EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 130 AM EDT TUE MAR 18 2014 VALID 12Z FRI MAR 21 2014 - 12Z TUE MAR 25 2014 ...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENTS... THE 18 UTC GFS/GFS ENSEMBLE MEAN AND 12 UTC ECMWF/ECMWF ENSEMBLE MEAN OFFER A REASONABLY WELL CLUSTERED MEDIUM RANGE SOLUTION FOR THE LOWER 48 AND VICINITY INTO THE WEEKEND...KEEPING FORECAST CONFIDENCE AT SLIGHTLY ABOVE NORMAL LEVELS. PERSISTENT ALASKAN AS PART OF A DEVELOPING REX BLOCK OVER THE NE PAC THOUGH BY THIS WEEKEND AND ONWARD DOES LEAD TO INCREASED FORECAST SPREAD WITH THE DOWNSTREAM WRN US RIDGE AND ERN NOAM MEAN TROUGH COUPLET. THE 12 UTC ECMWF AND TO A LESSER EXTENT THE ECMWF ENSEMBLE MEAN OFFER A SOMEWHAT LESS PROGRESSIVE/MORE AMPLIFIED SOLUTION THAN THE 18 UTC GFS/GFS ENSEMBLE MEAN...BUT WITH THE LATTER TRENDING FAVORABLY COMPARED TO THEIR 12 UTC VERSIONS. GFS/GEFS TEND TO STRUGGLE WITH AMPLIFIED FLOW WHILE THE ECMWF CAN BE OVER-AMPLIFIED AT TIMES. ACCORDINGLY...WPC MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH OUR SENSIBLE WEATHER GRIDS HAVE BEEN DERIVED PRIMARILY FROM A COMPOSITE OF THESE GUIDANCE PIECES... BUT HAVE LEANED A BIT MORE ON THE ECMWF/ECMWF ENSEMBLE MEAN. THIS KEEPS GOOD WPC CONTINUITY. ...SENSIBLE WEATHER HIGHLIGHTS... A SERIES OF MID-UPPER LEVEL TROUGHS AND SPAWNED SURFACE SYSTEMS DIGGING INTO/THROUGH A MEAN ERN US TROUGH POSITION ALOFT WILL FAVOR TWO MAIN SWATHS OF MAINLY NRN TIER STATE SNOWS AS LATE SEASON LOWS TRACK FROM THE N-CENTRAL TO NERN US FRI-SAT AND THEN AGAIN AROUND NEXT MON/TUE. COLDER AIR IS DRAWN IN THE WAKE OF THESE WAVY FRONTAL SYSTEM PASSAGES IN CONTRAST TO LEAD WARMING WITH MODEST MOISTURE/PCPN...AND THERE IS SOME POTENTIAL ROOM FOR ADDITIONAL SYSTEM INTENSITY GIVEN LARGER SCALE FLOW AMPLIFICATION AND LONGER TIME FRAME EMBEDDED IMPULSE SPECIFICS UNCERTAINTY. SCHICHTEL