MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1125 PM EST THU JAN 08 2015 VALID JAN 09/0000 UTC THRU JAN 12/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...SERIES OF FAST-MOVING SHORTWAVES CROSSING THE UPPER MIDWEST/GREAT LAKES/NORTHEAST TODAY THROUGH SUNDAY... ...REINFORCING ARCTIC SURFACE COLD FRONT CROSSING THE EASTERN U.S.... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE CLOSED 500 HPA LOW NORTH OF HUDSON BAY WILL DRIFT SLOWLY SOUTHWARD OVER THE NEXT FEW DAYS BUT WILL REMAIN A DOMINANT FEATURE IN THE LARGE-SCALE FLOW. A SERIES OF FAST-MOVING SHORTWAVES WILL ROTATE AROUND THE CLOSED LOW...CROSSING THE UPPER MIDWEST...GREAT LAKES AND THE NORTHEAST. MODEL SPREAD IS RELATIVELY LOW WITH THE FIRST OF THESE SHORTWAVES CROSSING THE NORTHEAST ON FRIDAY WHICH WILL HELP DRIVE A REINFORCING ARCTIC COLD FRONT THROUGH THE EASTERN U.S. THE GUIDANCE DEPICTS A SECOND WAVE SKIRTING THE UPPER GREAT LAKES ON FRIDAY AND THE NORTHEAST EARLY SATURDAY. A THIRD WAVE WILL CROSS THE SAME AREAS ON LATE SATURDAY AND SATURDAY NIGHT. GIVEN RATHER MINIMAL MASS FIELD SPREAD...A GENERAL MODEL COMPROMISE WILL BE FAVORED ACROSS THESE AREAS THROUGH THE PERIOD. ...SOUTHERN STREAM SHORTWAVE MOVING INTO CALIFORNIA LATE FRIDAY AND CROSSING THE SOUTHERN INTERMOUNTAIN STATES AND CENTRAL/SOUTHERN PLAINS SATURDAY INTO SUNDAY... PREFERENCE: NON-UKMET CONSENSUS CONFIDENCE: ABOVE AVERAGE A SOUTHERN STREAM SHORTWAVE WILL APPROACH THE SOUTHERN CALIFORNIA COAST ON FRIDAY. THE WAVE BEGINS TO SHEAR OUT AS IT MOVES INTO THE SOUTHERN INTERMOUNTAIN STATES ON SATURDAY. THE 12Z UKMET IS A SLOW AND RELATIVELY DEEP OUTLIER WITH THIS SYSTEM THROUGH SATURDAY. ALL OF THE MODELS SHEAR THIS ENERGY OUT INTO THE CENTRAL AND SOUTHERN PLAINS BY SUNDAY. A NON-UKMET CONSENSUS WILL BE PREFERRED. ...SLOW-MOVING UPPER LOW OVER NORTHWEST MEXICO SHEARING INTO THE SOUTHERN PLAINS LATE SATURDAY... ...INVERTED SURFACE TROUGH NEAR THE WESTERN GULF COAST... PREFERENCE: BLEND OF THE 00Z NAM/00Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE A BROAD CLOSED LOW OVER NORTHWEST MEXICO IS FORECAST BY THE MODELS TO ADVANCE EAST AND SHEAR OUT ACROSS THE SOUTHERN PLAINS THROUGH SATURDAY. THIS ENERGY WILL BE INSTRUMENTAL IN FOSTERING AN INVERTED TROUGH OVER THE WESTERN GULF COAST AREA JUST EAST OF THE TX COASTLINE. THE 00Z NAM/00Z GFS AND 12Z ECMWF ARE ALL A LITTLE FASTER TO SHEAR OUT THE ENERGY COMPARED TO THE MODESTLY SLOWER AND DEEPER 12Z GEM AND 12Z ECMWF. THE 12Z ECENS MEAN AND 18Z GEFS SEEM TO FAVOR THE SLIGHTLY MORE PROGRESSIVE/SHEARED CAMP. ...SOUTHERN STREAM SHORTWAVE MOVING INTO CALIFORNIA ON SUNDAY... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THERE WILL BE ANOTHER SOUTHERN STREAM SHORTWAVE TROUGH ARRIVING ACROSS CALIFORNIA ON SUNDAY AND INTO THE GREAT BASIN ON SUNDAY. THE 00Z GFS IS PERHAPS A TAD DEEPER THAN THE GLOBAL MODEL CONSENSUS EARLY IN THE PERIOD...AND BY THE END OF THE PERIOD THE 00Z NAM/12Z UKMET AND 12Z GEM SHOW SOMEWHAT STRONGER HEIGHT FALLS OVER THE GREAT BASIN VERSUS THE 00Z GFS AND 12Z ECMWF. WILL PREFER A GENERAL MODEL COMPROMISE TO RESOLVE THESE MASS FIELD DIFFS WHICH ARE RELATIVELY MINOR. ...SHORTWAVE APPROACHING THE PACIFIC NORTHWEST ON SUNDAY... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE THE 00Z GFS AND 12Z ECMWF APPEAR TO CLUSTER REASONABLY WELL WITH THE ARRIVAL OF A SHORTWAVE TROUGH OVER THE PACIFIC NORTHWEST ON SUNDAY. THESE SOLNS ARE A LITTLE SLOWER THAN THE 12Z UKMET AND 12Z GEM SOLNS. THE 00Z NAM IS A BIT DEEPER THAN THE GFS/ECMWF CAMP. WILL PREFER A GFS/ECMWF BLEND ATTM. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON