MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1241 PM EDT TUE APR 07 2015 VALID APR 07/1200 UTC THRU APR 11/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...SURFACE LOW OVER THE MID MS VALLEY THROUGH EARLY WED... PREFERENCE: BLEND OF THE 00Z ECMWF/00 UKMET AND 00Z CMC CONFIDENCE: AVERAGE ALL OF THE MODELS TAKE A SURFACE LOW OVER CENTRAL KS THIS MORNING SLOWLY EAST-NORTHEAST ACROSS NORTHERN MO AND INTO CENTRAL IL THROUGH EARLY WED WHILE TRACKING ALONG A STRONG FRONT. THERE IS GENERALLY GOOD AGREEMENT WITH THE TIMING AND TRACK OF THE WAVE...ALTHOUGH THE NON-NCEP MODELS ARE PERHAPS JUST A TAD MORE PROGRESSIVE TO ADVANCE IT ACROSS MO/IL VERSUS THE NAM AND GFS. SINCE THERE IS FAST AND RATHER UNIDIRECTIONAL FLOW ALOFT...A SOMEWHAT MORE PROGRESSIVE SCENARIO MAKES MORE SENSE...AND SO A BLEND OF THE ECMWF/UKMET AND CMC SOLUTIONS WILL BE PREFERRED. ...WESTERN UPPER TROUGH AXIS REACHING THE CENTRAL PLAINS THURS MORNING... ...ACCOMPANYING SURFACE LOW TRACKING INTO THE GREAT LAKES THURS NIGHT... PREFERENCE: BLEND OF THE 12Z NAM/12Z GFS AND 00Z UKMET CONFIDENCE: BELOW AVERAGE A VERY TOUGH FORECAST FOR MASS FIELDS...AS THE 12Z GFS HAS TRENDED FASTER AND AFTER ABOUT 48 HOURS BECOMES ONE OF THE FASTER AND DEEPER SOLUTIONS WITH THE TROUGH EVOLUTION AND THE ACCOMPANYING SURFACE LOW. THE 00Z ECMWF IS ALSO VERY PROGRESSIVE...BUT MUCH WEAKER WITH THE SHORTWAVE TROUGH/SURFACE LOW AS IT CROSSES THE MIDWEST AND THE GREAT LAKES REGION. THE 00Z CMC IS A SLOW OUTLIER WITH THE ENERGY. THIS LEAVES THE 12Z NAM AND 00Z UKMET WHICH ACTUALLY DO CLUSTER TOGETHER REASONABLY WELL WITH THE SURFACE LOW EVOLUTION AND ARE A BIT SLOWER THAN THE GFS. THE LATEST GEFS MEAN OFFERS THE BEST MASS FIELD SUPPORT FOR THE NAM/GFS/UKMET CLUSTER. GIVEN THE LARGE MASS FIELD SPREAD STILL SEEN IN THE GUIDANCE AND WITH THE ENSEMBLE HEIGHTS/SURFACE LOW PLOTS...CONFIDENCE IS BELOW AVERAGE...BUT WILL FAVOR A BLEND OF THE NAM/GFS AND UKMET AT THIS POINT. DIFFERENCES WITH THE MODELS CONCERNING QPF ARE EVEN MORE EGREGIOUS...PLEASE CONSULT THE LATEST QPFPFD FOR MORE DETAILS ON THIS. ...MID LEVEL SHORTWAVE TROUGH DROPPING INTO THE DAKOTAS/UPPER MS VALLEY... PREFERENCE: BLEND OF THE 12Z NAM AND 12Z GFS CONFIDENCE: BELOW AVERAGE THE MODELS ARE STRUGGLING WITH THE DEGREE OF SHORTWAVE ENERGY THAT DROPS DOWN INTO THE NORTHERN U.S. THURS NIGHT AND FRI WITH POOR RUN TO RUN CONTINUITY AND GREATER THAN AVERAGE SPREAD IN THE ENSEMBLE SPAGHETTI HEIGHT PLOTS. A SIGNIFICANT PERCENTAGE OF THE DETERMINISTIC MODELS HAVE TRENDED TOWARD A STRONG SHORTWAVE DIVING INTO NORTHERN MN WITH POTENTIAL INTERACTION OR PHASING WITH THE SHORTWAVE LIFTING ACROSS THE UPPER MS VALLEY. THE 12Z NAM AND 12Z GFS CONTINUE TO HINT AT THIS...AND THE 00Z UKMET AND 00Z CMC ARE EVEN MORE EMPHATIC ON DROPPING A ROBUST NORTHERN STREAM SHORTWAVE TROUGH SOUTH DOWN INTO THE DAKOTAS OR THE UPPER MS VALLEY REGION. THE 00Z ECMWF IS THE WEAKEST OF THE DETERMINISTIC MODELS WHILE THE 00Z UKMET IS THE STRONGEST. THE STRONGER/WESTERN TRACK OF THE UKMET IS AN OUTLIER SOLUTION. THE STRONGER MODEL CLUSTERING ACCOUNTING FOR THE WEAK ECMWF AND STRONG UKMET...WOULD BE THE NAM AND GFS WHICH CLUSTER IN BETWEEN THE TWO CAMPS. THE CMC APPEARS OVERALL TO BE A BIT TOO DEEP IN SOMEWHAT SIMILAR FASHION TO THE UKMET. CONFIDENCE IS LIMITED WITH THIS FEATURE DUE TO THE POTENTIAL FOR PHASING/INTERACTION WITH THE ENERGY JUST TO THE SOUTH. ...SURFACE WAVE EXITING OFF THE MID-ATLANTIC COAST ON WED... PREFERENCE: BLEND OF THE 12Z NAM AND 00Z ECMWF CONFIDENCE: AVERAGE THE MODELS SHOW A WEAK SURFACE WAVE CROSSING SOUTHERN VA AND EXITING OFF THE MID-ATLANTIC REGION ON WED. THE 00Z UKMET IS FARTHER NORTH WITH THE LOW PLACEMENT...WITH THE 12Z GFS THE FARTHEST SOUTH. THE 00Z CMC AT LEAST EARLY IN THE PERIOD IS A BIT QUICKER TO EXIT THE WAVE OUT TO SEA. THIS LEAVES THE 00Z ECMWF AND 12Z NAM WHICH SHOW BETTER MASS FIELD CLUSTERING THROUGH DAY 1. A BLEND OF THESE SOLUTIONS WILL BE PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON