EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1058 AM EST FRI DEC 04 2015 VALID 12Z MON DEC 07 2015 - 12Z FRI DEC 11 2015 ...WET AND WINDY WEATHER FOR THE WEST COAST... ...OVERVIEW... PROGRESSIVE PACIFIC INFLUENCE WILL MIGRATE THROUGH THE LOWER 48 THIS FORECAST PERIOD...CULMINATING (DAY 7-8) WITH THE DEEP-LAYERED MARITIME AIRMASS INTRUSION ACROSS CALIFORNIA...THE DESERT SOUTHWEST...GREAT BASIN AND FOUR CORNERS. DOWNWIND ACROSS THE EASTERN THIRD OF THE NATION---EAST OF THE DIVIDE...A RATHER MILD PATTERN WITH A WEST TO SOUTHWEST FLOW ALOFT AND LOW-AMPLITUDE MID-LEVEL WAVE PROGRESSION. ...MODEL GUIDANCE... A BLEND OF THE DETERMINISTIC ECMWF (4/00Z RUN) AND THE 4/00Z ECENS/NAEFS MEANS PROVIDES AMPLE LEE-WAY FOR SLIGHT VARIANCE IN THE LOWER 48 FORECAST THROUGH DAY 4. THE GFS/GEFS CONTINUES TO BE THE VERY SLOW 'CLOSED LOW' SOLUTION OVER CENTRAL APPALACHIA DAY 3-4 --- AND THERE IS NO REAL THOUGHT AS TO WHY?! THE PREVAILING THEME STILL HOLDS ACROSS THE NORTHEAST WITH THE IDEA THAT THERE IS ROOM FOR A SURFACE CYCLONE TO FORM ALONG/OVER THE GULF STREAM --- AND MIGRATE THE SYSTEM PROGRESSIVELY NORTHEAST INTO THE NORTHWEST ATLANTIC BASIN. AFTER 10/00Z...WILL TREND AWAY FROM ANY MEANINGFUL DETERMINISTIC DETAIL. BUT ONLY BECAUSE THE DEEP CYCLONE IN THE GULF OF ALASKA --- AND THE SERIES OF PROGRESSIVE AND INCREASINGLY-DEEP SHORTWAVES THAT MIGRATE ACROSS THE WEST COAST WILL 'PERTURB' THE MID-LEVEL PATTERN ALONG/DOWNWIND OF THE SIERRA AND CONTINENTAL DIVIDE. THAT SAID...THOUGHT THE NAEFS/ECENS WILL BE A GOOD 'PLACEHOLDER' FOR THE GULF OF ALASKA CYCLONE/VORTEX AND THE TRAJECTORY OF THE SHORTWAVE ENERGY MIGRATING ACROSS THE GREAT BASIN/INTERMOUNTAIN WEST. ...UNCERTAINTY ASSESSMENT... NO ISSUES/CONCERNS WITH THE FIRST HALF OF THE FORECAST. EVEN THE 4/00Z GEFS/GFS HAVE TRENDED GRADUALLY AWAY FROM A COMPLETE 'SEPARATION' OF THE FLOW FOR THE EAST CENTRAL US. BUT STUBBORNLY SLOW WITH THAT TREND. THAT 'SLOWNESS' COMPLICATES ITS RECENT SOLUTION UPSTREAM AND BEHIND THIS 'CLOSED' LOW. IN A SENSE...ALMOST TRYING TO CREATE A 'BLOCK' ACROSS EASTERN NORTH AMERICA --- WHERE IT DOES NOT EXIST. THAT GEFS/GFS IDEA EXTENDS BACK TO THE CONTINENTAL DIVIDE. IN THIS LIGHT --- THE LEAD PACIFIC SYSTEM --- EXITING THE NORTHERN ROCKIES DAY 4 --- AND MIGRATING ACROSS THE NORTHERN PLAINS AND GREAT LAKES --- DAYS 5-6 --- HAS TRENDED STRONGER/WETTER VERSUS 24 HOURS AGO. ANOTHER ASPECT OF THE SYSTEM (AFTER 10/00Z) --- THE GFS/UKMET SOLUTION BEGIN TO SPLIT THE SYSTEM ALONG/EAST OF THE MISSISSIPPI VALLEY AND THE CANADIAN/ECMWF CLOSE OFF THE WAVE. THE 'SPLIT' AND/OR CLOSED OFF SOLUTION HAS LITTLE/NO CONTINUITY. AND THEREFORE FELT... USING A BLEND OF THE NAEFS AND ECENS IS IN ORDER FOR THE TIME BEING --- DAY 6-7 --- BOTH OF WHICH PROVIDE SOME PROGRESSION OF THE FLOW NORTHEASTWARD ACROSS THE OHIO VALLEY--- IN LIEU OF A 'BLOCKY' HIGH-AMPLITUDE UPPER-LEVEL RIDGE SOLUTION BETWEEN 80W-90W AT DAY 8. ...SENSIBLE WEATHER HIGHLIGHTS... MODERATE/HEAVY RAINFALL SIGNATURE BEGINS TO MIGRATE SOUTHWARD ALONG THE WEST COAST (DAY 5-6) WITH 'DEEP-LAYERED' COLD ADVECTION AND CHANGE TO SCATTERED SHOWERS (LOW SNOW LEVELS) NORTH OF THE UPPER-LEVEL JET. AN END TO THE SERIES OF WINDY WARM WARM FRONTS---AND HIGH-END SEASONAL PRECIPITATION TOTALS (DAY3-5) FOR OREGON AND WASHINGTON. VERY MILD (AND OCCASIONALLY WINDY CONDITIONS) ALONG AND DOWNSTREAM FROM THE CONTINENTAL DIVIDE FROM MONTANA TO NORTHEASTERN COLORADO WITH WARM ADVECTION SPREADING TO THE UPPER MS VALLEY. UNSETTLED NORTHEAST FLOW REGIME AND SOUTHEAST CANADIAN HIGH KEEPS EAST COAST IN A 'BACK DOOR' FRONTAL SITUATION (POST DAY4) --- BEHIND OFFSHORE-MOVING COASTAL LOW (DAY3-4). VOJTESAK