MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1110 AM EST TUE MAR 07 2017 VALID MAR 07/1200 UTC THRU MAR 11/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION WITH FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DEEP CYCLONE AND ASSOCIATED SURFACE COLD FRONT MOVING EAST THROUGH THE OHIO VALLEY/ERN U.S. THROUGH WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THERE REMAIN VERY SMALL DIFFERENCES WITH RESPECT TO THE UPPER LOW...DEEP SURFACE LOW INTO ONTARIO AND COLD FRONT TRACKING ACROSS THE OH/TN VALLEY TODAY AND ACROSS THE NORTHEAST/MID-ATLANTIC AND SOUTHEAST WED. HOWEVER...THESE DIFFERENCES APPEAR TO BE IN THE NOISE OF ANY GIVEN RUN TO RUN VARIATION AS THE OVERALL DEPTH/PLACEMENT AND TIMING OF EACH FEATURE HAVE COME INTO OVERALL BETTER AGREEMENT. AS SUCH WILL FAVOR A GENERAL MODEL BLEND BUT GIVEN THE REMAINING SMALL DETAIL DIFFERENCES CONFIDENCE REMAINS SLIGHTLY ABOVE AVERAGE. FAST MOVING SHORTWAVE RIPPLE AMPLIFIES OUT OF UPPER MIDWEST THURS INTO GREAT LAKES/MID-ATLANTIC TROF BY FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS AND 00Z ECMWF/CMC BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE IN THE WAKE OF THE DOMINATING UPPER LOW EXITING INTO CANADA... ZONAL FLOW BEGINS TO ESTABLISH OVER THE NORTHERN TIER. THERE IS SOLID SUGGESTION THAT A RIPPLE OF SHORTWAVE ENERGY OUT OF THE PACIFIC FLOW CROSSES THE ROCKIES INTO THE NORTHERN PLAINS BY THURS. SOME TIMING/PHASING WITH ARCTIC SHORTWAVE ENERGY INCREASES AMPLIFICATION OF THE WAVE THROUGH THE LOWER CENTRAL GREAT LAKES EARLY FRIDAY. THE 00Z ECMWF IS GENERALLY FLATTER HAVING SHEARED THE WEAK RIPPLE COMING THROUGH THE ROCKIES A BIT MORE THAN THE REST OF THE GUIDANCE SUITE. THIS ALSO MAKES IT A BIT FASTER AND BARELY DEVELOPS A WEAK SURFACE LOW OFF THE S MID-ATLANTIC COAST WHICH WELL SOUTH OF ANY ENSEMBLE MEMBER...THOUGH IN THIS ZONAL FLOW REGIME STILL SEEMS QUITE PLAUSIBLE. THE 00Z UKMET AND 12Z NAM BOTH SHOW TYPICAL LATE NEAR-TERM FORECAST BIAS OF A DEEPER/MORE CONSOLIDATED SHORTWAVE...WHICH SLOWS THEIR PROGRESS COMPARED TO THE ENSEMBLE SOLUTIONS MAKING THEM LESS DESIRABLE. THE 12Z GFS AND 00Z CMC SEEM MIDDLE OF THE ROAD WITH RESPECT TO THE AMPLIFICATION OF THE WAVE. ALL CONSIDERED A BLEND OF THE FLATTER SOLUTIONS (12Z GFS AND 00Z ECMWF/CMC) ARE MORE LIKELY IN THIS FLOW REGIME THOUGH THERE REMAINS MODEST SPREAD NORTH AND SOUTH IN SURFACE SOLUTION GIVEN THE SOLUTIONS ARE FLAT AND GENERALLY WEAK LEADING TO SLIGHTLY BELOW AVERAGE CONFIDENCE OVERALL IN THIS BLEND. OF NOTE: THE GFS/NAM ARE QUITE WET AND NORTH OF THE ECMWF/UKMET...THIS SEEMS A BIT OUT OF PLACE GIVEN THE FLOW AND LIKELY AVAILABLE MOISTURE... SO PLEASE REFER TO WPC QPFPFD FOR ADDITIONAL INFORMATION AND PREFERENCES REGARDING THIS SYSTEM. ZONAL FLOW INTO THE PACIFIC NORTHWEST WITH EMBEDDED SUBTLE SHORTWAVE ON TUE/WED AND ASSOCIATED SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE ZONAL FLOW IS STARTING TO ESTABLISH OVER THE NORTHERN TIER OF THE U.S. AS THE WESTERN LOBE OF THE LARGER VORTEX OVER CANADA BEGINS TO FILL AND FLATTEN. A WEAK SHORTWAVE UNDERCUTTING THE MEAN TROF IN THE ZONAL FLOW IS MILDLY PHASED WITH A STRONGER VORT CENTER NEAR THE SLIGHTLY DIVERGENT HEIGHT FIELDS IN S BC... SUPPORTING A TROF OF LOW PRESSURE TO TRACK ASHORE LATER TODAY WITH A WELL AGREED UPON SURFACE LOW THAT WILL CROSS THE MOUTH OF THE COLUMBIA RIVER TOWARD 08/00Z. THIS AGREEMENT IS STRONG ENOUGH TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. AFTER THE WAVE...FAIRLY PERSISTENT ONSHORE FLOW/MST FLUX REGIME SETS UP...THE SPREAD REGARDING THE ORIENTATION IS DRIVEN MORE BY THE APPROACH OF THE NEXT SYSTEM...PLEASE SEE SECTION BELOW FOR ADDITIONAL DETAILS. POTENTIAL SURFACE CYCLONE REACHING THE PACIFIC NORTHWEST FRI MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE BROAD UPPER LOW NORTH OF HAWAII WILL SHED A MILDLY AMPLIFIED WAVE NORTHEAST INTO THE ZONAL FLOW DIRECTED INTO THE PACIFIC NORTHWEST THURSDAY INTO FRIDAY WITH ACCOMPANYING SURFACE REFLECTION. THERE HAS BEEN INCREASING CLUSTERING WITH RESPECT TO THIS WAVE; HOWEVER GIVEN ITS ORIGINS AND PROGRESS THROUGH THE MEAN RIDGING BETWEEN FLOW REGIMES THERE REMAINS MODEST SPREAD MAINLY IN AMPLIFICATION OF THE WAVE...LEADING TO DIFFERENCES IN TIMING AND TRACK. THE 00Z UKMET CONTINUES TO RESOLVE THE DEEPEST MOST WOUND UP SYSTEM WHICH IS ALSO A BIT FURTHER NORTH THAN THE MEAN ENSEMBLE LOCATION. THE 12Z NAM IS ALSO WELL AMPLIFIED THOUGH MODESTLY TIMED A BIT NORTH OF THE ENSEMBLE MEANS. THE REMAINING GUIDANCE IS MORE TOWARD EXPECTATION OF A FLATTER SOLUTION (GIVEN THE PROGRESSION THROUGH THE RIDGE INTO ZONAL FLOW). THE 00Z CMC MAY TAKE THIS TO THE EXTREME BEING VERY FAST AND IS NORTH OF THE ENSEMBLE SUITE INCLUDING THE MAJORITY OF CMCE MEMBERS LEADING TO SOME CONCERN FOR INCLUSION INTO THE BLEND. THE 12Z GFS CONTINUES TO TREND TO A DEEPER SOLUTION AWAY FROM THE BETTER CONSENSUS OF THE 00Z ECMWF/ECENS MEAN AND 06Z GEFS. STILL THE 12Z GFS IS STILL FASTER THAN THE NAM/UKMET AND FOLLOW A SOUTHERN TRACK COMPARED TO THE CMC. GIVEN THE 00Z ECMWF IS A BETTER REPRESENTATIVE WITH RESPECT TO TIMING IN THE ENSEMBLES WILL KEEP A 12Z GFS/00Z ECMWF BLEND BUT WEIGHT THE ECMWF A BIT HIGHER IN THE BLEND OVERALL. ALSO GIVEN THE LONGER TERM CONTINUITY REMAINS VARIABLE AND EXACT STRENGTH/PLACEMENT IN HIGH VARIABLE DUE TO TIMING/PLACEMENT THROUGH THE RIDGE INTO ZONAL FLOW...CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE EVEN THOUGH THERE IS INCREASED CLUSTERING/REDUCED SPREAD. THERE HAS BEEN GROWING CONFIDENCE WITH THE PLACEMENT OF A SURFACE LOW EXPECTED TO APPROACH THE PACIFIC NORTHWEST FRI MORNING. THE LATEST ENSEMBLE SCATTER LOW PLOTS SHOW A GREAT DEAL OF SPREAD...BUT SOME CLUSTERING IS BEGINNING TO SHOW BETWEEN THE 00Z GFS AND 12Z CMC. RUN TO RUN CONTINUITY HAS BEEN DECENT IN THE GFS AND OTHER MODELS APPEAR TO BE JOINING...MOST NOTABLY THE 00Z ECMWF/UKMET AND 00Z NAM. THE 00Z CMC REMAINED SIMILAR TO ITS PREVIOUS RUN HERE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA