MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 136 AM EST TUE JAN 24 2017 VALID JAN 24/0000 UTC THRU JAN 27/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED LOW LIFTING ACROSS THE MID-ATLANTIC/COASTAL NEW ENGLAND AND ASSOCIATED STRONG SURFACE LOW LIFTING NORTHEAST ALONG THE COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE SMALL INTERNAL DIFFERENCES REMAIN WITH RESPECT TO THE UPPER LOW AND EXACT PLACEMENT OF THE OCCLUDED SURFACE LOW AND TRIPLE POINT AS THE SYSTEM LIFTS ALONG THE COAST. THE 00Z NAM AND 12Z UKMET ARE A BIT CLOSER TO THE COAST AT LEAST INITIALLY AND THE 00Z GFS/12Z CMC ARE A BIT FURTHER OFFSHORE BEFORE THE MAIN WAVE WITH THE 12Z ECMWF MOST CENTRAL BUT ALL IN ALL THIS IS MILD OR WEAK SPREAD FOR SUCH A LARGE/STRONG SYSTEM TO FAVOR ONE OVER ANOTHER PARTICULARLY AS WE HAVE SEEN THESE SMALL RUN TO RUN ADJUSTMENTS FOR THE LAST FEW DAYS/CYCLES. AS SUCH A GENERAL MODEL BLEND IS SUPPORTED WITH HIGHER WEIGHTING TO THE TRADITIONALLY BETTER VERIFYING MODELS OF THE ECMWF/GFS. STILL THESE INTERNAL RUN TO RUN VARIATIONS LEAD TO SOME DOUBT OVERALL THAT CONFIDENCE STILL ONLY REMAINS AT SLIGHTLY ABOVE AVERAGE. 07Z UPDATE: THE 00Z NON-NCEP SOLUTIONS CONTINUE FAIRLY TIGHT AGREEMENT THOUGH HAVE SMALL MASS DIFFERENCES IN EXACT POSITIONING OF SURFACE LOW/CLOSED HEIGHT CONTOURS AS THE OVERALL TROF CONTINUES TO ELONGATE WEST TO EAST THROUGH NEW ENGLAND AND THEREAFTER. STILL THIS SEEMS MINOR OVERALL TO PREFER ONE MODEL OR RUN OVER ANOTHER...AND AS SUCH WILL CONTINUE INITIAL PREFERENCE OF GENERAL MODEL BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE AS THIS SMALLER SCALE DETAILS REMAIN IMPORTANT AND VARIANT RUN TO RUN TO HAVE ABOVE AVERAGE CONFIDENCE. LONGWAVE TROUGH/SURFACE LOW OVER THE WEST EJECTING OUT INTO THE PLAINS WITH ENERGY LIFTING NORTHEAST INTO THE GREAT LAKES REGION BY WED. ATTENDANT COLD FRONT ADVANCING THROUGH THE EASTERN U.S. THROUGH THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE WV LOOP INDICATES EASTERN SIDE OF THE BROAD LONGWAVE TROF IS BEGINNING TO CONSOLIDATE/WIND UP ACROSS WY UNDER INCREASING DIFFLUENT FLOW AND SPURRING LARGE SURFACE PRESSURE FALLS IN THE LEE OF THE ROCKIES. BETTER SAMPLING OF THE OVERALL PATTERN HAS LEAD TO INCREASED CONVERGENCE OF MODEL SOLUTIONS THROUGH THE MIDWEST INTO THE GREAT LAKES. THERE WERE SOME NOTED THERMAL DIFFERENCES BETWEEN THE GFS AND ECMWF PARTICULARLY ACROSS NE NEB/IA BUT THE 00Z GFS HAS COOLED A BIT MORE TO HAVE SOME INCREASED CONFIDENCE IN KEEPING WITHIN ANY BLEND. OTHERWISE THE MASS FIELDS SEEM TO JIVE WELL UNTIL WED NIGHT/THURSDAY AS THE SYSTEM GROWS UP SCALE WITH THE NORTHWESTERN SIDE OF THE PRECEDING DEEP WAVE...INTO THE NEW CENTROID OF CIRCULATION IN THE MID-LEVELS ACROSS THE ONTARIO/QUEBEC BORDER. THIS IS WERE THE WEAKER CMC BECOMES FASTER AND REDUCES THE SURFACE AND LOWER LEVEL WAVE FASTER ACROSS THE GREAT LAKES WED INTO THURS. THE 00Z NAM AS IT IS KNOWN TO DO IS THE MOST STUBBORN TO WIND DOWN THOUGH IS ACCOMPANIED BY THE ECMWF AND LESSER SO THE UKMET/GFS. AS SUCH A NON-CMC BLEND WILL BE PREFERRED THOUGH MORE WEIGHTING WILL BE GIVEN TO THE 00Z NAM/12Z ECMWF. CONFIDENCE IS FAIRLY GOOD GIVEN THE LARGE SCALE OF THE SYSTEM WITH SMALLER MESO-SCALE FEATURES HAVING IMPACT...AND IS SLIGHTLY ABOVE AVERAGE IN THE BLEND. 07Z UPDATE: THE 00Z ECMWF STARTS A BIT SOUTH OF THE PRIOR 12Z RUN ACROSS THE CENTRAL PLAINS WITH THE SURFACE LOW BUT CONTINUES TO MATCH WELL WITH THE INITIAL PREFERENCE/THOUGHTS. LIKEWISE THE 00Z UKMET HAS SOME SMALL HEIGHT DIFFERENCES (DEEPER FURTHER WEST) IN THE MID-LEVELS INITIALLY BUT QUICKLY MATCHES THE INITIAL PREFERENCE AS WELL. THE 00Z CMC WHILE MAY CONTINUE TO A MORE OF AN OUTLIER THOUGH THE GREAT LAKES (A BIT NORTH AT SAY 7H) THIS TOO IS QUITE TIGHT TO THE OVERALL CONSENSUS TO BUILD FURTHER CONFIDENCE OVERALL. AS SUCH A GENERAL MODEL BLEND IS NOW SUFFICIENT FOR SLIGHTLY ABOVE AVERAGE CONFIDENCE THOUGH NEARING ABOVE AVERAGE. SURFACE LOW DROPPING SOUTH DOWN OFF THE WEST COAST THROUGH TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE INNER CORE ALONG THE WESTERN SIDE OF THE LONGWAVE TROF AND ASSOCIATED SURFACE CYCLONE CAN BE SEEN IN GOES-WV FILLING AND TRACKING ALONG THE CA COAST ATTM. MODELS SHOW STRONG ENOUGH SIMILARITY WITH RESPECT TO THIS WAVE/SFC LOW TO SUPPORT GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. SHORTWAVE DROPPING ACROSS THE UPPER MIDWEST/GREAT LAKES THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM BLEND CONFIDENCE: AVERAGE IN THE WAKE OF THE BROAD TROF TRANSLATING ACROSS THE MIDDLE OF THE CONTINENT... A VAST POSITIVE TILT TROF DOMINATES THE PATTERN WITH SMALLER EMBEDDED SHORTWAVES WITHIN IT. AT THE NORTHERN SIDE OF THE TROF...AN ELONGATED BUT ILL-DEFINED WAVE WILL DESCEND OUT OF CANADA SHORTENING THE WIDTH OF THE TROF FROM SE ONTARIO TO THE FOUR CORNERS BY THE END OF THE FORECAST PERIOD. THE 00Z NAM/12Z CMC BOTH ARE A BIT SLOWER IN THE WEST WITH A BIT MORE AMPLIFICATION WITH SOME OF THE EMBEDDED SHORTWAVES CROSSING THE GREAT LAKES...WHILE THE GFS/UKMET/ECMWF ARE A BIT MORE IN LINE WITH COMMON AXIS/ORIENTATION. THE 00Z GFS DID INDICATE A SHARPER/NARROW WESTERN BASE HAVING A MUCH MORE WOUND UP MID-LEVEL VORT CENTER THAN THE UKMET/ECMWF BUT ENSEMBLE SPREAD SUPPORTS BOTH A BROADER WAVE LIKE THE UKMET/ECMWF AS WELL AS THE TIGHTER GFS. AT THIS POINT FEEL FOCUS/IMPORTANCE ON ORIENTATION/TIMING OF THE TROF THAN THE EXACT DEPTH...PARTICULARLY GIVEN THE LACK OF QPF/SENSIBLE WEATHER WITH IT. CONFIDENCE IN THIS BLEND IN ONLY AVERAGE GIVEN THESE WESTERN DEPTH DIFFERENCES THAT REMAIN. 07Z UPDATE: OVERALL THE 00Z NCEP SOLUTIONS HAVE GRAVITATED TOWARD TIGHTER AGREEMENT WITH THE 00Z GFS INCLUDING A BIT MORE AGREEMENT PARTICULARLY OF THE CMC AND UKMET TO THE 00Z GFS WITH THE FAR WESTERN PORTION OF THE TROF IN THE SOUTHWEST. THE 00Z ECMWF REMAINS A BIT MORE BROAD OVERALL IN THE BASE THOUGH THE PLACEMENT/TIMING OF THE TROF LOOK FAIRLY GOOD OVERALL. AS SUCH A NON-NAM BLEND IS SUGGESTED FOR WPC PREFERENCE. SHORTWAVE APPROACHING THE WEST COAST LATE WED/EARLY THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/ECMWF BLEND CONFIDENCE: AVERAGE A NARROW BUT ELONGATED TROF WILL EXTEND FROM THE GULF OF AK TO ABOUT 40N BY 12Z WED WITH AN ACCOMPANYING COLD FRONT. DOWNSTREAM AN EQUALLY NARROW RIDGE WILL CONTINUE TO AMPLIFY INTO SW CANADA AND ALLOW THE TROF ENERGY TO UNDERCUT THE RIDGE BY THURSDAY MORNING BRINGING LIGHT SHOWERS. THE 12Z CMC IS A BIT SLOWER MAINLY IN THE BASE OF THE TROF (MORE IMPACTING PORTION OF THE TROF) COMPARED TO OTHERWISE GOOD MODEL AGREEMENT THROUGH 12Z THURSDAY. AS SUCH A NON-CMC BLEND IS SUPPORTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. AFTER THURSDAY THERE IS INCREASED MODEL DIFFERENCE HOW THE ENERGY ENTERS THE WESTERN "BASE" OF THE ELONGATED POSITIVE TILT TROF. PLEASE SEE SECTION ABOVE ADDITIONAL DETAILS. 07Z UPDATE: 00Z UKMET/CMC BOTH TRENDED TO THIN THE ELONGATED SHORTWAVE TROF EVEN FURTHER SPLITTING IT INTO THE NORTHERN PORTION LIFTING NORTH WHILE A MORE CONCENTRIC AND THEREFORE FASTER SHORTWAVE AT THE BASE ROLLS IN CA IN ADVANCE OF THE APPROACHING S/W FROM THE GREAT BASIN. THE GFS/ECMWF ARE MORE PHASED IN BRINGING THE BASE OF THE SHORTWAVE TOGETHER WITH THE NORTHERN STREAM TROF AS A WHOLE. AS SUCH A BLEND OF THE 00Z GFS/ECMWF IS A STRONGER/TIGHTER EVOLUTION OF THE SHORTWAVE TROF AS A WHOLE INTO THE WEST COAST AND IS PREFERENCE. THE CONFIDENCE HOWEVER IS A BIT REDUCED GIVEN THIS VARIATION...TO AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA