EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 203 AM EDT MON OCT 12 2015 VALID 12Z THU OCT 15 2015 - 12Z MON OCT 19 2015 ...OVERVIEW... AMPLIFIED TROUGH PATTERN EAST OF THE CONTINENTAL DIVIDE WILL FEATURE A MIGRATORY STORM TRACK THAT SKIRTS THE CANADIAN BORDER FROM THE UPPER GREAT LAKES TO NORTHERN NEW ENGLAND---WITH A SERIES OF CANADIAN COLD FRONTS SPREADING SOUTHEASTWARD INTO THE LOWER 48. WEST OF THE DIVIDE... AN AMPLIFIED UPPER-LEVEL RIDGE AND CUTOFF MID-LEVEL ARE FEATURED THROUGH DAY 4...THEN A PATTERN CHANGE ---TO A WETTER ONE AND ACTIVE EAST PACIFIC TROUGH---SCHEDULED TO MIGRATE SEVERAL WARM ADVECTION EVENTS INLAND---ACROSS THE WEST COAST--- BY NEXT WEEKEND (DAY5-6). ...MODEL PREFERENCES... THE 11/12Z MODEL GUIDANCE LOOKED TO BE ON-TARGET HEADING INTO DAY 6---WITH LITTLE CHANGE FROM THE PREVIOUS FORECAST PHILOSOPHY. BEYOND DAY 6...A BLEND OF THE ENSEMBLE MEANS BEST SERVES THE FORECAST AND PATTERN CHANGE---WITH THE EAST PACIFIC 'WAVE TRAIN' BEGINNING TO OVERWHELM THE DOWNSTREAM PATTERN. IN ESSENCE---THE PACIFIC INFLUENCES...AND A DEEPER MARITIME AIRMASS BEGINS TO WORK ITS WAY ACROSS THE SOUTHERN CANADIAN AND NORTHERN US ROCKIES. ...UNCERTAINTY ASSESSMENT... OVERALL...THOUGHT THE GFS/ECMWF DETERMINISTIC GUIDANCE WAS PRETTY GOOD---EVEN HEADING INTO DAY 7. THESE DETERMINISTIC SOLUTIONS HAVE PICKED UP ON THE IDEA THAT THERE IS A NOTABLE INCREASE IN THE FREQUENCY OF MIGRATORY CYCLONES FROM PACIFIC TO ATLANTIC BASINS. IN THE EAST... FOR THE SHORTWAVE DETAILS ALONG THE MIGRATORY CYCLONE TRACK EMBEDDED WITHIN THE BASE OF THE NORTH AMERICAN TROUGH...THE 11/12Z AND 11/18Z GFS ARE THE WEAKER SURFACE PRESSURE SOLUTIONS CONCERNING THE FRIDAY-SATURDAY CYCLONE TRACK FROM THE UPPER GREAT LAKES TO NORTHERN NEW ENGLAND. BUT...THE DEPTH OF THE COLD ADVECTION SURGING IN BEHIND THIS SYSTEM...DOES NOT SEEM TO BE THE ISSUE. IT'S MORE A QUESTION OF HOW QUICKLY THE COLD POOL WILL VACATE NEW ENGLAND AND MIGRATE EAST-NORTHEASTWARD---DUE TO A PERSISTENCE OF PACIFIC SHORTWAVE ENERGY ADVANCING FROM THE WEST AND SOUTHWEST. BEING THAT IT IS OCTOBER...NOT MID-JANUARY...THINK THE DETERMINISTIC GFS/ECMWF (REGARDLESS OF SURFACE WAVE DEPTH) WILL VERIFY BETTER RATHER THAN THE CONSIDERABLY SLOWER 11/12Z CANADIAN BY DAY 7. BOTH THE GFS/ECMWF ARE RATHER CONSISTENT WITH THE BROAD PACIFIC TROUGH ADVANCING INLAND BETWEEN 40N-55N BY DAY AND SPREADING BROAD WARM ADVECTION EASTWARD INTO THE MIDSECTION OF THE CONTINENT. IN THE WEST... THERE REMAINS SOME QUESTION EXACTLY HOW FAR NORTH THE VORTICITY ASSOCIATED WITH THE CUTOFF CIRCULATION ALONG THE SOUTHWEST COAST OF CALIFORNIA WILL EXTEND INLAND---PRIOR TO THE ARRIVAL OF THE HEIGHT FALLS ORIGINATING IN THE EAST CENTRAL PACIFIC. BUT AGAIN...THE FORECAST PHILOSOPHY HAS BEEN TO ALLOW THE EAST PACIFIC TROUGH TO DETERMINE THIS...AND THIS SCENARIO HAS NOT CHANGED. STILL NEED TO TREAT THE CUTOFF AS A SINGULAR ENTITY---AND ITS INFLUENCE BROADENING THROUGH TIME AND MOVING IN TANDEM WITH A SHORTWAVE RIDGE TO ITS NORTH. ONCE THE MID-LEVEL TROUGH---APPROACHING ALONG ITS NORTHWEST PERIPHERY COMES INTO THE PICTURE...THIS CUTOFF CONTINUES TO MOVE NORTHWARD. RECOMMEND A BLEND OF THE 11/12Z ECENS/GEFS---BUT WOULD NOT QUIBBLE WITH ANY LOCAL OFFICE 'PREFERENCE'---ON THE DISPERSION OF THE CUTOFF AND TIMING OF THE MID-LEVEL ENERGY MIGRATION NORTH AND NORTHEASTWARD AFTER DAY 5. ...SENSIBLE WEATHER HIGHLIGHTS... ACROSS THE EAST....THE NIGHTS WILL FEEL LIKE AUTUMN EAST OF THE DIVIDE WITH THE DRY CANADIAN SURFACE HIGHS MIGRATING ACROSS THE LOWER 48 THIS PERIOD. THE SLIM PROSPECTS FOR SIGNIFICANT CLOUD COVER AND RAINFALL ALONG THE LEADING EDGES OF THESE FRONTS SHOULD ALLOW 'FULL-SUN' DAYTIME HIGHS TO BE REFRESHING---IF NOT MILD. PRECIPITATION FOCUS REMAINS TIED TO THE MIGRATORY CYCLONE TRACK AND IS MORE PREVALENT INVOF THE GREAT LAKES AND NORTHEAST (MAINLY NEW ENGLAND AND NORTHWEST NEW YORK STATE). COLD ADVECTION WILL BE A PREVAILING FEATURE OF THE FLOW---WHICH WOULD GENERATE SOME CHANCE FOR LOW-TOP CUMULUS AND SHOWERS IN THE MOUNTAINS...WITH OCCASIONALLY BREEZY CONDITIONS DURING THE DAYS AHEAD ---MAKING FOR UNPLEASANT OUTDOOR ACTIVITIES. BUT IT IS MID-OCTOBER. OUT WEST...THE UNSEASONABLY MILD...EVEN HOT WEATHER PATTERN WILL COME TO AN END. SCATTERED SHOWERS RETURN TO THE CENTRAL GREAT BASIN...SOUTHWEST AND ROCKIES. AND THE PACIFIC STORM TRACK BECOMES NOTICEABLY 'ACTIVE' ALONG THE WEST COAST. VOJTESAK