EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 233 AM EDT WED MAY 14 2014 VALID 12Z SAT MAY 17 2014 - 12Z WED MAY 21 2014 ...OVERVIEW AND PREFERENCES... LARGE SCALE ASPECTS OF THE MEDIUM RANGE FCST ARE CURRENTLY FAIRLY STRAIGHTFORWARD. GUIDANCE AGREES UPON AN AMPLIFYING WRN TROUGH WITH AN EMBEDDED UPR LOW LIKELY TO BE POSITIONED OVER/NEAR THE GRTBASIN BY NEXT WED... WHILE ERN NOAM TROUGH ENERGY IS FCST TO CONSOLIDATE INTO AN UPR LOW THAT DRIFTS ACROSS AND JUST OFFSHORE THE NERN STATES. BETWEEN THESE FEATURES EXPECT A RIDGE TO PROGRESS FROM THE INTERIOR WEST TOWARD THE MS VLY. WITH THE 12Z GFS/GEFS MEAN GENERALLY FITTING CONSENSUS/TRENDS BETTER THAN THEIR 18Z VERSIONS... THEY ARE INCLUDED WITH THE 12Z ECMWF/ECMWF MEAN DURING DAYS 3-4 SAT-SUN TO YIELD A REASONABLE INTERMEDIATE SOLN FOR SYSTEMS OF INTEREST. PREFER THE ENSEMBLE MEANS WITH EQUAL WEIGHTING BY DAYS 5-7 MON-WED TO DOWNPLAY OPERATIONAL DETAILS THAT BECOME A LITTLE MORE UNCERTAIN WITH TIME. ...GUIDANCE EVALUATION... FOR THE WRN TROUGH THE MOST NOTABLE TRENDS IN BOTH THE GEFS AND ECMWF MEANS ARE TOWARD GREATER DEPTH AND AMPLITUDE WITH A HIGHER POTENTIAL FOR AN UPR LOW TO CLOSE OFF NEAR THE GRTBASIN BY DAY 7 WED. THE 12Z GEFS MEAN FITS THIS TREND AND THE 12Z ECMWF MEAN BETTER THAN THE 18Z RUN. GFS RUNS OVER THE PAST 24-36 HRS HAVE BEEN STEADIER WITH THE FCST SCENARIO IN PRINCIPLE. HOWEVER FASTER PROGRESSION OF LEADING HGT FALLS RESULT IN THE GFS BEING EXCLUDED FROM THE FAVORED BLEND AFTER DAY 4 AS THE ONGOING/DEVELOPING BLOCKING SHOULD KEEP PROGRESSION ON THE SLOWER SIDE. THE NEW 00Z GFS COMPARES BETTER TO OTHER GUIDANCE FOR THIS ASPECT OF THE FCST. MEANWHILE IT APPEARS UPSTREAM ISSUES LED THE OLD 00Z/13 ECMWF RUN TO HAVE A FLATTER THAN CONSENSUS TROUGH. THE 12Z ECMWF ADJUSTED BACK TOWARD CONSENSUS. THERE IS STILL SOME SPREAD AMONG ENSEMBLE MEMBERS OVER THE ERN PAC/WRN CONUS BUT LESS PRONOUNCED THAN SEEN YDAY. OVER RECENT DAYS THE GUIDANCE HAS BEEN WAFFLING SOMEWHAT REGARDING THE TRACK OF AN UPR LOW OVER THE NERN STATES INTO THE WRN ATLC. LATEST MAJORITY CLUSTER IS NEAR THE MIDDLE OF THE MULTI-DAY AVG OF GUIDANCE AND A LITTLE SWD FROM 24 HRS AGO. THE 12Z GEFS MEAN IS SOMEWHAT BETTER DEFINED SFC/ALOFT THAN THE 18Z RUN AND PROVIDES A BETTER BLENDING COMPANION TO THE 12Z ECMWF MEAN MID-LATE PERIOD. THIS FEATURE IS EXPECTED TO SUPPORT A PERSISTENT BUT RELATIVELY WEAK SFC LOW NOT FAR FROM SERN NEW ENGLAND. ...SENSIBLE WEATHER HIGHLIGHTS... THE TROUGH ALOFT SETTLING OVER THE WEST WILL SPREAD PCPN OF VARYING INTENSITY FROM THE NORTHWEST/GRTBASIN THROUGH THE NRN PLAINS AND PSBLY PARTS OF THE UPR MS VLY/GRTLKS. TERRAIN ENHANCEMENT OVER SOME AREAS ALONG WITH INCREASINGLY SLOW MOVEMENT OF THE SYSTEM LATER IN THE PERIOD MAY LEAD TO HVY PCPN TOTALS AT SOME LOCATIONS. SNOW SHOULD BE CONFINED TO HIGHEST ELEVS OF THE ROCKIES. NARROW BAND OF MDT-HVY RNFL ACCOMPANYING THE FRONT REACHING NEW ENGLAND BY THE WEEKEND SHOULD TREND LIGHTER BUT THE UPR LOW CROSSING THE NORTHEAST AND SFC WAVE LINGERING OFF THE SERN NEW ENGLAND COAST MAY KEEP AREAS OF RNFL OVER THE REGION FOR MULTIPLE DAYS. ONE OR MORE SHRTWV IMPULSES FLOWING AROUND THE WRN/SRN SIDE OF THE UPR LOW MAY ALSO HELP TO GENERATE SCT DIURNALLY ENHANCED SHWRS/TSTMS OVER THE EAST. BETWEEN THE TWO DOMINANT SYSTEMS EXPECT A FAIRLY NARROW BAND OF RNFL DURING THE FIRST HALF OF THE PERIOD FROM THE NRN-CNTRL ROCKIES/HIGH PLAINS SEWD. A SIGNIFICANT PORTION OF THE ERN HALF OF THE CONUS SHOULD SEE HIGHS 10-15F BELOW NORMAL SAT WITH STEADY MODERATION THEREAFTER. EXPECT TEMPS OVER WRN AREAS TO TREND BELOW NORMAL WITH THE DEEPENING TROUGH... WHILE WARMING OVER THE SRN HALF OF THE PLAINS SHOULD LEAD TO PLUS 10-15F ANOMALIES FOR HIGHS AT SOME LOCATIONS BY THE FIRST HALF OF NEXT WEEK. RAUSCH