ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 242 PM EDT SAT APR 22 2017 VALID 12Z WED APR 26 2017 - 12Z SUN APR 30 2017 GUIDANCE HAS STABILIZED PRETTY WELL WITH THE IDEA OF A MEAN RIDGE EXTENDING OVER THE MAINLAND FROM WRN CANADA WHILE ALEUTIANS LOW PRESSURE AND UPR LOW/TROUGH GRADUALLY WEAKEN AS THE SYSTEM APPROACHES THE SWRN MAINLAND, LIKELY DISSIPATING BY EARLY SAT. THE MEAN RIDGE ALOFT SHOULD PERSIST IN SOME FASHION THROUGH DAY 8 SUN WHILE SFC HIGH PRESSURE OVER THE ARCTIC EXTENDS INTO NRN CANADA. THERE ARE STILL TYPICAL UNCERTAINTIES FOR STRENGTH/SHAPE OF THE RIDGE ALOFT WITH A MODEL/ENSEMBLE MEAN CONSENSUS ACCOUNTING FOR THESE ISSUES WELL. THIS SOLN REFLECTS A SLIGHTLY STRONGER TREND VS PRIOR FCST AT SOME VALID TIMES. THE NERN PACIFIC CONTINUES TO BE THE MOST TROUBLESOME AREA OF THE FCST WITH INDIVIDUAL MODELS AND ENSEMBLE MEMBERS STILL AT ODDS OVER WHETHER ONE OR MORE MID-LATITUDE WAVES COULD TRACK FAR ENOUGH N TO HAVE SOME INFLUENCE ON THE PANHANDLE/GULF OF ALASKA. EARLY IN THE PERIOD WED-THU 00Z CANADIAN ENSEMBLES ON A PERCENTAGE BASIS SHOWED A HIGHER POTENTIAL FOR A FARTHER N SFC LOW TRACK WITH THE 12Z CMC AND ESPECIALLY 12Z UKMET PART OF THIS CAMP. IT STILL LOOKS LIKE A FINE LINE BTWN SUPPORTING ENERGY ALOFT BEING DEFLECTED AROUND THE WRN SIDE OF THE NRN BC PART OF THE RIDGE ALOFT OR UNDERCUTTING TO THE S. THEN THE 00Z GFS AND ALONG WITH SOME GEFS MEMBERS SHOWED SUCH POTENTIAL BY FRI ONWARD. THIS GFS FEATURE (FARTHER SE IN THE 06Z RUN) ORIGINATES FROM ENERGY OVER THE WRN BERING SEA AS OF 12Z TODAY AND FLOWS ALL THE WAY AROUND THE MEAN CYCLONIC CIRCULATION. THE 00Z UKMET/NAVGEM AGREED WITH THE 00Z ECMWF/CMC THAT ANY DEVELOPMENT FOR THIS SPECIFIC FEATURE SHOULD BE WEAKER/FARTHER SE. THE 12Z GFS/UKMET/CMC FURTHER AGREE IN LEANING AWAY FROM THE 00Z/06Z GFS FOR THIS FEATURE. INCONSISTENT SIGNALS EARLY AND MAJORITY TRENDS LATER FAVOR A DETERMINISTIC FCST THAT KEEPS ANY WELL DEFINED SFC WAVES TO THE S OF THE GULF OF ALASKA/PANHANDLE FOR THE TIME BEING. OVERALL THE 00Z ECMWF/ECMWF MEAN/NAEFS MEAN PROVIDED THE BEST COMBINATION OF CLUSTERING AND CONTINUITY FOR THE NWRN PAC SYSTEM FCST TO TRACK NEAR THE ALEUTIANS DURING THE LATTER HALF OF THE PERIOD. THREE OF THE PAST FOUR OPERATIONAL ECMWF RUNS (00Z/21 RUN BEING THE EXCEPTION) HAVE BEEN FAIRLY CLOSE TO THIS CONSENSUS. THE LAST COUPLE GEFS MEAN RUNS SLOWED DOWN VERSUS EARLIER RUNS WHILE THE LATEST ECMWF MEAN HAS ACCELERATED A BIT. INCLUDING THE SLIGHTLY SLOWER NAEFS MEAN WOULD HELP TO NUDGE THE ECMWF-BASED SOLNS BACK A BIT TO ACCOUNT FOR CONTINUITY. THE FULL MODEL/ENSEMBLE SPREAD IS STILL FAIRLY BROAD, INCLUDING SOME GFS RUNS THAT HAVE BEEN HOLDING THE PARENT LOW WELL WWD WHILE THE LEADING WAVY FRONT CONTINUES ALONG AT A PACE MORE SIMILAR TO THE FAVORED SFC LOW CLUSTER. BASED ON CONSIDERATIONS FOR THE ABOVE AREAS/SYSTEMS, TODAY'S FCST STARTED WITH A BLEND OF MOSTLY 12Z GFS/00Z ECMWF DAYS 4-5 WED-THU TRENDING TO A NEARLY EVEN WEIGHT OF THE MODELS AND 00Z NAEFS/ECMWF MEANS DAY 6 WED. THE LAST TWO DAYS OF THE FCST CONSISTED PRIMARILY OF THE ENSEMBLE MEANS WHILE RETAINING 25 PCT OF THE 00Z ECMWF. RAUSCH