MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 236 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/UKMET/CMC AND FINAL MODEL PREFERENCES ...SHORTWAVE/SURFACE LOW OFF THE SOUTHEAST U.S. COAST TODAY... 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... 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... PREFERENCE: GFS/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 ECMWF...AND THUS DEPICTS A NARROW BAND OF HEAVY PRECIPITATION FROM NORTHEASTERN TEXAS INTO THE MS VALLEY LATE THURSDAY INTO FRIDAY. THE UKMET CONTINUES TO BE A BIT FAST WITH THE SHORTWAVE FROM THE PLAINS TO THE OHIO VALLEY THURS/FRI...WHILE THE CMC IS GENERALLY CLOSE TO THE GFS/ECMWF. 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 ECMWF. ...SURFACE LOW DEVELOPING ALONG THE SOUTHERN MID-ATLANTIC STATES ON SATURDAY... PREFERENCE: GFS/ECMWF/CMC 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/CMC SOLUTIONS ARE VERY CLOSE WITH RESPECT TO THE TIMING AND INTENSITY OF THE SURFACE LOW THROUGH 00Z SUN...WITH THE ECMWF/UKMET JUST A HAIR FARTHER EAST. THE 12Z GEFS MEAN NOW ALIGNS MORE CLOSELY WITH THE DETERMINISTIC GFS THAN IN ITS 06Z CYCLE...LEAVING THE 00Z ECMWF ENSEMBLE MEAN ON THE SLOW SIDE OF THE SPREAD. GIVEN THE RELATIVELY LOW SPREAD FOR 84 HOURS AMONG THE DETERMINISTIC GUIDANCE...WILL RECOMMEND A MULTI-MODEL BLEND OF THE GFS/ECMWF/CMC -- AS THESE THREE SOLUTIONS SEEM TO BEST REPRESENT A CONSENSUS AT THE SURFACE AND UPPER-LEVELS. ...UPPER-LEVEL LOW ALONG THE WEST COAST THURS/FRI/SAT... PREFERENCE: GFS/ECMWF/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 INCLUDING THE UKMET/ECMWF/CMC 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/ECMWF/UKMET/CMC KEEP THE UPPER LOW INTACT LONGER...SIMILAR TO THE 00Z ECMWF ENSEMBLE MEAN/12Z GEFS MEAN. THE CMC APPEARS TO BE TOO AMPLIFIED WITH A SHORTWAVE ROTATING AROUND THE WESTERN SIDE OF THE LOW FRIDAY NIGHT/SAT MORNING. AT THIS TIME...WILL RECOMMEND A BLEND OF THE GFS AND ECMWF ALONG WITH THE GEFS MEAN AND THE 00Z ECMWF ENSEMBLE MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN