EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 142 AM EST WED JAN 21 2015 VALID 12Z SAT JAN 24 2015 - 12Z WED JAN 28 2015 ...UNCERTAINTY ASSESSMENT/MODEL PREFERENCES... THE MODELS/ENSEMBLES CONTINUE TO SHOW THE PATTERN OF THE HIGHLY AMPLIFIED WESTERN US RIDGE AND EASTERN US TROUGH. THE UPPER RIDGE OUT WEST MOVES ONSHORE FROM THE EASTERN PACIFIC OVER THE WEEKEND AND THEN MOVES INLAND EARLY TO MID NEXT WEEK. THIS OPENS THE DOOR FOR HEIGHT FALLS OFF THE WEST COAST THE MIDDLE OF NEXT WEEK. THE ENSEMBLE MEANS OF THE ECMWF/GEFS/NAEFS ARE IN GOOD AGREEMENT ON THE WAVE PATTERN...LEADING THE SITUATION TO A CONSENSUS BASED APPROACH. IN THE EAST...THE WEEKEND STORM HAS DRIFTED WEST WITH TIME AND NOW IS EXPECTED TO IMPACT A LARGE PORTION OF THE EAST COAST FRIDAY-SATURDAY AND DEPARTING INTO THE CANADIAN MARITIMES AND BEYOND SUNDAY. THERE ARE TYPICAL TIMING AND INTENSITY DIFFERENCES BUT OVERALL GOOD CLUSTERING WITH AN INTENSE CYCLONE DEVELOPING. THE SECOND IMPULSE DEVELOPS IN THE LEE OF THE CANADIAN ROCKIES ON SAT 24 JAN AND MOVES STEADILY SOUTHEAST TO THE UPPER MS VALLEY 12Z SUN AND OH VALLEY MONDAY. IT IS HERE THAT DIFFERENCES DEVELOP WITH THE OPERATIONAL 18Z -00Z GFS TAKING A MORE SOUTHERN CYCLONE TRACK THAN THE ECMWF/ECMWF ENSEMBLE MEAN. ONCE THE SYSTEM REACHES THE CENTRAL APPALACHIANS...ANOTHER LEE LOW REFORMATION IS EXPECTED ALONG OR OFF THE EAST COAST MON 26 JAN AND THE SYSTEM DEPARTING TUE 27 JAN INTO THE CANADIAN MARITIMES. THE GEFS MEAN CYCLONE TRACK MATCHES THE ECMWF MEAN TRACK WELL AND CONTINUES NORTH OF THE 18-00Z GFS SFC CYCLONE TRACK. THE WPC MANUAL GRAPHICS AND NATIONAL FORECAST IS A BLEND OF THE 12Z ECENS/12Z NAEFS/18Z GEFS MEANS (DAYS 3-7) AND THE DETERMINISTIC 12Z ECMWF/18Z GFS (THROUGH DAY 5 AND OMITTED AFTERWARD WITH THE ENSEMBLE MEANS USED DAYS 6-7). ON DAY 7 THE 00Z GFS MADE A RADICAL SHIFT AND BROUGHT CANADIAN LOW PRESSURE MUCH FURTHER SOUTH ACROSS LK SUPERIOR 00Z 28 JAN TO LK ERIE 12Z WED 28 JAN....WITH THE 18Z RUN AND 18Z GEFS MEAN FURTHER NORTH IN CANADA WITH THE CYCLONE TRACK. ALSO ON DAY 7...THE DEPTH AND PHASING OF THE EASTERN PACIFIC TROUGH SHOWS DIFFERENCES THAT RESULT IN CHANGES AS TO WHERE IN CA/OR THE ONSHORE MOISTURE FLUXES AND LOW LEVEL CONVERGENCE WILL BE FOCUSED AND LEAD TO A THREAT OF SHOWERS. ...SENSIBLE WEATHER HIGHLIGHTS... THE CYCLONE MOVING UP THE EAST COAST SATURDAY LEADS TO A LARGE SHIELD OF PRECIPITATION WITH CHALLENGES OF POTENTIAL WINTER PRECIP ON THE NORTH AND WEST FRINGES OF THE SHIELD. THE NEXT CYCLONE LEADS TO A LARGE AREA OF PRECIPITATION WITH RAIN IN THE WARM SECTOR AND SNOW IN THE COLD SECTOR ACROSS THE MID-UPPER MS VALLEY TO THE GREAT LAKES AND OH VALLEY SUN AND CENTRAL APPALACHIANS TO THE MID ATLANTIC AND NY/NEW ENGLAND MONDAY 26 JAN. A VERY MILD PATTERN CONTINUES TO BE FORECAST FOR THE WEST AND THE PLAINS STATES. TEMPERATURES 10-15 DEGREES ABOVE NORMAL WILL BE COMMON...PEAKING NEAR 20 DEGREES ABOVE NORMAL IN THE NORTHERN PLAINS DAY 3-6...SHIFTING TO THE CENTRAL PLAINS/CENTRAL ROCKIES AND GREAT BASIN DAY 7. THE COLDEST CONDITIONS APPEAR TO BE BELOW NORMAL TEMPS IN THE LOWER LAKES/NEW YORK/NEW ENGLAND ON DAYS 4-7. BELOW NORMAL TEMPERATURES ARE ALSO FORECAST IN FLORIDA WITH THE HIGH AMPLITUDE EASTERN TROUGH ALLOWING COLD FRONTS TO MOVE ACROSS THE STATE. PETERSEN