EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 300 AM EDT MON APR 06 2015 VALID 12Z THU APR 09 2015 - 12Z MON APR 13 2015 ...A VERY ACTIVE APRIL PATTERN... AN ESTABLISHED MIDWEEK LEAD FRONT WILL SEPARATE A SUBSTANTIAL S-CENTRAL TO E-CENTRAL/SERN US WARM SECTOR FROM RECEEDING SURFACE HIGH PRESSURE TO THE NORTH THAT HELPED DEFINE AN IMPRESSIVE BAROCLINIC ZONE. THE STARKLY COOLER HIGH PRESSURE AIRMASS LINGERS ACROSS THE MIDWEST/GREAT LAKES AND TO A DAMMED NORTHEAST/MID-ATLANTIC AS SUPPORTED BY UPPER LEVEL CONFLUENCE BETWEEN AN EXITING ERN CANADIAN NRN STREAM TROUGH AND A BROADENING SRN/SERN US RIDGE. UPSTREAM...AN AMPLIFIED AND UNSETTLING/COOLING MID-UPPER LEVEL CLOSED TROUGH WORKS BODILY THROUGH THE S-CENTRAL ROCKIES INTO THU. POTENT HEIGHT FALLS SUPPORT A DYNAMIC PCPN SWATH WITH SYSTEM PASSAGE...INCLUDING TERRAIN ENHANCED SNOWS. CLOSED SRN STREAM TROUGH EJECTION THU FAVORS CYCLO/FRONTOGENESIS OVER THE CENTRAL US. SUBSEQUENT SIGNIFICANT SYSTEM NEWD TRANSLATION OCCURS OVER THE E-CENTRAL US TO ERN NOAM FRI-SUN. FAVORABLE JET FLOW ALOFT AND LEAD FRONTAL/MOISTURE RETURN FROM THE GULF OF MEXICO THEN WRN ATLANTIC WILL FUEL WARM SECTOR AND FRONTAL/BOUNDARY CONVERGENCE FOCUSING RAINFALL/CONVECTION. SPC IS MONITORING THIS SCENARIO FOR AN INCREASING SEVERE WEATHER THREAT. ADDITIONAL WIDESPREAD OVER-RUNNING/WRAP-BACK PCPN MAY ALSO INCLUDE SOME HEAVIER RAINS AND EVEN SOME LATE SEASON SNOW POTENTIAL ON THE NRN PERIPHERY OF THE PCPN SHIELD OVER THE US FAR NRN TIER. THE 12 UTC ECMWF/CANADIAN OFFER A SLIGHTLY MORE AMPLIFIED/LESS PROGRESSIVE SRN STREAM FLOW THAT REMAINS MORE SEPARATED FROM A LESS AMPLIFIED CANADIAN NRN STREAM FLOW MID-LATE WEEK COMPARED TO THE 12/18/00 UTC GFS/GEFS MEAN. PREFER TO LEAN ON THE MORE AMPLIFIED SIDE OF THE FULL ENVELOPE OF SOLUTIONS FOR BOTH STREAMS CONSIDERING UPSTREAM AMPLITUDE OF WRN CANADIAN RIDGING AND THE CLOSED NATURE OF THE MAIN SRN STREAM SYSTEM. THIS SCENARIO SEEMS A GOOD FIT WITH THE 12 UTC ECMWF ENSEMBLE MEAN OVERALL. BY NEXT WEEKEND...DYNAMIC TROUGH ENERGIES AND HEIGHT FALLS PUNCHING SEWD FROM THE NERN PACIFIC THROUGH THE NWRN US SHOULD CHANGE THE FLOW AND SUPPORT AN INCREASING POTENTIAL FOR WIDESPREAD PCPN SPREAD ACROSS THE REGION AND INLAND. EMERGENCE SUN/NEXT MON IS ACROSS THE CENTRAL US WITH RENEWED HEIGHT FALLS AND ADVANCE MOISTURE/WAA/PCPN RETURN INTO AND THROUGH THE LINGERING/LIFTING TRAILING FRONT LEFT IN THE WAKE OF THE MID-LATE WEEK MAIN SYSTEM. A LATE PERIOD WILDCARD IS ANY ADDITIONAL INFLUNCE FROM AN UNCERTAIN APPROACH OF AN ORGANIZED SRN STREAM SYSTEM SPLITING SEWD OVER THE ERN PACIFIC THU-SAT THAT MAY WORK IN SOME FASHION CENTERED OVER NWRN MEXICO BY DAYS 6/7. THE 12 UTC ECMWF WAS PARTICULARLY ROBUST WITH ASSOCIATED CENTRAL US SURFACE LOW RESPONSE...BUT RUN TO RUN CONTINUITY IS LESS THAN STELLAR AND THAT NOW INCLUDES A MUCH LESS PROGRESSIVE NEWER 00 UTC RUN. RECENT CANADIAN AND GFS RUNS OFFER A DECENT SYSTEM...BUT ALSO WITH SLOWER TIMING...AND LATEST ENSEMBLES ARE MIXED. PREFER TO MAINTAIN WPC CONSISTENCY WITH A SOLUTION CLOSEST TO THE 12 UTC ECMWF ENSEMBLE MEAN THAT OFFERS NEAR COMPOSITE TIMING AND ADDED MANUAL ADJUSTMENTS TO INSURE DECENT SYSTEM AMPLITUDE AS PER MODEL TRENDS...BUT COGNISANT OF LINGERING UNCERTAINTY. SCHICHTEL