MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 255 PM EDT SAT APR 15 2017 VALID APR 15/1200 UTC THRU APR 19/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING FINAL MODEL PREFERENCES AND CONFIDENCE ...MID-LEVEL CIRCULATION SHEARING ACROSS THE GULF COAST... PREFERENCE: NON-12Z CMC CONSENSUS CONFIDENCE: ABOVE AVERAGE A MID-LEVEL CIRCULATION CURRENTLY SPINNING JUST SOUTH OF THE CENTRAL GULF COAST WILL CONTINUE TO ADVANCE EASTWARD DURING THE NEXT 24 TO 36 HOURS AND GENERALLY SHEARING OUT AS IT APPROACHES THE FL PENINSULA. THE 12Z CMC APPEARS TO BE A RELATIVELY WEAK OUTLIER AGAINST THE OTHERWISE WELL-CLUSTERED GUIDANCE. A NON-CMC CONSENSUS WILL BE PREFERRED. ...SHORTWAVE ENERGY SHEARING ACROSS THE GREAT LAKES/NEW ENGLAND THROUGH THE WEEKEND... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE SHORTWAVE ENERGY WORKING ITS WAY THROUGH THE UPPER MIDWEST/GREAT LAKES INCLUDING A COUPLE OF SMALLER SCALE MCVS WILL GRADUALLY SHEAR ACROSS THE GREAT LAKES AND NEW ENGLAND THROUGH SUN. A GENERAL MODEL COMPROMISE WILL BE PREFERRED GIVEN ONLY VERY MINOR MODEL MASS FIELD DIFFERENCES. ...LONGWAVE TROUGH STRETCHING OVER THE NORTHWESTERN SECTOR OF THE CONUS... ...PROGRESSIVE HEIGHT FALLS SLIDING EASTWARD ALONG THE INTERNATIONAL BORDER WITH CANADA... ...ATTENDANT FRONTAL FEATURES... PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF CONFIDENCE: AVERAGE A PROGRESSIVE AND GRADUALLY WEAKENING LONGWAVE TROUGH OVER THE NORTHERN ROCKIES HIGH PLAINS REGION THIS MORNING WILL ADVANCE DOWNSTREAM THROUGH SUN AND MON ALONG WITH MULTIPLE EMBEDDED SMALLER SCALE SHORTWAVES. THE ENERGY SHOULD CROSS THE GREAT LAKES AND NORTHEAST WITH MULTIPLE WAVES OF LOW PRESSURE ALONG A FRONTAL ZONE...INCLUDING A COLD FRONT THAT WILL CROSS THE MIDWEST/OH VALLEY AND NORTHEAST. HOWEVER...THE SOUTHWEST TAIL END OF THE BOUNDARY WILL LIKELY SLOW DOWN AND TEND TO STALL OUT OVER THE MID MS VALLEY AND SOUTHERN PLAINS REGION. THE 12Z CMC HAS FINALLY TRENDED A BIT SLOWER COMPARED TO PREVIOUS RUNS AND IS CLOSE TO THE MODEL CONSENSUS WITH THE SHORTWAVE ENERGY EVOLUTION. THE 12Z NAM APPEARS TO BE POSSIBLY BE A TAD TOO DEEP WITH LOW PRESSURE INITIALLY CROSSING NEAR NORTHERN NEW ENGLAND...AND THEN TOO SLOW AND DEEP WITH THE UPSTREAM WAVE CROSSING THE GREAT LAKES THAT EVENTUALLY ALSO CROSSES NORTHERN NEW ENGLAND. BETTER MODEL CLUSTERING AND ENSEMBLE SUPPORT FAVORS A BLEND OF THE 12Z GFS AND 12Z ECMWF AT THIS TIME. ...POTENT SHORTWAVE/CLOSED LOW REACHING THE NORTHERN CA COAST BY SUN... ...FAST-MOVING WAVE CROSSING THE NORTHERN PLAINS/UPPER MIDWEST BY TUES... PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH 60 HOURS BLEND OF THE 12Z UKMET/12Z ECMWF/00Z ECENS MEAN...AFTER 60 HOURS CONFIDENCE: ABOVE AVERAGE...BECOMING AVERAGE AFTER 60 HOURS PROGRESSIVE MID-LATITUDE FLOW WILL USHER IN A STRONG SHORTWAVE TOWARD THE NORTHERN CA/SOUTHWEST OR COAST BY SUN EVE. THIS ENERGY WILL QUICKLY TRAVERSE THE INTERMOUNTAIN WEST AND STREAK EAST ACROSS THE DAKOTAS MON NIGHT AND THE UPPER GREAT LAKES REGION ON TUES. THE 12Z NAM FOR ITS PART BY MON NIGHT/TUES APPEARS TO BE TRACKING ITS LOW PRESSURE CENTER A TAD TOO FAR NORTH AS THE 12Z GFS/UKMET/CMC AND ECMWF ARE ALL GENERALLY FARTHER SOUTH WITH THE. THE 12Z GFS IS OVERALL THE FARTHEST SOUTH. THE ECMWF WHICH HAD PREVIOUSLY BEEN A BIT SLOWER THAN THE MODEL CONSENSUS WITH THE PROGRESSION OF THE SURFACE LOW HAS TRENDED A BIT FASTER AND IS VERY CLOSE TO THE UKMET SOLUTION. THE CMC IS NOW OVERALL THE SLOWEST. THERE REMAINS RATHER STRONG GEFS SUPPORT FOR A LOW TRACK A LITTLE BIT FARTHER SOUTH...BUT THE LATEST UKMET/ECMWF SOLUTIONS ALONG WITH THE ECENS MEAN SUGGEST A LOW TRACK A LITTLE FARTHER NORTH...AND BASED ON THE LATEST TRENDS...THE UKMET/ECMWF AND ECENS MEAN BEST APPROXIMATE THE MODEL CONSENSUS. THUS A UKMET/ECMWF/ECENS MEAN BLEND WILL BE PREFERRED AFTER ABOUT 60 HOURS...WITH A GENERAL MODEL CONSENSUS PRIOR TO THIS GIVEN THE GOOD AGREEMENT OF THE GUIDANCE AS THE ENERGY CROSSES THE WEST. ...BROAD NEGATIVE HEIGHT ANOMALY ENCOMPASSING MUCH OF THE EASTERN PACIFIC AT THE END OF THE PERIOD... PREFERENCE: BLEND OF THE 12Z NAM/12Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE VERY LATE IN THE PERIOD...A RATHER EXTENDED LONGWAVE TROUGH BEGINS TO TAKE SHAPE OVER THE EASTERN PACIFIC. THERE REMAIN SOME SPATIAL-TEMPORAL DIFFERENCES RELATING ESPECIALLY TO A LEAD SHORTWAVE TROUGH CROSSING THE WEST COAST BY TUES. THE 12Z UKMET AND 12Z CMC ARE BOTH A LITTLE FASTER TO BRING SOME OF THIS ENERGY INLAND...BUT HAVE TRENDED A BIT CLOSER TO THE MODEL CONSENSUS AS SUPPORTED BY THE 12Z NAM/12Z GFS AND 12Z ECMWF AND ALSO THE LATEST GEFS MEAN AND ECENS MEAN. WILL PREFER A NAM/GFS/ECMWF BLEND AS A RESULT. ...BROAD TROUGH OVER THE WESTERN GULF OF MEXICO/LOWER MS VALLEY BY TUES... PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF CONFIDENCE: AVERAGE A SOUTHERN STREAM TROUGH GRADUALLY DEEPENS AND BROADENS OUT OVER THE LOWER MS VALLEY AND THE WESTERN GULF OF MEXICO BY TUES IN RESPONSE TO VORT ENERGY THAT AMPLIFIES EJECTING ACROSS THE RIO GRANDE VALLEY MON AND MON NIGHT. THE 12Z NAM AND 12Z UKMET WERE THE MOST INTENSE WITH THE VORT ENERGY THAT CROSSES THE RIO GRANDE VALLEY AND INTO PORTIONS OF CENTRAL/EASTERN TX. THE 12Z GFS/12Z CMC AND 12Z ECMWF WERE AL RELATIVELY WEAKER. ALL OF THE MODELS THOUGH STILL HAVE A BROAD UPPER TROUGH THAT EVOLVES REGARDLESS OF THE EXACT DETAILS OF THE EJECTING VORT ENERGY. A BLEND OF THE 12Z GFS AND 12Z ECMWF WILL BE PREFERRED AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON