MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1156 PM EST THU FEB 13 2014 VALID FEB 14/0000 UTC THRU FEB 17/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...VIGOROUS UPPER LOW LIFTING THROUGH COASTAL NEW ENGLAND OVERNIGHT... ...DEEPENING SURFACE CYCLONE AFFECTING THE NORTHEASTERN U.S... PRELIMINARY PREFERENCE: A NON-12Z CMC SOLUTION FORECAST CONFIDENCE: ABOVE AVERAGE A DYNAMIC UPPER LOW WHICH HAS SPREAD WIDESPREAD WINTRY PRECIPITATION ACROSS THE NORTHEASTERN U.S. WILL CONTINUE TO LIFT NORTHWARD WHILE GAINING ADDITIONAL STRENGTH. AS THIS OCCURS...A COASTAL LOW WILL RAPIDLY DEEPEN ALONG THE EASTERN SEABOARD WITH THE MODELS IN SUFFICIENT AGREEMENT WITH THE EXCEPTION OF THE 12Z CMC WHICH IS A BIT TOO FAST. THUS...THE PREFERENCE IS A NON-12Z CMC SOLUTION. ...SHORTWAVE TRACKING ACROSS THE GREAT LAKES EARLY IN THE PERIOD... PRELIMINARY PREFERENCE: GENERAL MODEL CONSENSUS FORECAST CONFIDENCE: HIGH AN AXIS OF WEAK HEIGHT FALLS ARE EXPECTED TO SLIDE ACROSS THE GREAT LAKES EARLY THIS MORNING WITH THE ENERGY GRADUALLY SHEARING AS IT BECOMES SOMEWHAT ABSORBED BY THE CLOSED LOW ALONG THE EASTERN SEABOARD. GIVEN THE FORECAST IS PRIMARILY DURING THE FIRST 18 HOURS...MODELS AGREE WITH ONE ANOTHER ENOUGH TO SUPPORT A GENERAL MODEL CONSENSUS HERE. ...CLIPPER SYSTEM SLIDING THROUGH THE LOWER TN VALLEY BY 15/0600Z... ...COASTAL LOW EMERGING OFF THE OUTER BANKS/VA CAPES... PRELIMINARY PREFERENCE: BLEND OF THE 00Z NAM/12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE A MULTITUDE OF SHORTWAVES SEEN ON WATER VAPOR IMAGERY TRACKING THROUGH THE NORTHERN HIGH PLAINS WILL QUICKLY BEGIN TO NOSE SOUTH AND EAST WHILE AMPLIFYING PRETTY DRAMATICALLY BY FRIDAY EVENING. MODELS AGREE THAT THIS CLIPPER SYSTEM WILL BECOME NEGATIVELY-TILTED AS IT EMERGES OFF THE COASTAL CAROLINAS EARLY SATURDAY WHICH SHOULD HELP INVIGORATE AN AREA OF SURFACE LOW PRESSURE. AS WAS THE CASE YESTERDAY...THE 12Z UKMET LOOKS MUCH TOO SLOW WITH THE EVOLUTION WITH NO SUPPORT FROM THE ENSEMBLE SPAGHETTI PLOTS. OVERALL...THE ENSEMBLE LOW PLOTS LOOK RATHER MESSY SHOWING THE INHERENT UNCERTAINTY IN THE FORECAST. A MAJORITY OF THE MEMBERS DEPICT THE LOW TRACKING EAST OF THE 40N/70W BENCHMARK ALTHOUGH THE 00Z GFS SUGGESTS A SCENARIO WHERE THE SYSTEM CROSSES DIRECTLY OVER THIS SPOT. WHILE POSSIBLE...IT STILL LOOKS LIKE A MINORITY SOLUTION WITHIN THE BROAD SPREAD. WILL PREFER THE TRACK SUGGESTED BY THE 00Z NAM/12Z ECMWF. THE 00Z NAM IS A BIT SLOWER THAN THE 12Z ECMWF BUT WILL AVERAGE OUT THESE DIFFERENCES IN THE PREFERENCE. ...WEAKLY AMPLIFIED UPPER TROF CROSSING THE LOWER MID-ATLANTIC BY MIDDAY SUNDAY... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: AVERAGE ON THE HEELS OF THE CLIPPER SYSTEM WILL BE ANOTHER AREA OF SHORTWAVE ENERGY RACING THROUGH THE MIDDLE MS VALLEY BY MIDDAY SATURDAY. GIVEN THE PROGRESSIVE PATTERN DEPICTED...THE 00Z NAM SEEMS A BIT SLOWER THAN THE CONSENSUS. THE 18Z GEFS MEAN DID SUPPORT THE 00Z NAM...BUT THE 00Z GFS HAS SHIFTED GEARS TOWARD A FASTER SOLUTION SO EXPECT THE ENSEMBLE MEAN TO FOLLOW SUIT. THE 00Z GFS NOW SUPPORTS THE 12Z ECMWF/ECMWF ENSEMBLE MEAN PRETTY READILY SO WILL RECOMMEND A COMBINATION OF THESE TWO. ...PAIR OF SYSTEMS TRACKING ACROSS THE NORTHERN/CENTRAL PLAINS EARLY NEXT WEEK... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE A FAIRLY PRONOUNCED UPPER TROF WILL SWING EASTWARD TOWARD THE PACIFIC NORTHWEST COAST BY LATE SATURDAY NIGHT. THE 00Z NAM/GFS AND 12Z ECMWF APPEAR REASONABLY WELL WITH THE ENSEMBLE MEANS WITH REGARD TO THE SURFACE EVOLUTION. THE 12Z UKMET TENDS TO WRAP UP A LOW A BIT FURTHER NORTHWEST THAN OTHER MODELS. AS THE SHORTWAVE ENERGY MOVES INLAND...IT APPEARS THE SYSTEM WILL SPLIT IT INTO PAIR OF WAVES...EACH WITH A DEFINED LOW TRACK. A SLEW OF MODEL DIFFERENCES ARE NOTED WITH THE 12Z CMC EMPHASIZING THE NORTHERN SYSTEM MORE READILY WHILE THE 12Z UKMET IS SLOWER WITH ITS EVOLUTION. THE LATTER MAKES SENSE AS THE 12Z UKMET WAS MORE WRAPPED UP WITH THE INITIAL PACIFIC CYCLONE. A VARIETY OF SOLUTIONS ARE ADVERTISED BY EARLY MONDAY SO THE CONFIDENCE IS RATHER LOW WITH ANY PREFERENCE. ONE THING TO NOTE IS THE PAST FEW CYCLES OF THE ENSEMBLE LOW PLOTS SHOW THE ECMWF ENSEMBLE MEMBERS HAVE FAVORED A LOW POSITION ACROSS OK/KS ON MONDAY MORNING. MEANWHILE...THE 18Z GEFS MEAN SHOWS A FASTER SOLUTION WHICH THE 00Z GFS HAS BACKED OFF ON AND SLOWED A BIT MORE TOWARD THE ECMWF SUITE. THE PREFERENCE WILL LEAN ON THE STABILITY OF THE ECMWF ENSEMBLE MEAN BUT ADD THE 00Z GFS/12Z ECMWF TO THE MIX AS THEY OFFER REASONABLE DETAILS DURING THE PERIOD. ...NEXT PACIFIC SYSTEM IMPACTING THE PACIFIC NORTHWEST EARLY MONDAY... PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: AVERAGE AS ZONAL FLOW BECOMES REESTABLISHED ACROSS THE WESTERN U.S...ANOTHER MYRIAD OF IMPULSES BEGIN TO TRACK INTO THE PACIFIC NORTHWEST/UPPER INTERMOUNTAIN WEST BY EARLY NEXT WEEK. OVERALL...THERE ARE ENOUGH DETAIL DIFFERENCES THAT A COMBINATION OF THE ENSEMBLE MEANS WILL BE THE BEST WAY TO RESOLVE THIS ISSUE. FOR NOW WILL LEAN ON THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS WITH AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... RUBIN-OSTER