MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EST TUE JAN 17 2017 VALID JAN 17/1200 UTC THRU JAN 21/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... ...TRIO OF SHORTWAVES MOVING THROUGH THE OH VALLEY/MID-ATLANTIC... ...SURFACE LOW FORMING OFF THE NJ COAST BY 18/1200Z... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF FORECAST CONFIDENCE: AVERAGE WATER VAPOR IMAGERY THIS MORNING SHOWED A PAIR OF LEAD SHORTWAVES CROSSING THE LOWER GREAT LAKES. BOTH OF THESE IMPULSES SHOULD GRADUALLY FLATTEN/SHEAR AS THEY EXIT THE NEW ENGLAND COAST EARLY WEDNESDAY MORNING. ON ITS HEELS...A MORE DEFINED SYSTEM CURRENTLY CROSSING THE MIDDLE MS VALLEY WILL SLIDE THROUGH THE UPPER OH VALLEY BY 18/1200Z WITH SOME TIMING DIFFERENCES NOTED IN THE GUIDANCE. ON THE QUICKER SIDE ARE THE 12Z NAM/GFS AS WELL AS THE 06Z GEFS/09Z SREF MEANS. ENSEMBLE SPAGHETTI PLOTS HAVE SHOWN A GENERAL DICHOTOMY BETWEEN THE GFS/ECMWF CAMPS WITH THE LATTER CONTINUING TO SHOW SUPPORT FOR A SLOWER FORECAST. AT THIS POINT...WILL SPLIT THE DIFFERENCE BETWEEN THE TWO CAMPS UNTIL FUTURE GUIDANCE ARRIVES. THE PREFERENCE IS A BLEND OF THE 12Z GFS/00Z ECMWF. ...BROAD UPPER LOW EJECTING OUT OF THE SOUTHERN HIGH PLAINS... ...EVENTUAL NEGATIVELY-TILTED TROUGH/WEAK SURFACE WAVE ACROSS THE MIDDLE MS VALLEY... PRELIMINARY PREFERENCE: A NON-12Z NAM/09Z SREF MEAN BLEND FORECAST CONFIDENCE: ABOVE AVERAGE CURRENTLY...A BROAD POSITIVELY-TILTED UPPER TROUGH IS POSITIONED OVER WESTERN MX AND EXTENDING UP INTO THE FOUR CORNERS REGION. A SERIES OF EMBEDDED SHORTWAVES WILL LIFT NORTHEASTWARD AS THE LONGWAVE TROUGH MIGRATES SLOWLY TOWARD THE EAST. DIFFERENCES ARE MINIMAL THROUGH 19/0000Z BEFORE SOME DIVERGENCE IN THE SOLUTIONS IS NOTED THEREAFTER. ON THURSDAY...THE 12Z NAM BECOMES NOTABLY FASTER WHICH SOMEWHAT MIMICS THE 09Z SREF MEAN. THE OVERALL SPREAD IS NOT TERRIBLY LARGE THROUGH THE REMAINDER OF THE WORK WEEK. CONSEQUENTLY...A NON-12Z NAM/09Z SREF MEAN WILL BE THE RECOMMENDATION HERE. ...SERIES OF PERTURBATIONS MOVING INTO THE PACIFIC NORTHWEST/BRITISH COLUMBIA EARLY ON... ...LONGWAVE TROUGH DIGGING INTO THE SOUTHWESTERN U.S. BY EARLY THURSDAY... PRELIMINARY PREFERENCE: INITIAL SYSTEM: BLEND OF 12Z GFS/00Z UKMET...LONGWAVE TROUGH: MODEL COMPROMISE BETWEEN THE 12Z GFS AND 00Z ECMWF/UKMET FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE MULTIPLE PERTURBATIONS WITHIN AN ACTIVE PATTERN ACROSS THE EASTERN PACIFIC WILL PUSH THROUGH THE PACIFIC NORTHWEST/BRITISH COLUMBIA THE NEXT 24 HOURS OR SO. ONE PARTICULAR WAVE SHOULD BE RATHER INTENSE AS NOTED IN THE 12Z GFS/00Z UKMET WITH MORE OF A NEGATIVE TILT TO THEIR SHORTWAVES. ADDITIONALLY...THE 12Z GFS IS QUICKER THAN THE 00Z ECMWF/ECMWF ENSEMBLE MEAN WHICH WAS ALSO A THEME FURTHER DOWNSTREAM WITH THE OH VALLEY SYSTEM. THIS PARTICULAR SYSTEM IS CURRENTLY IN THE VICINITY OF 50N/160W CROSSING SOUTH OF THE ALEUTIANS. GIVEN THE INTENSE NATURE OF THIS SHORTWAVE AS NOTED ON WATER VAPOR IMAGERY...WILL LEAN IN THE DIRECTION OF STRONGER HERE AND FAVOR A 12Z GFS/00Z UKMET MODEL BLEND. REGARDING THE LONGWAVE TROUGH DIGGING INTO CA AND EVENTUALLY INTO THE FOUR CORNERS REGION ON THURSDAY/FRIDAY...MODELS ARE IN DECENT AGREEMENT EXCEPT FOR THE 00Z CMC WHICH WAS A HAIR FASTER. BY 20/0000Z...THE 12Z NAM BECOMES QUICKER AND AWAY FROM THE STRONGER CONSENSUS FORMED BY THE 12Z GFS AND 00Z ECMWF/UKMET. THIS IS IN REMARKABLE CONTRAST FROM A FEW RUNS AGO WHERE THE ECMWF SUITE WAS DECIDEDLY FASTER LEADING TO A LARGE AMOUNT OF SPREAD. OVERALL...WILL SUGGEST SOME FORM OF MODEL COMPROMISE BETWEEN THE 12Z GFS AND 00Z ECMWF/UKMET. ...SECONDARY HEIGHT FALLS REACHING THE WEST COAST BY FRIDAY/INAUGURATION DAY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE ON THE HEELS OF THE INITIAL LONGWAVE TROUGH PUSHING THROUGH THE SOUTHWESTERN U.S...AN EVEN STRONGER UPPER TROUGH BEGINS TO APPROACH THE WEST COAST BY FRIDAY. ON THE LARGE SCALE...THERE ARE NOT A WHOLE LOT OF DISCERNIBLE DIFFERENCES. EVEN COMPARING THE SPAGHETTI PLOTS OVER THE LAST FEW MODEL CYCLES DOES NOT SHOW ANY MAJOR DIFFERENCES OCCURRING. AS SUCH...A GENERAL MODEL COMPROMISE IS WARRANTED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER