EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
329 PM EDT TUE OCT 23 2012
VALID 12Z FRI OCT 26 2012 - 12Z TUE OCT 30 2012
...POTENTIAL FOR MAJOR STORM OVER THE MID ATLANTIC & NORTHEAST
EARLY NEXT WEEK...
PRELIMINARY UPDATE...
UPDATED THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7
USING THE 00Z/23 EUROPEAN CENTRE ENSEMBLE MEAN, WITH A SMALL
INCORPORATION OF THE 00Z/23 EUROPEAN CENTRE DETERMINISTIC MODEL TO
LEND MORE DEFINITION TO THE SYNOPTIC GRADIENTS ACROSS THE NATION.
USED THE MOST RECENT FORECAST FROM THE NATIONAL HURRICANE CENTER
FOR THE TRACK OF TROPICAL STORM SANDY THROUGH DAY 5, WITH A CURVE
TO THE NORTHWEST DAYS 6 AND 7 BASED ON THE ECENS MEAN. THE 00Z/23
GEM GLOBAL CONTINUES TO CLUSTER WITH THE ECMWF FOR THE BEHAVIOR OF
SANDY ONCE IT TRANSITIONS TO AN EXTRATROPICAL SYSTEM, INDICATING
THAT THE CYCLONE GETS PULLED BACK TOWARD THE SHARP UPPER TROUGH
CLOSING OVER THE OHIO VALLEY. THE ECMWF AND GEM GLOBAL HAVE
SEVERAL RUNS OF CONTINUITY NOW WITH THE EVOLUTION OF THIS EVENT,
WITH THE DETERMINISTIC GFS LESS STABLE. THERE HAVE BEEN GFS
ENSEMBLE MEMBERS QUITE SIMILAR TO THE ECMWF/GEM CAMP FOR THE LAST
FEW DAYS OF MODEL CYCLES, PUTTING THE DETERMINISTIC GFS SOLUTIONS
IN A BROADER FRAMEWORK WITH THEIR TRACK OF SANDY WELL OVER THE
OPEN ATLANTIC. WILL BE UPDATING THE TRACK OF SANDY THROUGH DAY 5
FOR THE FINAL PACKAGE WITH THE ADVENT OF THE NEW NATIONAL
HURRICANE CENTER FORECAST, AND ITS BEHAVIOR AS AN EXTRATROPICAL
LOW THEREAFTER AS PER OUR HOTLINE COORDINATION.
FINAL...
ELECTED TO STAY THE COURSE BY KEEPING THE MAJOR EAST COAST STORM
IN PLAY FOR THE FINAL FORECAST. THE 12Z/23 DETERMINISTIC GFS SENDS
SANDY'S CIRCULATION OUT PAST BERMUDA BY THE END OF THE PERIOD,
WHILE THE 12Z/23 GEFS MEAN INCORPORATES IT ALONG THE EAST COAST IN
LINE WITH THE HPC MANUAL FORECAST. THE 12Z/23 GEM GLOBAL KEEPS
SANDY OUT OF REACH OF THE DIGGING TROUGH OVER NORTH AMERICA,
THOUGH LIKE THE LATEST GFS, IT IS PERHAPS BEST TO REGARD SUCH A
DETERMINISTIC SOLUTION AS A SLIGHTLY SOUPED-UP ENSEMBLE MEMBER.
THE 12Z/23 ECMWF STILL INCORPORATES AN EXTREMELY DEEP
POST-TROPICAL SANDY INTO THE MID-LEVEL PIVOT POINT OF THE POLAR
JET IN THE VICINITY OF LONG ISLAND EARLY NEXT TUESDAY, THE DYNAMIC
TRANSFER RESULTING IN A MINIMUM PRESSURE OF AT LEAST 932MB.
THEREIN LIES THE STORM'S MENACE- A POWERHOUSE CAPABLE OF WHIPPING
THE ATLANTIC INTO A FRENZY AND CHURNING UP DANGEROUS TIDES. OF
PARTICULAR NOTE IS THE COINCIDENCE OF THE FULL MOON ON SUNDAY,
OFTEN A SIGNIFICANT FACTOR IN HISTORICAL EVENTS. THE OCEAN EFFECTS
OF THE SYSTEM MAY STILL BE REALIZED EVEN IF POST-TROPICAL SANDY
DOES NOT MAKE LANDFALL IN THE UNITED STATES. BESIDES THE WIND, THE
OTHER SENSIBLE WEATHER THREAT IS HEAVY RAINS, WITH HEAVY SNOWS
POSSIBLE ON THE SOUTHWEST SIDE OF THE HYBRID CIRCULATION WHERE
CONTINENTAL POLAR AIR RUSHES ACROSS THE CENTRAL APPALACHIANS.
HAVE PREFERRED THE EUROPEAN CENTRE GUIDANCE FOR HANDLING OF THE
MAIN BAND OF WESTERLIES FOR SEVERAL DAYS NOW, ITS SYNOPTIC NUANCES
BEST SERVING THE CENTRAL AND WESTERN UNITED STATES WHERE THE FLOW
OPENS UP IN THE WAKE OF THE AMPLIFICATION OF THE EASTERN TROUGH.
CISCO
