MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 208 PM EST THU FEB 04 2016 VALID FEB 04/1200 UTC THRU FEB 08/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...SHARPENING UPPER TROUGH CROSSING THE LOWER MID-ATLANTIC ON FRIDAY MORNING... ...SURFACE WAVE DEVELOPING OFF THE OUTER BANKS... FINAL PREFERENCE: A NON-09Z SREF MEAN MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE WATER VAPOR IMAGERY THIS AFTERNOON SHOWED AN AXIS OF MID-LEVEL HEIGHT FALLS MOVING THROUGH THE OZARKS WITH GRADUAL SHARPENING OF THIS SYSTEM DURING THE NEXT 24 HOURS. THERE ARE SUBTLE TIMING DIFFERENCES AS THE SHORTWAVE TRACKS ACROSS THE SOUTHERN MID-ATLANTIC ON FRIDAY MORNING. MOST NOTABLY...THE 09Z SREF MEAN IS ON THE SLOWER SIDE OF THE SPREAD. REGARDING SURFACE WAVE DEVELOPMENT OFF THE OUTER BANKS...THERE HAS BEEN A SLIGHT MOVE IN THE OFFSHORE DIRECTION WHEN COMPARING THE PAST TWO ENSEMBLE LOW PLOTS. OVERALL...GIVEN REASONABLE AGREEMENT AMONG THE GUIDANCE...A NON-09Z SREF MEAN SOLUTION WILL BE RECOMMENDED. ...SPLIT FLOW OVER THE CENTRAL U.S. ON FRIDAY... ...STRENGTHENING SOUTHERN STREAM FEATURE EXITING THE SOUTHEASTERN U.S. COAST BY 07/1800Z... ...LOW PRESSURE DEVELOPMENT OFF THE GA/SC COAST... FINAL PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: AVERAGE LOW AMPLITUDE SPLIT FLOW TRACKING THROUGH THE INTERMOUNTAIN WEST WILL REACH THE CENTER OF THE COUNTRY BY EARLY FRIDAY. MODELS AGREE THE SOUTHERN MOST SYSTEM SHOULD DOMINATE AS IT GAINS ADDITIONAL AMPLITUDE OVER THE SOUTHERN U.S. THIS IS THE POINT WHERE THE GUIDANCE DIVERGE...PRIMARILY WITH TIMING. ON THE MORE PROGRESSIVE SIDE ARE THE 12Z NAM/GFS AND 12Z GEFS MEAN/06Z GFS-PARALLEL WITH THE 12Z GFS TRENDING QUICKER DURING THIS CYCLE. THIS BRINGS ITS SOLUTION OUT AHEAD OF ANY OTHER PIECE OF GUIDANCE. ENSEMBLE SPAGHETTI PLOTS IN RECENT DAYS HAVE SHOWN THE ECMWF SUITE TO BE QUITE CONSISTENT WITH THIS PATTERN FAVORING SOMETHING SLOWER AND A BIT MORE AMPLIFIED. THE 12Z ECMWF HAS MAINTAINED THIS CONSISTENCY WHILE THE 12Z CMC/UKMET MOVED TOWARD THE FASTER SIDE...PARTICULARLY THE LATTER. GIVEN THE ASSESSMENT ABOVE...THE PREFERENCE WILL REMAIN A COMBINATION OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN. ...NORTHERN STREAM AMPLIFICATION ACROSS THE NORTHERN TIER FRIDAY THROUGH SUNDAY... FINAL PREFERENCE: BLEND OF THE 09Z SREF/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE A SYSTEM CURRENTLY NEAR THE BORDER BOUNDING THE NORTHWEST TERRITORIES AND CONTINENTAL NUNAVUT WILL SINK SOUTHWARD CARRYING A STRONG LOBE OF VORTICITY JUST SOUTH OF HUDSON BAY BY FRIDAY EVENING. THIS AMPLIFICATION PROCESS WILL DRAG SHORTWAVE ENERGY FROM THE UPPER MIDWEST TOWARD NEW ENGLAND THROUGH SUNDAY MORNING WITH TIMING DIFFERENCES BEING A PREVALENT ISSUE. THE 12Z GFS TRENDED SIGNIFICANTLY SLOWER WHICH CARRIES IT AWAY FROM ALL OF THE MEANS WHICH ARE SITUATED FARTHER DOWNSTREAM. RUN-TO-RUN VARIABILITY CONTINUES TO PLAGUE THE FORECAST WITH MANY CHANGES NOTED IN AMONG THE 12Z CMC/UKMET/ECMWF SOLUTIONS. THUS...FEEL INCLINED TO FOLLOW THE ENSEMBLE MEANS HERE. INITIALLY HAD INCLUDED THE GEFS MEAN INTO THE MIX BUT THE 12Z CYCLE LOOKS MORE LIKE THE 12Z GFS. THE 09Z SREF MEAN BEING INCLUDED WITH THE 00Z ECMWF ENSEMBLE MEAN WOULD OFFER A MORE CONSERVATIVE APPROACH AMIDST THE COMPLEX PATTERN. ...PACIFIC SYSTEM AFFECTING THE NORTHWESTERN CONUS ON FRIDAY... ...LONGWAVE TROUGH GAINING AMPLITUDE OVER THE MIDWEST... ...ATTENDANT SURFACE LOW/FRONTAL SYSTEM... FINAL PREFERENCE: BLEND OF THE 09Z SREF/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE HEIGHT FALLS ACCELERATING TOWARD THE PACIFIC NORTHWEST COAST WILL EVENTUALLY REACH THE NORTHERN ROCKIES BY 06/1800Z. MODELS VARY IN AMPLITUDE WITH TWO CAMPS SETTING UP. ON THE FLATTER SIDE ARE THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN AND 09Z SREF MEAN WHILE THE 12Z NAM/GFS/UKMET DEPICT MORE AMPLITUDE. THE 12Z GFS MADE A MOVE TOWARD THE SLOWER/MORE AMPLIFIED DIRECTION WHICH TAKES IT AWAY FROM THE BETTER ENSEMBLE SUPPORT NOTED IN ENSEMBLE SPAGHETTI PLOTS. WILL STICK WITH THE FLATTER/MORE PROGRESSIVE SOLUTION WHICH IS MORE ALONG THE LINES OF THE 09Z SREF/00Z ECMWF ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER