EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 114 AM EST FRI DEC 30 2016 VALID 12Z MON JAN 02 2017 - 12Z FRI JAN 06 2017 ...OVERVIEW... A RATHER DRAMATIC PATTERN SHIFT WILL BEGIN TO OCCUR OVER THE UPCOMING WEEKEND TO ESTABLISH A HUGE NEGATIVE ANOMALY OVER THE NWRN QUAD OF THE COUNTRY BY MONDAY. THIS AMPLIFIED UPPER TROUGH... AOA 2.5 STANDARD DEVIATIONS BELOW AVG VIA GFS/ECMWF MEANS... WILL FEATURE AN IMPRESSIVE ARCTIC BLAST WHICH WILL GRADUALLY BROADEN AND SPREAD DOWNSTREAM. BY NEXT FRI... THE ENTIRE COUNTRY WILL BE BELOW AVG FOR TEMPS WITH THE EXCEPTION BEING FL. THE BOTTOM LINE IS THE FIRST WEEK OF 2017 WILL BE FRIGID FOR MUCH OF THE COUNTRY WITH LIKELY RECORD COLD. ...GUIDANCE/PREDICTABILITY ASSESSMENT... MODELS AND ENSEMBLES HAVE BEEN IN PRETTY GOOD AGREEMENT ON THE BEGINNING MEAN PATTERN AND OVERALL SYNOPTIC EVOLUTION FOR NEXT WEEK. HOWEVER INCREASING DETAIL DIFFERENCES WITH THE OPERATIONAL GUIDANCE OF THE GFS AND ECMWF ALONG WITH CANADIAN/UKMET SUPPORTS A LARGE USAGE OF THE MEANS... GEFS/NAEFS AND ECMWF. WPC WENT THIS ROUTE TUES THROUGH NEXT FRI TO CALM THE OVERALL PATTERN TRANSITIONING FROM MULTI-STREAMS TO A BROAD AND EXPANSIVE AMPLIFIED POSITIVE TILTED UPPER TROUGH. THE 5 DAY MEAN MAX TEMP ANOMALY WILL BE WELL BELOW AVG WEST OF THE MS RIVER... AS MUCH AS 20 TO 30 DEG BELOW THE NORM FROM WA/OR AND NERN CA/NRN NV THROUGH ID AND MUCH OF MT/WY INTO THE DAKOTAS ...WEATHER HIGHLIGHTS/THREATS... A SNAPSHOT AT NEXT WEEK... STARTING MON A THE NEG ANOMALY WILL BE OVER THE NORTHWEST AS THE ASSOCIATED ARCTIC COLD FRONT PUSHES SOUTH THROUGH THE GREAT BASIN AND SOUTH AND EAST THROUGH PARTS OF THE PLAINS/MS VALLEY. MEANWHILE AN UPPER DISTURBANCE DROPPING SOUTH ALONG THE CA COASTLINE THIS WEEKEND WILL EJECT OUT INTO TX AND PROCEED DOWNSTREAM SHEARING-OUT INTO THE OH VALLEY/GREAT LAKES. THIS COULD RESULT IN HEAVY RAINFALL ACROSS THE SOUTH/SOUTHEAST AND ALONG THE IMMEDIATE WEST/CENTRAL GULF COAST... WHILE A POSSIBLE EXPANDING ZONE OF SNOW WILL BE POSSIBLE FROM THE MID TO UPPER MS VALLEY. THEN ON TUES AND WED... THE DEEP UPPER TROUGH OVER THE NW WILL SEE UPPER DYNAMICS TRANSITION DOWNSTREAM INTO THE UPPER MIDWEST... WHILE UPPER DYNAMICS IN THE BASE OF THE TROUGH WILL DIG SOUTH AND EAST THROUGH THE GREAT BASIN... BASICALLY A BROADENING AND EXPANSION OF THE BELOW AVG UPPER HEIGHTS. MAX TEMPS EACH DAY BEHIND THE ARCTIC COLD FRONT WILL RANGE FROM 15 TO 30 DEG BELOW AVG. A ZONE FROM THE CA SIERRA TO CO ROCKIES COULD ALSO SEE SOME ENHANCED OROGRAPHIC SNOWFALL. MEANWHILE AHEAD OF THE POLAR AND ARCTIC BOUNDARIES OVER THE EAST... EXPECT WET CONDITIONS BUT TOUGH TO SPOT THE HEAVIEST QPF AT THIS POINT. FINALLY FINISHING UP WITH NEXT THURS/FRI... ADDITIONAL SHORT WAVE DYNAMICS DIG FROM BRITISH COLUMBIA INTO THE NW AND SHOULD BE A KICKER TO DRIVE ENERGY OVER THE GREAT BASIN/FOUR CORNERS REGION DOWNSTREAM. THE UNCERTAINTY REVOLVES AROUND THIS BATCH OF UPPER DYNAMICS... AS SOME SOLUTIONS KEEP THIS ENERGY INTACT... WHILE OTHERS SHEAR THE SYSTEM OUT. THIS IS RATHER IMPORTANT... AS THE ARCTIC COLD FRONT GENERALLY STALLS ACROSS FL INTO THE GULF OF MEXICO AND MOISTURE COULD BEGIN TO OVERRUN INTO THE THEN ESTABLISHED COLD SECTOR OVER THE EAST/SOUTH. THE MORE AMPLIFIED SOLUTIONS MEANS MOISTURE EASILY REACHING THE COLD SECTOR FOR A POSSIBLE EXPANSIVE AREA OF FROZEN PRECIP... WHILE THE SHEARED-OUT SOLUTIONS MEANS A SUPPRESSED SOLUTION OF MAINLY RAIN AND NOT OF MUCH MOISTURE SPREADING NORTHWARD. THIS LATE WEEK SCENARIO WILL EVOLVE OVER THE NEXT WEEK BUT BEARS WATCHING. MUSHER