EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT MON APR 18 2016 VALID 12Z THU APR 21 2016 - 12Z MON APR 25 2016 ...OVERVIEW... THE THU-MON PERIOD WILL FEATURE THE ESTABLISHMENT OF A MEAN TROUGH OVER THE WEST... STEADY PROGRESSION OF AN INITIAL INTERIOR WEST/ROCKIES RIDGE AND PLAINS/MS VLY TROUGH... AND LIKELY LOWERING OF HGTS OVER THE NORTHEAST IN RESPONSE TO A STRONG RIDGE OVER/SE OF SERN GREENLAND. THE MOST MEANINGFUL DETAIL DIFFS ARE WITHIN THE WRN MEAN TROUGH AND DEVELOPING NERN CONUS CYCLONIC FLOW. ...GUIDANCE EVALUATION/PREFERENCES... THROUGH THE 06Z CYCLE... THE 00Z ECMWF/ECMWF MEAN OVERALL PROVIDED THE MOST CONSISTENT GUIDANCE RELATIVE TO CONTINUITY AND LEANED IN THE DIRECTION FAVORED BY FULL GUIDANCE EVALUATION. THEREFORE THE PRIOR WPC FCST WAS BLENDED PRIMARILY WITH THOSE TWO SOLNS TO MAINTAIN A SIMILAR EVOLUTION THROUGH THE PERIOD. WITHIN THE WRN TROUGH SIGNIFICANT DIFFS ARISE ALREADY BY EARLY DAY 4 FRI DUE IN PART TO DETAILS UPSTREAM IN THE NRN PAC. BY SAT 00Z/06Z GFS RUNS AND 00Z CMC TRACK A CLOSED LOW WELL SWD OF THE ECMWF-BASED GUIDANCE. INDIVIDUAL MEMBERS FROM EACH OF THE 00Z ENSEMBLE PACKAGES ALLOW FOR THE FARTHER SWD TRACK. HOWEVER AS RECENTLY AS 24-48 HRS AGO GFS RUNS WERE TRACKING THIS ENERGY TO THE N OF ECMWF RUNS. FAST APPROACH OF UPSTREAM FLOW SEEMS TO FAVOR SOMEWHAT MORE PROGRESSION THAN THE LATEST GFS RUNS SO WILL MAINTAIN A FCST CLOSEST TO THE ECMWF/ECMWF MEAN ALBEIT WITH ONLY MODERATE CONFIDENCE GIVEN CURRENT SPREAD. TOWARD THE END OF THE PERIOD THERE IS ALSO CONSIDERABLE SPREAD WITH THE NEXT TROUGH AMPLIFYING INTO THE WEST. THE CONTINUITY/EC-EC MEAN COMPROMISE PROVIDES AN INTERMEDIATE TRACK FOR THE CORE OF THE UPR TROUGH/PSBL EMBEDDED LOW BY DAY 7 MON... BTWN THE MORE NRN GFS AND ENSEMBLE MEAN RUNS AND SRN 00Z ECMWF/CMC. ISSUES WITH THE WRN TROUGH BECOME SIGNIFICANT OVER THE PLAINS BY SUN-MON AS THE LOWER-PROBABILITY CLUSTER OVER THE WEST MID-PERIOD WOULD LEAD TO STRONGER DYNAMICS REACHING THE CNTRL-SRN PLAINS. FOR THE INITIAL TROUGH CROSSING THE EAST THE 06Z GFS HAS MADE A FAVORABLE SLOWER ADJUSTMENT TOWARD CONSENSUS VS THE 00Z RUN BUT THE ASSOC SFC WAVE MAY STILL BE A LITTLE FAST. STRONG RIDGE OVER/SE OF GREENLAND SUPPORTS THE GENERAL IDEA OF FAIRLY DEEP TROUGHING OVER THE NERN CONUS AND ERN CANADA. THE 06Z GFS/GEFS MEAN APPEAR TO HAVE THEIR ELONGATED TROUGH AXIS TOO FAR NWD. THE ECMWF/ECMWF MEAN OFFER THE MOST REASONABLE FCST AT THIS TIME WHILE THE 00Z GFS MAY BE ON THE DEEP SIDE AND THE 00Z CMC ON THE SRN SIDE WITH THEIR RESPECTIVE UPR LOWS. MULTI-DAY MEANS AT D+8 REFLECT THE STRONG CORE OF POSITIVE HGT ANOMALIES JUST SE OF GREENLAND AND A LESS PRONOUNCED NEG ANOMALY CENTER TO THE S OF THE ALEUTIANS. TELECONNECTIONS RELATIVE TO BOTH ANOMALIES SUPPORT ERN CONUS TROUGHING... CORRESPONDING TO A MODERATELY SUPPRESSED MEAN SFC FRONT... BUT GIVE MIXED MESSAGES OVER THE WEST WITH A TENDENCY FOR MODERATE TO LOWER AMPLIFIED FLOW. ...SENSIBLE WEATHER HIGHLIGHTS... PROGRESSION/EVOLUTION OF THE PATTERN OVER THE WEST/PLAINS WILL ULTIMATELY PUSH INITIAL WRN WARMTH INTO THE PLAINS WHILE THE WRN STATES TREND STEADILY COOLER AND MORE UNSETTLED WITH INCREASING COVERAGE OF PCPN. PARTS OF THE NORTHWEST/NRN ROCKIES MAY SEE HIGHS 15-25F ABOVE NORMAL THU-FRI. EXPECT MOST OF THE WEST TO SEE BELOW NORMAL HIGHS BY NEXT MON. COOLER AIR WILL PUSH INTO THE NRN PLAINS AFTER FRI SO THE CNTRL PLAINS SHOULD SEE THE MOST PERSISTENT WARMTH FROM THE WEEKEND INTO EARLY NEXT WEEK. ACROSS THE PLAINS INTO THE UPR MS VLY THERE WILL LIKELY BE ONE OR MORE AREAS OF ORGANIZED ENHANCED RNFL... UNCERTAINTY OVER SPECIFICS OF IMPORTANT DETAIL DIFFS ALOFT REDUCES CONFIDENCE IN PINPOINTING WHERE THESE AREAS WILL BE AT THIS TIME. FRONTAL SYSTEM CROSSING THE EAST WILL BRING RAIN OF VARYING INTENSITY THU-FRI WITH DRIER WEATHER AFTER ITS DEPARTURE. THE ONE EXCEPTION MAY BE WITH A NARROW BAND OF RNFL ALONG A MEAN FRONTAL BNDRY SETTING UP ON THE SRN PERIPHERY OF THE DEVELOPING NERN TROUGH ALOFT. BY THE LATTER HALF OF THE PERIOD THIS FRONT EXTENDING EWD/SEWD FROM THE N-CNTRL PLAINS SHOULD BE FAIRLY STRONG... WITH SOME WARM ANOMALIES PSBLY EXCEEDING 10F TO THE S AND SIMILAR COOL EXTREMES TO THE N. UNCERTAINTY IN EXACT POSN OF THIS FRONT LEADS TO CONSIDERABLE SPREAD FOR ENSEMBLE TEMP FCSTS... AS MUCH AS 30-40F AT SOME LOCATIONS. RAUSCH