MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1216 AM EDT FRI APR 15 2016 VALID APR 15/0000 UTC THRU APR 18/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ UPPER LOW CURRENTLY OVER THE LOWER MISSISSIPPI VALLEY...SHIFTING EAST AS PART OF A REX BLOCK THROUGH SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS (18Z GEFS/12Z ECENS MEAN) CONFIDENCE: BELOW AVERAGE THE UPPER LOW ACROSS AR CONTINUES TO WEAKEN AS THE ANTICYCLONE NORTH OF IT BEGINS TO AMPLIFY THE OVERALL REX BLOCK OVER THE EASTERN THIRD OF THE US. MODELS ARE GENERALLY AGREEABLE WITH THE DEVOLUTION OF THE UPPER LOW SHEARING TOWARD THE EAST...THOUGH THE 12Z ECMWF SHIFTED DRAMATICALLY TOWARD A DEEPER SOLUTION WITH WHAT APPEAR TO BE SOME CONVECTIVE FEEDBACK FEATURES LIKELY HELPING TO MAINTAIN THE UPPER LOW A BIT LONGER THAN WHAT IS REALISTIC. THE 12Z ECENS MEAN SUPPORTS MAINTAINING A STRONGER TROF THAN THE 00Z RUN BUT NOT AS DRAMATIC AS THE 12Z ECMWF ITSELF; IT IS MORE IN LINE WITH THE 18Z GEFS AND 00Z GFS. THE 00Z NAM APPEARS TO BE SHIFTED FURTHER SOUTH AND MAYBE A BIT FASTER EASTWARD AS WELL THAN MUCH OF THE REST OF THE GUIDANCE AND AWAY FROM ITS CONTINUITY. THE 12Z CMC/UKMET ARE WEAKEN THE TROF ACROSS THE SOUTHEAST FASTER WITH MORE FOCUS OFFSHORE. WILL FAVOR CLOSER PROXIMITY TOWARD THE ENSEMBLE MEANS... WHICH IS BEST SUPPORTED BY THE 00Z GFS. CONFIDENCE REMAINS BELOW AVERAGE GIVEN THE WEAK NATURE OF THE SYSTEM INTO THE WEEKEND...DRIVEN BY LOCALIZED/STORM SCALE AFFECTS REDUCING THE PREDICTABILITY. NRN STREAM UPPER TROUGH OVER THE N-CNTRL U.S. THROUGH WEEKEND SLOW MOVING COLD FRONT MOVING ALONG THE U.S.-CANADIAN BORDER ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND WEIGHTED TOWARD 00Z NAM/12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE CONTINUITY CONTINUES TO FAVOR A ECMWF/ECENS MEAN SOLUTION, THE 00Z NAM SHIFTED EVER SO SLIGHTLY WEAKER AND SLOWER TO BE VERY FAVORABLE WITH THE TIMING/ORIENTATION OF THE INVERTED SURFACE TROF AND MID-LEVEL TROF AXIS. THE 12Z UKMET IS ALIGNED THOUGH IS A BIT MORE AMPLIFIED ACROSS CANADA BY MONDAY. THE 00Z GFS REMAINS A BIT OFF WITH THE ORIENTATION OF THE TROF ALOFT ACROSS THE DAKOTAS...BUT HAVING SLOWED SIGNIFICANTLY THE OVERALL TROF AND SURFACE REFLECTION ARE MORE ALIGNED TO HAVE SOME INCLUSION IN THE BLEND IF AT A SLIGHTLY LOWER WEIGHTING. THE 12Z CMC IS MOST OUT OF PHASE AT THIS POINT NOW...GIVEN IT IS MUCH SLOWER AND FURTHER WEST OVERALL. AS SUCH WILL FAVOR A NON-CMC BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE WEIGHTED TOWARD THE 00Z NAM/12Z ECMWF. FOUR CORNERS CUT-OFF LOW THIS WEEKEND ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM AND 12Z ECMWF/UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS CONTINUE TO SHOW GOOD AGREEMENT WITH THE EVOLUTION OF A LARGE CLOSED LOW TO CROSS THE FOUR CORNERS REGION ON SAT. THE 00Z GFS CONTINUES TO BE SHIFTED A BIT NORTH AND EAST WITH THE OVERALL ORIENTATION BEING A BIT FASTER...AND GIVEN THE HIGH MERIDIONAL FLOW/DEEP CUT-OFF WITH LITTLE STEERING THIS SEEMS A BIT LESS LIKELY. LIKEWISE THE 12Z CMC IS A BIT BROADER. ADDITIONALLY INTERACTION/ORIENTATION TOWARD THE SLOWER NORTHERN STREAM MAKES THE 12Z CMC A BIT LESS FAVORABLE AS WELL. THE 00Z NAM CONTINUES TO STRONGLY SUPPORT THE CONTINUITY OF THE 12Z ECMWF AND UKMET AND AS SUCH WILL KEEP A 00Z NAM/12Z ECMWF/UKMET BLEND AT SLIGHTLY ABOVE AVERAGE CONTINUITY. PLEASE NOTE: THERE REMAINS SOME IMPORTANT DIFFERENCES WITHIN THIS BLEND IN THE QPF FIELDS...SO PLEASE REFER TO THE QPFPFD FOR ADDITIONAL INFORMATION ON MODEL PREFERENCES/SELECTION. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA