ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 119 PM EST FRI NOV 20 2015 VALID 12Z TUE NOV 24 2015 - 12Z SAT NOV 28 2015 ...A PATTERN MAJOR BERING SEA THEN ALEUTIANS LOWS WITH LEAD WARMING INTO AK... ...LATEST GUIDANCE/PREDICTABILITY ASSESSMENT... THE WPC ALASKAN MEDIUM RANGE GUIDANCE SUITE WAS PRIMARILY DERIVED FROM A BLEND OF THE VERY COMPATABLE 12 UTC GFS AND 00 UTC ECMWF DAYS 4 INTO 5 TUE INTO WED. THESE ARE SUPPORTED BY THE ENSEMBLES AND PREDICTABILITY IS ABOVE NORMAL. FORECAST SPREAD AND UNCERTAINTY THAT QUICKLY INCREASES LATER WED-NEXT SAT WARRANTS A SWITCH TO A BLEND OF THE 06 UTC GEFS MEAN AND 00 UTC ECMWF ENSEMBLE MEAN. THESE MEANS ARE ONLY MARGINALLY COMPATABLE WITH PROGRESSIVE NATURE OF THE OVERALL FLOW...BUT THIS OVERALL SOLUTION MAINTAINS DECENT WPC CONTINUITY AFTER MANUAL ADJUSTMENTS WERE APPLIED TO MAINTAIN DEEP SURFACE LOW DEPTH CONSISTENT WITH FAVORABLE DYNAMIC SUPOPRT ALOFT. ...WEATHER PATTERN HIGHLIGHTS/THREATS... LATEST MODELS/ENSEMBLES STILL OFFER A REASONABLE CLUSTER OF SOLUTIONS INTO EARLY NEXT WEEK AND TAKES A WEAK SHORT RANGE LOW ACROSS THE GULF. A STRENGTHENING SURFACE HIGH IN THE YUKON MEANWHILE SHOULD ALLOW COLDER AIR TO WORK INTO THE SERN AK PANHANDLE IN ITS WAKE INTO MIDWEEK. IT REMAINS EVIDENT THAT THE LONGWAVE PATTERN OVER THE MID-HIGH LATITUDES WILL TREND TOWARD INCREASED AMPLIFICATION DUE TO UPSTREAM AND DOWNSTREAM BUCKLING OF THE FLOW. THIS WILL BUILD RIDGING UP THROUGH ERN AK NEXT WEEK AHEAD OF A POTENT BERING SEA LOW. THIS DEEP LOW IS A BIT MORE PROGRESSIVE NOW IN GUIDANCE AND SPREADS WIDESPREAD HEAVY WEATHER WHILE FORCING A LEAD SURGE OF WARMER AIR NORTHWARD OVER THE INTERIOR/N SLOPE. THIS LOW IS EXPECTED TO GRADUALLY WEAKEN WHILE WORKING UP THE PERIPHERY OF THE RIDGE UP THROUGH THE BERING STRAIT INTO THE SRN ARCTIC LATER WEEK...WITH MORE LIMITED PCPN POTENTIAL INLAND INTO WRN/NWRN AK. UPSTREAM...LOW SYSTEM ENERGY FROM NEAR HAWAII CURRENTLY IS NOW MORE UNIFORMLY BROUGHT NORTHWARD TOWARD ALASKA ON THE WRN PERIPHERY OF THE NERN PACIFIC/ERN ALASKAN BUILDING MID-UPPER LEVEL RIDGE WITH LATEST GUIDANCE...BUT SMALLER SCALE INTERACTIONS AND LOWS TIMING REMAIN PROBLEMATIC. THE ENSEMBLE MEAN BLEND MITIGATES SOME OF THIS AND THE RESULTANT FEATURE AND ASSOCIATED WEATHER REACHES ALASKAN WATERS THEN SW/SRN ALASKA AS A POTENTIALLY WELL ORANGIZED LOW IN THE WED/THU TIME FRAME. LATER...POTENT DYNAMICS ASSOCIATED WITH THE APPROACH FROM THE WEST OF AN AMPLIFIED AND PROGRESSIVE NRN PACIFIC MID-UPPER LEVEL TROUGH IS NOW EXPECTED TO SUPPORT A DEEP LOW WITH POTENTIALLY HEAVY WIND/WAVES/PCPN ACROSS THE VICINITY OF THE ALEUTIANS DAYS 6-8. FORECAST SPREAD AND UNCERTAINTY IS ABOVE NORMAL WITH THE EVOLUTION/PROGRESSION OF THIS LOW...BUT GUIDANCE DOES OVERALL SUPPORT ANOTHER DEEP SYSTEM. SCHICHTEL