MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 236 PM EST SAT MAR 11 2017 VALID MAR 11/1200 UTC THRU MAR 15/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC AND ECMWF ...INITIAL ELONGATED AXIS OF VORTICITY STRETCHING ALONG THE WESTERN GULF COAST... ...ATTENDANT SURFACE WAVE DEVELOPMENT IN THE GULF OF MX... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW A GRADUAL SHEARING OUT OF SOUTHERN STREAM VORT ENERGY ACROSS NORTHEAST MX AND THE WESTERN AND CENTRAL GULF COAST OVER THE NEXT COUPLE DAYS. THERE IS EXPECTED TO BE SOME WEAK SURFACE LOW DEVELOPMENT OVER THE WESTERN GULF OF MEXICO...BUT THIS ENERGY SHOULD DAMPEN OUT ON MON AS THE SOUTHERN STREAM ENERGY WEAKENS IN FAVOR OF MUCH STRONGER NORTHERN STREAM HEIGHT FALLS ARRIVING JUST TO THE NORTH. WILL PREFER A GENERAL MODEL COMPROMISE AT THIS POINT GIVEN RATHER GOOD MASS FIELD AGREEMENT. ...SHORTWAVE SHEARING SOUTHEAST ACROSS THE MID MS/TN VALLEYS/SOUTHERN MID-ATLANTIC THROUGH SUN... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A PROGRESSIVE AND RELATIVELY WEAK SHORTWAVE CROSSING THE HIGH PLAINS WILL SHEAR SOUTHEAST TONIGHT THROUGH SUN ACROSS THE MID MS AND TN VALLEYS BEFORE THEN CROSSING THE SOUTHERN MID-ATLANTIC REGION BY LATE SUN. THERE IS RATHER MINIMAL MASS FIELD SPREAD AT THIS TIME...AND SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED. ...SHORTWAVE CROSSING THE PACIFIC NORTHWEST/NORTHERN ROCKIES TONIGHT THROUGH SUN... ...AMPLIFYING SOUTHEAST ACROSS TOWARD THE MID MS/LOWER OH/TN VALLEYS THROUGH MON... ...TROUGH GOING NEGATIVE TILT ACROSS THE MID-ATLANTIC/NEW ENGLAND THROUGH TUES... ...PARENT SURFACE LOW CROSSING FROM THE HIGH PLAINS TO THE OH VALLEY SUN/MON... ...INTENSE SECONDARY CYCLOGENESIS ALONG THE EAST COAST MON NIGHT/TUES... PREFERENCE: NON-NAM CONSENSUS...WEIGHTED TOWARD THE 12Z UKMET/12Z CMC/12Z ECMWF CONFIDENCE: AVERAGE...BECOMING BELOW AVERAGE A STRONG SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW JUST OFFSHORE THE PACIFIC NORTHWEST AND SOUTHERN BRITISH COLUMBIA WILL MOVE INLAND BY TONIGHT AND WILL CROSS INTO THE NORTHERN ROCKIES ON SUN WHILE TRAVERSING A MEAN LAYER RIDGE OVER THE WESTERN U.S. THE ENERGY IS THEN EXPECTED TO DIG DOWN THE EAST SIDE OF THIS RIDGE AXIS AND BEGIN AMPLIFYING AS IT CROSSES THE MID MS/LOWER OH AND TN VALLEYS SUN NIGHT THROUGH MON. THIS WILL DRIVE A WELL-DEFINED AREA OF LOW PRESSURE FROM THE NORTHERN HIGH PLAINS EARLY SUN SOUTHEAST INTO THE OH VALLEY BY MON EVENING. THE AMPLIFYING NORTHERN STREAM SHORTWAVE WILL BEGIN TO BACK THE MID LEVEL FLOW ALONG THE EAST COAST...AND WILL INITIATE A SECONDARY CYCLOGENESIS OFF THE SOUTHEAST COAST EARLY TO MIDDAY ON MON IN VICINITY OF A STRENGTHENING BAROCLINIC ZONE JUST OFF THE MID-ATLANTIC AND SOUTHEAST COAST. THE UPSTREAM SHORTWAVE IS THEN EXPECTED TO GO NEGATIVE TILT AS IT CROSSES THE CENTRAL APPALACHIANS MON NIGHT AND THE MID-ATLANTIC AND NEW ENGLAND ON TUES. THIS WILL RESULT IN RAPIDLY DEEPENING LOW PRESSURE THAT WILL LIFT NORTHEAST UP OFF THE MID-ATLANTIC AND NEW ENGLAND COASTS MON NIGHT AND TUES. MODEL DIFFERENCES WITH THE SHORTWAVE TROUGH BEGIN AROUND 36 HOURS AND BEYOND AS THE 12Z NAM BECOMES A TAD SLOWER THAN THE MODEL CONSENSUS AS THE SYSTEM ADVANCES ACROSS THE MID MS/OH VALLEYS. THE 12Z CMC FOR ITS PARTS APPEARS TO BECOME JUST A TAD WEAKER. THE 12Z GFS/12Z ECMWF AND 12Z UKMET ARE BETTER CLUSTERED. AS SECONDARY LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST AND LIFTS NORTHEAST UP OFF THE EASTERN SEABOARD...THE 12Z NAM IS OVERALL THE WEAKEST AND FASTEST SOLUTION...AND IS ALSO FARTHEST LEFT/WEST WITH THE LOW TRACK. THE 12Z GFS IS ONLY A LITTLE SLOWER BUT IS FARTHER RIGHT/EAST WITH ITS LOW TRACK. THE 12Z UKMET/12Z CMC AND 12Z ECMWF ARE ALL COLLECTIVELY A LITTLE SLOWER THAN THE 12Z GFS...BUT DO TEND TO COME INTO BETTER TIMING AGREEMENT AS THE SYSTEM APPROACHES NEW ENGLAND. THE NON-NCEP MODELS...ESPECIALLY THE UKMET AND ECMWF HAVE TENDED TO GENERALLY TREND FARTHER EAST AS THE SYSTEM LIFTS FROM OFFSHORE THE MID-ATLANTIC TO OFFSHORE NEW ENGLAND. AT THIS TIME POINT...THE NAM IS AN OUTLIER SOLUTION AND WILL NOT BE PREFERRED. ACCOUNTING FOR SOME OF THE FASTER TRENDS SEEN IN THE GFS AND THE NON-NCEP TRENDS A TAD FARTHER EAST...WILL PREFER A NON-NAM CONSENSUS WEIGHTED MORE HEAVILY TOWARD THE UKMET/CMC AND ECMWF SOLUTIONS. HOWEVER...CONFIDENCE IS LIMITED GIVEN THE MULTI-DAY TRENDS. ...DEEP CLOSED LOW DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST/GREAT LAKES MON/TUES... PREFERENCE: BLEND OF THE 12Z UKMET/12Z CMC AND 12Z ECMWF CONFIDENCE: AVERAGE ALL OF THE MODELS SHOW A DEEP CLOSED LOW AND ASSOCIATED TROUGH DIGGING SOUTHEAST ACROSS THE UPPER MIDWEST AND THE GREAT LAKES REGION MON AND TUES. THESE STRONG HEIGHT FALLS WILL BE LARGELY RESPONSIBLE FOR THE NORTHEAST ADVANCE OF THE NEGATIVELY TILTING TROUGH CROSSING THE MID-ATLANTIC AND NORTHEAST ALONG WITH THE INTENSE EAST COAST SURFACE LOW THIS PERIOD. THE 12Z NAM AND 12Z GFS ARE NOW IN A CAMP WHERE THEY ARE STRONGER WITH THE ENERGY CROSSING THE LOWER GREAT LAKES AND EXTENDING DOWN INTO THE UPPER OH VALLEY ON TUES...WHICH HAS SOME IMPLICATIONS ON THE DEGREE OF PHASING THAT OCCURS RELATIVE TO THE EAST COAST LOW CENTER AND THE PRECIPITATION SHIELD OVER THE INTERIOR NORTHEAST. THE NON-NCEP MODELS HAVE GENERALLY A BIT MORE SEPARATION AND ARE NOT QUITE AS STRONG WITH THE FORCING ROUNDING THE EAST SIDE OF THE UPPER LOW ON TUES OVER THE LOWER GREAT LAKES. BASED ON THE LATEST TRENDS AND CLUSTERING...WILL EDGE TOWARD THE NON-NCEP CAMP WITH THE UPPER LOW DETAILS OVER THIS REGION. ...AMPLIFYING TROUGH/DEEPENING SURFACE LOW OFF THE PACIFIC NORTHWEST ON TUES... PREFERENCE: BLEND OF THE 12Z GFS/12Z UKMET AND 12Z GEFS MEAN CONFIDENCE: BELOW AVERAGE MOST OF THE MODELS SHOW A LONGWAVE TROUGH AMPLIFYING OFFSHORE THE PACIFIC NORTHWEST BY TUES ALONG WITH A DEEPENING AREA OF LOW PRESSURE. THE 12Z ECMWF IS THE WEAKEST SOLUTION WITH THIS SYSTEM AND SHOWS A LACK OF A SURFACE LOW PRESSURE COMPARED TO THE MODEL CONSENSUS. THE 12Z GFS/12Z UKMET AND THE 12Z GEFS MEAN SHOW A RATHER STRONG AND WELL-DEFINED LOW CENTER OFFSHORE WITH SOME MODEST SPREAD ON LOCATION AT THE END OF THE PERIOD. THE 12Z NAM AND 12Z CMC HAVE A LOW CENTER...BUT THEY ARE WEAKER.. CONFIDENCE IS A BIT LIMITED GIVEN THE SPREAD...BUT FOR NOW...WILL FAVOR A GFS/UKMET/GEFS MEAN COMPROMISE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON