MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 246 PM EDT TUE APR 14 2015 VALID APR 14/1200 UTC THRU APR 18/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ COLD FRONT EXTENDING ACROSS THE MID-ATLANTIC COAST AND LOW PRESSURE DEVELOPING OFF OF THE SRN DELMARVA PENINSULA TONIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS DO NOT SHOW ANY SIGNIFICANT DIFFERENCES WITH LOW PRESSURE EXPECTED TO FORM OFF OF THE MID-ATLANTIC COAST TONIGHT UNTIL THE SYSTEM IS WELL OUT TO SEA. REGARDING THE FRONTAL PLACEMENT...DECENT AGREEMENT EXISTS AT THE SURFACE...BUT THE MODELS DIFFER SOME WITH THE 850 MB PLACEMENT WHICH STARTS TO TIE INTO THE 4TH SECTION OF THIS MESSAGE REGARDING LOW PRESSURE NEAR THE SOUTHEAST COAST. UPPER LOW OVER WEST TEXAS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW SIMILARLY WITH THIS SYSTEM. CLOSED LOW FORMING OVER THE WRN U.S. THROUGH THE END OF THE WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET/CMC BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE OUTSIDE OF THE GFS...THE MODELS CONTINUE TO SHOW RELATIVELY GOOD AGREEMENT IN HANGING BACK A CLOSED MID-LEVEL LOW OVER THE SOUTHWEST. THERE HAS BEEN SOME WOBBLING OF DETERMINISTIC SOLUTIONS OVER THE PAST THREE OR FOUR 12/00Z RUNS...BUT THE 12Z GFS IS ON THE PROGRESSIVE SIDE OF THE LATEST ENSEMBLE MEMBER SPREAD. AMONG THE NON-GFS MODELS...SOME MINOR DIFFERENCES IN TIMING/PLACEMENT APPEAR WITH THE UPPER LOW INTO FRI...WITH THE 12Z ECMWF/UKMET/CMC REPRESENTING THE BEST MIDDLE GROUND AND RUN TO RUN CONTINUITY AT THIS TIME. LOW PRESSURE POSSIBLY FORMING ALONG THE SC/NC COAST THU-FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS...12Z ECMWF...00Z UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE SPREAD REMAINS LARGE WITH THIS FEATURE...BUT THE 12Z NAM/CMC APPEAR TO BE LOW PROBABILITY SOLUTIONS GIVEN THEIR NRN DISPLACEMENT WITH RESPECT TO THE SREF/GEFS/EC ENSEMBLES. WHILE THE CMC ENSEMBLES SUPPORT THE 12Z CMC...ITS STRENGTH IS NOT SUPPORTED IN OTHER GUIDANCE. THE 12Z GFS/ECMWF AND 00Z UKMET REPRESENT A GOOD MIDDLE GROUND WITH REASONABLE RUN TO RUN CONTINUITY ABOUT A COMMON POSITION/STRENGTH. THE 12Z UKMET TRENDED TO THE ERN SIDE OF THE ENSEMBLE SPREAD BY FRI EVENING AND IS NOT PREFERRED. ALSO WORTH NOTING IS THAT THE 12Z ECMWF IS ON THE SOUTH SIDE OF THE GFS/ECMWF/UKMET TRIO...SO MORE WEIGHT TOWARD THE NORTH VIA THE 12Z GFS AND 00Z UKMET IS PREFERRED. PROGRESSIVE NRN STREAM TROUGH REACHING THE UPPER MISS VALLEY FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z CMC / 09Z SREF MEAN BLEND CONFIDENCE: AVERAGE THE ENSEMBLES DO NOT SUPPORT A DEEPER OR SHARPER TROUGH AS SHOWN BY THE 12Z NAM/GFS. SOME OF THESE DIFFERENCES ARE DUE TO UPSTREAM AMPLIFICATION...WITH THE 12Z ECMWF/UKMET FALLING FLATTER WITH THE 00Z EC MEAN DEEPER THAN THE DETERMINISTIC ECMWF. THE 12Z CMC AND 09Z SREF MEAN SUPPORT A STRENGTH/TIMING THAT IS MOST REPRESENTED IN THE LATEST ENSEMBLE SPREAD. SHORTWAVE REACHING THE PACIFIC NORTHWEST LATE FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z UKMET/CMC BLEND CONFIDENCE: AVERAGE THE 12Z CMC/UKMET FIT THE MIDDLE OF THE LATEST DETERMINISTIC/ENSEMBLE SPREAD THE BEST AND WHILE THE 12Z CMC SLOWED SOME FROM ITS PREVIOUS RUN...THE 12Z UKMET NOW LOOKS SIMILAR TO THE EARLIER PREFERRED 00Z CMC. A COMPROMISE OF THE TWO MODELS TIMING IS PREFERRED GIVEN EQUAL STRENGTH. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO