EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM EST SAT MAR 01 2014 VALID 12Z TUE MAR 04 2014 - 12Z SAT MAR 08 2014 ..ACTIVE/WET NW US WINTER FLOW AS CENTRAL/ERN US ARCTIC FREEZE LEADS TO A SE/ERN US STORM.. ...PATTERN OVERVIEW AND PREFERENCES... FORECAST CONTINUITY IS OVERALL PRETTY GOOD...ALBEIT WITH LINGERING DIFFERENCES WITH IMPORTANT SMALLER SCALE SYSTEM VARIANCES THAT FOCUS SENSIBLE WEATHER LOCALLY. FOR MOST OF THE PERIOD EXPECT TWO PRIMARY STREAMS... ONE FROM THE PACIFIC ACROSS THE LOWER 48 AND ANOTHER ACROSS SRN CANADA/NRN CONUS. GUIDANCE MAINTAINS AGREEMENT IN PRINCIPLE UPON TWO PRIMARY TROUGHS WITHIN THE PAC/CONUS STREAM. THE LEADING ONE SHOULD AMPLIFY INTO THE PLAINS/SOUTHEAST WED-FRI AND SUPPORT A SIGNIFICANT STORM SYSTEM TRACKING FROM THE GULF NEWD UP OFF THE EAST COAST OVER THE WRN ATLC. THEN A PACIFIC TROUGH SHOULD REACH THE WEST COAST AROUND THU AND CONTINUE INTO THE ROCKIES/PLAINS FRI-SAT... BRINGING ACTIVE WEATHER FROM PARTS OF THE WEST INTO THE CNTRL US. BEHIND THIS SYSTEM A DRYING RIDGE ALOFT SHOULD BUILD INTO THE WEST NEXT SAT. THE DETERMINISTIC MODELS AND INDIVIDUAL ENSEMBLE MEMBERS STILL DISPLAY SOME SPREAD AND RUN TO RUN VARIABILITY WITH BOTH SYSTEMS...INCLUDING ASPECTS OF NRN STREAM FLOW THAT WILL LIKELY PLAY A PART IN THE ULTIMATE EVOLUTION. HOWEVER...FORECAST SPREAD AND UNCERTAINTY CERTAINLY OVERALL SEEMS DECREASED FROM PRIOR LEVELS. PRIOR WPC GUIDANCE PACKAGES FAVORED AN ENSEMBLE MEAN EMPHASIS...BUT OPT TO INCORPORATE MORE DETERMINITIC MODEL INPUT TODAY AS THE 00 UTC GFS/ECMWF IN PARTICULAR HAVE CONVERGED UPON A MORE COMPATABLE MASS FIELD SOLUTION OVERALL CONSISTENT WITH THE MAIN ENSEMBLE MEMBER CLUSTERINGS AND WPC CONTINUITY. WPC ALSO INCLUDED INTO THE MIX A SMALLER PORTION OF THE 00 UTC ECMWF ENSEMBLE MEAN TO ADDRESS LINGERING UNCERTAINIES. ...GUIDANCE EVALUATION... WITH THE TROUGH AMPLIFYING INTO THE SOUTHEAST RECENT ECMWF RUNS CONTINUE TO BE THE MOST ENTHUSIASTIC IN CLOSING OFF AN UPR LOW BUT WITH SOME RUN TO RUN TIMING DIFFS THAT AFFECT THE ASSOC SFC LOW AS WELL. GFS/GEFS MEAN RUNS HAVE BEEN LESS CONSISTENT WITH THE DEGREE TO WHICH MID LVL FLOW MAY SEPARATE AND THUS MORE VARIABLE WITH THEIR SFC SOLNS...BUT ARE CERTAINLY TRENDING IN LINE. ALSO AFFECTING THE FCST TO SOME DEGREE IS SRN CANADA/NRN CONUS FLOW. OF THE ENSEMBLE SYSTEMS...THE ECMWF MEAN HAS BEEN QUITE CONSISTENT AND OFFERS A SOLUTION AMPLITUDE MOST IN LINE WITH THE 00 UTC GFS/ECWMF...WITH THE 06 UTC GEFS COMING INCREASINGLY IN THE FOLD. MEANWHILE LATEST SOLNS FOR THE ERN PAC TROUGH HEADING TOWARD AND INTO THE WEST DISPLAY MEDIUM TO SMALLER SCALE DETAIL DIFFS THAT ARE TYPICALLY DIFFICULT TO RESOLVE IN THE DAYS 4-6 TIME FRAME... FAVORING A COLLECTIVE 00 UTC GFS/ECMWF AND ENSEMBLE MEAN EMPHASIS. GIVEN THE AMPLIFYING RIDGE EXPECTED TO REACH THE WEST COAST BY DAY 7 SAT AS WELL AS ECMWF MEAN CONTINUITY THAT IS A LITTLE SLOWER THAN THE GEFS MEANS... WOULD PREFER GREATER WEIGHTING OF THE ECMWF MEAN IN THAT MIX BY THE LATTER HALF OF THE PERIOD. ...SENSIBLE WEATHER HIGHLIGHTS... AREAS FROM THE PAC NW AND NRN CA INTO THE NRN ROCKIES SHOULD SEE PERIODS OF LOCALLY MDT-HVY RNFL AND HIGHER ELEV SNOW DURING TUE-THU. AS THE APPROACHING TROUGH ALOFT MOVES INTO THE WEST/PLAINS AND A RIDGE TAKES ITS PLACE... EXPECT SOME OF THIS MSTR TO EXTEND FARTHER SWD INTO THE GRTBASIN/CNTRL ROCKIES WHILE A DRYING TREND TAKES PLACE OVER THE NORTHWEST. TEMPS SHOULD BE ABOVE NORMAL MOST AREAS EXCEPT NEAR NORMAL EXTREME NORTH. CONTINUE TO EXPECT MUCH BELOW NORMAL TEMPS TO THE E OF THE ROCKIES EARLY IN THE PERIOD WITH A BROAD AREA OF MINUS 15-30F ANOMALIES AND PSBL DAILY RECORD COLD MIN/MAX TEMPS TUE-WED. READINGS SHOULD TREND CLOSER TO NORMAL THEREAFTER. HOWEVER THE SYSTEM MOVING FROM THE WEST INTO THE PLAINS LATE IN THE PERIOD SHOULD BRING MORE CHILLY AIR INTO THE PLAINS BY NEXT FRI OR SAT WITH HIGH PLAINS RAIN AND/OR SNOW PSBLY ENHANCED BY A PERIOD OF LOW LVL UPSLOPE FLOW. FARTHER EWD... THE SYSTEM FCST TO TRACK FROM THE GULF OF MEX INTO SERN US AND OFF THE EAST COAST OEVR THE WRN ATLC SHOULD GENERATE SIGNIFICANT PCPN FROM NEAR THE WRN GULF COAST NEWD THROUGH THE SOUTHEAST AND SRN MID ATLC DURING WED-FRI. COLD AIR IN PLACE AHEAD OF THIS SYSTEM SUGGESTS TO POTENTIAL FOR SOME SIGNIFICANT WINTRY PCPN... MOST LIKELY OVER AND JUST E OF THE APLCHNS. EXACT EVOLUTION OF THE MID LVL SYSTEM WILL ALSO SERVE A ROLE IN DETERMINING WINTER WEATHER COVERAGE. SCHICHTEL