EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1059 AM EST WED MAR 08 2017 VALID 12Z SAT MAR 11 2017 - 12Z WED MAR 15 2017 ...PATTERN OVERVIEW AND MODEL EVALUATION... OVER THE NEXT WEEK NEARLY ZONAL/FLAT FLOW OVER THE WEST WILL TRANSITION TO A RIDGE WHICH WILL AMPLIFY THE TROUGH DOWNSTREAM OVER THE CENTRAL AND EASTERN U.S. THIS IS WELL SUPPORTED IN THE MOST CURRENT GUIDANCE. PERSISTENT RUN TO RUN VARIABILITY OVER THE PAST FEW DAYS HAVE NOT IMPROVED CONFIDENCE ON THE SPECIFICS FOR EMBEDDED SHORTWAVES IN THE PROGRESSIVE FLOW. HOWEVER...THE 00Z/06Z GFS HAS TRENDED TOWARD A MORE PROGRESSIVE/AMPLIFIED TROUGH DIGGING INTO THE UPPER MIDWEST BY EARLY SUNDAY MORNING. AS IT SWINGS THROUGH THE GREAT LAKES/OHIO VALLEY MONDAY INTO THE MEAN TROUGH IT IS SIGNALING SUPPORT FOR THE DEVELOPMENT/STRENGTHENING OF A COASTAL SYSTEM BY THE END OF THE PERIOD. THE ECWMF ALSO DEPICTS A COASTAL SYSTEM...BUT PLACED FARTHER UP THE COAST TO THE SOUTH OF MAINE. ALTHOUGH MODELS ARE STARTING TO CONVERGE ON THIS SIGNAL QUITE OF BIT OF SPREAD IS PRESENT WITH THE LOW PLACEMENT AND DEPTH OF THE PRESSURE CENTER...WHICH WILL AFFECT HOW CLOSE TO THE COASTLINE OR OUT OVER THE ATLANTIC THE SYSTEM WILL TRACK. THIS SYSTEM COULD POTENTIALLY BRING LATE SEASON SNOW, POSSIBLY WITH HIGHER SNOWFALL AMOUNTS, FROM THE MID-ATLANTIC TO NEW ENGLAND. THE WPC DAY 3-7 FORECAST STARTED WITH A BLEND OF THE 00/06Z GFS/GEFS MEAN AND 00Z ECMWF/ECWMF ENSEMBLE MEAN...WITH MORE OPERATIONAL MODEL WEIGHTING EARLY IN THE PERIOD. THIS SOLUTION SEEMED TO BEST TAKE INTO ACCOUNT THE SOUTHWARD TREND IN THE GUIDANCE WITH THE LOW TRACKING OFF THE SOUTHEAST COAST ON SUNDAY WHILE ALSO NOT STRAYING TOO FAR FROM THE PREVIOUS WPC FORECAST. MORE EVEN MODEL/ENSEMBLE WEIGHT WAS USED TOWARD THE ENSEMBLE MEANS BY THE DAY 6/7 FORECAST (TUESDAY/WEDNESDAY) SINCE THERE REMAINS A LARGE AMOUNT OF SPREAD AMONG DETERMINISTIC GUIDANCE WITH THE SHORTWAVE POSSIBLY AMPLIFYING OVER THE EASTERN U.S. EARLY NEXT WEEK. ...WEATHER HIGHLIGHTS... OVER THE COURSE OF THE WEEKEND/THIS COMING WEEK TEMPERATURES WILL BE ABOVE NORMAL IN THE WEST... WITH BELOW OR WELL-BELOW NORMAL EAST OF THE CONTINENTAL DIVIDE. AN ARCTIC AIRMASS WILL SETTLE IN OVER MUCH OF THE CENTRAL AND EASTERN STATES RESULTING IN AFTERNOON TEMPERATURES FORECAST RANGING 10 TO 30 DEGREES COOLER THAN THOSE TYPICAL FOR EARLY/MID-MARCH. A FEW LOCATIONS ACROSS NEW ENGLAND POTENTIALLY COULD SET NEW LOW MAXIMUM TEMPERATURE RECORDS ON SATURDAY. FOR THE WEST...TEMPERATURES WILL RANGE 5 TO 20 DEGREES ABOVE NORMAL -- OVERNIGHT TEMPERATURE RECORDS MAY BE BROKEN FOR SEVERAL LOCATIONS ACROSS SOUTHERN CALIFORNIA/THE GREAT BASIN/DESERT SOUTHWEST. TEMPERATURES SHOULD BEGIN TO MODERATE ACROSS THE CENTRAL U.S. EARLY NEXT WEEK AS UPPER RIDGING IN THE WEST GRADUALLY EDGES EAST. IN TERMS OF PRECIPITATION ACROSS THE NATION...MODERATE TO HEAVY RAINS WITH EMBEDDED THUNDERSTORMS ARE EXPECTED WITHIN WARM ADVECTION INCREASING AHEAD A SHORTWAVE AND SURFACE LOW TRACKING FROM THE SOUTHERN PLAINS TO THE SOUTHEAST COAST SATURDAY INTO SUNDAY...WITH LATE SEASON SNOW POSSIBLE ON THE NORTHERN EDGE OF THE PRECIPITATION SHIELD. MODERATE TO HEAVY PRECIPITATION WILL ALSO BE POSSIBLE WITH AN UPSTREAM SHORTWAVE EJECTING OUT INTO THE NORTH CENTRAL U.S. ON MONDAY...ESPECIALLY IF IT HELPS DEEPEN A SURFACE CYCLONE ALONG THE EASTERN SEABOARD TUESDAY/WEDNESDAY...BUT THE DETAILS OF THE FORECAST REMAIN EXTREMELY UNCERTAIN. COASTAL RAIN AND HIGHER ELEVATION SNOW...WITH PERIODS OF HIGHER INTENSITY...WILL SPAN FROM THE PACIFIC NORTHWEST TO THE NORTHERN ROCKIES FOR SEVERAL DAYS. CAMPBELL/GERHARDT