EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 145 AM EST FRI FEB 02 2018 VALID 12Z MON FEB 05 2018 - 12Z FRI FEB 09 2018 ...OVERVIEW... LATEST GUIDANCE SHOWS A CONTINUATION OF THE SHORT RANGE PATTERN, FEATURING A STRONG EASTERN PACIFIC RIDGE ALOFT AND FAIRLY AMPLIFIED CYCLONIC FLOW OVER MUCH OF THE LOWER 48 STATES/CANADA WITH PERIODIC EAST PACIFIC SHORTWAVES GENERATING SURFACE SYSTEMS AS THEY CONTINUE INLAND. FLOW WITHIN THE CANADIAN STREAM MAY ALSO HAVE SOME INFLUENCE ON SYSTEM EVOLUTION. THE FIRST FEATURE IN THE SERIES WILL BE DEPARTING FROM NEW ENGLAND ON DAY 3 MON. THE NEXT SYSTEM SHOULD CROSS THE WESTERN-CENTRAL U.S. MON-TUE AND THEN TRACK NORTHEASTWARD OVER THE EASTERN STATES BY DAY 5 WED. THERE IS LESS CONSENSUS THUS FAR FOR A TRAILING SYSTEM THAT MAY EXIST DURING THE LATTER HALF OF THE WEEK. ...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES... IN MOST RESPECTS A BLEND OF OPERATIONAL GUIDANCE REPRESENTED CONSENSUS IDEAS WITH MINIMAL ADJUSTMENT TO CONTINUITY FOR THE EARLY TO MIDDLE PART OF THE FORECAST. FOR THE LEADING SYSTEM EXITING THE NORTHEAST BY AROUND THE START OF THE PERIOD EARLY MON, THERE HAVE BEEN SOME SIGNIFICANT TRENDS FOR IMPORTANT ASPECTS OF DEVELOPMENT OVER THE PAST COUPLE DAYS BUT LATEST SOLUTIONS ARE SIMILAR ASIDE FROM MINOR DETAILS THAT CAN STILL TAKE A PORTION OF THE SHORT RANGE TIME FRAME TO BE RESOLVED. GUIDANCE SPREAD FOR THE MON-TUE ROCKIES/PLAINS SYSTEM REACHING THE EAST BY WED--SUPPORTED BY A SHORTWAVE REACHING THE NORTHWEST AS OF EARLY MON--HAS NARROWED CONSIDERABLY OVER THE PAST 24 HOURS. HOWEVER THE BEHAVIOR OF THE PRECEDING SYSTEM AS WELL AS A FAIR AMOUNT OF LINGERING MODEL AND ENSEMBLE SPREAD FOR EXACT TIMING/ORIENTATION OF SHORTWAVE ENERGY BY WED SUGGEST THERE IS STILL THE RISK THAT MEANINGFUL CONTINUITY CHANGES MAY OCCUR IN FUTURE RUNS. AS DIFFERENCES BECOME NOTICEABLE OVER THE EAST, PREFER AN INTERMEDIATE SOLUTION AS YESTERDAY'S 00Z/12Z ECMWF RUNS ARE ON THE STRONG/WESTERN SIDE OF THE SPREAD (AND WEST OF THE ECMWF MEAN) WHILE THE NEW 00Z GFS IS ON THE EASTERN SIDE OF THE ENVELOPE. THE 12Z/18Z GFS WERE A LITTLE CLOSER TO THE MIDDLE OF THE SPREAD. UKMET/CMC RUNS OFFER THE POSSIBILITY FOR SLIGHTLY SLOWER TIMING OVER THE EAST BUT WITH INTERMEDIATE TRACK. UNCERTAINTY INCREASES TO A GREATER EXTENT BEHIND THIS SYSTEM AS THERE IS A FAIRLY WIDE SPREAD WITH RESPECT TO TIMING AND OTHER DETAILS OF THE NEXT SHORTWAVE PROGRESSING AROUND THE EAST PACIFIC RIDGE AROUND MIDWEEK. BASED ON GUIDANCE THROUGH THE 12Z/18Z CYCLES, THE 12Z/18Z GFS AND 00Z/01 ECMWF RUNS WERE CLOSEST IN PRINCIPLE TO THE 12Z/18Z GEFS AND 12Z ECMWF MEANS WITH A SYSTEM REACHING THE NORTHERN TIER BY LATE IN THE WEEK--WITHIN THE GENERAL AREA OF LOWER PRESSURES SUGGESTED IN THE MEANS BY FRI. THE 12Z ECMWF IS FASTER DUE IN PART TO A BRIEF FLATTENING OF THE UPSTREAM RIDGE NOT INDICATED BY MOST OTHER MODELS/MEANS. ON THE OTHER SIDE OF THE SPECTRUM SOME INDIVIDUAL ENSEMBLES (MORE FROM THE CMC THAN GEFS/ECMWF) AS WELL AS THE NEW 00Z GFS SHOW POTENTIAL FOR GREATER AMPLIFICATION OF INCOMING SHORTWAVE ENERGY OVER THE WEST, WHICH WOULD LEAD TO DIFFERING SURFACE EVOLUTION. THUS CONFIDENCE IN FORECAST SPECIFICS DECREASES CONSIDERABLY BY NEXT THU-FRI IN SPITE OF THE MUCH BETTER CONFIDENCE IN THE OVERALL MEAN PATTERN. WITH THE ABOVE CONSIDERATIONS IN MIND, THE DAYS 6-7 THU-FRI FORECAST BROUGHT TOTAL ENSEMBLE MEAN WEIGHT TO 60 PERCENT WITH REMAINING INPUT FROM THE 12Z/18Z GFS AND 00Z/01 ECMWF. ...WEATHER HIGHLIGHTS/THREATS... ACROSS THE WEST EXPECT MOST PRECIP DURING THE PERIOD TO BE CONFINED TO SNOW AND LOW ELEVATION RAIN OVER THE PACIFIC NORTHWEST AND NORTHERN-CENTRAL ROCKIES, WITH HIGHEST TOTALS OVER FAVORED WINDWARD TERRAIN. ACTIVITY SHOULD TEND TO BECOME LIGHTER/MORE SCATTERED TOWARD WED-THU BUT LATE WEEK DETAILS BECOME MORE UNCERTAIN GIVEN FORECAST SPREAD FOR INCOMING SHORTWAVE ENERGY. EAST OF THE ROCKIES A BAND OF MOSTLY LIGHT SNOW MAY CROSS THE NORTH-CENTRAL STATES EARLY IN THE WEEK. THEN LOW PRESSURE EMERGING OVER THE PLAINS BY TUE AND TRACKING THROUGH THE EAST AROUND WED WILL GENERATE A BROAD AREA OF VARIOUS PRECIP TYPES OVER THE EASTERN HALF OF THE U.S. EXPECT A BAND OF MEANINGFUL SNOW TO THE NORTH/WEST OF THE SURFACE LOW CENTER, WITH A MOST LIKELY AXIS FROM THE LOWER GREAT LAKES AND/OR UPPER OH VALLEY INTO NEW ENGLAND/SOUTHEASTERN CANADA. SOME OF THE SNOW MAY EXTEND BACK INTO THE CENTRAL PLAINS. MEANWHILE THERE IS POTENTIAL FOR OVER THE LOWER MS VALLEY INTO THE TN VALLEY. SOME OF THIS MOISTURE SHOULD EXTEND TO THE EAST/NORTHEAST. THE MEAN PATTERN ALOFT WILL KEEP TEMPS QUITE WARM OVER THE WEST THROUGH THE PERIOD WITH SOME AREAS SEEING PLUS 10-20F ANOMALIES ON MULTIPLE DAYS. POTENTIAL FOR DAILY RECORD MAX/WARM MIN VALUES AT SOME LOCATIONS SHOULD BE BEST DURING THE LATTER HALF OF THE WEEK. TO THE EAST OF THE ROCKIES EXPECT THE COLDEST TEMPS TO BE ANCHORED OVER THE NORTHERN PLAINS MON-WED WITH SOME READINGS 10-20F BELOW NORMAL. THE PLAINS INTO EASTERN U.S. SYSTEM WILL BRING A BRIEF EPISODE OF WARMER TEMPS TO THE SOUTH AND EAST AROUND MIDWEEK BEFORE BRINGING COLDER TEMPS INTO THE EAST FOR THU-FRI. BY THAT TIME THE CORE OF COLDEST READINGS WILL BE SENSITIVE TO EXACT LOCATION OF NEW SNOW COVER. MEANWHILE THE PLAINS SHOULD SEE A WARMING TREND BY THU-FRI. RAUSCH