EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1008 AM EST FRI DEC 09 2016 VALID 12Z MON DEC 12 2016 - 12Z FRI DEC 16 2016 ...PATTERN OVERVIEW... IT REMAINS THE CASE THAT A DEEP UPR LOW FCST TO BE JUST W OF HUDSON BAY AS OF EARLY MON SHOULD TRACK SEWD INTO MIDWEEK AND CONTINUE EWD INTO ERN CANADA THOUGH WITH INCREASING TIMING UNCERTAINTY. UPSTREAM THE MEAN RIDGING OVER THE NERN PAC/ALASKA SHOULD ENCOURAGE SOME DEGREE OF ERN PACIFIC TROUGHING WHOSE AXIS MAY REACH THE WEST TOWARD LATE NEXT WEEK. EXPECT THE LOWER 48 TO REMAIN UNDER FAST AND LOW AMPLITUDE FLOW. PSBL INTERACTIONS AMONG NRN STREAM FLOW AND INCOMING PAC IMPULSE/S WILL ADD TO THE UNCERTAINTIES THAT ARE ALREADY TYPICALLY GREATER THAN AVG DUE TO THE PROGRESSIVE NATURE OF THE FLOW. THE LARGE SCALE PATTERN WILL LIKELY MAINTAIN VERY COLD TEMPS DOWN FROM THE NRN TIER STATES WHILE ANOTHER COLD SURGE WILL REACH THE S-CENTRAL/SERN STATES BY THE LATTER HALF OF THE WEEK. HEAVIEST PRECIP SHOULD FOCUS BE ALONG CENTRAL LATITUDES OF THE WEST. ...GUIDANCE EVALUATION/PREFERENCES... THE WPC PRODUCT SUITE FCST WAS PRIMARILY DERIVED FROM THE GEFS/ECMWF MEAN BLEND AS OPERATIONAL SOLNS SHOW FURTHER DIVERGENCE AND REMAINING TIMING DIFFS ARE WITHIN TYPICAL ERROR RANGE FOR THE VALID TIME. TELECONNECTIONS RELATIVE TO NERN PAC/ALASKA RIDGING RECOMMEND GOING AT LEAST 2/3 TOWARD THE GEFS MEAN VS THE ECMWF MEAN AND THAT ALLOWS FOR BETTER CONTINUITY. WRN CANADIAN AND NWRN US GUIDANCE TROUGH/HEIGHT FALLS DEVELOPMENTS STILL OFFER SOME TIMING ISSUES BUT HAVE BECOME BETTER CLUSTERED INTO EARLY NEXT WEEK AND ALLOW FOR A WINTERY COLD PUSH ACROSS THE REGION UNDERNEATH. DOWNSTREAM...UNCERTAINTY ACROSS THE EAST-CENTRAL US ACCOMPANIES A POTENT ARCTIC SURGE FRONT REACHING THE EAST COAST PAST MIDWEEK...WITH SOME SOLNS SHOWING POTENTIAL FOR SFC DEVELOPMENT WITHIN AN AREA COVERING FROM OFF THE MID ATLC COAST THROUGH NEW ENGLAND INTO THE CANADIAN MARITIMES. VERY WIDE SPREAD AMONG INDIVIDUAL MODEL RUNS/ENSEMBLE MEMBERS FAVORS A CONSERVATIVE APPROACH CLOSER TO THE MEANS AT THIS TIME THAT OFFERS DECENT WPC CONTINUITY. OVER THE WEST THE PRIMARY QUESTION MARKS INVOLVE ONE OR MORE WAVES THAT MAY COME IN FROM THE PAC CORRESPONDING TO SHRTWV ENERGY WITHIN COMPLEX MEAN TROUGHING. THE ELONGATED NATURE OF ENERGY INITIALLY OFF THE PAC NW COAST LEADS TO REDUCED PREDICTABILITY FOR HOW IT EVOLVES WITH TIME. THEN GUIDANCE SUGGESTS POTENTIAL FOR THIS ENERGY TO INTERACT WITH AN UPR TROUGH THAT WILL BE PASSING ACROSS/N OF HAWAII EARLY IN THE WEEK. BY MID-LATE WEEK GUIDANCE REALLY BEGINS TO DIVERGE ON THE AMPLITUDE/POSN OF TROUGHING