EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1156 AM EDT THU APR 09 2015 VALID 12Z SUN APR 12 2015 - 12Z THU APR 16 2015 ...OVERVIEW... FCST CONFIDENCE CONTINUES TO INCREASE AS MOST GUIDANCE APPEARS TO BE IN THE PROCESS OF CONVERGING FOR LARGE TO MEDIUM SCALE DETAILS. THIS IS A WELCOME TREND AFTER THE SIGNIFICANT SPREAD AND RUN TO RUN VARIABILITY SEEN OVER RECENT DAYS. THERE WILL BE THREE PRIMARY FEATURES OF INTEREST DURING THE PERIOD... A NRN STREAM TROUGH PROGRESSING EWD FROM THE PLAINS... A COMPACT TROUGH/UPR LOW TRACKING NEWD FROM EXTREME NWRN MEXICO... AND AN AMPLIFYING TROUGH REACHING THE WEST COAST AROUND MON NIGHT-TUE AND CONTINUING INTO THE WRN HALF OF THE CONUS THEREAFTER. ...GUIDANCE EVALUATION AND PREFERENCES... WITH THE NRN STREAM TROUGH PROGRESSING ACROSS THE NRN TIER CONUS/SRN CANADA... LATEST RECENT TRENDS HAVE PRIMARILY BEEN TOWARD A LITTLE GREATER AMPLITUDE. THIS SUPPORTS A SOMEWHAT FARTHER SWD LATITUDE FOR THE SFC FRONT EXPECTED TO SETTLE OVER THE ERN HALF OF THE LOWER 48 EARLY NEXT WEEK AND THEN SOMEWHAT SLOWER NWD PROGRESSION AS A WARM FRONT TO THE W OF THE APLCHNS. PRIMARILY BY SLOWER ECMWF TRENDS OVER THE PAST TWO DAYS THERE IS NOW REASONABLY GOOD AGREEMENT FOR THE TIMING/TRACK OF THE COMPACT UPR TROUGH/EMBEDDED LOW EXPECTED TO PROGRESS FROM EXTREME NWRN MEXICO INTO THE PLAINS... WITH A CONSENSUS BLEND LOOKING GOOD FOR BOTH THIS FEATURE AND THE NRN STREAM TROUGH DESCRIBED ABOVE. FOR THE AMPLIFYING WRN TROUGH TUE-THU... OPERATIONAL MODEL RUNS ARE STILL SHOWING GREATER POTENTIAL FOR AN EMBEDDED LOW TO CLOSE OFF RELATIVE TO THE ENSEMBLE MEANS BUT SEEM TO WAIT UNTIL THE TROUGH REACHES A LITTLE FARTHER EWD BEFORE CLOSURE OCCURS. MEANWHILE THE ENSEMBLE MEANS HAVE GENERALLY STABILIZED IN TERMS OF STRENGTH/AMPLITUDE VERSUS THE PREVIOUS COUPLE DAYS WHEN THERE WAS A STRONGER TREND. AT THE MOMENT THE 06Z GEFS MEAN IS THE ONLY SOLN THAT APPEARS MORE QUESTIONABLE RELATIVE TO OTHER GUIDANCE AS IT SHOWS FASTER PROGRESSION OF FEATURES FROM THE ERN PAC THROUGH NOAM. THE FASTER SCENARIO SEEMS LESS LIKELY GIVEN THE INCREASINGLY HIGH AMPLITUDE OF THE OVERALL PATTERN. TELECONNECTIONS RELATIVE TO THE UPSTREAM RIDGE SUPPORT THE POSITIVELY TILTED OPEN TROUGH OF THE ENSEMBLE MEANS BUT WITH OPERATIONAL MODEL RUNS AT LEAST SIGNALING SOME CONCENTRATION OF EMBEDDED ENERGY FOR A TIME... AND A BETTER DEFINED SFC REFLECTION OVER THE PLAINS... MINORITY INCLUSION OF OPERATIONAL GUIDANCE APPEARS REASONABLE EVEN THROUGH DAY 7 THU. THE FAVORED CONSENSUS BLEND INCLUDES THE 00Z GFS/ECMWF AND THEIR RESPECTIVE ENSEMBLE MEANS WITH A LITTLE MORE WEIGHTING TOWARD THE OPERATIONAL RUNS FOR DAYS 3-5 SUN-TUE. OPERATIONAL WEIGHTING IS REDUCED MODESTLY FOR DAYS 6-7 WED-THU WITH THE 00Z NAEFS MEAN ADDED INTO THE ENSMEAN PART OF THE BLEND AS WELL. AS THE 06Z GFS/GEFS MEAN COMPARED LESS FAVORABLY TO THE FULL RANGE OF GUIDANCE IN SOME RESPECTS THEY WERE NOT INCLUDED IN THE BLEND. ...SENSIBLE WEATHER HIGHLIGHTS... MULTIPLE DAYS OF LOW LVL INFLOW FROM THE GULF OF MEXICO SHOULD SUPPORT AREAS OF HVY RNFL WITH HIGHEST TOTALS FOR THE FCST PERIOD EXPECTED FROM THE SERN PLAINS/WRN GULF COAST E-NE INTO THE TN VLY AND VICINITY. SUCH RNFL MAY BE PROBLEMATIC AT SOME LOCATIONS WHERE SIGNIFICANT RNFL HAS OCCURRED OVER RECENT WEEKS. MEANWHILE ENHANCED ACTIVITY MAY ALSO ACCOMPANY THE COMPACT UPR TROUGH/CLOSED LOW TRACKING FROM EXTREME NWRN MEXICO THROUGH THE SRN ROCKIES INTO THE CNTRL PLAINS. STRENGTHENING SYSTEM MOVING INTO THE WRN/CNTRL STATES WILL FIRST BRING RNFL AND HIGHER ELEV SNOW ACROSS THE NRN HALF OF THE WEST AND THEN SPREAD MSTR INTO THE NRN PLAINS AND PROMOTE A NWD PROGRESSION OF MSTR FARTHER EWD. WHETHER AND WHERE AN UPR LOW CLOSES OFF WITHIN THE TROUGH ALOFT... AN EVOLUTION THAT TYPICALLY HAS MEDIUM TO LOW PREDICTABILITY 6-7 DAYS OUT IN TIME... WILL BE CRUCIAL IN DETERMINING THE LOCATION AND EXTENT OF SIGNIFICANT PCPN FROM THE NRN ROCKIES INTO THE NRN PLAINS. TEMPS SHOULD AVG NEAR TO ABOVE NORMAL OVER THE CNTRL-ERN STATES FOR THE FCST PERIOD... WITH SOME REGIONS SEEING ONE OR MORE DAYS OF PLUS 10-20F ANOMALIES FOR MIN AND/OR MAX TEMPS. ANY DAILY RECORDS THAT OCCUR ARE MOST LIKELY TO BE OF THE WARM MIN VARIETY. THE WEST WILL BE WARM AS WELL EARLY IN THE PERIOD BUT THEN TREND MUCH COOLER AS THE UPR TROUGH MOVES INTO THE REGION. THIS COOLING TREND SHOULD EXTEND INTO THE PLAINS BY NEXT THU. RAUSCH