EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1042 AM EST THU MAR 05 2015 VALID 12Z SUN MAR 08 2015 - 12Z THU MAR 12 2015 ...OVERVIEW... THE MODELS AND ENSEMBLE MEANS ARE AGREEABLE/CONSISTENT WITH THE MAIN THEMES OF THE LARGE SCALE PATTERN. THESE INCLUDE PROGRESSIVE NRN CONUS/SRN CANADA FLOW THAT SHOULD SUPPORT A SERIES OF SFC FRONTS... A SRN ROCKIES/PLAINS INTO MEXICO MEAN TROUGH AND STRONG RIDGE E OF THE BAHAMAS BTWN WHICH SHOULD LIE A WAVY SFC FRONT FROM JUST OFF THE SERN COAST SWWD THROUGH THE GULF OF MEXICO... AND AN ERN PAC UPR LOW INITIALLY NEAR 150W GRADUALLY TRACKING CLOSER TO THE WEST COAST. HOWEVER OVER THE PAST COUPLE DAYS THERE HAVE BEEN IMPORTANT DIFFS WITH AMPLITUDE/TIMING WITHIN THE CONSENSUS MEAN PATTERN... IMPACTING THE SENSIBLE WEATHER FCST FOR SOME AREAS. ...GUIDANCE EVALUATION/PREFERENCES... RECENT ISSUES WITH NRN STREAM FLOW HAVE TENDED TO ORIGINATE FROM TROUGH ENERGY OVER THE EXTREME NERN PAC EARLY IN THE PERIOD. GFS RUNS AND TO SOME EXTENT GEFS MEANS FROM THE PAST COUPLE DAYS HAVE BEEN MORE AMPLIFIED THAN MOST OTHER SOLNS WITH THIS TROUGHING AS IT PROGRESSES INTO AND ACROSS CANADA. THUS FAR TELECONNECTIONS RELATIVE TO THE MOST DOMINANT HGT ANOMALY CNTRS MID-LATE PERIOD AS WELL AS SLOW PROGRESSION OF THE ERN PAC UPR LOW/PERSISTENCE OF THE DOWNSTREAM RIDGE HAVE FAVORED LEANING AWAY FROM THE AMPLIFIED GFS TROUGH REACHING WRN CANADA... WITH MORE ENERGY LIKELY FEEDING INTO A FLAT TROUGH OVER ERN CANADA AND NERN QUADRANT OF THE LOWER 48. AMONG RECENT GEFS MEANS THE 00Z RUN COMES CLOSEST TO THE NON-GFS CLUSTER. THE SRN ROCKIES/PLAINS INTO MEXICO TROUGH SHOULD AMPLIFY DURING THE FIRST HALF OF THE PERIOD AND THEN BEGIN TO WEAKEN AS UPSTREAM FLOW BECOMES SOMEWHAT FLATTER. SLOWER GFS TRENDS WITH EJECTING INITIAL ENERGY HAVE BROUGHT GUIDANCE CLOSER TOGETHER RELATIVE TO 24 HRS AGO... THOUGH THE 00Z-06Z GFS/00Z CMC ARE STILL A LITTLE FASTER THAN OTHER SOLNS. A GUIDANCE AVG LOOKS REASONABLE FOR THE REST OF THE PERIOD. FOR THE SYSTEM APPROACHING THE WEST COAST THE 00Z ECMWF MEAN REVERSED ITS QUESTIONABLY FASTER TREND FROM THE 12Z CYCLE. THIS BRINGS THE ECMWF MEAN MORE IN LINE WITH OTHER ENSEMBLE MEANS BUT THE OPERATIONAL MODELS MAINTAIN A SLOWER AND BETTER DEFINED SYSTEM... CERTAINTY A PLAUSIBLE SCENARIO SINCE THE FEATURE SHOULD BE RELATIVELY DETACHED FROM THE WESTERLIES UNTIL LATE IN THE PERIOD. NOTE THAT THE 00Z ECMWF REFLECTS A SLOWER TREND FROM PRIOR RUNS AND THE CMC HAS ADJUSTED MUCH SLOWER OVER THE PAST 24 HRS. MOST GFS RUNS HAVE BEEN RELATIVELY SLOW OVER THE PAST DAY. COMBINING THE ABOVE CONSIDERATIONS YIELDS A STARTING FCST CONSISTING OF 40 PCT WEIGHTING OF THE 00Z ECMWF WITH EQUAL REMAINING PARTS OF THE 00Z GEFS MEAN/NAEFS MEAN/ECMWF MEAN. BY LATE IN THE PERIOD THE 00Z ECMWF FCST OVER THE ERN PAC IS SUFFICIENTLY WELL DEFINED TO HEDGE THE ERN PAC/WEST COAST PATTERN A LITTLE MORE TOWARD ITS SOLN THAN THE INDICATED WEIGHTING. ...SENSIBLE WEATHER HIGHLIGHTS... POTENTIAL CONTINUES TO EXIST FOR ONE OR MORE EPISODES OF ENHANCED RNFL FROM THE GULF COAST THROUGH THE SOUTHEAST AND PERHAPS EXTREME SRN MID ATLC. BEST FOCUS WILL BE WITH ONE OR MORE INDIVIDUAL SHRTWVS EJECTING FROM THE UPSTREAM MEAN TROUGH ALOFT AND ON THE COOL SIDE OF A WAVY FRONT EXTENDING FROM JUST OFF THE SERN COAST INTO THE GULF OF MEXICO. PERSISTENT SWLY FLOW ALOFT BTWN THE MEAN TROUGH AND RIDGE E OF THE BAHAMAS WILL PROVIDE A STEADY STREAM OF UPR LVL MSTR. LATE IN THE PERIOD SOME MSTR SHOULD BEGIN TO REACH THE WEST COAST AHEAD OF THE APCHG ERN PAC SYSTEM BUT WITH RELATIVELY LGT AMTS GIVEN PREFS FOR MODERATELY SLOW TIMING. ALSO BY NEXT WED-THU A FRONT DROPPING INTO THE NRN TIER/TRAILING UPSLOPE FLOW MAY SUPPORT LGT PCPN OVER THE NRN HIGH PLAINS/ROCKIES. ACROSS THE GRTLKS/NEW ENGLAND EXPECT THE SERIES OF FRONTAL PASSAGES TO BRING AT LEAST A COUPLE PERIODS OF MOSTLY LGT SNOW. FOR TEMPS THE MOST PROMINENT TREND WILL BE STEADILY INCREASING COVERAGE OF ABOVE NORMAL READINGS AS THE MEAN PATTERN ALOFT BECOMES FLATTER. COOLEST ANOMALIES OF MINUS 10-20F FOR DAYTIME HIGHS SHOULD BE OVER THE SRN PLAINS/LWR MS VLY SUN-MON. LOCATIONS FROM THE WRN STATES THROUGH THE NRN-CNTRL PLAINS INTO UPR MS VLY SHOULD SEE THE MOST PERSISTENT WARMTH... WITH SOME PLUS 10-20F ANOMALIES ON MULTIPLE DAYS. THE NRN TIER SHOULD RETURN CLOSER TO NORMAL BY NEXT THU THOUGH. RAUSCH