EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1051 AM EST TUE DEC 22 2015 VALID 12Z FRI DEC 25 2015 - 12Z TUE DEC 29 2015 ...EXCESSIVE RAIN THREAT FROM THE S-CENTRAL US TO MID-LOWER MS/OH VALLEYS... ...S-CENTRAL ROCKIES TO N-CENTRAL US HEAVY SNOW THREAT... ...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER HIGHLIGHTS... A COMBINATION OF S-CENTRAL TO E-CENTRAL US FRONTO/CYCLOGENSIS AND LEADING RETURN OF DEEP LAYERED GULF MOISTURE IS EXPECTED TO FUEL AN EXTENDED PERIOD FAVORABLE FOR REPEAT/TRAINING OF CONVECTIVE AND OVERRUNNING RAINFALL ACTIVITY HEADING THROUGH THIS WEEKEND AND CONTINUING THROUGH EARLY NEXT WEEK. THIS OCCURS IN RESPONSE TO THE SUBSEQUENT GRADUAL EJECTION INTO THE S-CENTRAL THEN E-CENTRAL US OF AMPLIFIED MID-UPPER LEVEL TROUGH ENERGIES THAT DIG INTO THE SWRN US INTO THIS WEEKEND. RECENT TRENDS OF THE GFS/GFSP AND TO A LESSER EXTENT THE GEFS HAVE BEEN DOWNPLAYED IN FAVOR OF LESS PROGRESSIVE/MORE AMPLIFIED FLOW EVOLUTION SPEARHEADED BY THE 12/00 UTC ECMWF AND ECMWF ENSEMBLES. THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A BLEND OF 60 PERCENT ECMWF ENSEMBLE MEAN ALONG WITH 20 PERCENT EACH OF YESTERDAYS 12 UTC ECMWF AND OVERNIGHT WPC CONTINUITY WHOSE FORECAST FIELDS SEEM TO CLUSTER QUITE WELL. SUSPECT THAT KICKER ENERGIES SHOULD BE LESS AGGRESSIVELY WORKING INLAND ACROSS THE WEST COAST THROUGH AN AMPLIFIED UPSTREAM MID-UPPER LEVEL RIDGE TO SUPPORT THIS. THIS SOLUTION MAINTAINS GOOD WPC CONTINUITY IN A PATTERN WITH AT LEAST AVERAGE PREDICTABILITY. IN THIS SCENARIO...A MAIN THREAT AREA FOR EXCESSIVE RAINS WOULD FOCUS FROM THE S-CENTRAL US NEWD THROUGH THE MID-LOWER MS/OH VALLEYS. MEANWHILE...A SECONDARY NRN STREAM PLAINS FRONTAL SURGE WILL ENHANCE UPSLOPE FETCH AND COMBINE WITH FAVORABLE AN QUITE AMPLIFIED SRN STREAM TROUGH BASED FLOW ALOFT TO SUPPORT ENHANCED SOUTH-CENTRAL ROCKIES SNOWS THIS WEEKEND. A PRIMARY HEAVY SNOW AND TRANSITIONAL ICING THREAT WILL ADDITIONALLY WORK NEWD ACROSS THE CENTRAL PLAINS WITH WRAP-BACK SNOWS LIFTING NEWD TO THE UPPER MIDWEST EARLY NEXT WEEK WITH DEVELOPMENT AND EJECTION OF TROUGH/LOW ENERGIES ALOFT AND AT THE SURFACE. SCHICHTEL