EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1255 AM EDT WED MAY 04 2016 VALID 12Z SAT MAY 07 2016 - 12Z WED MAY 11 2016 GENERAL FLOW PATTERN ~~~~~~~~~~~~~~~~~~~~ BLOCKY FLOW ACROSS THE COUNTRY (WITH TROUGHING IN THE SOUTHWEST AND NORTHEAST) SIMPLIFIES THIS PERIOD AS A SYSTEM MOVING THROUGH WESTERN CANADA MOVES THE WESTERN TROUGH INTO THE PLAINS, WHICH IN TURN MOVES RIDGING FROM THE PLAINS INTO THE EAST. THE PAIR OF CLOSED CYCLONES IN EASTERN CANADA AND THE NORTHEAST JOIN FORCES, FORMING A DEEP CYCLONE IN ATLANTIC CANADA WHICH THEN LIFTS NORTHEASTWARD. MODEL PREFERENCES ~~~~~~~~~~~~~~~~~ THE GUIDANCE IS MUCH MORE AGREEABLE THAN SEEN ON PAST DAYS. AS SUCH, FOR THE PRESSURES/500 HPA HEIGHTS/WIND GRIDS, USED A COMPROMISE OF THE 12Z CANADIAN/12Z UKMET/12Z ECMWF/18Z GFS FOR SATURDAY BEFORE ELIMINATING THE 12Z CANADIAN FROM CONSIDERATION THEREAFTER AS IT STRAYS FROM THE PACK. FOR SUNDAY INTO MONDAY, USED A COMPROMISE OF THE 12Z UKMET/12Z ECMWF/18Z GFS. FROM MONDAY INTO NEXT WEDNESDAY, USED A COMBINATION OF THE 12Z ECMWF/18Z GFS/12Z NAEFS MEAN/12Z ECMWF ENSEMBLE MEAN, WHICH INCREASINGLY SHIFTS IN THE DIRECTION OF THE ENSEMBLE MEANS AND AWAY FROM THE ECMWF WITH TIME DUE TO ITS ANOMALOUS UPPER LOW NEAR THE NORTHWEST NEXT WEDNESDAY. THIS KEPT GOOD CONTINUITY. FOR TEMPERATURES/DEW POINTS/CLOUDS/WEATHER/PRECIPITATION CHANCES, USED A 12Z NAEFS MEAN/12Z ECMWF ENSEMBLE MEAN HEAVY BLEND. HIGH TEMPERATURES IN THE SOUTHEAST NEEDED TO BE TONED DOWN BY A CATEGORY OR TWO BASED ON THE MODEL PREFERENCE -- CAPPED HIGHS IN NORTHEAST FL/EASTERN GA/SOUTHERN AND CENTRAL SC AT 90F AFTER COORDINATION WITH THE PEACHTREE CITY GA FORECAST OFFICE. THE PRECIPITATION FORECAST FOR DAYS 4-7 WAS DERIVED FROM A COMPROMISE OF THE 12Z ECMWF, 18Z GFS, AND 00Z GFS. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ THE NORTHWEST STAYS QUITE WARM AND DRY AS RIDGING ALOFT ATTEMPTS TO PERSIST NEARBY THROUGH THE PERIOD. A DEEP LOW/TROUGH WORKING NORTHEASTWARD OUT OF THE SOUTHWEST WILL SPREAD A BROAD AREA OF RAIN AND HIGHER ELEVATION SNOWS THROUGH THE GREAT BASIN INTO THE ROCKIES... WITH LEAD RAINS DEVELOPING OVER THE CENTRAL US SUNDAY INTO NEXT WEDNESDAY, INCLUDING THE RAIN-WEARY ARKLATEX. HIGHEST TOTALS ARE EXPECTED ACROSS PORTIONS OF CO/WY THEN OUT OVER THE PLAINS. SPC HAS A 15% RISK AREA OF SEVERE STORMS ON SATURDAY MAY 7 AHEAD OF THE COLD FRONT FROM W TEXAS NORTHWARD TO WESTERN KANSAS AND EASTERN COLORADO. TEMPERATURES WITH THE SYSTEM ARE EXPECTED TO BE 10-15F BELOW AVERAGE UNDER THE UPPER LOW. RIDGING ALOFT AHEAD OF THIS SYSTEM IS EXPECTED TO SUPPORT LEAD WARMING SPREADING FROM THE PLAINS SATURDAY INTO THE EAST WITH TIME. PRECIPITATION ACROSS THE NORTHEAST WILL BE SLOW TO CLEAR THIS PERIOD DUE TO A PERSISTENT DEEP CYCLONE NEAR ATLANTIC CANADA WHICH WON'T PULL AWAY FROM THE REGION UNTIL TUESDAY AND A FRONTAL ZONE MEANDERING ACROSS THE SOUTHERN MID-ATLANTIC STATES. ROTH