EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 103 AM EDT MON MAY 04 2015 VALID 12Z THU MAY 07 2015 - 12Z MON MAY 11 2015 ...OVERVIEW AND GUIDANCE PREFERENCES... MODELS AND ENSEMBLES CONTINUE TO FORECAST RIDGING IN THE NORTHEAST CONUS AS WELL AS NW CANADA... WHICH FAVORS TROUGHING IN THE SOUTHWESTERN STATES THAT WILL SLOWLY LIFT OUT ONTO THE PLAINS IN ABOUT A WEEK. OFF THE SOUTHEAST/FLORIDA COAST... A 'LOST' UPPER/SURFACE LOW -- PERHAPS SUBTROPICAL... BUT PROBABLY MINOR -- WILL MEANDER JUST OFF THE COAST UNDERNEATH THE RIDGE. THE DETERMINISTIC MODELS HAVE MOSTLY FALLEN WITHIN THE ENSEMBLE SPREAD OVER THE PAST SEVERAL DAYS AND THAT CONTINUES WITH THEIR 12 OR 18Z/03 RUNS... ON WHICH THIS FORECAST WAS BASED. THE ECMWF HAS BEEN CURIOUSLY QUICKER THAN THE CONSENSUS AND THE BLOCKY NATURE OF THE FLOW SEEMS TO ARGUE FOR A BIT SLOWER RATHER THAN QUICKER PACE. 18Z GFS SEEMED LIKE A REASONABLE SOLUTION AND USED IT FOR SOME DETAILS ALONG WITH THE 18Z GEFS MEAN AND 12Z ECENS MEAN. PESKY DETAILS YET TO BE WORKED OUT INCLUDE THE FRONTAL PLACEMENT/STRENGTH IN THE NORTHEAST.... WHICH WILL AFFECT SURFACE TEMPERATURES... AND TIMING OF THE NEXT TROUGH INTO THE PAC NW NEXT SUN/MON. OFF THE SE COAST... RECENT GFS RUNS AND ENSEMBLE MEANS -- GEFS/ECENS/CANADIAN -- FAVOR A BIT WESTWARD POSITION OF THE SFC LOW WHILE THE 12Z/03 ECMWF/CANADIAN GLOBAL/UKMET LIE FARTHER EAST. WEAK STEERING FLOW MEANS NOTHING IS REALLY FAVORED AT THIS POINT... BUT STAYING WITH THE ENSEMBLES SEEMS PRUDENT FOR NOW. ...SENSIBLE WEATHER HIGHLIGHTS... PRECIP FOCUS WILL LIE NEAR AND JUST DOWNSTREAM OF THE UPPER LOW IN THE WEST... FROM THE GREAT BASIN THROUGH MY/CO AND OVER MUCH OF THE PLAINS FROM TEXAS NORTHWARD. ECMWF ENSEMBLES WERE GENERALLY A BIT WETTER THAN THE GFS AND GEFS MEMBERS OVER TX/OK/KS... BUT ALL STILL INDICATE WIDESPREAD MODEST RAINS. LESSER PRECIP IS LIKELY IN THE NORTHEAST/MID-ATLANTIC AS WELL AS SOUTHERN CALIFORNIA... WHILE ZERO PRECIP LOOKS PROBABLE OVER SE CA INTO S AZ/NM. ULTIMATE TRACK OF THE ATLANTIC LOW WILL DETERMINE HOW MUCH... IF ANY... PRECIP WILL FALL OVER LAND. AT THE LEAST... ENOUGH INSTABILITY SHOULD EXIST AROUND ITS CIRCULATION TO HELP INITIATE SOME ISOLATED OR EVEN SCATTERED SHOWERS/CONVECTION. TEMPERATURES WILL BE MILD/WARM IN THE EAST THANKS TO RIDGING... WITH MANY PLACES REACHING THEIR HIGHEST TEMPS YEAR-TO-DATE. THE WEST WILL BE RATHER COOL... ESPECIALLY DAYTIME MAXES... OWING TO ABUNDANT CLOUDS AND SHOWERS. FRACASSO