANTS TO THE MED RANGE FORECAST... TWO LARGE AND
RATHER STATIONARY UPPER RIDGES COVERING THE PAC AND ATL OCEANS. IN
BETWEEN A BROAD LONG WAVE UPPER TROUGH WILL BE PRESENT WITH THE
AXIS OF THE FEATURE SETTLING BASICALLY THROUGH THE CENTER OF THE
COUNTRY. THE MODEL GUIDANCE GENERALLY HAS THIS FORECAST SCENARIO
BUT AS THE SMALL SCALE DIFFERENCES GRADUALLY INCREASE THROUGHOUT
THE FCST PERIOD... IT EVENTUALLY CATCHES UP TO THE LARGE SCALE
FEATURES TO ADD ENOUGH SPREAD AND UNCERTAINTY TO THE FCST. EARLY
PRELIMS OF HPC GENERALLY FOLLOWED A BLEND OF THE 00Z ECMWF...
UKMET AND GFS IN VARIOUS WAYS THROUGH D5 OR NEXT TUES. ON D6 AND
7... HPC GENERALLY FOLLOWED A BLEND OF THE 00Z GFS/ECMWF.
UPDATED MORNING PRELIMS
HOWEVER UPON SEEING NEWER 06Z GFS AND 00Z ECMWF ENSEMBLES A LARGER
DEGREE OF THE OPERATIONAL 06Z GFS WAS USED FOR DAYS 3-5 AND A
BLEND OF 06Z GFS AND 00Z GFS/00Z ECMWF ENS MEANS FOR DAYS 6 AND 7
THU/FRI. THIS BASICALLY TRENDS TOWARDS MORE WRN TROF AMPLIFICATION
AFTER DAY 5 CLOSER TO A CONSENSUS OF CMC/UKMET/06Z GFS OP
SOLUTIONS AND ENSEMBLE MEANS. OP 00Z ECMWF IS TE LEAST AMPLIFIED
SOLUTION AND NOT CONSIDERED TO HAVE ENOUGH EPAC RIDGING AND
DOWNSTREAM TROF AMPLIFICATION AT THIS TIME RANGE.
AFTN FINALS
12Z GFS FOLLOWS ITS 06Z VERSION BUT WITH A WEAKER LESS AMPLIFIED
SHORTWAVE MOVING THRU THE PLAINS/ CENTRAL AND UPPER MS VALLEY LATE
SUNDAY AND MONDAY. LATEST RUN BY DAYS 5 AND 6 TUES/WED FOLLOWS ITS
06Z AND 00Z CMC WITH A MID LEVEL CLOSED LOW IN THE NRN PLAINS AND
A DIGGING TROF IN THE SOUTHWEST. BY DAY 7 12Z GFS TRENDING TOWARDS
BUT MORE PROGRESSIVE OF THE CMC SOLUTION OF CUTTING OFF A MID
LEVEL CENTER OVER SONORA MEXICO INSTEAD OF SOCAL. THIS CUTOFF
SOLUTION IS BRIEF AS IT EXITS NEWD AS A STRONG CLOSED LOW
SHORTWAVE IN BOTH GFS AND 00Z CMC SOLUTIONS LATE DAY 7 INTO DAY 8.
12Z CMC KEEPS ITS AMPLIFIED STRONG SWRN CONUS TROF AT 144 HRS
WHILE UKMET IS MORE PROGRESSIVE WITH A SHARP TROF EWD FROM THE NRN
PLAINS INTO N CENTRAL MEXICO. HPC UPDATED PROGS WILL NOT CHANGE AT
THE SFC BUT MORE INCORPORATION OF THE 06Z GFS ENS MEAN..WHICH IS
CLOSER TO THE 00Z/12Z CMC AND 06Z/12Z GFS SOLUTIONS WILL BE USED
FOR H500 MB ADJUSTMENTS.
THE FCST PERIOD KICKS OFF WITH A BROAD UPPER LOW OVER THE UPPER
MIDWEST AND A SOLID COLD FRONT SLICING THROUGH THE MIDWEST. THIS
FEATURE WILL GRADUALLY PRESS AND LIFT OFF TO THE NORTH AND EAST...
DUE TO THE LARGE UPPER RIDGE AND HIGH HEIGHTS EXISTING ACROSS THE
EAST. THUS EXPECT THE SURFACE COLD FRONT TO GRADUALLY WEAKEN AS IT
ARRIVES INTO THE ERN US SAT. THEN RIGHT ON ITS HEELS WILL BE A
MORE POTENT PAC SYSTEM SLAMMING THROUGH THE NW/NRN ROCKIES ON MON
AND DIGGING INTO THE NRN PLAINS NEXT TUES UNDER FAST PAC SEMIZONAL
FLOW. A LARGE CLOSED LOW WILL FORM AND THE FEATURE WILL SLIDE
VERY SLOWLY OFF TO THE ENE INTO WRN ONTARIO AS MORE UPSTREAM JET
DYNAMICS DIG THROUGH THE GREAT BASIN TOWARD THE SRN PLAINS/LWR MS
VLY. THUS A VERY AMPLIFIED UPPER TROUGH WILL BE PRESENT OVER THE
PLAINS/MS VLY SOUTHWEST INTO NWRN MEXICO... WHILE UPPER HEIGHTS
SIGNIFICANTLY INCREASE ALONG THE ERN SEABOARD. EXPECT NOT ONLY A
SLOW MOVING STRONG COLD FRONT TO ACCOMPANY THIS SYSTEM BUT THE
SHARP NATURE OF THE UPPER TROUGH SHOULD PRODUCE QUITE A LARGE
SCALE PRECIP EVENT AHEAD OF THE UPPER TROUGH AXIS. FINALLY... YET
ANOTHER SYSTEM OUT OVER THE NERN PAC WITH A VERY STRONG JET WILL
SET ITS EYES FOR THE PAC NW NEXT THURSDAY. PAC HIGH PRESSURE
BUILDING EWD INTO THE GREAT BASIN WILL SET UP CONDITIONS FOR A
LARGE SCALE OFFSHORE EVENT OVER CA WITH SANTA ANA WINDS TUES INTO
THURS.
MUSHER/ROSENSTEIN
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