EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 AM EDT MON APR 14 2014 VALID 12Z THU APR 17 2014 - 12Z MON APR 21 2014 ...MODEL/PATTERN OVERVIEW... TO BEGIN THE PERIOD ON THURSDAY...APRIL 17...A HIGH-AMPLITUDE FLOW WILL BE IN PLACE WITH A BROAD UPPER TROF SWINGING THROUGH THE CENTRAL U.S. THIS FEATURE WILL CONSIST OF A SPLIT STREAM WITH THE SOUTHERN BRANCH OF THE JET SLIDING THROUGH THE CENTRAL PLAINS WHILE THE OTHER SYSTEM GRADUALLY SHEARS ALONG THE INTERNATIONAL BORDER. SOUTHWESTERLY FLOW ALOFT WILL CARRY THIS SYSTEM TOWARD THE NORTH AND EAST WITH AN AREA OF LOW PRESSURE RISING ACROSS THE OZARKS AND INTO THE MID MS VALLEY EARLY FRIDAY. THE 06Z GFS/00Z CMC ARE A TAD STRONGER ALOFT WHICH ALLOWS A DEEPER SOLUTION TO AFFECT THE MS RIVER VALLEY. THE MODELS BEGIN TO DIVERGE ENTERING THE WEEKEND WITH A POTENTIAL SPLIT IN THE JETS ACROSS THE EASTERN THIRD OF THE COUNTRY. THE LAST FEW RUNS OF THE GFS ALONG WITH THE 00Z CMC EMPHASIZE THE NORTHERN STREAM WITH THE LATTER BEING MUCH MORE DEVELOPED WITH A STRONG NEGATIVE TILT INDICATED. MEANWHILE...THE 00Z ECMWF/UKMET PUT MORE FOCUS ON THE SOUTHERN STREAM WHICH INDUCES A SURFACE LOW ACROSS THE NORTHERN GULF OF MEXICO AND EVENTUALLY ALONG THE SOUTHEASTERN U.S. COAST ON FRIDAY/SATURDAY. THE GLOBAL ENSEMBLE MEANS DEFINITELY ALL SHOW HINTS AT MODEST DEVELOPMENT ALONG THE EAST COAST SO LEANED IN THIS DIRECTION FOR THE WPC MEDIUM RANGE PROGS. OVERALL...A MAJORITY OF THE MODELS DO SHOW AT THE MINIMUM AN INVERTED TROF AXIS ALONG THE WESTERN ATLANTIC WITH THE MORE AGGRESSIVE SOLUTIONS DEVELOPING AN AREA OF LOW PRESSURE. AS THIS SYSTEM EVENTUALLY MOVES SLOWLY OFFSHORE BY LATER IN THE PERIOD...THE PATTERN CONTINUES TO REMAIN SPLIT IN NATURE ACROSS THE WESTERN/CENTRAL U.S. THE GUIDANCE DEPICT AN ELONGATED UPPER TROF IN THE VICINITY OF NORTHWESTERN MEXICO LATE IN THE WEEKEND WHILE THE NORTHERN STREAM REMAINS MUCH MORE ACTIVE. HOWEVER...IT APPEARS THERE WILL BE AMPLE SEPARATION BETWEEN THE STREAMS WITH THE NORTHERN BRANCH MAINTAINING A STEADY FLOW OF SHORTWAVES STRADDLING THE U.S./CANADIAN BORDER. BY EARLY NEXT WEEK...THE UPPER PATTERN WILL REMAIN WELL DEFINED WITH A RIDGE ACROSS THE WESTERN U.S. WHILE A TROF ANCHORS THE EASTERN STATES. ...WPC PREFERENCES... THE GUIDANCE AVAILABLE WERE IN CLOSE ENOUGH AGREEMENT WITH THE EXCEPTION OF THE 00Z CMC TO WARRANT A BLEND OF THE 06Z GFS AND 00Z ECMWF/UKMET THROUGH DAY 4...FRIDAY WITH A BIT MORE EMPHASIS ON THE 06Z GFS/00Z ECMWF SOLUTIONS. MOVING INTO SATURDAY...DECIDED TO REMOVE THE 06Z GFS FROM THE MIX GIVEN ITS AFOREMENTIONED LACK OF A SOUTHERN STREAM SYSTEM AFFECTING THE SOUTHEASTERN U.S. ADDITIONALLY...THE AGGRESSIVE 00Z CMC SEEMED TO BE AN OUTLIER WITH LITTLE TO NO SUPPORT FROM THE ENSEMBLE MEANS NOR THE SPAGHETTI PLOTS. WPC LEANED ON A 00Z ECMWF/UKMET SOLUTION ON DAY 5...SATURDAY GIVEN THE REASONABLE HANDLING OF THE DEVELOPMENT OF LOW PRESSURE ALONG THE SOUTHEASTERN U.S. COAST. THEREAFTER...ENOUGH SPREAD WITH THE TRACK OF THIS SYSTEM ALONG WITH DIFFERENCES NOTED UPSTREAM WITHIN THE AMPLIFIED/SPLIT FLOW REGIME THAT A COMBINATION OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS WERE UTILIZED THROUGH APRIL 21. ...SENSIBLE WEATHER HIGHLIGHTS... THE FIRST COUPLE OF DAYS OF THE PERIOD...THURSDAY/FRIDAY...WILL BE QUITE CHILLY ACROSS THE CENTER OF THE COUNTRY WITH TEMPERATURES 15 TO 20 DEGREES BELOW NORMAL...PARTICULARLY IN THE CENTRAL PLAINS. THE ACCOMPANYING AREA OF LOW PRESSURE CROSSING THE CO ROCKIES AND INTO THE SOUTHERN PLAINS WILL SUPPORT AN AREA OF MODERATE/HEAVY PRECIPITATION ACROSS THE CENTRAL ROCKIES ON THURSDAY. ENHANCED UPSLOPE FLOW SHOULD AID IN LOCALLY HEAVIER AMOUNTS ALONG THE FAVORED TERRAIN. GIVEN THE NEGATIVE HEIGHT ANOMALIES IN PLACE...WINTRY PRECIPITATION MAY BE POSSIBLE ACROSS THE HIGHER ELEVATIONS. TEMPERATURES SHOULD GRADUALLY MODERATE BY THE WEEKEND AS THE FLOW BECOMES MORE ZONAL AND WARMER THICKNESSES PREVAIL. AS THIS SYSTEM MIGRATES EASTWARD...COOLER AND WETTER CONDITIONS ARE POSSIBLE ACROSS THE CENTRAL/EASTERN GULF COAST AS WELL AS ALONG THE EASTERN SEABOARD. DEPENDING UPON THE MODEL...IT MAY BE QUITE AN UNSETTLED PERIOD FROM FRIDAY AND INTO THE WEEKEND. ELSEWHERE...BUILDING HEIGHTS ACROSS THE WESTERN U.S. SHOULD BRING ABOVE NORMAL TEMPERATURES TO THE REGION WHICH HAS BEEN THE COMMON THEME FOR QUITE SOME TIME. RUBIN-OSTER