EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT WED MAY 04 2016 VALID 12Z SAT MAY 07 2016 - 12Z WED MAY 11 2016 GENERAL FLOW PATTERN ~~~~~~~~~~~~~~~~~~~~ A BLOCKY UPPER-LEVEL FLOW PATTERN ACROSS THE COUNTRY COULD EVOLVE INTO A REX BLOCK BY MID-WEEK NEXT WEEK. A CUTOFF LOW IN THE SOUTHWEST IS FORECAST TO BECOME LESS AMPLIFIED AND LIFTS NORTHEASTWARD INTO THE CENTRAL/NORTHERN PLAINS BY NEXT WEDNESDAY WHEREAS ANOTHER CUTOFF LOW IN THE NORTHEAST IS EXPECTED TO LIFT OUT INTO THE CANADIAN MARITIMES. MODEL ENSEMBLES...ESPECIALLY THE ECMWF PACKAGE...ARE SUGGESTING THAT THE PATTERN WILL EVOLVE INTO A REX BLOCK BY NEXT WEDNESDAY AS A POSSIBLE CUTOFF HIGH IN CANADA BECOMES SITUATED NORTH OF THE DEAMPLIFYING LOW IN THE PLAINS. MODEL PREFERENCES ~~~~~~~~~~~~~~~~~ THE GUIDANCE IS MUCH MORE AGREEABLE THAN SEEN ON PAST DAYS. FROM DAYS 3/SAT TO 5/MON...THE WPC PRESSURE FIELD...500 HPA HEIGHTS AND WIND GRIDS...ARE DERIVED FROM A BLEND OF THE 00Z ECMWF AND THE 06Z GFS MIXING IN WITH SOME OF THE RESPECTIVE ENSEMBLE MEANS. THE GFS AND GEFS CONTINUE TO LAG BEHIND THE EC PACKAGES BUT HAVE SPED UP TOWARD THE ECMWF SOLUTION IN THE MOST RECENT RUNS. BY DAY 7/WED...THE ECMWF AND EC MEANS ARE SUGGESTING THE FORMATION OF A CUTOFF HIGH/HIGH AMPLITUDE RIDGE IN CENTRAL CANADA. THE 06Z GEFS MEAN HAS ALSO TRENDED TOWARD A HIGHER AMPLITUDE RIDGE IN THE SAME GENERAL AREA. IT APPEARS THAT THE ECMWF IS LEADING TOWARD A REX BLOCK SCENARIO BY DAY 7 NEXT WED...AND THUS MUCH OF THE WPC BLEND HAS BEEN WEIGHED TOWARD THE EC MEANS BY DAY 7. 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 AHEAD OF THE COLD FRONT FROM WEST 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. THERE APPEARS TO BE SOME CERTAINTY REGARDING THE PRESSURE FIELD IN THE NORTHERN PLAINS BY DAY 7 AS THE MODELS ARE STILL RESOLVING TO A STEADIER SOLUTION TO THE EVOLVING REX PATTERN. THE RAIN COULD MOVE FARTHER EASTWARD INTO THE MIDWEST AHEAD OF THE LOW IN THE PLAINS. KONG/ROTH