EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1050 AM EST SUN FEB 04 2018 VALID 12Z WED FEB 07 2018 - 12Z SUN FEB 11 2018 ...PATTERN OVERVIEW... MODELS AND ENSEMBLES GENERALLY AGREE IN MAINTAINING A STRONG MEAN EASTERN PACIFIC RIDGE WITH DOWNSTREAM TROUGHING COVERING A MAJORITY OF NORTH AMERICA. FINER DETAILS OF A MIDWEEK EASTERN U.S. SYSTEM ARE STILL IN THE PROCESS OF BEING RESOLVED BUT THE PRIMARY UNCERTAINTIES OF THE FORECAST CONTINUE TO INVOLVE ONE OR MORE BUNDLES OF SHORTWAVE ENERGY PROGRESSING AROUND/THROUGH THE EAST PACIFIC RIDGE AND CONTINUING INTO THE LOWER 48, WITH NORTHERN STREAM CANADIAN FLOW ALSO PLAYING A ROLE IN GUIDANCE SPREAD FOR INDIVIDUAL FEATURES. ...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES... GUIDANCE STILL SHOWS SOME SPREAD/TRENDING FOR SPECIFICS OF THE SYSTEM AFFECTING THE EAST WED INTO THU. COMPARING GUIDANCE THROUGH THE 12Z/18Z CYCLES, ENSEMBLES TEMPER CONFIDENCE IN SPECIFICS OF THE 12Z ECMWF OR 12Z/18Z GFS SOLUTIONS. SPECIFICALLY THE 12Z ECMWF IS A BIT ON THE FASTER SIDE OF THE SURFACE LOW SPREAD WITH ITS MEAN SLIGHTLY SLOWER. PREVIOUSLY FAST GFS RUNS HAVE SLOWED CONSIDERABLY BUT THE GFS HAS CONTINUED TO EXTEND LEADING HEIGHT FALLS ALOFT SOMEWHAT EAST OF CONSENSUS RESULTING IN A FARTHER EAST LOW TRACK. GEFS MEANS HAVE BEEN AT LEAST SOMEWHAT CLOSER TO OTHER GUIDANCE. THESE CONSIDERATIONS FAVOR A GENERAL MODEL/MEAN COMPROMISE. WITH THE ARRIVAL OF THE NEW 00Z GFS/GEFS MEAN AND UKMET/CMC, AGREEMENT IS IMPROVING WITH TIMING STILL SLOWER THAN THE 12Z ECMWF AND THE NEW GFS COMPARING BETTER TO CONSENSUS AT THE SURFACE AND ALOFT. DIFFERENCES FOR PACIFIC SHORTWAVE ENERGY HEADING INTO/AROUND THE RIDGE OFF THE WEST COAST BECOME NOTICEABLE ALREADY IN THE LATE SHORT RANGE TIME FRAME. THIS SEEMS TO REFLECT THE TENDENCY FOR MEDIUM-SMALLER SCALE SHORTWAVES AND DIFFICULTY IN FORECASTING ENERGY PASSING THROUGH/AROUND RIDGES TO KEEP PREDICTABILITY BELOW AVERAGE. AS THE ENERGY PROGRESSES INLAND, GUIDANCE DIVERGES IN TWO PRIMARY RESPECTS--ONE BEING THE TRACK AND TIMING OF LOW PRESSURE WHICH MOST GUIDANCE SUGGESTS WILL TRACK ACROSS THE NORTH-CENTRAL STATES EAST OF THE ROCKIES PLUS THE SOUTHWARD PUSH OF THE TRAILING FRONT, AND THE SECOND BEING THE AMPLITUDE OF POTENTIAL TROUGHING OVER THE WEST. FOR THE NORTHERN U.S. WAVE RECENT GFS RUNS HAVE BEEN ON THE SLOWER SIDE OF THE ENVELOPE WHILE THE ECMWF/CMC AND THEIR MEANS RESIDE ON THE FASTER BUT MAJORITY PART OF THE SPREAD. CONFIDENCE IS LOW IN ANY SPECIFIC SOLUTION GIVEN DEPENDENCE NOT ONLY ON THE PACIFIC ENERGY BUT ALSO SPECIFICS OF CANADIAN FLOW. MEANWHILE THERE IS STILL VERY WIDE MODEL/ENSEMBLE SPREAD ALOFT ACROSS THE WEST BY DAYS 5-7 FRI-SUN. CMC RUNS AND CORRESPONDING ENSEMBLES CONTINUE TO BE MOST AGGRESSIVE WITH DEEPENING A WESTERN TROUGH, WITH OPERATIONAL RUNS AND SOME MEMBERS CLOSING OFF AN UPPER LOW. AT THE SAME TIME A SOMEWHAT