EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 245 AM EDT TUE APR 26 2016 VALID 12Z FRI APR 29 2016 - 12Z TUE MAY 03 2016 ...A TRANSITIONAL MEDIUM RANGE WEATHER PATTERN REMAINS QUITE STORMY... ...PATTERN/THREATS AND GUIDANCE/UNCERTAINTY ASSESSMENT... A PERSISTENT RECENT PATTERN HIGHLIGHTED AT HIGHER LATITUDES BY BLOCKING FLOW FINALLY RELAXES OVER THE WEEKEND. LEAD SYSTEM ENERGY SHEARING UNDERNEATH A STILL BLOCKING ERN CANADIAN CLOSED LOW FRI SPREADS A WAVE DRIVEN LINGERING PCPN SWATH ACROSS THE MID-ATLANTIC. EXPECT A TRAILING FRONT WILL CONTINUE TO PROVIDE A WELL DEFINED AIRMASS DIVIDE BACK TO THE S-CENTRAL US. UPSTREAM AS THE BLOCKING WEAKENS OVERTOP...AMPLIFIED MID-UPPER LEVEL TROUGH ENERGY FROM A STORMY/WINTERY SWRN US AND S-CENTRAL ROCKIES FRI EJECTS MORE NEWD THAN THE RECENT SERIES OF SYSTEMS FRI/SAT INTO THE S-CENTRAL PLAINS THEN E-CENTRAL STATES SUN-NEXT TUE...ALBEIT WITH INCREASING FORECAST SPREAD. CYCLOGENESIS AND INCREASINGLY FAVORABLE LEAD THETAE ADVECTION PATTERN SHOULD FUEL A WEEKEND WIDESPREAD RAINFALL EPISODE WITH HEAVIEST/EXCESSIVE POTENTIAL AND A SPC SUPPORTED SEVERE CONVECTION THREAT OVER THE WARMED S-CENTRAL US. ACTIVITY SPREADS INCREASINGLY NEWD OVER THE E-CENTRAL THEN ERN US EARLY NEXT WEEK. LESS PREDICTABLE ENERGIES MEANWHILE DIG SEWD FROM THE NWRN US INTO THE W-CENTRAL US IN THE WAKE OF THIS FEATURE TO PROVIDE DYNAMIC LIFT FOR SOME COOLED PCPN/TERRAIN SNOWS...BUT MOISTURE WILL BE MUCH MORE LIMITED. THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A 50-50 BLEND OF THE REASONABLY COMPATABLE 18 UTC GEFS MEAN AND 12 UTC ECMWF ENSEMBLE MEAN CONSISTENT WITH INCREASING FORECAST SPREAD IN A TRANSITIONAL FLOW REGIME. THE 12 UTC ECMWF AND NOW THE 00 UTC GFS HAVE GRAVITATED TOWARD A CLUSTERED SOLUTION MORE IN LINE WITH THIS ENSEMBLE MEAN BLEND AND THE LATEST 00 UTC GEFS MEAN TO BOLSTER CONFIDENCE IN MANUALLY ADDED DETAIL AND WPC CONTINUITY. SCHICHTEL