EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM EST MON FEB 17 2014 VALID 12Z THU FEB 20 2014 - 12Z MON FEB 24 2014 A WELL-ADVERTISED PATTERN CHANGE WITH AMPLE FLOW AMPLIFICATION FROM THE ERN PAFIFIC THROUGH NORTH AMERICA IS NOW SQUARELY IN THE CURRENT FORECAST PERIOD. THIS MEAN PATTERN WILL BE HIGHLIGHTED ALOFT BY A POSITIVE TILT ERN PACIFIC TROUGH...DRYING NOAM WEST COAST RIDGE...AND COOLING/UNSETTLING CENTRAL NOAM TROUGH...WITH EJECTING ENERGIES LIFTING NEWD OVER THE WARMING AND WETTENING E-CENTRAL THROUGH ERN US. LATEST MODEL AND ENSEMBLE GUIDANCE OFFERS FAIRLY REASONABLE FORECAST SPREAD INTO DAY 4/FRI...BUT PREDICTABILITY THEN REALLY CRUMBLES. WPC SURFACE FRONTS/PRESSURES AND 500 MB PROGS ARE PRIMARILY DERIVED FROM A COMPOSITE MODEL/ENSEMBLE/CONTINUITY COMPOSITE BLEND INTO DAY 4/FRI BEFORE SWITCHING TO THE ECMWF ENSEMBLE MEAN AND CONTINUITY AS THE SYNOPTIC GUIDE INTO DAYS 5-7. THE GEFS MEAN REMAINS QUITE SUBJECT TO NOISY SHIFTS OF LATE DUE TO THE DISPARITY AND VARIABLE CLUSTERING OF ITS INDIVIDUAL MEMBERS. THE ECMWF ENSEMBLE MEAN HAS ITS OWN SHARE OF CONTINUITY ISSUES...BUT THESE ARE RELATIVELY QUITE A BIT LESS THAN THE GEFS MEAN AND ESPECIALLY RECENT RUNS OF DETERMINISTIC MODELS. THE WPC SOLUTION FITS THE LARGER SCALE PATTERN AND MAINTAINS GOOD CONTINUITY...ALBEIT WITH ABOVE NORMAL UNCERTAINTY. THE PATTERN WILL SHIFT FORTUNES IN TERMS OF PRECIPITATION. THE PACIFIC NORTHWEST DRIES OUT AS THE FULL-LATITUDE RIDGE BUILDS...SHORTWAVES SPAWN SOME SNOW DOWN ACROSS THE N-CENTRAL ROCKIES AND OUT ACROSS THE N-CENTRAL US...AND THE EAST-CENTRAL US JUICES UP WITH SURFACE RESPONSE AS THE UPSTREAM TROUGH DIGS ALOFT AND IMPULSES ARE EJECTED. ANOMALOUS WARMTH IS EXPECTED FOR THE FIRST SEVERAL DAYS OF THE MEDIUM RANGE PERIOD FROM THE GULF STATES TO THE MID ATLANTIC...WITH ANOMALOUS COLD SHOWING UP ACROSS THE NORTHERN PLAINS AS SURFACE HIGH BUILDS OVER WESTERN CANADA AND BEGINS TO DISLODGE BY DAY 7. SCHICHTEL