EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 200 AM EST THU MAR 08 2018 VALID 12Z SUN MAR 11 2018 - 12Z THU MAR 15 2018 ...ANOTHER MAJOR ERN US COASTAL STORM THREAT EARLY NEXT WEEK... ...A WET PATTERN FOR THE WEST COAST BY NEXT MIDWEEK... ...PATTERN AND GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER/THREATS HIGHLIGHTS... GUIDANCE AGREES TO DEVELOP QUITE AN AMPLIFIED FLOW PATTERN ALOFT NEXT WEEK OVER THE LOWER 48 TO BE HIGHLIGHTED BY A RIDGE OVER THE ROCKIES SANDWICHED BETWEEN AN EXPANSIVE CLOSED LOW JUST OFF THE WEST COAST AND AN ERN U.S. TROUGH. A FAVORABLE INLAND MOISTURE SURGE WILL FUEL MODERATE TO HEAVY PRECIPITATION AROUND A DEVELOPING SYSTEM CENTERED OVER THE MID-SOUTH AND SOUTHEAST SUNDAY. HEAVIEST PRECIPITATION SHOULD SHIFT ACROSS THE APPALACHIANS TO THE MID-ATLANTIC THEN NERN US AND MARITIME INTERESTS INTO MON/TUE WITH AN AXIS DEPENEDENT ON ANOTHER POTENTIALLY SIGNIFICANT COASTAL STORM GENESIS AND TRACK. SNOW IS EXPECTED WITHIN THE NWRN PERIPHERY OF THE ORGANIZING PRECIPITATION SHIELD. GUIDANCE SUPPORT FOR THIS TYPE OF SYSTEM EVOLUTION IS NOW BETTER SUPPORTED BY LATEST GUIDANCE...BUT RECENT ECMWF/UKMET/CANADIAN MODEL VARIANCE IS NOT EASILY FORGOTTEN DESPITE MUCH MORE RUN TO RUN CONSISTENT GFS/GEFS ENSEMBLE GUIDANCE. OVER THE WEST...THERE REMAINS A STRONG SIGNAL FOR A SWATH OF ORGANIZED PRECIPITATION ACROSS CA AND THE SOUTHWEST/SRN ROCKIES SUN INTO MON AS AN ANOMALOUS SURGE OF PACIFIC MOISTURE MOVES INLAND OVER THE REGION WITHIN SRN STREAM FLOW. SPECIFICS ARE UNCERTAIN...BUT THERE IS A GOOD OVERALL SIGNAL FOR MODERATE TO HEAVIER PRECIPITATION TO SHIFT BACK TO THE PACIFIC NW/CA AND THEN GRADUALLY WORK INLAND ALONG WITH COOLING TO THE INTERMOUNTAIN WEST TUE-THU AS A LEAD FRONT AND HEIGHT FALLS FROM AN EXPANSIVE ERN PACIFIC CLOSED LOW/TROUGH DEEPENS/NUDGES TOWARD THE WEST COAST. ACCORDINGLY...WPC MEDIUM RANGE GUIDANCE WAS PRIMARILY DERIVED FROM AN ENSEMBLE MEAN FORECAST APPROACH WITH STRONGEST WEIGHTING APPLIED TO THE GEFS MEAN FOR CONSISTENCY. WPC SURFACE FRONTAL PROGS...QPF...WINTER WEATHER PROBABILITIES AND OTHER WEATHER INFORMATION CAN BE FOUND AT: WWW.WPC.NCEP.NOAA.GOV/#PAGE=MED WWW.WPC.NCEP.NOAA.GOV/#PAGE=QPF WWW.WPC.NCEP.NOAA.GOV/#PAGE=WWX SCHICHTEL