MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 201 AM EST THU FEB 09 2017 VALID FEB 09/0000 UTC THRU FEB 12/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION AND FINAL PREFERENCES ...SURFACE LOW DEVELOPING ACROSS THE SOUTHERN MID-ATLANTIC TONIGHT... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE A WAVE OF LOW PRESSURE IS FORECAST TO DEVELOP ALONG A FRONTAL BOUNDARY ACROSS THE SOUTHERN MID-ATLANTIC REGION TONIGHT. THE LOW IS THEN FORECAST TO DEEPEN RAPIDLY AS IT MOVES OFFSHORE OF THE DELMARVA PENINSULA THURS MORNING AND THEN NORTHEASTWARD OFF THE NEW ENGLAND COAST. THE NAM AND GFS SOLUTIONS ARE BOTH GENERALLY CLOSE TO THE MODEL CONSENSUS. THE NAM AND UKMET ARE TOWARD THE LEFT SIDE OF THE CONSENSUS AS THE LOW PASSES EAST OF CAPE COD THURS AFTERNOON. THE CMC IS ON THE EASTERN SIDE OF CONSENSUS WITH THE LOW TRACK. THE GFS IS VERY CLOSE TO THE ECMWF AS WELL AS THE ENSEMBLE CONSENSUS (12Z ECMWF ENS MEAN/00Z GEFS MEAN). THUS, WILL RECOMMEND A BLEND OF THE GFS AND ECMWF AT THIS TIME. ...SHORTWAVE AND PACIFIC COLD FRONT MOVING ONSHORE IN THE PACIFIC NORTHWEST THURSDAY MORNING... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: ABOVE AVERAGE MODEL SPREAD WITH RESPECT TOO THE SHORTWAVE AND FRONT REACHING THE PAC NW THURS MORNING IS RELATIVELY LOW. THE NAM AND UKMET APPEAR TO BE SLIGHTLY OVER AMPLIFIED WITH THE SHORTWAVE. AT THIS TIME, A CONSENSUS SOLUTION APPEARS TO BE BEST REPRESENTED BY A BLEND OF THE GFS AND ECMWF. ...SURFACE LOW DEVELOPING ACROSS THE SOUTHERN CANADIAN PRAIRIES EARLY FRIDAY THEN SKIRTING THE UPPER MIDWEST FRIDAY NIGHT... ...WEAK SURFACE LOW OFF THE COAST OF NEW ENGLAND LATE SATURDAY... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE THE SHORTWAVE MOVING INTO THE PAC NW THURS MORNING WILL CROSS THE NORTHERN ROCKIES AND RESULT IN THE DEVELOPMENT OF A SURFACE LOW ACROSS THE SOUTHERN CANADIAN PRAIRIES THURS NIGHT. THE NAM AND UKMET SEEM ON THE QUICK SIDE WITH PROGRESSING THIS SYSTEM EAST, WHILE THE GFS IS SIMILAR TO THE ECMWF WITH A SLIGHTLY SLOWER PROGRESSION. THE CMC COMES IN ON THE SLOW SIDE OF THE SPREAD. THE ENSEMBLE MEANS (12Z ECMWF ENS/00Z GEFS) BOTH FAVOR THE SLOWER SOLUTIONS SLOWER THAN THE NAM/UKMET. AS THE LOW AND THE ASSOCIATED SHORTWAVE CONTINUE TO PROGRESS EAST ON SATURDAY, ENERGY IS FORECAST TO TRANSFER TO A NEW SURFACE LOW WHICH WILL DEVELOP OFF THE COAST OF NEW ENGLAND LATE SATURDAY. SPREAD WITH RESPECT TO THIS FEATURE HAS DECREASED SOMEWHAT WITH THE ARRIVAL OF THE 00Z NON-NCEP GUIDANCE. THE 00Z RUN OF THE ECMWF IS NOT QUITE A SUPPRESSED AS THE 12Z RUN, AND THE 00Z UKMET IS NOT AS FAST AS ITS 12Z RUN. THE BEST CONSENSUS SOLUTION THROUGHOUT THE EVOLUTION AND PROGRESSION OF THIS SYSTEM CONTINUES TO BE A GFS/ECMWF BLEND. ...SECOND SHORTWAVE REACHING THE PACIFIC NORTHWEST FRIDAY MORNING THEN CROSSING THE NORTHERN ROCKIES FRIDAY NIGHT... ...SURFACE LOW SKIRTING THE NORTHERN PLAINS AND UPPER MIDWEST SAT/SAT NIGHT... PREFERENCE: GFS/UKMET BLEND CONFIDENCE: AVERAGE MODEL CONSENSUS IS FAIRLY GOOD WITH RESPECT TO THE GENERAL EVOLUTION OF THE MID/UPPER-LEVEL SHORTWAVE AS IT APPROACHES THE COAST. A DEGREE OF COMPLEXITY IS ADDED TO THE SITUATION AFTER 12Z FRI AS THE SHORTWAVE SPLITS, WITH ONE LESS AMPLIFIED PIECE OF ENERGY EJECTING QUICKLY INTO THE INTERIOR NORTHWEST, AND ANOTHER DIGGING SOUTHWARD ALONG THE WEST COAST AND AMPLIFYING. THE ECMWF/UKMET/CMC HAVE JOINED THE GFS AND NAM IN SHOWING A SLIGHTLY STRONGER INITIAL SHORTWAVE BEFORE THE SEPARATION OCCURS, WHICH SEEMS TO RESULT IN A STRONGER SURFACE LOW LINGERING FARTHER WEST FOR LONGER RELATIVE TO THE 12Z RUNS OF THE ECMWF/UKMET/CMC. THE GFS AND NAM MAINTAIN THEIR SLIGHTLY MORE AMPLIFIED SOLUTION FOR THIS WAVE EVEN AS IT MOVES INLAND AND CROSSES THE NORTHERN ROCKIES FRIDAY NIGHT. BY THIS TIME A SURFACE LOW SHOULD BE DEVELOPING EAST OF THE CANADIAN ROCKIES ACROSS THE SOUTHERN CANADIAN PRAIRIES. LIKELY THE DOWNSTREAM RESULT OF THE NOTED TRENDS WITH THE PARENT SYSTEM OFF THE PACIFIC NORTHWEST, THE UKMET/CMC/ECMWF HAVE JOINED THE NAM AND GFS AND ARE ARE A BIT SLOWER THAN PREVIOUS RUNS WITH THE SURFACE FRONTAL WAVE AS IT SKIRTS THE NORTHERN PLAINS AND UPPER MIDWEST SATURDAY NIGHT. THE GFS CONTINUES TO SHOW THE STRONGEST SURFACE LOW AS THE SYSTEM MOVES INTO WESTERN ONTARIO SAT NIGHT. GIVEN THE NOTED TREND TOWARD A SLOWER AND SLIGHTLY STRONGER WAVE AMONG THE 00Z MODEL SUITE, WILL LEAN IN THAT DIRECTION FOR THE PREFERENCE, AND FAVOR THE GFS AND UKMET. WILL ALSO BOOST CONFIDENCE A BIT, GIVEN THE REDUCTION IN SPREAD FROM THE PREVIOUS MODEL CYCLE. ...UPPER-LEVEL LOW MOVING INTO CALIFORNIA SATURDAY MORNING THEN DEEPENING ACROSS THE SOUTHWESTERN U.S... PREFERENCE: GFS/UKMET/ECMWF BLEND CONFIDENCE: AVERAGE AS DISCUSSED ABOVE, AS THE SHORTWAVE SPLITS INTO TWO PARTS OFF THE NORTHWEST U.S. COAST, THE SOUTHERN OF THE TWO COMPONENT WAVES WILL DIVE SOUTHEASTWARD ALONG THE WEST COAST AS IT UNDERGOES AMPLIFICATION. THE NAM AND GFS HANDLE THIS FEATURES SIMILARLY TO THE MODEL CONSENSUS AS THE SYSTEM BEGINS TO AMPLIFY AND AND UPPER LOW FORMS. TAKING A LOOK AT THE PAST COUPLE RUNS OF THE DETERMINISTIC MODELS AS WELL AS THE ENSEMBLES, THE ECMWF HAS SHOWN A BIAS TOWARD THE EASTERN SIDE OF THE SPREAD WITH RESPECT TO THIS FEATURE FOR A COUPLE RUNS, WHILE THE GFS/UKMET/CMC HAVE BEEN MORE CONSISTENT WITH KEEPING THE UPPER LOW DEEPER AND FARTHER SOUTHWEST FOR A LONGER PERIOD OF TIME. BY THE TIME THE SYSTEM REACHES THE SOUTHWESTERN U.S. AND NORTHWESTERN MEXICO LATE SATURDAY INTO SUNDAY MORNING, THE 00Z ECMWF HAS JOINED THE CAMP OF SOLUTIONS SHOWING A DEEPER UPPER LOW THAT REMAINS FARTHER WEST. THIS SHIFT IN THE ECMWF CONSTITUTES A SIGNIFICANT REDUCTION IN SPREAD BY 12Z SUNDAY, INCREASING CONFIDENCE SOMEWHAT. AT THIS TIME, A BLEND OF THE GFS/UKMET/ECMWF SHOULD REPRESENT THE CONSENSUS SOLUTION FOR A SLOWER/DEEPER SYSTEM. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN