EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 AM EDT WED APR 11 2018 VALID 12Z SAT APR 14 2018 - 12Z WED APR 18 2018 ...N-CENTRAL U.S. BLIZZARD THREAT WITH SNOW TO GREAT LAKES/NRN NORTHEAST AND STRONG CONVECTION/HEAVY RAINS SOUTH OVER THE E-CENTRAL TO ERN U.S... ...GUIDANCE/PREDICTABILITY ASSESSMENT... QUITE A BUSY PATTERN IS UNFOLDING OVER THE MEDIUM RANGE PERIOD ESPECIALLY FOR THE CENTRAL TO EASTERN PORTIONS OF THE U.S. BY THIS WEEKEND...A DEEP MID LEVEL LOW WILL BE CENTERED OVER THE CENTRAL PLAINS/MID MISSISSIPPI VALLEY AND BY MONDAY WILL BE OVER THE GREAT LAKES/MID-ATLANTIC. BY MIDWEEK...EXPECT THIS UPPER LOW TO BE OVER QUEBEC AND THE CANADIAN MARITIMES. THE WEST COAST WILL HAVE ANOTHER INCOMING SYSTEM BEGIN TO PUSH THROUGH BY THE END OF THE WEEKEND AND INTO EARLY NEXT WEEK. THE MID-UPPER LEVEL TROUGH WILL SWING OVER THE WEST COAST AND INTERMOUNTAIN WEST BY TUESDAY. ON WEDNESDAY...ANOTHER SYSTEM WILL BEGIN APPROACHING THE WEST COAST. BOTH THE 06Z GFS/GEFS AND 00Z ECMWF/ECENS WERE IN ALIGNED WELL ON THE EVOLUTION OF THE SYSTEM THAT WILL IMPACT THE CENTRAL AND EASTERN U.S. BY EARLY TO MID WEEK...THE 00Z ECMWF AND 06Z GFS BEGIN TO DIFFER ON HOW THE MID-UPPER LEVEL LOW PROGRESSES AS IT MOVES INTO EASTERN CANADA. FOR THE WEST COAST SYSTEM...THE ECMWF AND THE ECMWF ENSEMBLE MEAN HAS BEEN CONSISTENT RUN TO RUN WITH THIS SYSTEM. THE GFS AND GEFS HAS NOT BEEN AS CONSISTENT...HOWEVER THE 06Z GFS/GEFS BEGAN TO TREND TOWARD THE ECMWF. THUS...WPC MEDIUM RANGE PRODUCT SUITE IS BASED ON A BLEND OF THE 06Z GFS/GEFS AND 00Z ECMWF/ECMWF ENSEMBLE MEANS...WITH MORE WEIGHT BUT ON THE MEANS BY THE END OF THE PERIOD TO ACCOUNT FOR DIFFERENCES ESPECIALLY FOR THE WEST COAST SYSTEM. ...WEATHER/THREAT HIGHLIGHTS... WITH DEEP CYCLOGENESIS EXPECTED OVER THE CENTRAL PLAINS ON FRIDAY...MOISTURE IS EXPECTED TO WRAP AROUND THE CLOSED MID-UPPER LEVEL LOW AND PRODUCE WIDESPREAD HEAVY SNOW. IN ADDITION...STRONG PRESSURE GRADIENT FROM THIS SYSTEM WILL CONTRIBUTE TO HIGH WINDS...THUS BLIZZARD-LIKE CONDITIONS ARE FAVORABLE. THE HEAVY SNOW WILL IMPACT THE CENTRAL PLAINS AND MISSISSIPPI VALLEY THROUGH THE WEEKEND. SNOW WILL THEN SHIFT TO THE GREAT LAKES AS THE UPPER LEVEL LOW SWINGS NORTHWARD INTO CANADA. FARTHER SOUTH...A STRONG COLD FRONT WILL SEPARATE DISTINCT AIR MASSES...WITH TEMPERATURES WELL ABOVE NORMAL ACROSS THE SOUTHEAST INTO NEW ENGLAND ON SATURDAY. HIGH TEMPERATURES IN THE PLAINS WILL BE WELL BELOW FREEZING BEHIND THE FRONT. DEEP SOUTHERLY FLOW WILL FEED COPIOUS AMOUNTS OF MOISTURE FROM THE GULF OF MEXICO AHEAD OF THIS STRONG COLD FRONT. WITH PLENTY OF INSTABILITY IN PLACE...CONVECTION IS EXPECTED TO DEVELOP IN THE LOWER MISSISSIPPI VALLEY AND SOUTHERN PLAINS ON FRIDAY INTO SATURDAY AND CONTINUE ACROSS THE TENNESSEE VALLEY AND SOUTHEAST BY SUNDAY. HEAVY RAINFALL CONTINUES TO BE A THREAT WITH THIS SYSTEM ALONG WITH SEVERE WEATHER POTENTIAL WITH THE CONVECTION MONITORED BY THE STORM PREDICTION CENTER. PRECIPITATION WILL BEGIN TO INCREASE ACROSS THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA AS THE MID-UPPER LEVEL TROUGH MOVES TOWARD THE REGION ON SUNDAY. RAINFALL ALONG WITH HIGHER ELEVATION SNOW IS EXPECTED THROUGH TUESDAY ACROSS THE GREAT BASIN AND INTERMOUNTAIN WEST THROUGH TUESDAY. WPC MEDIUM RANGE 500MB PROGS...SURFACE/FRONTS PROGS...SENSIBLE WEATHER GRIDS...QPF GUIDANCE...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITY FORECASTS CAN BE FOUND AT... http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 REINHART