EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 137 AM EST SAT FEB 20 2016 VALID 12Z TUE FEB 23 2016 - 12Z SAT FEB 27 2016 ...OVERVIEW... A HIGH AMPLITUDE PATTERN WILL BE FEATURED FOR MUCH OF NEXT WEEK WITH SPLIT FLOW COMPLICATING THE FORECAST ACROSS THE CENTRAL/EASTERN U.S. AMPLIFIED FLOW IN THE NORTHERN/SOUTHERN STREAM WILL HELP ANCHOR A BROAD UPPER TROUGH FROM THE PLAINS TO THE EASTERN SEABOARD. GENERAL MEAN RIDGING IS EXPECTED TO CONTINUE ITS DOMINANCE OVER THE WEST WITH A LOW AMPLITUDE SHORTWAVE EVENTUALLY POKING INTO THE RIDGE BY LATE FRIDAY. WHILE DETAILS HAVE CHANGED COMPARED TO RECENT FORECASTS...THE GENERAL SYNOPTIC PATTERN HAS NOT BUDGED MUCH. ...GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES... RELATIVE TO THE FORECAST MADE YESTERDAY...MODELS HAVE MADE RATHER ABRUPT CHANGES. WHILE THE GUIDANCE CONTINUES TO FAVOR LOWER HEIGHTS OVER THE CENTRAL/EASTERN U.S. THROUGHOUT MUCH OF THE PERIOD...HOW THEY ARRIVE AT THIS SOLUTION VARIES. THE INITIAL SHORTWAVE ROUNDING THE BASE OF THE UPPER TROUGH WILL INDUCE A WEAK AREA OF LOW PRESSURE WHICH IS EXPECTED TO LIFT UP THE EAST COAST. EXCEPT FOR THE ECMWF SUITE...MOST OTHER GUIDANCE TENDED TO SHEAR THIS FEATURE AS IT MOVED UP THE GULF STREAM. MOVING AHEAD TO THE NEXT FEATURE...THE DEGREE OF PHASING BETWEEN THE SPLIT STREAMS WILL PLAY A KEY ROLE IN HOW DEEP THE RESULTANT SURFACE CYCLONE BECOMES. THE GUIDANCE VARY WITH THE EVOLUTION AND INTENSITY OF THIS SYSTEM WITH A NOTABLE WESTWARD TREND IN THE MODELS. RECENT GEFS MEMBERS AND THE PAST FEW DETERMINISTIC GFS RUNS HAVE FAVORED THE MORE WESTERN TRACK TOWARD THE LOWER GREAT LAKES WITH PRETTY SIGNIFICANT CYCLOGENESIS UNFOLDING. THERE ARE A LARGE NUMBER OF GEFS MEMBERS TOWARD THE COAST AS WELL. MEANWHILE...RECENT ECMWF SOLUTIONS HAVE FAVORED A POSITION TOWARD THE EAST WITH A LOW TRACK CLOSER TO THE APPALACHIANS. HOWEVER...PLENTY OF THE ECMWF ENSEMBLE MEMBERS CONTINUE TO BE CLOSER TO THE COAST WHICH THE 12Z ECMWF FOLLOWED. WHILE EVOLUTIONS VARY FROM MODEL TO MODEL...SYNOPTIC AGREEMENT EXISTS IN ESTABLISHING LOWER HEIGHTS ACROSS THE GREAT LAKES/NORTHEASTERN U.S. DURING THE LATTER PART OF THE MEDIUM RANGE. OVER IN THE WESTERN U.S...GUIDANCE AS A WHOLE ARE FAIRLY CONSISTENT IN MAINTAINING POSITIVE HEIGHT ANOMALIES FOR MUCH OF THE PERIOD. MULTIPLE LOW-AMPLITUDE PERTURBATIONS NUDGE THE RIDGE EARLY ON BEFORE HEIGHTS BUILD FURTHER TOWARD THE MIDDLE/LATTER PART OF THE WEEK. BY LATE FRIDAY...MODELS SHOW A MORE