EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT TUE APR 10 2018 VALID 12Z FRI APR 13 2018 - 12Z TUE APR 17 2018 ...MAJOR N-CENTRAL U.S. SNOWSTORM THREAT WITH SNOW TO SPREAD TO THE NRN GREAT LAKES/NERN U.S... ...STRONG CONVECTION AND WIDESPREAD HEAVY RAINFALL THREAT FOR A WARMED E-CENTRAL TO ERN U.S... ...GUIDANCE/PREDICTABILITY ASSESSMENT... A VERY ACTIVE PERIOD CAN BE EXPECTED OVER THE MEDIUM RANGE PERIOD AS A DEEP CYCLONE DEVELOPS OVER THE CENTRAL U.S. BY LATE THIS WEEK AND WILL CONTINUE MOVING TOWARD THE EAST COAST BY THE WEEKEND. ON FRIDAY...A CLOSED 500 MB LOW WILL BE CENTERED ALONG THE HIGH PLAINS AND WILL DRIFT ACROSS THE CENTRAL PLAINS BY SATURDAY. BY SUNDAY AND INTO MONDAY...THIS CLOSED LOW WILL CONTINUE ITS EASTWARD TREK OVER THE MISSISSIPPI VALLEY AND MOVE TOWARDS THE OHIO VALLEY/GREAT LAKES REGION. BY THE END OF THE MEDIUM RANGE PERIOD...THIS LOW WILL LIFT NORTHWARD TOWARDS SOUTHERN QUEBEC. MEANWHILE...TO THE WEST...AN UPPER RIDGE WILL BUILD ACROSS THE REGION AT THE BEGINNING OF THE FORECAST PERIOD. THE RIDGE WILL BEGIN TO BREAK DOWN BY SUNDAY AS ANOTHER MID-UPPER LEVEL TROUGH BEGINS APPROACHING THE PACIFIC NORTHWEST. BY THE BEGINNING OF NEXT WEEK...THIS TROUGH WILL SWING ACROSS THE PACIFIC NORTHWEST AND MOVE OVER THE INTERMOUNTAIN WEST. FOR THE PLAINS TO EAST COAST SYSTEM...INITIALLY THE 06Z GFS AND 00Z ECMWF WERE IN FAIR AGREEMENT WITH THE POSITION OF THE CLOSED LOW...HOWEVER THE 06Z GFS WAS DEEPER WITH IT. BY THE WEEKEND...THE 06Z GFS IS STILL THE MORE AGGRESSIVE AND FASTER SOLUTION. THE ECMWF HAS BEEN CONSISTENT WITH ITS LAST FEW RUNS WITH THE EVOLUTION OF THIS SYSTEM WHEREAS THE GFS HAS TRENDED TOWARD THE ECMWF. AS FOR THE EAST PAC SYSTEM...THE 06Z GFS WAS FASTER AND HAD AN OPEN TROUGH. BY TUESDAY...EVEN THE ENSEMBLES DIFFERED IN THEIR TIMING WITH THE 00Z GEFS TROUGHING OVER THE INTERMOUNTAIN WEST AND THE 00Z ECENS HAD TROUGHING BACK OVER CALIFORNIA. THUS...WPC TOOK A BLEND OF THE 00Z ECMWF/06Z GFS AND THEIR ENSEMBLES THROUGH SUNDAY...AND TOOK MORE WEIGHT OVER THE 00Z ECMWF AND 00Z ECENS BY MONDAY AND TUESDAY ALONG WITH 00Z GEFS. ...SENSIBLE WEATHER HIGHLIGHTS... THE DEEP CYCLONE WILL IS EXPECTED TO BRING MULTIPLE HAZARDS ACROSS THE U.S. ON FRIDAY AND INTO SATURDAY...MOISTURE WRAPPING AROUND THE COLD AIR IN PLACE OVER THE NORTHERN AND CENTRAL ROCKIES INTO THE NORTHERN PLAINS WILL BRING WIDESPREAD HEAVY SNOW. THE HEAVY SNOW WILL CONTINUE TO MOVE INTO THE MID AND UPPER MISSISSIPPI VALLEY ON SUNDAY AND INTO MONDAY. BY THE BEGINNING OF NEXT WEEK...THE GREAT LAKES WILL EXPERIENCE WIDESPREAD SNOWFALL. FARTHER SOUTH...DEEP SOUTHERLY FLOW AHEAD OF THE INCOMING COLD FRONT WILL HELP DEVELOP THUNDERSTORMS ALONG THE BOUNDARY IN THE SOUTHERN PLAINS BY THE END OF THE WEEK AND WILL CONTINUE TOWARD THE EASTERN SEABOARD BY EARLY NEXT WEEK. HEAVY RAIN AND SEVERE WEATHER ARE A CONCERN...WITH SPC ALREADY MONITORING THE SEVERE WEATHER POTENTIAL. WITH THE INCOMING WEST COAST SYSTEM...PRECIPITATION WILL INCREASE ACROSS THE PACIFIC NORTHWEST...NORTHERN CALIFORNIA AND INTERMOUNTAIN WEST BY THE BEGINNING OF THE WORK WEEK. REINHART