EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1024 AM EST TUE DEC 13 2016 VALID 12Z FRI DEC 16 2016 - 12Z TUE DEC 20 2016 ...OVERVIEW... MODELS AND ENSEMBLES SHOW THE PATTERN SETTLING INTO A POSITIVELY TILTED MEAN TROUGH BTWN A BUILDING WRN ATLC RIDGE AND SLOWLY FLATTENING ERN PAC RIDGE. TELECONNECTIONS RELATIVE TO THIS CONFIGURATION SHOW THE STRONGEST SIGNALS FOR ABOVE AVG PCPN POTENTIAL FROM THE CENTRAL GULF COAST AND LWR MS VLY TO TN VLY EWD-NEWD... CONSISTENT WITH WHERE MOST GUIDANCE SHOWS HIGHER PCPN TOTALS IN ASSOC WITH THE LOW PRES/FRONTAL SYSTEM TRACKING OUT OF THE WEST AND THROUGH THE PLAINS/EAST LATE THIS WEEK THROUGH THE WEEKEND. HOWEVER PERSISTENT SWLY FLOW ALOFT MAY KEEP SOME THREAT FOR PCPN OVER THIS AREA AFTER FRONTAL PASSAGE... THIS REMAINS MORE UNCERTAIN. THE MEAN TROUGH WILL LIKELY BECOME SOMEWHAT MORE SHALLOW DURING THE FIRST HALF OF NEXT WEEK AS VERY STRONG NRN PAC FLOW PUSHES ACROSS THE NRN TIER CONUS AND SRN CANADA... BRINGING MSTR TO THE PAC NW AND FINALLY A WARMING TREND TO THE NRN TIER. FOR SUCH A COMPLEX UPPER PATTERN WITH MULTIPLE STREAMS... THE GUIDANCE IS IN SOLID SHAPE FOR THE MOST PART. IN FACT... WPC FELT VERY CONFIDENT WITH AN EARLY BLEND OF MAINLY THE 00Z/13 ECMWF AND 06Z/13 GFS THROUGH THE WEEKEND AND INTRODUCED EACH OF ITS MEANS FOR EARLY NEXT WEEK. ...WEATHER HIGHLIGHTS/THREATS... THE FORECAST STARTS OFF FRI WITH A SPLIT FLOW UPPER TROUGH DIGGING OVER THE NWRN QUAD OF THE COUNTRY... NRN POLAR DIGGING FROM NW TO GREAT BASIN AND NEXT VERY IMPRESSIVE ARCTIC INTRUSION DIVING FROM WEST CENTRAL CANADA INTO THE NRN PLAINS/UPPER MIDWEST. THIS SHOULD YIELD DECENT PAC MOISTURE TRANSPORT INTO CENTRAL CA... ESPECIALLY OROGRAPHICS FROM THE SIERRA INTO THE NRN WASATCH/WRN WY TETONS... WITH OVERRUNNING SNOWFALL STREAKING FROM WY INTO SD AND SRN MN/NRN IA. THE UPPER DYNAMICS AND SHORT WAVE TROUGH WILL SHEAR-OUT AND EJECT OUT OF THE GREAT BASIN ON SAT TO INDUCE A SURFACE LOW OVER CENTRAL MO TO CENTRAL IL... WHILE TREMENDOUS COLD ADVECTION OCCURS DOWN THE FRONT RANGE OF THE ROCKIES AND ACROSS THE MIDWEST. THE HEAVIEST QPF APPEARS TO CONCENTRATE ACROSS THE FAVORED TERRAIN ACROSS THE FOUR CORNERS REGION... A PLUME OF MOISTURE FROM THE OH VALLEY AND MID-ATL WHICH WILL LIKELY BE STARTING AS SNOW/FROZEN PRECIP CHANGING TO RAIN AND MAINLY SNOW ACROSS THE UPPER MS VALLEY TO UPPER GREAT LAKES/INTERIOR NORTHEAST. THEN ON SUN... THE SURFACE LOW WILL GO THROUGH RAPID CYCLOGENESIS WHILE LIFTING FROM SRN QUEBEC TO THE CANADIAN MARITIMES. THE ARCTIC AIR WILL SPREAD DOWN THROUGH TX AND EXTEND INTO A GOOD PART OF THE EASTERN PORTION OF THE COUNTRY... AS THE SURFACE COLD FRONT MOVES OFF THE EAST COAST. THE MAIN MOISTURE PLUME WILL STRETCH FROM THE CENTRAL GULF COAST INTO THE SRN APPALACHIANS WITH ENOUGH MOISTURE IN THE COLD SECTOR FOR WINTRY PCPN TYPES FAR NWWD WHICH COULD PERSIST ON MON. MEANWHILE... NEXT MON AND TUE STRONG NRN PAC FLOW SHOULD BRING HEAVIER RAIN/HIGHER ELEV SNOW TO THE PAC NW INTO THE NRN ROCKIES. VERY COLD TEMPS OVER THE EAST ON FRI MAY BE NEAR DAILY RECORD VALUES FOR MIN AND/OR MAX AT A FEW PLACES IN THE NORTHEAST. APPROACHING SYSTEM WILL BRING A PRONOUNCED BUT BRIEF WARMUP FOR THE WEEKEND BEFORE COLDER AIR MOVES IN ONCE AGAIN EARLY NEXT WEEK. WHILE THIS TRAILING COLD AIR IS OVER THE NRN PLAINS/MIDWEST SOME LOCATIONS MAY SEE TEMPS AS MUCH AS 20-35F BELOW NORMAL FOR THE FRI-SUN PERIOD. AT THE SAME TIME SRN PLAINS WARMTH UP TO 10-20F ABOVE NORMAL ON FRI WILL BE REPLACED BY NEGATIVE ANOMALIES OF AT LEAST THAT MAGNITUDE BY SUN. TEMPS WILL MODERATE EARLY NEXT WEEK... MOST NOTABLY OVER THE NRN PLAINS WHICH MAY TREND ABOVE NORMAL BY NEXT TUE. THE FLORIDA PENINSULA SHOULD BE THE ONE AREA CONSISTENTLY ABOVE NORMAL AFTER FRI WITH A FEW RECORD WARM MINS PSBL. COLD TEMPS OVER NRN PARTS OF THE WEST WILL SPREAD SEWD EARLY IN THE PERIOD. THE WEST WILL TREND CLOSER TO NORMAL BY NEXT TUE. MUSHER/RAUSCH