MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1230 PM EDT WED MAY 18 2016 VALID MAY 18/1200 UTC THRU MAY 22/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM/GFS AND PRELIMINARY MODEL PREFERENCES ...SHORTWAVE/SURFACE LOW OFF THE SOUTHEAST U.S. COAST TODAY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODEL AGREEMENT WITH RESPECT TO THIS SYSTEM IS GOOD...WITH THE NAM AND GFS BOTH IN LINE WITH THE CONSENSUS SOLUTION. THEREFORE...A GENERAL MODEL COMPROMISE IS RECOMMENDED. ...SHORTWAVE CROSSING THE GREAT LAKES/NORTHEAST THROUGH FRI... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODEL AGREEMENT WITH RESPECT TO THIS SYSTEM IS GOOD...WITH THE NAM AND GFS BOTH IN LINE WITH THE CONSENSUS SOLUTION. THEREFORE...A GENERAL MODEL COMPROMISE IS RECOMMENDED. ...CLOSED ACROSS THE SOUTHWEST EJECTING OUT INTO THE CENTRAL PLAINS BY THURS... ...ENERGY MOVING INTO THE OH/TN VALLEYS ON FRI... ...SURFACE LOW DEVELOPMENT OVER THE TN VALLEY... PRELIMINARY PREFERENCE: GFS/00Z ECMWF BLEND CONFIDENCE: AVERAGE MODELS CONTINUE WITH GOOD AGREEMENT AND CONTINUITY WITH THE CLOSED LOW DIGGING ACROSS THE SOUTHWEST AND THEN EJECTING EAST OUT INTO THE CENTRAL PLAINS/MID MS VALLEY BY THURS/FRI. THE NAM AND GFS ARE BOTH VERY CLOSE TO CONSENSUS WITH THE LARGE-SCALE MASS FIELDS AS THIS SYSTEM MOVES ACROSS THE PLAINS THURS AND FRI. BY 00Z SAT...THE GFS IS SLIGHTLY ON THE FAST SIDE OF THE SPREAD WITH THE NAM SLIGHTLY ON THE SLOW SIDE OF THE SPREAD. NEITHER SOLUTION APPEARS TO BE AN OUTLIER...HOWEVER. THE NAM AND GFS BOTH DEVELOP A CONVECTIVE VORTICITY MAXIMUM ACROSS TEXAS THURSDAY AFTERNOON. THE NAM KEEPS THIS FEATURE STRONGER THAN THE GFS OR 00Z ECMWF...AND THUS DEPICTS A NARROW BAND OF HEAVY PRECIPITATION FROM NORTHEASTERN TEXAS INTO THE MS VALLEY LATE THURSDAY INTO FRIDAY. ADDITIONALLY...AS A SURFACE LOW DEVELOPS ACROSS THE TN VALLEY AHEAD OF THE SHORTWAVE ON FRIDAY...THE NAM IS A BIT SLOWER/FARTHER WEST. GIVEN THESE DIFFERENCES...WILL RECOMMEND A BLEND OF THE GFS AND 00Z ECMWF. ...SURFACE LOW DEVELOPING ALONG THE SOUTHERN MID-ATLANTIC STATES ON SATURDAY... PRELIMINARY PREFERENCE: GFS/00Z ECMWF/00Z ECMWF ENSEMBLE MEAN/06Z GEFS MEAN BLEND CONFIDENCE: AVERAGE AS THE PREVIOUSLY DESCRIBED SHORTWAVE CROSSES THE OH VALLEY/CENTRAL APPALACHIANS FRI NIGHT/SAT...A SURFACE LOW IS FORECAST BY ALL MODELS TO DEVELOP ACROSS THE SOUTHERN MID-ATLANTIC STATES. THE GFS AND 00Z ECMWF SOLUTIONS ARE VERY CLOSE WITH RESPECT TO THE TIMING AND INTENSITY OF THE SURFACE LOW THROUGH 00Z SUN. INTERESTINGLY...THE SOLUTIONS SHOWN BY THE 00Z ECMWF ENSEMBLE MEAN/06Z GEFS MEAN ARE BOTH A BIT FARTHER SOUTH/SLOWER THAN THE RESPECTIVE DETERMINISTIC SOLUTIONS. WITH THIS IN MIND...WILL RECOMMEND A BLEND OF THE GFS/00Z ECMWF/00Z ECMWF ENS MEAN/06Z GEFS MEAN. ...UPPER-LEVEL LOW ALONG THE WEST COAST THURS/FRI/SAT... PRELIMINARY PREFERENCE: GFS/00Z ECMWF BLEND/00Z ECMWF ENSEMBLE MEAN/06Z GEFS MEAN CONFIDENCE: AVERAGE THE MODELS ALL SHOW STRONG AGREEMENT IN BRINGING A ROBUST UPPER-LEVEL LOW SOUTH ACROSS THE NORTHWEST ON THURS...WITH THE ENERGY THEN SLOWLY ENCOMPASSING A LARGE AREA OF THE WEST COAST BY SAT. THE GFS AND NAM ARE BOTH IN GOOD AGREEMENT WITH THE MODEL CONSENSUS THROUGH 00Z FRIDAY AS THE LOW MOVES SOUTH ALONG THE NORTHWESTERN U.S. COAST. AFTER THAT TIME...THE NAM APPEARS TO WEAKEN THE UPPER LOW A BIT TOO MUCH AND REFOCUSES THE LOWEST HEIGHTS FARTHER EAST ACROSS THE BITTERROOT RANGE. THE GFS KEEPS THE UPPER LOW INTACT LONGER...SIMILAR TO THE 00Z ECMWF/00Z ECMWF ENSEMBLE MEAN/06Z GEFS MEAN. AT THIS TIME...WILL RECOMMEND A BLEND OF THESE FOUR SIMILAR SOLUTIONS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN