EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 251 AM EDT MON OCT 24 2016 VALID 12Z THU OCT 27 2016 - 12Z MON OCT 31 2016 ...OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT... THE LARGE SCALE PATTERN ALOFT SHOULD CONTINUE TO BE DOMINATED BY AN AMPLIFIED ERN PACIFIC TROUGH/W-CNTRL U.S. RIDGE CONFIGURATION... WITH A MIGRATORY TROUGH CROSSING THE NORTHEAST CORNER OF THE COUNTRY. A CLOSED ANTICYCLONE OVER THE SOUTHERN ROCKIES AND PLAINS PERSISTS FOR MOST OF THE FORECAST PERIOD. DUE TO CONSIDERABLE SPREAD IN SOLUTIONS AMONG THE MODELS/ENSEMBLE MEMBERS...CONFIDENCE IS BELOW NORMAL FOR DAYS 5-7 ACROSS THE UPPER MS VALLEY/GREAT LAKES/OH VALLEY AND MID ATLANTIC/NEW ENGLAND. FOR DAYS 3-4 SOLNS ARE STILL CLUSTERED WELL FOR THE SYSTEM HEADING ACROSS THE GREAT LAKES AND THEN INTO NEW YORK AND NEW ENGLAND. AGREEMENT BREAKS DOWN ONCE THIS SYSTEM DEPARTS. GUIDANCE DISPLAYS CLUSTERING FOR SIGNIFICANT FEATURES THROUGH DAY 3 WED BUT THEN QUICKLY DIVERGES FOR SHRTWV DETAILS WITHIN THE ERN PAC TROUGH. HANDLING OF WAVES EJECTING FROM THE EASTERN PACIFIC TROUGH DIFFER FROM ONE MODEL/ENSEMBLE CLUSTER TO ANOTHER. FOR EXAMPLE...THE LAST FEW RUNS OF THE GFS AND NOW THE 00Z CANADIAN GLOBAL HAVE AMPLIFIED NORTHERN STREAM ENERGY COMING ONSHORE AND THEN CARRY A MORE AMPLIFIED TROUGH CROSSING THE NORTHERN ROCKIES/PLAINS THU-FRI AND BEYOND. THE 12Z ECMWF MOVED A ROSSBY WAVE IN THE SOUTHERN STREAM PORTION OF THE EASTERN PACIFIC TROUGH AND MOVED IT OVER THE TOP OF THE WESTERN RIDGE AND THEN AMPLIFIED THE WAVE AS IT SAME INTO THE EASTERN US TROUGH. MOST OF THE ECMWF ENSEMBLE MEMBERS DID NOT REPLICATE THE BEHAVIOR WITH THE WAVE WEAKENING AS IT CRESTED THE WESTERN US RIDGE. AS A RESULT OF THE DEAMPLIFICATION OF THE WAVE AS USUALLY HAPPENS CROSSING A MEAN RIDGE...MORE WEIGHTING WAS GIVEN TO THE ENSEMBLE MEAN SOLUTION. THE 00Z ECMWF HAS NOW SHIFTED MORE TOWARDS THE IDEA OF THE NORTHERN STREAM PORTION OF THE TROUGH COMING ASHORE IN THE PACIFIC NORTHWEST AND THIS WAVE CROSSING THE NORTHERN TIER...INCLUDING THE GREAT LAKES/NEW YORK/NEW ENGLAND ON SAT. THIS BRINGS THE ECMWF CLOSER TO THE GFS SOLUTION. AS A RESULT THE ECMWF HAS BACKED ON THE 12Z RUN AND NOW DOES NO AMPLIFY THE TROUGH AS MUCH CROSSING THE MS VALLEY/OH VALLEY/CENTRAL APPALACHIANS/MID ATLANTIC. ...WEATHER HIGHLIGHTS/THREATS... CONTINUE TO EXPECT A BROAD AREA OF VERY WARM TEMPS AVERAGING 10-20F ABOVE NORMAL FROM THE CNTRL-SRN ROCKIES ACROSS THE PLAINS AND INTO THE SOUTHEAST.A FEW RECORD HIGH TEMPERATURES ARE EXPECTED IN THESE AREAS. HIGHEST ANOMALIES MAY BE OVER THE CNTRL PLAINS WITH SOME DEPARTURES FROM NORMAL FOR HIGHS PSBLY EXCEEDING PLUS 20F. CLOUDS/PCPN SHOULD KEEP THE WEST COAST STATES BELOW NORMAL. MEAN CYCLONIC FLOW ALOFT... AND SPECIFICALLY COOL ERN HIGH PRESSURE AND TRAILING MIDWEST TO NEW ENGLAND LOW PRESSURE SHOULD SUPPORT NEAR TO BELOW NORMAL TEMPS OVER THE NERN QUADRANT OF THE COUNTRY. AS THE EASTERN PACIFIC CYCLONE IS SLOW TO MOVE ONSHORE...MUCH OF THE PCPN WILL FOCUS IN CALIFORNIA NORTHERN TO WESTERN OR AND WA. THE MAIN PCPN FOCUS OVER THE EAST WILL BE WITH A SWATH OF MODERATE RAINS FROM THE UPR MS VLY/GRTLKS AND ACROSS THE NORTHEAST ACCOMPANYING MIDWEST TO NEW ENGLAND LOW PRESSURE. THERE IS POTENTIAL FOR SOME PCPN TO FALL IN THE FORM OF SNOW IN THE HIGHER ELEVS OF INTERIOR NEW ENGLAND. SHOWERS ARE PSBL IN THE SOUTHEAST FL PENINSULA AND FL KEYS. PETERSEN