EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1131 AM EDT MON APR 04 2016 VALID 12Z THU APR 07 2016 - 12Z MON APR 11 2016 A COMPLEX DEEPENING TROUGH WILL AFFECT THE EASTERN UNITED STATES THROUGH THE ENTIRE MEDIUM RANGE PERIOD/DAYS 3 - 7/THURSDAY THROUGH MONDAY...WITH MULTIPLE SHORTWAVES INFLUENCING THE WEATHER PATTERN RATHER THAN ONE DOMINATING AN INTENSIFYING PHASED SYSTEM AS SOME EARLIER SOLUTIONS SUGGESTED. A STRONG UPPER RIDGE OVER THE WESTERN UNITED STATES EARLY IN THE FORECAST PERIOD WILL BE IMPACTED BY THE MOVEMENT OF TWO SEPARATE SYSTEMS...ONE AN UPPER LOW WEST OF THE SOUTHERN CALIFORNIA COAST THAT WILL GRADUALLY MOVE EASTWARD AND THEN BE FOLLOWED BY ANOTHER UPPER LOW THAT WILL CROSS THE COAST LATER IN THE WEEKEND. THE WESTERN RIDGE WILL ALSO BE IMPACTED BY ANOTHER SHORTWAVE MOVING SOUTHWARD ACROSS WESTERN CANADA THAT WILL LIKELY BRING COOLER TEMPERATURES TO THE NORTHWEST CORNER OF THE NATION LATER IN THE PERIOD. THE MEDIUM RANGE PERIOD CAN BE CHARACTERIZED BY AN ACTIVE EARLY APRIL PATTERN MORE REMINISCENT OF MARCH WITH ADDITIONAL INTRUSIONS OF LATE SEASON COLD TO COOL AIR ACROSS MUCH OF THE EAST WITH A DEVELOPING STORM SYSTEM IN THE MIDDLE OF THE NATION BY THE END OF THE PERIOD THAT WILL SEE A SHIFT OF THE COLDER AIR FARTHER WESTWARD ACROSS THE ROCKIES INTO THE PLAINS. RAINFALL WILL ACCOMPANY THE EAST COAST SYSTEM ON DAY 3/THURSDAY WITH THUNDERSTORMS AHEAD OF THE COLD FRONT AND THE POSSIBLE OF WET SNOW ACROSS THE WESTERN FRINGES OF THE STORM SYSTEM. PULSES OF COLDER AIR SPILLING SOUTH AND EASTWARD ACROSS THE OHIO AND TENNESSEE VALLEYS TOWARD THE EAST COAST ON THURSDAY AND FRIDAY WILL LIKELY BE ACCOMPANIED BY SOME RAIN AND SNOW SHOWER ACTIVITY THROUGHOUT THE AREA AS WELL AS THE APPALACHIANS FOLLOWED BY COLD TEMPERATURES DOMINATING THE MIDWEST AND EAST ON FRIDAY INTO SATURDAY POSSIBLY MODIFYING BY SUNDAY. THE COMBINATION OF UPPER LOWS CROSSING SOUTHERN CALIFORNIA WILL INCREASE THE RISK OF SHOWERS OVER THE SOUTHWEST ON THURSDAY AND FRIDAY THAT WILL THEN SPREAD ACROSS THE GREAT BASIN LATER SATURDAY INTO SUNDAY. THE SECOND UPPER LOW WILL AGAIN INCREASE THE CHANCES FOR SHOWERS ACROSS THE SOUTHWEST AGAIN ACROSS THE GREAT BASIN AND ROCKIES ON SUNDAY INTO MONDAY. A POSSIBLE SURGE OF COLDER AIR ACROSS THE NORTHERN ROCKIES AND PLAINS ON MONDAY MAY INCREASE THE RISK FOR UPSLOPE SNOWFALL LATE SUNDAY AND MONDAY INTO PARTS OF THE ROCKIES AND THE DEVELOPING STORM SYSTEM OVER THE SOUTH CENTRAL UNITED STATES ON MONDAY MAY HAVE THE POTENTIAL FOR SEVERE WEATHER ACROSS SOUTHERN PLAINS AND LOWER AND CENTRAL MISSISSIPPI VALLEY. THE MODEL CHOICES FOR THE PERIOD INCLUDED THE OPERATIONAL RUNS DOMINATING THE BLENDS OF DAYS 3 AND 4 SINCE MANY OF THE RUNS WERE IN SYNC WITH THE ENSEMBLE MEANS WHILE THE MEANS STARTED TO BECOME A MORE IMPORTANT COMPONENT OF THE BLENDS FROM DAYS 5 THROUGH 7 AS THE SPREAD INCREASES. THE 00Z ECMWF/CMC AND 06Z GFS ALL CONTRIBUTED TO THE FORECAST THROUGH DAY 5 WHILE THE ECMWF WAS THE LARGER OPERATIONAL COMPONENT LATER IN THE FORECAST EVEN THOUGH THE ECMWF/GEFS MEANS CONTRIBUTED MORE TO THE BLENDS. KOCIN