EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1114 AM EST WED DEC 07 2016 VALID 12Z SAT DEC 10 2016 - 12Z WED DEC 14 2016 ...PATTERN OVERVIEW AND GUIDANCE PREFERENCES... THE WPC MANUAL PRODUCT SUITE WAS PRIMARILY DERIVED FROM A BLEND OF THE EXPERIMENTAL 00 UTC GFS PARALLEL RUN AND 00 UTC GEFS/ECMWF ENSEMBLE MEANS. THE PARALLEL RUN IS BEING EVALUATED FOR EMC IMPLIMENTATION AND OFFERS A SOLUTION COMFORTABLY BETWEEN THE OPERATIONAL 00 UTC GFS/ECMWF. THIS SOLUTION MAINTAINS GOOD WPC CONTINUITY...TAKES INTO ACCOUNT LATEST MODEL TRENDS...AND IS WITH CONDIERATION OF INCREASED SHORT AND MEDIUM RANGE UNCERTAINTY ASSOCIATED WITH A PATTERN INHERENT WITH A SERIES OF EMBEDDED SMALLER SCALE FEATURES WITHIN GENERALLY FLATTENED AND PROGRESSIVE FLOW DEVELOPMENT OVER THE LOWER 48. ON DAYS 3-4 AGREEMENT IS GOOD WITH AN AREA OF LOW PRESSURE JUST OFF THE PACIFIC NORTHWEST COAST ALONGED WITH A STATIONARY FRONTAL DRAPE EXTENDING INLAND ACROSS THE NORTHERN ROCKIES TO A FRONTAL SYSTEM DEVELOPING ON THE IN CENTRAL ROCKIES THEN PLAINS THAT MOVES NORTHEAST TOWARDS THE UPPER MS VALLEY AND GREAT LAKES SUN 11 DEC. GUIDANCE DIFFERENCES GROW SUN INTO MON AS THE LOW MOVES INTO SOUTHEAST CANADA WITH A TRAILING AND WAVY COLD FRONT MOVING ACROSS THE NORTHEAST TO THE OH VALLEY AND APPALACHIANS. THE ECMWF SHOWS LESS EMPHASIS WITH THIS LOW THAN RECENT OPERATIONAL GFS RUNS AND INSTEAD DEVELOPS A MORE ORGANIZED AND PCPN FOCUSING NEW WAVE BACK ALONG A LESS PROGRESSIVE FRONTAL PUSH OVER THE E-CENTRAL TO E/SERN US. THE PARALLEL GFS OFFERS MORE EVEN LOW DEVELOPMENT AMID UNCERTAIN SUPPORTING FLOW ALOFT. FOLLOWING THESE SYSTEMS WILL BE MODEST COLD AIR INTRUSION FOLLOWED BY A MORE AMPLE SURGE OF COLD CANADIAN/ARCTIC AIR FROM SOUTHWEST CANADA INTO NRN WRN US/ROCKIES EARLY NEXT WEEK THAT SURGES THROUGH THE PLAINS AND EAST-CENTRAL US INTO DAYS 6/7. ADDITIONAL SPREAD DEVELOPS OVER THE EASTERN PACIFIC AND ADJACENT POSITIONS OF THE PACIFIC NORTHWEST AND NORTHERN CA AS THE ECMWF/GFS/CANADIAN GLOBAL ALL SHOW LOW PRESSURE DEVELOPING ON A WAVY SURFACE FRONT WITH EACH MODEL INDICATING A DIFFERING CYCLONE TRACK/SPEED/INTENSITY. THIS LEADS TO STRONG ONSHORE FLOW AND A POTENTIAL HEAVY PRECIP EVENT OVER OR/NRN CA. ...WEATHER HIGHLIGHTS/THREATS... OVER THE WEST THE LARGE SCALE PATTERN WILL LIKELY PROMOTE PERSISTENT VALLEY RAIN AND INLAND/HIGHER ELEV SNOW ACROSS THE PACIFIC NORTHWEST/NRN CA/NORTHERN GREAT BASIN/NORTHERN ROCKIES WITH A PRONOUNCED COASTAL/TERRAIN FOCUS FOR HIGHEST AMTS. THE POTENTIAL EXISTS FOR ONE OR MORE EPISODES OF LOCALLY HVY PCPN...MOST LIKELY OVER NRN CALIFORNIA AND/OR WRN OREGON. ABOVE NORMAL TEMPS PERSISTS IN THE DESERT SOUTHWEST THROUGH THE WEEKEND AND EARLY NEXT WEEK BUT BECOME BELOW NORMAL IN THE CENTRAL TO NORTHERN GREAT BASIN/CENTRAL TO NORTHERN ROCKIES/PACIFIC NORTHWEST. WITH THE FORECAST ARCTIC SURGE COMING OUT OF SOUTHWEST CANADA INTO THE NORTHERN PLAINS...AN IMPRESSIVE AREA OF TEMPERATURES WELL BELOW NORMAL DEVELOPS IN THE NORTHERN HIGH PLAINS AND SPREADS/MODIFIES SOUTHWARD/EASTWARD. THE WEEKEND SYSTEM TRAVERSING FROM THE CENTRAL PLAINS TO UPPER MS VALLEY/UPPER LAKES HAS POTENTIAL TO PRODUCE SOME LOCALLY HEAVY SNOW ALONG THE STORM TRACK...WITH LIGHTER AMOUNTS IN THE DOWNSTREAM WARM ADVECTION ACROSS THE LOWER LAKES AND NORTHEAST. WAVES ALONG THE TRAILING FRONT WOULD ALSO BE ABLE TO TAP LEADING POOLED MOISTURE FOR SOME MODEST RAINFALL. MEANWHILE...HEAVY SNOWS ARE ALSO EXPECTED OVER WIDESPREAD FAVORED TERRAIN OF MUCH OF THE NWRN QUARTER OF THE US AS PACIFIC IMPULSES MOVE OVER THE REGION TO ENHANCE LOCAL MOISTURE/LIFT. SCHICHTEL