PRONOUNCED BATCH OF HEIGHT FALLS APPROACHING NORTHERN CA/SOUTHERN OR WHICH WILL HELP ADVANCE THE STOUT RIDGE TOWARD THE INTERMOUNTAIN WEST BY SATURDAY. REGARDING PREFERENCES...WPC LEANED ON A COMBINATION OF THE 12Z GFS/ECMWF/CMC FOR DAY 3 GIVEN REASONABLE AGREEMENT. HOWEVER...QUICKLY LOWERED CONTRIBUTIONS FROM THE 12Z GFS/CMC IN FAVOR OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS BY DAY 4. THIS WAS DUE TO INCREASING UNCERTAINTY WITH THE EVOLVING SURFACE PATTERN ACROSS THE GULF COAST AND EASTERN U.S. ALL IN ALL...THE 12Z ECMWF HAS BEEN THE MOST STABLE SOLUTION AMONG THE DETERMINISTIC MODELS. WITH THAT SAID...WAS ABLE TO KEEP SOME PERCENTAGE OF THE MODEL THROUGH DAY 6 WHILE INCREASING ENSEMBLE INFLUENCES. GENERALLY SPLIT THE DIFFERENCE BETWEEN THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS WHEN UTILIZED GIVEN SIMILAR OUTPUTS. ...WEATHER HIGHLIGHTS/THREATS... THE HIGHLY SINUSOIDAL SYNOPTIC PATTERN WILL CREATE FAIRLY DISCERNIBLE TEMPERATURE SPREADS ON THE MAP. EARLY IN THE FORECAST...TEMPERATURES WILL BE 5 TO 10 DEGREES BELOW NORMAL IN AREAS OF ACTIVE PRECIPITATION WHICH SPREADS FROM THE CENTRAL ROCKIES THROUGH THE SOUTHERN PLAINS/LOWER MS VALLEY AND INTO THE MID-ATLANTIC. AS HEIGHTS FURTHER LOWER ACROSS THE EASTERN THIRD OF THE CONUS...THESE BELOW NORMAL READINGS WILL EXPAND IN COVERAGE ALTHOUGH ANOMALIES SHOULD NOT SINK MUCH BELOW THE 10 TO 15 DEGREE DEPARTURE RANGE. AN ACTIVE PRECIPITATION PATTERN IS EXPECTED WITH MODERATE/HEAVY RAINFALL POSSIBLE FROM THE SOUTHERN PLAINS EASTWARD THROUGH THE TN VALLEY AND INTO THE CAROLINAS/MID-ATLANTIC REGION. WINTRY ASPECTS OF THESE SYSTEMS SHOULD FOCUS FROM THE CENTRAL APPALACHIANS UP THROUGH THE HIGHER TERRAIN OF PA AND INTO MUCH OF INTERIOR NEW ENGLAND. GIVEN THE CANADIAN SURFACE HIGH WILL HAVE LIFTED INTO THE MARITIMES DURING THIS PRECIPITATION EVENT...THE BEST CHANCES FOR WINTRY PRECIPITATION SHOULD BE ACROSS HIGHER ELEVATIONS. OUT WEST...WELL ABOVE NORMAL TEMPERATURES WILL PREVAIL UNDERNEATH THE STOUT UPPER RIDGE. FORECAST HIGHS ARE ROUGHLY 10 TO 15 DEGREES ABOVE CLIMATOLOGY WHICH SHOULD HELP DESERT SOUTHWEST LOCATIONS APPROACH 90 DEGREES DURING THE PERIOD. MODELS INDICATE TEMPERATURES SHOULD REACH THE LOW 60S ACROSS THE PACIFIC NORTHWEST WHICH INCLUDES THE CITIES OF PORTLAND OR AND SEATTLE WA. THE BEST THREAT FOR PRECIPITATION IS FORECAST TO BE LATE IN THE PERIOD AS THE RIDGE BREAKS DOWN WITH A SHORTWAVE NEARING THE NORTHERN CA COAST ON FRIDAY. RUBIN-OSTER