EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1039 AM EST MON FEB 22 2016 VALID 12Z THU FEB 25 2016 - 12Z MON FEB 29 2016 ...GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES... MODELS AND ENSEMBLES REMAIN WELL CLUSTERED WITH A HIGHLY ADVERTIZED INLAND STORM TO TRACK FROM THE GREAT LAKES/NORTHEAST TO ERN CANADA THU/FRI. A BLEND OF 06 UTC GFS/00 UTC ECMWF RUNS ALONG WITH ENSEMBLES MITIGATES LINGERING SMALL SCALE VARIANCE. AMPLIFIED WRN NOAM RIDGE DEVELOPMENT LEADS TO PERIODIC REAMPLIFICATION OF THE ERN US TROUGH...BUT THE RESPONSE IS COMPLICATED BY UNCERTAIN INTERACTIONS WITH/UNDERNEATH A LESS CERTAIN EVOLUTION OF A N-CENTRAL CANADIAN POLAR VORTEX. IN PARTICULAR...THE GFS/ECMWF/UKMET/CANADIAN HAVE SHOWN SHARP VARIABILITY ON THE DEPTH AND AMPLITUDE OF THE 500 MB TROUGH ACROSS SRN CANADA AND THE UPPER MS VALLEY/GREAT LAKES/NORTHEAST SAT-MON. THIS LEAVES THE REGION THE PRIMARY FOCUS OF UNCERTAINTY AS GUIDANCE HAS BEEN ALL OVER THE PLACE WITH EFFECTS WHOSE EMPHASIS AT LOWER LEVELS CHANGES SIGNIFICANTLY ON A RUN TO RUN BASIS. A COMPOSITE BLEND OF SOMEWHAT MORE CONSISTENT GEFS/ECMWF/NAEFS ENSEMBLE MEAN WAS USED TO MITIGATE THE DIFFERENCES AND LIMIT CONTINUTY CHANGE. OVER THE NWRN US/WRN CANADA INDIVIDUAL MODELS AND ENSEMBLE MEMBERS STILL DISPLAY CONSIDERABLE SPREAD WITH INCOMING ERN PAC SHRTWV ENERGY SAT-MON ON THE WRN PERIPHERY OF THE AMPLIFIED RIDGE....BUT SHOW A SIMILAR OVERALL PATTERN. OPTED TO TRANSITION FROM A GFS/ECMWF AND ENSEMBLE COMPOSITE THU/FRI TO ONLY AN ENSEMBLE BLEND DAYS 5-7. ...WEATHER HIGHLIGHTS/THREATS... A DEEP STORM TRACKING OVER THE GREAT LAKES/NE US AND ERN CANADA THU/FRI GENERATES A BROAD AREA OF SIGNIFICANT WEATHER INCLUDING STRONG WINDS/HEAVY PCPN. SNOW WILL MAINLY FOCUS NW OF THE 850 MB LOW TRACK OVER THE GREAT LAKE STATES THU. SYSTEM PASSAGE BRINGS A PERIOD OF LAKE EFFECT SNOW WITH TERRAIN ENHANCEMENT SUPPORTING SOME APPALACHIANS SNOW. THE WEEKEND OFFERS PERIODS MIDWEST/GREAT LAKES/NORTHEAST PCPN WITH WAVY FRONT PASSAGE. GUIDANCE RECENTLY OFFER POOR RUN-RUN CONSISTENCY WITH FLOW/TEMPS FROM THE N-CENTRAL US TO ERN US SAT-MON WITH UNRESOLVED EMPHASIS/TIMING AS IMPULSES INTERACT WITH A DRAPED FRONT. LATEST MODEL TRENDS OFFER LESS DIGGING/COLD AIR SURGE IN THIS PATTERN. MEANWHILE UPSTREAM...INBOUND MODEST TO TERRAIN ENHANCED PCPN WILL WORK INTO THE NWRN US FRI WITH LIGHTER POTENTIAL WORKING GRUDINGLY INLAND WITH HIGH MID WINTER SNOW LEVELS INTO A MEAN RIDGE POSITION FROM THE WEEKEND INTO EARLY NEXT WEEK. SCHICHTEL