EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1002 AM EDT SUN APR 24 2016 VALID 12Z WED APR 27 2016 - 12Z SUN MAY 01 2016 ...HEAVY, POSSIBLY EXCESSIVE RAINS ADDING TO RECORD 366 DAY TOTALS ACROSS PORTIONS OF TX/OK/LA/AR WEDNESDAY, THEN MORE SIGNIFICANTLY DURING THE FOLLOWING WEEKEND...SEVERE WEATHER ALSO POSSIBLE... GENERAL FLOW PATTERN/MODEL PREFERENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MODELS AND ENSEMBLES SHOW GENERAL AGREEMENT WITH THE REPETITIVE GENERAL FLOW PATTERN. A STRONG GREENLAND RIDGE/EASTERN CANADIAN UPPER LOW BLOCKING COUPLET CONTINUES TO DOMINATE THE EASTERN NORTH AMERICAN FLOW. TO THE WEST MID-CONTINENT, A REX BLOCK CONFIGURATION REMAINS RELATIVELY STEADFAST, WITH DEEP CYCLONES MOVING SLOWLY UNDER ITS BASE THROUGH THE SOUTHWEST INTO THE PLAINS. BELOW NORMAL FORECAST SPREAD MAY PORTEND BETTER THAN NORMAL PREDICTABILITY INTO SMALLER SCALES WEDNESDAY INTO FRIDAY. MEANWHILE...ANOTHER ROBUST MID-UPPER LEVEL TROUGH/CLOSED LOW SLAMS INTO CA AND THE GREAT BASIN/ROCKIES BY THURSDAY/FRIDAY TO LEAD TO ANOTHER ROUND OF CYCLOGENESIS/FRONTOGENESIS OVER THE SOUTHERN PLAINS NEXT WEEKEND. LATE WEEK TIMING ISSUES FROM THE WEST TOWARDS THE PLAINS DEVELOP WITH RECENT ECMWF/ECMWF ENSEMBLE MEANS OUTPACING THE REST OF GUIDANCE. DECENT UPSTREAM RIDGE AMPLITUDE LENDS WPC PREFERENCE FOR A SOLUTION ON THE STEADILY PROGRESSIVE BUT OVERALL SLOWER SIDE OF THE FULL ENVELOPE OF SOLUTIONS. FOR THE PRESSURES, WINDS, AND 500 HPA HEIGHTS, USED A COMPROMISE OF THE 00Z CANADIAN/00Z UKMET/00Z ECMWF/06Z GFS ON WEDNESDAY AND THURSDAY BEFORE TRANSITIONING TO A 06Z GFS/00Z BIAS-CORRECTED NAEFS MEAN COMPROMISE THEREAFTER. THE TEMPERATURE/CLOUD/DEW POINT/WEATHER/PRECIPITATION CHANCES WERE BASED ON A MORE 00Z NAEFS-HEAVY SOLUTION. OUR PREFERENCE ALSO MAINTAINS REASONABLY GOOD WPC CONTINUITY. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ MULTIPLE ENERGETIC/STEADILY PROGRESSIVE EMBEDDED SYSTEMS WILL BRING A SIGNIFICANT COVERAGE OF ACTIVE WEATHER ACROSS THE LOWER 48 DURING THE MEDIUM RANGE PERIOD. AN EMPHASIS FOR HIGHER PRECIPITATION TOTALS SHOULD EXTEND ACROSS THE WEST THEN SPREAD OVER MUCH OF THE PLAINS AS WELL AS THE EASTERN/NORTHEAST UNITED STATES. HEAVIEST SNOWS SHOULD FOCUS OVER FAVORED HIGHER TERRAIN OF THE WEST/ROCKIES. SOME ADDITIONAL SPRING SNOW IS ALSO POSSIBLE THE NORTHERN FRINGE OF THE PRECIPITATION SHIELD NEAR THE CANADIAN BORDER. THERE IS A HEAVY RAIN SIGNAL FOR OK/TX/AR/LA THROUGH PORTIONS OF THE MEDIUM RANGE PERIOD, FIRST ON WEDNESDAY AND MORE SIGNIFICANTLY BETWEEN LATE FRIDAY INTO NEXT SUNDAY. SINCE APRIL 22 LAST YEAR, A SWATH OF EASTERN TX, SOUTHEAST AND CENTRAL OK, AS WELL AS PORTIONS OF AR AND LA HAVE RECORDED RECORD RAINFALL PRIOR TO THESE WAVES OF PRECIPITATION. THERE IS ALSO THE POTENTIAL FOR STRONG TO SEVERE PLAINS/MS VALLEY THUNDERSTORMS -- CONSULT LATEST SPC OUTLOOKS FOR UPDATED SEVERE WEATHER THREAT INFORMATION. ROTH/SCHICHTEL