EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1020 AM EDT MON MAR 21 2016 VALID 12Z THU MAR 24 2016 - 12Z MON MAR 28 2016 ...OVERVIEW AND GUIDANCE PREFERENCES... UPPER RIDGING IS FORECAST TO BUILD IN THE NORTHEAST PACIFIC AND IN THE NW ATLANTIC, SUPPORTING BROAD/PROGRESSIVE TROUGHING ACROSS MUCH OF THE CONUS. THIS WILL TAKE A LEAD SYSTEM FROM THE GREAT LAKES EAST-NORTHEASTWARD INTO NEW ENGLAND THU-FRI AND A DUAL-STREAM PAIR OF SYSTEMS ACROSS THE CONUS THU-MON. THE MODELS CONTINUE TO WAVER WHILE THE ENSEMBLE MEANS SHOW BETTER CONTINUITY, THOUGH THE RECENT 00Z/06Z RUNS WERE AT LEAST MORE COMPATIBLE. A MULTI-MODEL/ENSEMBLE BLEND (INCLUDING OVERNIGHT WPC PROGS) WAS USED THROUGH THE FORECAST. THE QUICKER 00Z GFS AND SLOWER 00Z CANADIAN LIED NEAR THE EDGE OF THE ENSEMBLE SPREAD, WHILE THE 00Z ECMWF WAS MOSTLY IN THE MIDDLE. 06Z GFS SLOWED A BIT COMPARED TO ITS EARLIER RUN BY LATER IN THE PERIOD BUT WAS STILL DISPLACED ENOUGH TO PRECLUDE IT IN THE BLEND AFTER THURSDAY. FRACASSO ...FLOW PATTERN HIGHLIGHTS/THREATS... A MAIN LEAD LOW AND SURFACE FRONTAL SYSTEM WILL FOCUS A WIDESPREAD EAST-CENTRAL TO ERN US PCPN SWATH FUELED BY DEEPENING GULF OF MEXICO THEN ATLANTIC MOISTURE RETURN. IN THIS PATTERN EXPECT A THREAT OF HEAVY LATE SEASON OVERRUNNING SNOW WITH SOME ICE FOR PARTS OF THE UPPER MIDWEST/GREAT LAKES AND NORTHEAST ON THE COLDER NRN PERIPHERY OF THE OVERALL PCPN SHIELD. CLIPPER LOW PASSAGE INTO/ACROSS THE US NRN TIER FRI-SUN MAY LAY DOWN A COOLED AIRMASS AND SUPPORT SOME MODEST SNOWS AGAIN ACROSS THIS AREA. MEANWHILE...IMPULSE ENERGIES ALOFT DIGGING SEWD BACK INTO THE WRN US FRI/SAT SUPPORTS SNOW AS ENHANCED BY TERRAIN OVER THE N-CENTRAL GREAT BASIN THEN ROCKIES. EJECTING ENERGIES DOWNSTREAM SUPPORT MOISTURE/PCPN RETURN OVER THE S-CENTRAL PLAINS AND WITH LEAD INFLOW OVER AN OLD/STALLED FRONT INTO THE GULF COAST AND SERN US STATES ENHANCING A HEAVY RAIN THREAT OVER THE WEEKEND THEN UP THE EAST COAST INTO EARLY NEXT WEEK. SCHICHTEL