ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 332 PM EDT MON OCT 23 2017 VALID 12Z FRI OCT 27 2017 - 12Z TUE OCT 31 2017 MEDIUM RANGE FORECAST OVER THE HIGH LATITUDES OF THE NORTH PACIFIC CONTINUES TO BE A CHALLENGE ON SYSTEM TIMING/TRACK/STRENGTH DUE TO YET ANOTHER FORECAST EXTRATROPICAL TRANSITION OF WHAT IS NOW TROPICAL STORM 27W (AND WHAT IS NOW IN THE SHORT TERM EX-LAN). THE PATH OF LEAST RESISTANCE (OR LEAST REGRET) IS TO USE AN ENSEMBLE CONSENSUS IN ORDER TO MINIMIZE DAY TO DAY CHANGES. THE ECMWF ENSEMBLE MEAN IS USUALLY BETTER THAN THE GEFS MEAN IN AN AMPLIFIED PATTERN, BUT THE INCLUSION OF A COUPLE OF FICKLE TROPICAL SYSTEMS HAS PROVED TO BE A CHALLENGE FOR EVEN THE USUALLY STEADFAST ECMWF EPS. NEVERTHELESS, THE 06Z GEFS AND 00Z ECMWF ENSEMBLE MEAN OFFERED REASONABLY CLOSE SOLUTIONS THAT A BLEND OF THE TWO FORMED A GOOD STARTING POINT. INCLUSION OF THE 12Z GFS AND 00Z ECMWF IN THE FIRST FEW DAYS OFFERED AT LEAST SOME DETAILS THOUGH CONFIDENCE IS RATHER LOW IN SPECIFICS THROUGH THE PERIOD. FIRST SYSTEM SHOULD CREEP OUT OF THE NORTH PACIFIC THIS WEEKEND INTO THE EASTERN ALEUTIANS/AKPEN AND PERHAPS THE GULF THEREAFTER, BUT THE ENSEMBLES HAVE NOT LATCHED ONTO CONSISTENT TIMING WITH THIS STORM (LIKELY DUE TO A COMBINATION OF THE UPSTREAM FLOW AND UNCERTAIN EVOLUTION IN THE BERING FRI-SAT). AGAIN, ENSEMBLE CONSENSUS FORMED THE BASIS TO THE FRONTS. FARTHER UPSTREAM, AN UPPER TROUGH IS FORECAST TO PUSH THROUGH THE WESTERN BERING AT THE END OF THE WEEK AND FIGHT DOWNSTREAM BUILDING RIDGING ALONG 140W INTO W CANADA. THAT SHOULD SLOW DOWN THE PATTERN BUT EMBEDDED SYSTEMS (SEE ABOVE) HAVE MADE THAT AN UNSTEADY TREND. CURRENT TROPICAL STORM 27W IS FORECAST TO RECURVE JUST EAST OF 130E AND SE OF JAPAN LATER THIS WEEK BUT THE MODEL/ENSEMBLES DO SO AT VERY DIFFERENT LONGITUDES. THE GFS WAS FARTHER WEST THAN THE CANADIAN/ECMWF AND THUS WAS SLOWER TO BRING IT INTO THE WESTERLY FLOW AND ACROSS THE NORTH PACIFIC. DESPITE THAT, THE GFS MANAGED TO CATCH UP TO THE ECMWF AND THE ENSEMBLE CONSENSUS AND BRING THAT SYSTEM INTO THE WESTERN ALEUTIANS BY NEXT TUESDAY. PATTERN SHOULD SUPPORT INITIAL PRECIPITATION ALONG SOUTHCENTRAL INTO THE PANHANDLE WITH THE LEAD SYSTEM (EX-LAN) FOLLOWED BY SOME CLEARING THANKS TO UPPER RIDGING. GIVEN THE TIMING OF THE NEXT SYSTEM OUT OF THE NORTH PACIFIC, MORE RAIN/SNOW IS EXPECTED BY NEXT WEEK AS THE FRONT LIFTS INTO THE GULF. FRACASSO