MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1201 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 NAM/GFS EVALUATION AND PRELIMINARY MODEL PREFERENCES ...SURFACE LOW DEVELOPING ACROSS THE SOUTHERN MID-ATLANTIC TONIGHT... PRELIMINARY PREFERENCE: GFS/12Z 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 IS TOWARD THE LEFT SIDE OF THE CONSENSUS AS THE LOW PASSES EAST OF CAPE COD THURS AFTERNOON. THE GFS IS VERY CLOSE TO THE 12Z ECMWF AS WELL AS THE ENSEMBLE CONSENSUS (12Z ECMWF ENS MEAN/18Z GEFS MEAN). THUS, WILL RECOMMEND A BLEND OF THE GFS AND THE 12Z ECMWF AT THIS TIME. ...SHORTWAVE AND PACIFIC COLD FRONT MOVING ONSHORE IN THE PACIFIC NORTHWEST THURSDAY MORNING... PRELIMINARY PREFERENCE: GFS/12Z ECMWF/12Z UKMET BLEND CONFIDENCE: ABOVE AVERAGE MODEL SPREAD WITH RESPECT TOO THE SHORTWAVE AND FRONT REACHING THE PAC NW THURS MORNING IS RELATIVELY LOW. THE NAM APPEARS TO BE SLIGHTLY OVER AMPLIFIED WITH THE SHORTWAVE, WHILE THE 12Z CMC WAS A ON THE UNDER AMPLIFIED SIDE OF THE SPREAD. AS THIS ENERGY AT THIS TIME, A CONSENSUS SOLUTION APPEARS TO BE BEST REPRESENTED BY A BLEND OF THE GFS/12Z ECMWF/12Z UKMET. ...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... PRELIMINARY PREFERENCE: GFS/12Z 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 ALONG WITH THE 12Z UKMET SEEM ON THE QUICK SIDE WITH PROGRESSING THIS SYSTEM EAST, WHILE THE GFS IS SIMILAR TO THE 12Z ECMWF/CMC WITH A SLIGHTLY SLOWER PROGRESSION. THE ENSEMBLE MEANS (12Z ECMWF ENS/18Z GEFS) BOTH FAVOR THE SLOWER SOLUTIONS. 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. THE UKMET REMAINS ON THE QUICK SIDE WITH THIS LOW, WHILE THE GFS/NAM ALONG WITH THE 12Z ECMWF ARE ON THE SLOW SIDE. THE ECMWF IS ALSO A BIT SUPPRESSED RELATIVE TO THE GFS/NAM. AT THIS TIME, A BLEND OF THE GFS/12Z ECMWF SEEMS TO BE THE BEST CONSENSUS SOLUTION THROUGHOUT THE EVOLUTION AND PROGRESSION OF THIS SYSTEM. ...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... PRELIMINARY PREFERENCE: GFS/12Z CMC BLEND CONFIDENCE: BELOW 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 GFS AND NAM ARE STRONGER THAN THE MODEL CONSENSUS WITH THE INITIAL SHORTWAVE BEFORE THE SEPARATION OCCURS, WHICH RESULTS IN A SOMEWHAT DIFFERENT SURFACE EVOLUTION, WITH A STRONGER SURFACE LOW LINGERING FARTHER WEST FOR LONGER RELATIVE TO THE 12Z ECMWF/UKMET/CMC. A FIRST LOOK AT THE 00Z UKMET AS IT IS STARTING TO COME IN SHOWS AN EVOLUTION MORE LIKE THE NAM/GFS, WHICH SEEMS TO INDICATE A TREND IN THAT DIRECTION. 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 DUE TO THEIR MORE AMPLIFIED WAVE THROUGHOUT THE EVOLUTION OF THE SYSTEM, THE NAM AND GFS ARE A BIT SLOWER WITH THE SURFACE FRONTAL WAVE AS IT SKIRTS THE NORTHERN PLAINS AND UPPER MIDWEST SATURDAY NIGHT. THE GFS DEVELOPS THE MOST WELL DEFINED SURFACE LOW AS THE SYSTEM MOVES INTO WESTERN ONTARIO SAT NIGHT. THE 12Z CMC SHOWS A SIMILAR SOLUTION TO THE NAM/GFS DURING THIS TIME FRAME, BUT WITH A SLIGHTLY WEAKER SURFACE LOW, AND SLIGHTLY FASTER. GIVEN THE NOTED TREND SEEN AS NEW GUIDANCE IS COMING IN THIS EVENING, AM FAVORING A SOMEWHAT MORE AMPLIFIED AND SLOWER SOLUTION SIMILAR TO THE GFS. WILL INCLUDE THE GFS ALONG WITH THE 12Z CMC IN THE PREFERENCE AT THIS TIME, SINCE THE 12Z CMC SERVES A BIT OF A MODERATING INFLUENCE, PENDING THE ARRIVAL OF THE ADDITIONAL 00Z MODEL SUITE. ...UPPER-LEVEL LOW MOVING INTO CALIFORNIA SATURDAY MORNING THEN DEEPENING ACROSS THE SOUTHWESTERN U.S... PRELIMINARY PREFERENCE: GFS/12Z UKMET/18Z GEFS MEAN BLEND CONFIDENCE: BELOW 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. BY THE TIME THE SYSTEM REACHES THE SOUTHWESTERN U.S. LATE SATURDAY, THE NAM AND GFS, ALONG WITH THE 12Z CMC/UKMET AS WELL AS THE 18Z GEFS MEAN, KEEP THE UPPER LOW FARTHER WEST THAN THE 12Z ECMWF. 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 HAS BEEN MORE CONSISTENT WITH KEEPING THE UPPER LOW DEEPER AND FARTHER SOUTHWEST FOR A LONGER PERIOD OF TIME. GIVEN THE CONSISTENCY THE LATTER GROUP, AND THE TRENDS NOTED IN THE ECMWF IN THAT DIRECTION, WILL FAVOR THIS SOLUTION AT THIS TIME. A BLEND OF THE GFS/12Z ECMWF/18Z GEFS MEAN WILL BE THE PRELIMINARY PREFERENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN