MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1241 AM EDT THU APR 10 2014 VALID APR 10/0000 UTC THRU APR 13/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...FRONT SWEEPING THE NORTHEAST QUARTER OF THE U.S... ...BAND OF PRECIPITATION FRI/SAT... PREFERENCE: BLEND OF 12Z ECMWF/CANADIAN MODELS ARE SIMILAR WITH THE INITIAL MOVEMENT OF A FRONT THROUGH THIS REGION ON DAY 1. THEN DIFFERENCES APPEAR IN THE HANDLING OF AN UPSTREAM SHORTWAVE TROUGH. THIS TROUGH HELPS FORCE THE SURFACE FRONT TO STALL AND BEGIN LIFTING...AND ALL GUIDANCE PRODUCES A BAND OF PRECIPITATION NEAR AND JUST NORTH OF THE BOUNDARY ON FRI/SAT. THE ECMWF AND CANADIAN PLACE THE BAND FARTHER NORTH BY VIRTUE OF A SHARPER AND SLOWER MOVING SHORTWAVE. THE FEATURE IS OF LOW AMPLITUDE...SO TRENDS IN THE MASS FIELDS ARE RATHER SUBTLE. SPAGHETTI PLOTS SUGGEST THE ECMWF MAY BE TOO SHARP/DEEP...BUT IT IS SUPPORTED CONCEPTUALLY BY THE CANADIAN AND A MAJORITY OF THE ECMWF ENSEMBLE MEMBERS. THE 12Z UKMET PRODUCED A SIMILAR...THOUGH FASTER...WAVE. THIS LEAVES THE NAM/GFS LOOKING VERY FLAT AND PROGRESSIVE. GIVEN THE AVAILABLE BAROCLINICITY AT THIS LATITUDE IN APRIL...AND WITH THE LARGER SCALE UPSTREAM PATTERN AMPLIFYING OVER THE NORTHERN ROCKIES...WE PREFER THE MORE AMPLIFIED SHORTWAVE THAT THE ECMWF/CANADIAN BRING INTO THE NORTHEAST. ...MID-LEVEL LOW APPROACHING CALIFORNIA... PREFERENCE: BLEND OF 00Z NAM/GFS WITH 12Z ECMWF THIS LOW...WHICH IS RELATIVELY DRY...IS POSITIONED FORWARD OF THE DEVELOPING SHORTWAVE RIDGE IN THE NORTHERN STREAM OFF THE WEST COAST. THIS INCREASES THE ODDS OF ITS INTERACTING WITH THE AMPLIFYING TROUGH IN THE WESTERN U.S. RELATIVELY EARLY IN THE DAY 2/3 PERIOD...ESPECIALLY AS THE GUIDANCE HAS BEEN TRENDING TOWARD THE DEEPER ECMWF-LIKE SOLUTIONS IN THE NORTHERN STREAM OVER THE WEST. THE 12Z UKMET AND CANADIAN WERE NOT AS DEEP...AND KEEP THE TWO STREAMS MORE SEPARATED THROUGH TIME...YIELDING SLOWER MOVEMENT TO THE SOUTHERN STREAM LOW. WE PREFER THE AGREEMENT SEEN IN THE NAM/GFS/ECMWF...WITH PLENTY OF SUPPORT FROM THE GEFS AND ECMWF ENSEMBLE. ...BROAD TROUGH DIGGING ACROSS THE NORTHERN U.S. FRI/SAT... PREFERENCE: 12Z ECMWF RECENT RUNS OF THE GFS HAVE BEEN SOMEWHAT ERRATIC AT THE SURFACE. THE LATEST 00Z RUN IS CHARACTERISTICALLY FAST AND OF LESSER INTENSITY WITH LOW PRESSURE DRAGGING A COLD FRONT THROUGH THE NORTHERN U.S. SATURDAY. LARGE SCALE AMPLIFICATION OF THE NORTHERN STREAM ALOFT ARGUES FOR A MORE AMPLIFIED SURFACE PATTERN WITH LOW PRESSURE FARTHER NORTH...AS SEEN IN THE OTHER OPERATIONAL MODELS. THE UKMET IS ON THE FAST SIDE WITH THIS AND OTHER FEATURES IN THE NORTHERN STREAM. THE ECMWF HAS SHOWN GOOD CONSISTENCY FROM RUN TO RUN...AND FITS OUR CONCEPTUAL MODEL FOR A COMBINATION OF MODERATE DEEPENING AND MODERATE PROGRESSION. THE 18Z AND 00Z NAM AND 12Z CANADIAN ALSO SUPPORT THE ECMWF THROUGH THE BEGINNING OF DAY 3 BEFORE THEY TREND TOWARD A DEEPER LOW LIFTING NORTH RATHER THAN PROGRESSING EAST. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE