EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 145 AM EST TUE JAN 17 2017 VALID 12Z FRI JAN 20 2017 - 12Z TUE JAN 24 2017 ...OVERVIEW... LATEST MODEL AND ENSEMBLE RUNS ARE CONSISTENT WITH THE IDEA OF A VERY STRONG CORE OF POSITIVE HGT ANOMALIES NEAR THE ERN SHORE OF HUDSON BAY... LIKELY SUPPORTING BELOW AVG HGTS ALOFT OVER MOST OF THE LOWER 48 ASIDE FROM THE NRN PLAINS TO NORTHEAST. MULTI-DAY MEANS BY D+8 DIFFER THE MOST NEAR THE WEST COAST WHERE TELECONNECTIONS RELATIVE TO THE POSITIVE HGT ANOMALY CENTER WOULD FAVOR SOLNS THAT HAVE BELOW NORMAL HGTS. THE RELATIVELY LOW MEAN HGTS OVER MOST OF THE LOWER 48 WILL BE REFLECTED IN THE DAILY FCSTS AS A SERIES OF SYSTEMS BRINGING HVY RAIN/STRONG WINDS TO THE WEST COAST WITH ACTIVE WEATHER ALSO EXTENDING WELL EWD. FOR THE MOST PART LATEST SOLNS IDENTIFY INDIVIDUAL SYSTEMS FAIRLY WELL WITH DECENT CONTINUITY BUT THERE ARE SOME DETAIL UNCERTAINTIES REQUIRING MORE TIME TO BE RESOLVED. ...GUIDANCE EVALUATION/PREFERENCES... THE DOMINANT FEATURE AFFECTING THE LOWER 48 DURING THE PERIOD STARTS NEAR THE WEST COAST EARLY DAY 3 FRI WITH A VERY STRONG LOW SFC/ALOFT OFF THE PAC NW COAST AND FRONTAL SYSTEM EXTENDING WELL SWD. THE 12Z UKMET WAS THE ODD MODEL OUT IN TRACKING THE SFC LOW SEWD INSTEAD OF KEEPING IT OFFSHORE. THE NEW 00Z RUN HAS JOINED THE MAJORITY CLUSTER. ENERGY IN THE SRN PART OF THE UPR TROUGH WILL STREAM ACROSS NRN MEXICO AND LIKELY SUPPORT A CLOSED LOW OVER THE SRN HALF OF THE PLAINS BY EARLY DAY 5 SUN. THE OVERALL SYSTEM SHOULD THEN TRACK NEWD. ONCE E OF THE PLAINS THE ENSEMBLE SPREAD FOR SFC LOW TRACKS HAS NARROWED FROM 24 HRS AGO WITH A SIMILAR CENTROID... SO CONSENSUS FCST MAINTAINS GOOD CONTINUITY. THE 18Z GEFS MEAN WAS SOMEWHAT SLOWER/SWD THAN MOST OTHER SOLNS. REVIEWING TIME PERIODS CENTERED ON COMPOSITE ANALOG DATES THAT WERE CLOSEST TO THE FCST D+8 PATTERN REVEALED A JAN 19-21,1995 SYSTEM THAT HAD A DIFFERENT ORIGIN BUT DURING THAT WINDOW FROM THE MS VLY INTO THE ERN STATES HAD THE COMMON TRAITS OF ERN CANADA RIDGING AND A TRACK SIMILAR TO CURRENT CONSENSUS. BASED ON THAT SYSTEM IT WOULD APPEAR REASONABLE THAT THE CURRENT SYSTEM MAY REACH AT LEAST AS FAR NWD AS THE OH VLY/NRN MID ATLC AND PSBLY SRN NEW ENGLAND. THE NEXT STRONG ERN PAC UPR TROUGH SHOULD APPROACH THE WEST COAST BY SUN AND THEN CONTINUE GRADUALLY EWD INTO NEXT WEEK. RECENT GFS RUNS HAVE BEEN DIFFERING FROM CONSENSUS FOR THIS SYSTEM... IN VARYING WAYS DEPICTING FASTER PROGRESSION OF LEADING HGT FALLS. IN THE NEW 00Z GFS THIS TRAIT LEADS TO TRACKING A SFC WAVE THROUGH THE NWRN STATES ON SUN INSTEAD OF HAVING A CONSOLIDATED AND DEEPER SYSTEM OFFSHORE AT THAT TIME. ECMWF/CMC RUNS AND THE ENSEMBLE MEANS AGREE IN PRINCIPLE THROUGH DAY 7 TUE AS THE UPR TROUGH REACHES THE INTERIOR WEST. ...WEATHER HIGHLIGHTS/THREATS... DETAILS WILL STILL BE SUBJECT TO CHANGE GIVEN THE TIME FRAME... BUT CONFIDENCE REMAINS ABOVE AVG FOR AT LEAST A COUPLE EPISODES OF SIGNIFICANT RNFL/HIGH ELEV SNOW AND STRONG WINDS ALONG THE WEST COAST WITH THIS ENHANCED ACTIVITY EXTENDING INTO THE SIERRA NEVADA RANGE AND SOUTHWEST. CONTINUE TO EXPECT AREAL AVERAGE AMOUNTS TO EXCEED 5 INCHES ALONG SOME COASTAL LOCATIONS AND OVER THE SIERRA NEVADA WITH HIGHEST TOTALS ALONG WINDWARD FACING SLOPES. FOR SRN CA/AZ THE HEAVIEST PRECIP SHOULD OCCUR AROUND FRI-FRI NIGHT AND AGAIN AROUND SUN-MON. MUCH OF THE REMAINDER OF THE WEST SHOULD SEE LESS INTENSE RAIN AND INLAND/HIGHER ELEV SNOW. THE UNSETTLED WEATHER WILL TEND TO KEEP TEMPERATURE RANGES MORE NARROW THAN USUAL WITH BELOW NORMAL HIGHS... ON A LOCALIZED BASIS BY GREATER THAN 10F... AND NEAR TO ABOVE NORMAL LOWS. PORTIONS OF THE EAST/MIDWEST WILL SEE SOME RAIN ON FRI FOLLOWED BY A BRIEFLY DRIER PERIOD. LOCALLY MDT/HVY RNFL MAY DEVELOP NEAR THE GULF COAST AROUND FRI NIGHT-SAT ALONG A LINGERING FRONT. AS ENERGY FROM THE INITIAL WEST COAST STORM CROSSES THE PLAINS/SOUTHEAST... MORE HVY RNFL MAY DEVELOP AND SPC IS MONITORING THE POTENTIAL FOR SEVERE CONVECTION NEAR THE ERN HALF OF THE GULF COAST DURING THE WEEKEND. CONSULT LATEST SPC PRODUCTS FOR FURTHER INFO. THE PLAINS TO OH VLY/MID ATLC SYSTEM WILL SPREAD A BROAD AREA OF PCPN MOSTLY IN THE FORM OF RAIN ACROSS THE ERN HALF OF THE COUNTRY. THERE IS STILL A FAIRLY GOOD SIGNAL FOR A PERIOD OF STRONG LOW LVL INFLOW FROM THE ATLC THAT WOULD ENHANCE RNFL FOR A TIME ALONG THE EAST COAST/ERN SLOPES OF THE APLCHNS. IT STILL APPEARS THAT ANY SNOW THAT DOES OCCUR WOULD BE LIMITED TO NEAR THE UPR LOW AND AT THE NRN FRINGE OF THE MSTR SHIELD IF IT REACHES CLOSE TO THE CANADIAN BORDER. WITHIN A PATTERN OF ABOVE TO MUCH ABOVE NORMAL TEMPS OVER MOST AREAS E OF THE ROCKIES... THE UPR MS VLY CONTINUES TO BE THE EXPECTED FOCUS FOR HIGHEST ANOMALIES... AVERAGING PLUS 25-35F FOR MINS OVER THE 5-DAY PERIOD. THERE MAY BE MULTIPLE DAYS WITH MORNING LOWS NEAR OR ABOVE RECORD WARM VALUES. RAUSCH