MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 300 PM EDT THU APR 27 2017 VALID APR 27/1200 UTC THRU MAY 01/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH FINAL MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...WEAKENING CYCLONE EXITING FROM OFFSHORE NEW ENGLAND TODAY/TONIGHT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE ONLY MINOR DIFFERENCES REMAIN WITH THIS SYSTEM AND A GENERAL MODEL BLEND CAN BE USED GIVEN THE SIMILAR GUIDANCE. ...LARGE UPPER TROUGH/FRONTAL SYSTEM CROSSING THE GREAT LAKES/UPPER MS VALLEY TODAY/TONIGHT... ...COLD FRONT REACHING THE MID-ATLANTIC/NORTHEAST ON FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE REMAINING DIFFERENCES WITH THIS SYSTEM RELATE TO THE TIMING OF THE COLD FRONT INTO THE EAST/NORTHEAST U.S. WITH THE 12Z UKMET SLIGHTLY SLOWER THAN THE CONSENSUS. HOWEVER...THESE AND OTHER MINOR DIFFERENCES WITH THE SURFACE LOW TRACK INTO ONTARIO ARE SMALL ENOUGH TO ALLOW A GENERAL MODEL BLEND FOR THE PREFERENCE. ...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS SASKATCHEWAN BY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE ADJUSTMENTS IN THE 12Z CMC COMPARED TO ITS 00Z CYCLE WERE IN THE DIRECTION OF THE REMAINING DETERMINISTIC GUIDANCE BY SUN MORNING ACROSS SASKATCHEWAN. THERE IS GOOD ENSEMBLE SUPPORT FOR A GENERAL MODEL BLEND. ...LEADING EDGE OF LARGE UPPER TROUGH ACROSS THE CNTRL HIGH PLAINS ON FRI... ...WEAK SURFACE LOW TRACKING FROM THE CNTRL HIGH PLAINS TO THE MIDWEST... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: AVERAGE SOMEWHAT EARLY IN THE EVOLUTION OF THE LARGE UPPER LEVEL TROUGH OVER THE ROCKIES...DESCRIBED IN THE BELOW SECTION...FROM FRI INTO SAT THERE ARE SOME DIFFERENCES WORTH MENTIONING ACROSS THE PLAINS INTO THE MIDWEST. FROM 00Z/28-00Z/29...THE 00Z ECMWF STOOD OUT FROM THE REMAINING MODEL GUIDANCE ACROSS THE CNTRL HIGH PLAINS WITH A WEAKER LOW-MID LEVEL LOW REFLECTION. THE 12Z ECMWF ADJUSTED TOWARD THE REMAINING MODEL GUIDANCE BUT REMAINS SOMEWHAT WEAKER THAN THE DETERMINISTIC CONSENSUS. WHILE SOME OF THE MODELS APPEAR TO BE SUFFERING FROM CONVECTIVE FEEDBACK GIVEN AREA APPEARS TO BE DRIVEN BY CONVECTION...THE 12Z CONSENSUS SHOWS REASONABLE AGREEMENT NOW WITH RESPECT TO A WEAK SURFACE LOW TRANSLATING FROM THE CNTRL HIGH PLAINS TONIGHT...AND ACROSS THE MID-MISSISSIPPI VALLEY FRI EVENING. GIVEN THERE IS NOT A STRONG ENSEMBLE CONSENSUS FOR A STRONGER 12Z CMC OR 12Z GFS-LIKE SOLUTION...AND GIVEN THE FACT THAT CONVECTIVE UNCERTAINLY PLAYS A ROLE...CONFIDENCE IS ONLY AVERAGE IN THE PREFERENCE. ...AMPLIFYING TROUGH OVER THE INTERMOUNTAIN WEST THURS/FRI... ...CLOSED LOW EVOLUTION INTO THE CENTRAL/SOUTHERN PLAINS BY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE THERE CONTINUES TO BE GOOD LARGE SCALE AGREEMENT WITH THE EVOLUTION OF A LARGE CLOSED LOW/TROUGH EVOLVING ACROSS THE CNTRL/SRN ROCKIES AND INTO THE PLAINS THIS WEEKEND. DETAIL DIFFERENCES WORTH NOTING INCLUDE THE 12Z NAM ON THE FASTER/MORE PROGRESSIVE SIDE OF THE LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE THROUGH SUNDAY OVER THE PLAINS. THE 12Z NAM IS NOT PREFERRED FOR THIS REASON. THE 12Z GFS AND 12Z UKMET ARE ALSO ON THE FASTER SIDE OF THE MODELS TO KICK THE UPPER LOW EWD ACROSS THE PLAINS INTO THE MIDWEST...WHILE THE 00Z CMC/ECMWF REMAIN SLOWER. WHILE THE CMC/ECMWF HAVE BEEN TRENDING SLOWER OVER THEIR PAST 3 CYCLES...ENDING WITH THE 00Z/27 CYCLE...THE GFS/UKMET HAVE BEEN GENERALLY CONSISTENT AND FASTER. THE 12Z ECMWF/CMC REMAINED REASONABLY SIMILAR TO THEIR PREVIOUS CYCLES. BOTH SLOWER AND FASTER SOLUTIONS ARE WELL WITHIN THE LATEST ENSEMBLE CLUSTERING...WHICH HAVE BEEN TRENDING SLIGHTLY SLOWER OVER THEIR PAST 4 CYCLES VERIFYING SUNDAY. AT THIS TIME...NO CLEAR DIRECTION STANDS OUT AND GIVEN THE REASONABLY SIMILAR TRACKS IN THE GFS/ECMWF...A BLEND OF THE TWO IS PREFERRED FOR NOW. ...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC NORTHWEST SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 12Z UKMET BLEND CONFIDENCE: AVERAGE THE120Z UKMET STANDS AS A NEAR OUTLIER TO THE SOUTH WITH A 500 MB TROUGH AMPLIFYING ACROSS THE NORTHWEST COAST OF THE CONUS COMPARED TO THE LATEST ENSEMBLE AND DETERMINISTIC SOLUTIONS. A NON 12Z UKMET BLEND IS PREFERRED GIVEN THE RELATIVELY SIMILAR NON 12Z UKMET SOLUTIONS. ALTHOUGH THERE HAVE BEEN SOME WOBBLES NORTH/SOUTH WITH THE NON-UKMET MODELS...MOST NOTABLY IN THE 12Z ECMWF...THE UKMET IS ON THE DEEPER EDGE OF THE ENSEMBLES AND THE ECMWF REMAINS WITHIN REASON ALTHOUGH ALSO TOWARD THE DEEPER SIDE OF THE ENSEMBLES. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ OTTO