EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1117 AM EST SAT FEB 25 2017 VALID 12Z TUE FEB 28 2017 - 12Z SAT MAR 04 2017 ...OVERVIEW AND GUIDANCE PREFERENCES... A LONGWAVE TROUGH INITIALLY ALIGNED OVER THE WESTERN U.S. ON TUESDAY WILL STEADILY PRESS EASTWARD THROUGH THE CENTRAL AND EASTERN U.S. WEDNESDAY AND THURSDAY, BEFORE RELATIVELY ZONAL FLOW SETS UP OVER THE NORTHERN TIER OF NATION BY THE END OF WEEK. MEANWHILE, SLOW-MOVING SOUTHERN STREAM ENERGY IS EXPECTED TO DIG FROM THE SOUTHWEST TO NORTHERN MEXICO DURING THE LATER HALF OF THE WEEK. DESPITE REASONABLE AGREEMENT WITH THE LARGE SCALE FLOW PATTERN, THERE IS STILL A CONSIDERABLE AMOUNT OF SPREAD AMONG MODEL GUIDANCE WITH THE SMALLER SCALE FEATURES IMPACTING THE LOWER 48 NEXT WEEK. DETERMINISTIC GUIDANCE CONTINUES TO TREND SLOWER WITH THE TIMING OF THE COLD FRONT PUSHING THROUGH THE EASTERN HALF OF THE COUNTRY WEDNESDAY INTO THURSDAY, WHERE THE GFS WAS ONCE A FAST OUTLIER AND IS NOW ON THE SLOWER SIDE OF MODEL SPREAD. ALSO, MODELS CONTINUE TO MAKE RUN-TO-RUN CHANGES WITH THE EVOLUTION OF SURFACE LOW/LOWS POSSIBLY STRENGTHENING ALONG THE BOUNDARY. THE LATEST ENSEMBLE MEAN GUIDANCE SHOWS THE POTENTIAL FOR A SURFACE LOW ALONG THE FRONT TO RAPIDLY DEEPEN WHILE LIFTING FROM THE LOWER GREAT LAKES TO SOUTHERN QUEBEC WEDNESDAY INTO THURSDAY. ELSEWHERE, THE GFS STILL APPEARS TO BE A STRONG OUTLIER WITH SHORTWAVE ENERGY AND POSSIBLE SURFACE WAVE DROPPING INTO THE NORTH CENTRAL U.S. THURSDAY, AND ENSEMBLE MEMBERS, ESPECIALLY ECMWF ENSEMBLE MEMBERS, ARE SHOWING AN ALARMINGLY LARGE AMOUNT OF SPREAD WITH FLOW SETTING UP OVER THE NORTHEAST PACIFIC/NORTHWESTERN U.S. LATE NEXT WEEK. THE WPC DAY 3-7 FORECAST STARTED WITH A BLEND BETWEEN THE 06Z GEFS MEAN, 00Z ECMWF ENSEMBLE MEAN, AND 00Z ECMWF, WHICH SEEMED TO BEST ACCOUNT FOR SOME OF THE UNCERTAINTY AND REPRESENT THE MIDDLE OF MODEL SPREAD WITH SOME OF THE SMALLER SCALE FEATURES. ...WEATHER HIGHLIGHTS/THREATS... SHOWERS WITH EMBEDDED HEAVY RAIN AND CONVECTION WILL BE POSSIBLE WITH THE COLD FRONT PUSHING THROUGH THE EASTERN HALF OF THE NATION TUESDAY-THURSDAY, AND THE STORM PREDICTION CENTER IS HIGHLIGHTING A RISK OF SEVERE WEATHER OVER PORTIONS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS. SNOW AND STRONG WINDS WILL BE POSSIBLE TO THE NORTHWEST OF A SURFACE LOW POTENTIALLY DEEPENING ALONG THE BOUNDARY, WHICH IS CURRENTLY EXPECTED TO TRACK FROM THE LOWER GREAT LAKES TO SOUTHERN QUEBEC WEDNESDAY INTO THURSDAY. BEHIND THIS SYSTEM, PRECIPITATION COVERAGE SHOULD DECREASE ACROSS THE CONUS LATER IN THE WEEK, WITH THE EXCEPTION OF THE NORTHWEST, WHERE MODERATE TO HEAVY RAIN AND HIGHER ELEVATION SNOW WILL BE POSSIBLE WITH STRONG ONSHORE FLOW. TEMPERATURES SHOULD TREND BACK TOWARD MORE TYPICAL LEVELS IN THE EAST AFTER THE FRONT CLEARS THE COAST, WHILE TEMPERATURES SHOULD RISE BACK ABOVE AVERAGE IN THE WEST AND THEN THE PLAINS BY NEXT FRIDAY AND SATURDAY. GERHARDT