MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 242 PM EDT TUE MAR 28 2017 VALID MAR 28/1200 UTC THRU APR 01/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE UKMET/CANADIAN GLOBAL/ECMWF ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...NORTHERN STREAM TROUGH AMPLIFYING ACROSS SOUTHEAST CANADA... ...UPPER TROUGH WEAKENING ACROSS THE MID-ATLANTIC ON TUE... ...SURFACE LOW CROSSING MID-ATLANTIC...DEEPENING OFFSHORE... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE OVERALL...MODELS REMAIN IN GOOD AGREEMENT WITH THE LARGER SCALE FEATURES. ...WEAK TROUGH OVER THE NORTHERN PLAINS/UPPER MIDWEST TUE/WED... ...STRONG CLOSED LOW EVOLUTION INTO THE SOUTHWEST ON TUE... ...EJECTING EAST ACROSS THE CENTRAL/SOUTHERN PLAINS WED... ...LIFTING THROUGH THE MID MS/TN/OH VALLEYS BY LATE THU/FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z GFS AND ECMWF CONFIDENCE: AVERAGE COMPARED WITH ITS 00Z RUN...THE NAM IS MORE PROGRESSIVE WITH THE UPPER LOW AS IT MOVES FROM THE CENTRAL PLAINS THROUGH THE MID MS VALLEY LATE THU-EARLY FRI. HOWEVER...DESPITE THE TREND...THE NAM REMAINS ON THE SLOWER EDGE OF THE DETERMINISTIC GUIDANCE. THIS MAY BE PARTLY ATTRIBUTED TO THE LESS AMPLIFIED NORTHERN STREAM TROUGH IT DEPICTS OVER THE NORTHERN PLAINS-UPPER MIDWEST. THE GFS IS ALSO FASTER WITH THE TIMING OF THE UPPER LOW/TROUGH AS IT MOVES ACROSS THE MID MS VALLEY EARLY FRI. IN FURTHER CONTRAST WITH ITS 00Z RUN...THE GFS HAS BACKED OFF ON THE AMPLITUDE OF THE ENERGY MOVING THROUGH THE BASE OF THE TROUGH OVER THE LOWER MS VALLEY/NORTHERN GULF OF MEX EARLY FRI. IT ALSO TRACKS THE SURFACE LOW FURTHER TO THE NORTH FROM THE MID MS VALLEY INTO THE OH VALLEY ON FRI. WHILE DIFFERENCES IN TIMING STILL EXIST...THIS PUTS THE GFS INTO BETTER AGREEMENT WITH THE ECMWF (WHICH HAS TRENDED A LITTLE SLOWER LATE IN THE PERIOD). TO ACCOUNT FOR CONTINUING TIMING DIFFERENCES...A COMPROMISE BETWEEN THE TWO IS RECOMMENDED. ...VIGOROUS TROUGH DIGGING INTO THE WEST ON THU/FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: ECMWF CONFIDENCE: AVERAGE THE 12Z NAM IS FASTER THAN ITS 00Z RUN DIGGING THE TROUGH SOUTHEAST ACROSS THE PACIFIC NORTHWEST INTO THE GREAT BASIN ON THU. THIS PLACES ITS TROUGH AXIS ALONG THE EASTERN EDGE OF THE LATEST DETERMINISTIC GUIDANCE FOR A PERIOD ON THU BEFORE CLOSING OFF A LOW THAT SETTLES SOUTH INTO THE SOUTHWEST CLOSE TO THE OTHER MODELS. AS THE UPPER LOW SETTLES SOUTH INTO THE FOUR CORNERS REGION ON FRI...THE GFS TRACKS THE LOW A LITTLE FURTHER NORTHEAST OF THE GREATER DETERMINISTIC MODEL CONSENSUS...WITH LOWER MID-UPPER LEVEL HEIGHTS EXTENDING OUT ACROSS THE CENTRAL HIGH PLAINS AND A STRONGER SURFACE LOW DEVELOPING IN THE LEE OF THE CENTRAL ROCKIES. THE GENERAL CONSENSUS OF THE 12Z DETERMINISTIC GUIDANCE AND THE GEFSMEAN SUGGEST GIVING MORE WEIGHT TO A SOLUTION MORE SIMILAR TO THE ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... PEREIRA