EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1156 AM EDT MON MAY 04 2015 VALID 12Z THU MAY 07 2015 - 12Z MON MAY 11 2015 ...OVERVIEW AND GUIDANCE PREFERENCES... THE LARGEST INFLUENCES ON THE SYNOPTIC FLOW ACROSS THE CONUS THE NEXT 7 DAYS INCLUDE THE DECAYING REX-BLOCK OVER THE BERING SEA...WHICH IS PROMOTING SPLIT-FLOW DOWNSTREAM AND A MEAN TROUGH IN THE WEST...AND THE SUBTROPICAL HIGH OVER THE ATLANTIC WHERE ANOMALIES ARE RUNNING ABOUT 3 STANDARD DEVIATIONS ABOVE NORMAL. THE HIGH IS IMPORTANT BECAUSE OF ITS STEERING INFLUENCE WITH ANY LOW OR LOWS THAT MIGHT FORM OVER OFF THE SOUTHEAST COAST THE NEXT SEVERAL DAYS. FOR THE MEAN TROUGH IN THE WEST...INCLUDING THE CLOSED LOW PORTION CROSSING THE FOUR CORNERS AND THE NORTHERN STREAM PORTION RUNNING ALONG THE CANADIAN BORDER...MODEL CLUSTERING AND RECENT TRENDS SUPPORT A SOLUTION TOWARD THE SLOWER SIDE OF THE SOLUTION ENVELOPE...INCLUDING THE GFS/GEFS MEAN. THE ECMWF AND ITS OWN ENSEMBLE MEMBERS HAVE SLOWED APPRECIABLY ACROSS CANADA THE LAST COUPLE OF DAYS...WITH THE GFS ALSO SHOWING STRONGER RUN-TO-RUN CONTINUITY. THIS PREFERENCE IMPACTS THE FRONTAL TIMING ACROSS THE NORTHERN TIER...WITH AGAIN THE SLIGHTLY SLOWER SOLUTIONS FAVORED...WITH SMALLER IMPLICATIONS FOR EVOLUTION OF THE LOW OVER THE FOUR CORNERS...WHICH IS MORE DEPENDENT ON THE UPSTREAM FLOW. FOR THE CLOSED LOW PORTION...ABOUT 70 PERCENT TOWARD THE SLOWER 06Z GEFS MEAN IS PREFERRED OVER THE 00Z ECMWF ENSEMBLE MEAN. THE FASTER ECMWF APPEARS TO ALSO HAVE SOME BEARING ON THE TRACK OF ANY LOW OR LOWS THAT MAY DEVELOP OFF THE SOUTHEAST THE NEXT FEW DAYS...BY NUDGING THE LOW MORE OUT TO SEA AFTER DAY 5/SAT...COMPARED TO THE GFS/GEFS MORE WESTWARD CAMP. MODELS HAVE BEEN VERY CONSISTENT THE LAST FEW DAYS WITH A LOW DEVELOPING NORTH OF THE BAHAMAS...THEN ENTERING WEAKER FLOW AND POSSIBLY MEANDERING...WHILE TRENDS IN THE MODEL CONSENSUS HAVE BEEN WESTWARD. AFTER COORDINATING WITH THE NHC AND OPC...WE ARE ALL IN AGREEMENT TO REPOSITION ANY ANTICIPATED LOW SLIGHTLY MORE WESTWARD AND STATIONARY FOR DAYS 5-7 IN ACCORDANCE WITH AN INTERMEDIATE CHOICE BETWEEN THE MORE WESTWARD 06Z GEFS MEAN AND MORE OFFSHORE 00Z ECMWF ENSEMBLE MEAN. CONFIDENCE IS LOW WITH THIS PARTICULAR SYSTEM OWING TO MULTIPLE UNCERTAINTIES IN CORE IDENTITY AND OTHER MESOSCALE PROCESSES...NOT THE MENTION ANY UPSTREAM INFLUENCES. ...SENSIBLE WEATHER HIGHLIGHTS... WIDESPREAD AND IN SOME CASES HEAVY RAINFALL WILL ACCOMPANY THE LEADING EDGES OF THE UPPER TROUGH ENTERING THE HIGH PLAINS AND CENTRAL CONUS...WITH ADDITIONAL BUT MORE SCATTERED PRECIPITATION FORMING BENEATH THE LOW EXTENDING FROM CALIFORNIA INTO THE INTERMOUNTAIN WEST...WHILE A SMALLER AREA OF POSSIBLY HEAVY RAINFALL WILL BECOME POSSIBLE WITH ANY LOW THAT DEVELOPS OFF THE SOUTHEAST COAST. INCREASED ONSHORE FLOW NORTH OF ANY COASTAL LOW MAY ALSO RESULT IN ADVERSE CONDITIONS FOR OTHER COASTAL AND MARINE INTERESTS. FINALLY...BETWEEN THE UPPER TROUGH IN THE WEST AND THE COMPENSATING UPPER RIDGE IN THE EAST...A DIPOLE OF BELOW NORMAL AND ABOVE NORMAL TEMPERATURES WILL DEVELOP BENEATH THE LOW AND HIGH RESPECTIVELY. JAMES