HIGHER PERCENTAGE OF 12Z ECMWF MEMBERS SUGGEST POTENTIAL FOR AN AMPLIFIED WESTERN TROUGH COMPARED TO GEFS MEMBERS. AS A RESULT BY LATE IN THE PERIOD, THE 12Z CMC MEAN HAS THE DEEPEST WESTERN TROUGH AMONG THE MEANS AND THE GEFS MEAN THE WEAKEST. ADDING TO THE COMPLEXITY OF THE FORECAST WILL LIKELY BE ANOTHER SHORTWAVE APPROACHING THE WEST COAST. THE 12Z ECMWF DOES NOT COMPARE WELL TO OTHER GUIDANCE FOR ITS FAST FRI-SAT FEATURE WHILE THERE IS A LITTLE MORE OF A SIGNAL FOR A SHORTWAVE ARRIVING AROUND DAY 7 SUN. ALBEIT WITH SOME SENSITIVITY TO THE EXACT POSITION OF THE POSITIVE HEIGHT ANOMALY CORE OVER THE EAST PACIFIC, TELECONNECTIONS RELATIVE TO THAT FEATURE ON AVERAGE STILL FAVOR BEST POTENTIAL FOR MODERATE TROUGHING SUCH AS REFLECTED BY A BLEND OF GEFS/ECMWF MEANS. BASED ON THE ABOVE CONSIDERATIONS, THE EARLY-MIDDLE PART OF THE FORECAST INCORPORATED EQUAL PARTS OF EACH SOLUTION AMONG THE 12Z ECMWF/GFS/UKMET AND 12Z GEFS/ECMWF MEANS TO PROVIDE THE CLOSEST REFLECTION OF CONSENSUS/INTERMEDIATE IDEAS. THEN THE FORECAST TRENDED TO THE ENSEMBLE MEANS EXCLUSIVELY BY DAY 7 SUN. ...WEATHER HIGHLIGHTS/THREATS... THE MIDWEEK SYSTEM AFFECTING THE EAST WILL LIKELY BRING SIGNIFICANT SNOWFALL TO PORTIONS OF THE NORTHEAST, WITH BEST PROBABILITIES FOR HIGHEST TOTALS OVER INTERIOR LOCATIONS. TYPICAL GUIDANCE ERROR 3-4 DAYS OUT IN TIME ALLOWS FOR SOME FURTHER ADJUSTMENT IN EXACT SURFACE LOW TRACK/AXIS OF HEAVIEST SNOW. IN THE WARM SECTOR EXPECT SOME AREAS OF LOCALLY HEAVY RAINFALL TO CROSS THE SOUTHEAST/SOUTHERN MID ATLANTIC WITH MORE MODERATE ACTIVITY FARTHER NORTH. BEHIND THIS SYSTEM, SHORTWAVE ENERGY COMING INTO THE NORTHWEST SHOULD HELP TO GENERATE A WAVE AND ASSOCIATED PRECIP STREAMING EASTWARD FROM THE NORTHERN ROCKIES THROUGH THE GREAT LAKES/NORTHEAST. A MAJORITY OF THIS PRECIP SHOULD FALL IN THE FORM OF SNOW ASIDE FROM PERHAPS THE SOUTHERN PERIPHERY OF THE MOISTURE SHIELD. FARTHER SOUTH, FROM LATE WEEK INTO THE WEEKEND RAINFALL SHOULD DEVELOP OVER THE SOUTHEAST PLAINS/LOWER MS VALLEY AND THEN EXTEND NORTHEASTWARD. UNCERTAINTY WITH DETAILS OF FLOW ALOFT BY THAT TIME MAKE IT DIFFICULT TO PINPOINT TIMING AND INTENSITY BUT THERE IS POTENTIAL FOR SOME OF THIS ACTIVITY TO BE LOCALLY HEAVY. IT IS POSSIBLE THAT WINTRY PRECIP TYPES MAY EXIST IN THE NORTHWEST FRINGE OF THIS MOISTURE DEPENDING ON SOUTHEASTWARD EXTENT OF COLD AIR. THE WESTERN STATES SHOULD SEE WARMEST TEMPS IN THE WED-FRI TIME FRAME WITH DECENT COVERAGE OF PLUS 10-20F ANOMALIES. BEST POTENTIAL FOR ISOLATED RECORD VALUES SHOULD BE ON THU. BY NEXT WEEKEND THERE SHOULD BE A COOLING TREND BUT WITH TEMPS MOST LIKELY REMAINING SOMEWHAT ABOVE NORMAL, BUT THERE IS CONSIDERABLE SENSITIVITY TO THE DEGREE OF TROUGHING ALOFT. MEANWHILE EXPECT THE COLDEST TEMPS RELATIVE TO NORMAL TO BE OVER THE PLAINS WITH ONE OR MORE DAYS OF READINGS AT LEAST 10-20F BELOW NORMAL. RAUSCH/HAMRICK