506
FXUS02 KWBC 261827
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
226 PM EDT FRI OCT 26 2012

VALID 12Z MON OCT 29 2012 - 12Z FRI NOV 02 2012

...DANGEROUS HURRICANE/POST-TROPICAL CYCLONE SANDY IS LIKELY TO
SPREAD HIGH WINDS/HEAVY RAINS AND INTERIOR HEAVY SNOWS FROM THE
CAROLINAS AND CENTRAL APPALACHIANS NORTHWARD INTO CANADA...

GENERAL FLOW PATTERN
====================
A RETROGRADING POSITIVE ANOMALY MOVING FROM SOUTHERN GREENLAND
INTO NORTHERN QUEBEC FAVORS A QUASI-STATIONARY DEEP CYCLONE NEAR
THE NORTHEAST, IN THIS CASE HURRICANE SANDY AND ITS POST-TROPICAL
REMAINS. OTHERWISE...RIDGING IS GENERAL EXPECTED OUT
WEST...THOUGH FLOW ACROSS THE PACIFIC IS EXPECTED TO SEND AMPLE
ENERGY/HEAVY PRECIPITATION ACROSS THE NORTHWEST. GUIDANCE IS IN
EXCELLENT AGREEMENT ON THE GENERAL FLOW PATTERN, THOUGH ISSUES
REMAIN WITH SANDY'S FUTURE COURSE AND STRENGTH.

MODEL PREFERENCE
================
THE NATIONAL HURRICANE CENTER (NHC) TRACK NOW BEST RESEMBLES THE
00 UTC ECMWF ENSEMBLE MEAN. THE EXTRATROPICAL TRANSITION OF SANDY
MAY HAVE ALREADY BEGUN BASED UPON RECENT SATELLITE IMAGERY...A
PROCESS EXPECTED TO COMPLETE TUESDAY PER NHC. THE DETERMINISTIC
GUIDANCE (PARTICULARLY THE 00 UTC ECMWF) SHOW PRESSURE SOLUTIONS
WELL BEYOND WHAT HAS EVER BEEN OBSERVED NEAR THE NEW JERSEY/NEW
YORK COAST (EVEN EXCEEDING THE 1938 LONG ISLAND EXPRESS HURRICANE)
EARLY IN THE MEDIUM RANGE PERIOD. THE DETERMINISTIC GUIDANCE
(CANADIAN, GFS, AND ECMWF INCLUDED) HAS SHOWN A VERY STRONG BIAS
WITH TROPICAL CYCLONES GAINING LATITUDE AND/OR TRANSITIONING INTO
NON-TROPICAL STORMS OVER THE PAST COUPLE YEARS... INCLUDING (BUT
NOT EXCLUSIVE TO) LESLIE 2012...ISAAC 2012...DEBBY 2012 IN THE
WESTERN SUBTROPICAL ATLANTIC IRENE 2011 AND IGOR 2010. PLEASE
REFER TO THE NHC FOR UPDATED INFORMATION ON SANDY.

THE 00 UTC ECMWF ENSEMBLE MEAN ALSO DEPICTS AN OVERALL FLOW
PATTERN UPSTREAM ACROSS THE W-CENTRAL CONUS AND ERN PACIFIC THAT
IS ON THE MORE AMPLIFIED AND LESS PROGRESSIVE SIDE OF THE FULL
ENVELOPE OF GUIDANCE SOLUTIONS OVER THE NEXT WEEK. THIS SEEMS
QUITE REASONABLE CONSIDERING DOWNSTREAM BLOCKING.

WEATHER IMPACTS
===============
PER THIS SOLUTION FROM SUNDAY THROUGH WEDNESDAY...WINDS AS HIGH AS
HURRICANE-FORCE ARE EXPECTED TO LASH EXPOSED AREAS OF THE
NORTHEAST/MID-ATLANTIC STATES (THE COAST AND TOPOGRAPHY)...LEADING
TO POTENTIALLY SERIOUS COASTAL EROSION AND COASTAL FLOODING. THE
TIMING OF THE FULL MOON AND THE BUILD-UP OF TIDES OVER MULTIPLE
TIDAL CYCLES SHOULD EXACERBATE THE SITUATION ALONG THE
COAST...PARTICULARLY IN CORNERS SUCH AS THE NEW YORK BIGHT. HEAVY
RAINS ARE EXPECTED TO FOCUS WITHIN SANDY'S WARM CONVEYOR BELT
CIRCULATION AS WELL AS ALONG ITS DRAPING WARM FRONT FROM THE
NORTHERN MID-ATLANTIC STATES AND INTO NEW ENG AND ERN
CANADA...WITH LOCAL AMOUNTS EXCEEDING 10 INCHES POSSIBLE. THIS
SOLUTION WOULD MEANWHILE ALLOW SIGNIFICANT SNOWS WITHIN ITS COMMA
HEAD PATTERN UNDER THE SUPPORTING/COOLING MID-UPPER LEVEL TROUGH
TO FALL AS CENTERED/FOCUSING OVER THE CENTRAL THEN NRN
APPALACHIANS AND VICINITY. LAKE EFFECT SNOWS ACROSS THE EASTERN
GREAT LAKES ARE POSSIBLE THROUGH THE PERIOD WITHIN THE CYCLONIC
FLOW IN THE SYSTEM'S COLD SECTOR. AS THE CYCLONE GRADUALLY WEAKENS
AS IT PULLS NORTHWARD THURSDAY INTO NEXT FRIDAY...WINDS SHOULD
SLACKEN AS SHOULD NERN US PRECIPITATION AMOUNTS/COVERAGE...BUT
EXPECT THAT AMOUNTS WILL REMAIN SIGNIFICANT CONSIDERING TROPICAL
ORIGIN OF THE LOW.

UPSTREAM...A SOLUTION CLOSEST TO THE 00 UTC ECMWF ENSEMBLE MEAN
SLOWS FROM HPC CONTINUITY SLIGHTLY THE INLAND PROGRESSION OF ERN
PACIFIC SYSTEM ENERGY ACROSS THE WRN US MID-LATE NEXT WEEK...MORE
SLUGGISH TO BUMP INTO A LEAD AMBIENT MEAN MID-UPPER RIDGE
POSITION. THIS SOLUTION OFFERS STRONG POTENTIAL FOR HEAVY
PRECIPIATION/MOUNTAIN SNOWS ACROSS MUCH OF THE NWRN US NEXT
WEEK...INCLUDING THE THREAT FOR MEDIUM RANGE DAYS 4-7 LIQUID
AMOUNTS UPWARDS TO 5 INCHES OVER MOST FAVORED PAC NW COASTAL
TERRAIN AND THE CASCADES...WITH DECREASING BUT STILL WIDESPREAD
AMOUNTS SPREADING FURTHER INLAND.

ROTH/SCHICHTEL
$$

bold emphasis added~danielw