NEAR THE WEST COAST. RECENT GFS RUNS APPEAR TO BE ON THE DEEPER SIDE. HOWEVER TELECONNECTIONS RELATIVE TO NERN PAC/ALASKA RIDGING SUPPORT A MORE WWD AND MODERATELY AMPLIFIED TROUGH AS PER RECENT GEFS MEANS VS THE QUITE DIFFERENT FLATTER/EWD RECENT ECMWF MEANS. PRECISE DETAILS OF THIS OVERALL EVOLUTION WILL BE CRITICAL FOR DETERMINING HOW MUCH LOW LATITUDE MSTR MAY GET DRAWN NEWD TOWARD THE WEST COAST AND WHERE THIS MSTR IS ORIENTED WITH THE 00 UTC GEFS/ECMWF ENSEMBLES OFFER A SEEMINGLY REASONABLE PCPN AREAL COVERAGE/FOCUS BETWEEN THE NWRN US WET TROUGH APPROACH SOLUTION OF AN OUTLIER AND RECENTLY ERRATIC DETERMINISTIC ECMWF AND SOUTHWARD SUPPRESSED QPF FOCUS FROM RECENT GFS RUNS. LOOKING AHEAD...THESE MODEL/ENSEMBLE DIFFERENCES LEAD TO SIGNIFICANT RETURN FLOW TIMING AND SYSTEM DEVELOPMENT UNCERTAINTIES DOWNSTREAM ACROSS THE US SRN TIER DAYS 7/8 TO BE DETERMINED. ...WEATHER HIGHLIGHTS/THREATS... ACROSS THE WEST...EXPECT BEST POTENTIAL FOR ONE OR MORE EPISODES OF ENHANCED COASTAL RAIN AND INLAND/HIGHER ELEV SNOW FROM NRN-CNTRL CA INTO THE CNTRL ROCKIES. COMPLEXITY OF ERN PAC EVOLUTION LOWERS CONFIDENCE IN SPECIFICS BUT THERE WILL BE POTENTIAL FOR SIGNIFICANT LOCALIZED TOTALS OVER PARTS OF NRN-CNTRL CA DEPENDING ON HOW MUCH TROPICAL MSTR MAY GET INCORPORATED INTO THE FLOW. ARCTIC BNDRY DUG/DRAPED THROUGH THE NORTHWEST AND N-CENTRAL ROCKIES/HIGH PLAINS MAY PROVIDE ANOTHER FOCUS FOR PCPN WITH SNOWS ENHANCED BY POST-FRONTAL UPSLOPE FLOW. EXPECT TEMPS TO RANGE TO 20-30F BELOW NORMAL FOR COLDER POST-FRONTAL AREAS. OVER THE ERN 2/3 OF THE COUNTRY...THE NRN PLAINS SHOULD BE MOST CONSISTENTLY VERY COLD WITH HIGHS LIKELY TO AVG 20-30F BELOW NORMAL FOR THE 5-DAY PERIOD. IN MODIFIED FORM SOME OF THIS COLD AIR WILL PUSH SEWD FROM THE NRN PLAINS MON ONWARD...BRINGING SOME MINUS 10-20F OR SO ANOMALIES TO THE NRN-CNTRL PARTS OF THE CENTRAL US THEN EAST FOR THE LATTER HALF OF THE WEEK. DAILY RECORDS ARE QUITE EXTREME BY THIS POINT IN THE SEASON SO CURRENT FCSTS MAY ONLY YIELD ISOLATED RECORD VALUES. GRTLKS/NERN SYSTEM MON WILL BRING A WIDESPREAD AREA OF SNOW TO LOCATIONS WITH LOW CIRCULATION AND RAIN FARTHER SWD. PASSAGE OF THIS SYSTEM AND UPSTREAM ARCTIC FRONT SHOULD PROMOTE A MULTI-DAY PERIOD OF LAKE EFFECT SNOW. TOWARD THE LATTER HALF OF THE WEEK THERE MAY BE ONE OR MORE AREAS OF MOSTLY LGT PCPN OVER PARTS OF THE CNTRL-ERN STATES BUT WITH LOW CONFIDENCE ON LOCATION/TIMING DUE TO UNCERTAINTIES WITH SHRTWV DETAILS ALOFT. THE SOUTHWARD EXTENT OF WINTER AIR AND WAVY TRAILING FRONT POTENTIAL MAY OFFER SOME OVER-RUNNING SNOW/ICE THREAT POTENTIAL. SCHICHTEL