MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1146 AM EST WED JAN 04 2017 VALID JAN 04/1200 UTC THRU JAN 08/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED LOW DEVELOPING OVER THE UPPER GREAT LAKES AND CANADA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE DEVELOPING CLOSED LOW CURRENTLY OVER THE NW GREAT LAKES APPEARS TO BE EVOLVING WELL TOWARD RECENT GUIDANCE HAS BEEN SUGGESTING. THIS MODEL AGREEMENT CONTINUES WITH THE MOST RECENT RUNS INCLUDING THE 12Z NAM AND GFS THROUGH THE REMAINDER OF ITS INFLUENCE ACROSS THE CONUS. THIS CONTINUES TO SUPPORT A GENERAL MODEL BLEND AS WPC PREFERENCE AT ABOVE AVERAGE CONFIDENCE. SECONDARY TROUGH SETTING UP ACROSS THE NORTH-CENTRAL U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/06Z GEFS/00Z ECENS MEAN/00Z UKMET BLEND CONFIDENCE: AVERAGE IN THE WAKE OF THE EXITING DEVELOPING UPPER LOW...BROAD TROUGHING REMAINS ACROSS THE NORTHERN TIER OF THE US THAT WILL BE REINFORCED BY A WEAK SHORTWAVE CURRENTLY SEEN IN WV ACROSS S SASKATCHEWAN. WV LOOP ALSO DENOTES SHORTWAVE ENERGY BEING SHED EASTWARD FROM PACIFIC LOW THAT WILL HELP ELONGATE THE POSITIVE TILT TROF NEARLY ACROSS THE ENTIRE COUNTRY. THE 00Z ECMWF IS A BIT SLOW TO DRAW THE ENERGY INTO THE NORTHERN STREAM (POST NORTHERN STREAM TROF AXIS PASSAGE) THIS IS MINOR BUT DOES LEAD TO A FLATTER SOLUTION WITHIN THE TROF WITH VERY LITTLE WAVY NATURE AS PRESENTED BY THE REST OF THE GUIDANCE WHICH SUPPORTS INCREASED POST TROF RIDGING. WHILE THE DIFFERENCES TO THE TROF/INTERACTIONS ITSELF ARE SMALL IT SETS THE STAGE FOR THE NEXT SYSTEM'S STARTING POINT TO BE WELL DIFFERENT INCLUDING AN NICELY CURVED ANTICYCLONIC 150KT 250MB JET...THAT SEEMS A BIT ROBUST AT THIS POINT. THE 12Z NAM AND 00Z CMC ALSO SUPPORT SOME SLOWER/MORE CONSOLIDATED SHORTWAVE ENERGY WITHIN THE TRAILING EDGE THAT LINGERS THE TROF ACROSS THE OHIO VALLEY A BIT LONGER THAN THE MEAN OF SOLUTIONS SUGGEST. THE 12Z GFS AND 00Z UKMET BOTH ARE MIDDLE GROUND SOLUTIONS AND REPRESENT THE GEFS/ECENS/CMCE MEANS. CONFIDENCE IS AVERAGE. SOUTHERN STREAM SHORTWAVE INTO THE SOUTHEAST THURS WITH ASSOCIATED SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: AVERAGE MODELS APPEAR TO BE HANDLING THE SHORTWAVE AND ASSOCIATED JET SPEED MAX FAIRLY WELL ACCELERATION IT ACROSS THE DEEP SOUTH TODAY AND THURSDAY AND ALONG WITH THE FAVORABLE ORIENTATION TO THE NORTHERN STREAM POSITIVE TILT TROF SUPPORT SOME AMPLIFICATION AND SURFACE LOW DEVELOPMENT OFF GA/SC LATE THURS/FRIDAY MORNING. THE 12Z NAM AND 00Z CMC ARE A BIT FASTER AND LEAD TO QUICKER SURFACE LOW SOLUTIONS WHEN COMPARED TO FAIRLY TIGHT 00Z ENSEMBLE CLUSTER. THE 12Z GFS HAS SHIFTED TOWARD THIS FASTER SOLUTION MATCHING THE CMC WELL. THE 00Z UKMET WITH A VERY STRONG JET ALOFT FRIDAY NIGHT INTO SAT...DEEPENS THE LOW AND CYCLONICLY TURNS IT TOWARD THE COAST/NEAR NW NOVA SCOTIA WHICH FITS WITH A TYPICAL BIAS AND LEADS TO AN OUTLYING SOLUTION. THE 12Z ECMWF REMAINS A GOOD REPRESENTATION TO THE ENSEMBLE MEANS (06Z GEFS/00Z ECENS MEAN). THE SHIFT OF THE GFS LEADS TO SOME PAUSE ON WHICH SOLUTION WILL COME TO FRUITION AND REDUCES CONFIDENCE TO AVERAGE; YET ONLY THE UKMET SEEMS TO BE WORTH REMOVING AT THIS TIME FROM THE BLEND. PACIFIC NORTHWEST TROUGH TRACKING TO THE SOUTHERN PLAINS FRI AND INTO THE SOUTHEAST SAT WITH SURFACE LOW DEVELOPING OUT OF EASTERN GULF TO EAST COAST. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECENS MEAN (12Z NAM/00Z UKMET COMPROMISE) CONFIDENCE: BELOW AVERAGE SMALL DETAILS DIFFERENCES IN TIMING AND MAGNITUDE OF ENERGY BEING SHEARED INTO THE NORTHERN FLOW CONTINUE TO LEAD TO COMPOUNDING SPREAD AS THE SYSTEM BEGINS TO SHIFT INTO THE SOUTHERN PLAINS BY FRI AND TOWARD THE EAST COAST BY SAT. THE 00Z CMC IS FASTEST ACCELERATING SOUTHEAST AS IT CONTINUES TO SUGGEST A MORE PHASED SOLUTION WITH THE NORTHERN STREAM. THE 00Z ECMWF IS ON THE OTHER SIDE OF THE SPECTRUM SUGGESTING A MUCH MORE CONSOLIDATED SHORTWAVE ROLLING THROUGH THE CENTRAL PLAINS...AND WITH DOWNSTREAM INCREASED RIDGING/FAVORABLE JET ORIENTATION/STRENGTH LEADS TO THE MOST AMPLIFIED SOLUTION STANDING OUT WITHIN THE SPAGHETTI ANALYSIS...AND SHOW LITTLE CONTINUITY WITH 3 PRIOR RUNS. THE 00Z UKMET IS NEXT MOST AMPLIFIED BUT IS CLOSER TO THE ECENS MEAN WHICH CONTINUES TO BE MOST MIDDLE GROUND. THE 12Z NAM/GFS AND GEFS MEAN ALL SUGGEST AN INITIALLY SLOWER SHORTWAVE THROUGH THE SOUTHERN PLAINS BUT WITH LESS ENERGY...IT ACCELERATES AROUND THE LARGER SCALE TROF BASE ACROSS THE SOUTHEAST PRESENTING THE FLATTEST SOLUTIONS. THE 12Z GFS AND 00Z GFS PARALLEL BOTH SUGGEST THE FLATTER SOLUTIONS. AS SUCH CONFIDENCE OVERALL HAS REDUCED WITH INCREASED SPREAD. CONTINUITY AND GENERAL MIDDLE GROUND WOULD SUGGEST SOMETHING CLOSE TO THE 00Z ECENS MEAN. AS THE UKMET IS A BIT AMPLIFIED BUT NOT AS MUCH AS THE ECMWF...AND THE 12Z NAM IS A BIT FLATTER BUT NOT AS MUCH AS THE GFS/GEFS WILL SUPPORT A 12Z NAM/00Z UKMET BLEND OF MASS FIELDS AS A COMPROMISE TO REPRESENT THE 00Z ECENS MEAN. CONFIDENCE IS BELOW AVERAGE. SHORTWAVE REACHING THE NORTHERN GREAT LAKES SATURDAY MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/NAM AND 00Z ECMWF BLEND CONFIDENCE: SLIGHTLY AVERAGE AVERAGE NEXT SHORTWAVE LOBE OF GLOBAL SCALE EASTERN CANADIAN VORTEX ENTERS THE GREAT LAKES INTO SATURDAY UNDER FAIRLY GOOD TIMING WITHIN THE MODELS. THE RELATIVELY SMALL SPREAD REMAINS IN REGARD TO SHAPE AND EVENTUALLY ORIENTATION...I.E. DEEPER SHARPER TROF AND THEREFORE GREATER INTERACTION WITH THE SOUTHERN STREAM REPRESENTED BY THE 00Z CMC AND LESSER SO THE 00Z UKMET. THE 12Z NAM/GFS AND 00Z ECMWF CONTINUE TO BE FAIRLY WELL ALIGNED AND ENSEMBLES SUPPORT IS FAIRLY STRONG. AS SUCH A 12Z NAM/GFS AND 00Z ECMWF BLEND WILL BE PREFERENCE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. LARGE/DEEP CLOSED LOW OFF PACIFIC NORTHWEST COAST PUMPING BROAD ZONE OF SOUTHWESTERLY FLOW ACROSS WEST COAST BY SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE (HIGH FOR LARGE SCALE PATTERN) AMPLIFICATION OF STRONG NORTHERLY FLOW ALONG THE AK/YUKON BORDER BEGINS TO CONSOLIDATE INTO A LARGE DEEP CYCLONE ACROSS THE SOUTHEAST GULF OF ALASKA BY FRIDAY NIGHT WITH FAIRLY GOOD AGREEMENT. THIS WILL SUPPORT INCREASED SOUTHWESTERLY FLOW OUT OF THE SUBTROPICS THAT WILL AFFECT A LARGE PORTION OF THE US WEST COAST INTO SUNDAY. AS THE UPPER LOW MATURES SOME SPREAD IN MODELS MANIFESTS MAINLY IN THE SHAPE OF THE WAVE; AS THE GFS/NAM/CMC ARE A BIT MORE CONCENTRIC WHILE THE ECMWF/UKMET ELONGATE SOUTHWEST AS THE LOW SLOWLY RETROGRADES THAT DIRECTION. STILL OVERALL THE SPREAD HERE IS MINOR. WHERE THE SPREAD AND REDUCED CONFIDENCE EXISTS IS THE TIMING AND STRENGTH OF THE SHORTWAVES EMBEDDED IN THE DUAL STREAM FLOW (POLAR/SUBTROPICAL) FROM WA/OR TO CENTRAL CA. THE 12Z GFS AND 00Z UKMET HAVE STRONGER AGREEMENT AND PLACEMENT OF SURFACE WAVE AND TIMING OF THE WAVE WITH SOME SUPPORT FROM THE 12Z NAM (THOUGH THE NAM IS LESS AMPLIFIED IN THE SUBTROPICAL STREAM). THE ECMWF IS NEXT CLOSEST TO THE GFS/NAM/UKMET BUT IS A BIT SLOWER OVERALL...THIS IS TYPICAL BUT IS DIFFICULT TO DISREGARD GIVEN THE LOW PREDICTABILITY OF THESE EMBEDDED SHORTWAVES. AS SUCH WILL FAVOR A NON-CMC BLEND AT AVERAGE CONFIDENCE (HIGH FOR THE LARGE SCALE/QUITE LOW FOR THE INTERNAL DETAILS). www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA