EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 200 AM EST TUE DEC 23 2014 VALID 12Z FRI DEC 26 2014 - 12Z TUE DEC 30 2014 WPC MEDIUM RANGE SURFACE PRESSURES/FRONTS AND 500 MB PROGS WERE COMPOSED FROM A COMPOSITE BLEND OF THE 18 UTC GFS/GEFS MEAN AND 12 UTC ECMWF/ECMWF ENSEMBLE MEAN. FORECAST CLUSTERING HAS IMPROVED OVER THE PAST FEW GUIDANCE CYCLES TO MORE AVERAGE LEVELS...AT LEAST AT MID-LARGER SCALES. LEANED A TAD MORE IN THE BLEND TOWARD THE GFS/ECMWF FRI/SAT AND THE ENSEMBLE MEANS SUN-NEXT TUE CONSISTENT WITH UNCERTAINTY. INITIALLY AMPLIFIED SRN STREAM MID-UPPER LEVEL TROUGHING EJECTS OUT FROM THE WRN US AND OVER THE S-CENTRAL US THIS WEEKEND BEFORE CHANNELING NEWD BETWEEN A MEAN SERN US RIDGE ALOFT AND MORE COMPLEX NRN STREAM TROUGHING EMERGING FROM S-CENTRAL/ERN CANADA INTO THE NRN TIER OF THE CENTRAL AND NERN US. THESE SHOULD COMBINE TO SUPPORT A ORGANIZED AND WAVY FRONTAL PROGRESSION AND PCPN FOCUS OVER THE CENTRAL AND ERN US AS MOISTURE MODESTLY REBOUNDS INLAND FROM THE GULF OF MEXICO. EXPECT SOME SNOW OVER THE NRN PERIPHERY OF THE PCPN SHIELD AND ONE GUIDANCE ISSUE CONCERNS THE EXTENT OF LOW DEVELOPMENT AROUND SUN OVER THE SERN/ERN US WITH THE BLEND AVERAGING THE DEEPER ECMWF WITH LESSER OPTIONS BUT MAINTAINING SOME THREAT. MEANWHILE UPSTREAM...UNSETTLING AND PCPN FOCUSING MID-UPPER LEVEL TROUGH ENERGY DIGS SEWD FROM THE NERN PACIFIC BACK INTO THE WETTENED NWRN US THIS WEEKEND THAT THEN REVIVES AN AMPLIFIED WRN US MID-UPPER LEVEL TROUGH POSITION REBUILT INTO EARLY NEXT WEEK...SPREADING COOLING/PCPN EVER INLAND. SCHICHTEL