MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 141 PM EST FRI FEB 10 2017 VALID FEB 10/1200 UTC THRU FEB 14/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES/FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLIPPER LOW IN S SASK TRACKING ALONG THE US/CANADIAN BORDER THROUGH SAT TRANSFERRING ENERGY TO NEW LOW ACROSS GULF OF MAINE/NORTHWEST ATLANTIC INTO EARLY SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND (OR GFS/ECMWF) CONFIDENCE: SLIGHTLY ABOVE AVERAGE WV LOOP SHOWS A SUBTLE ELONGATED WAVE OF ENERGY CROSSING THROUGH THE SOUTHERN CANADIAN PRAIRIES SUPPORTING A WEAK SURFACE REFLECTION AND MODEST WAA REGIME ACROSS THE NORTHERN US INTO THE GREAT LAKES THAT WILL SHIFT EASTWARD BEFORE WANING INTO LARGER SCALE CONFLUENCE BEHIND THE MAIN EXITING TROF OFF THE EAST COAST. WITH A LINGERING FRONT THE SURFACE LOW WILL THEN REDEVELOP THROUGH THE GULF OF MAINE INTO THE NORTHWEST ATLANTIC INTO SUNDAY. GIVEN THE WEAKNESS/BREADTH OF THE WAVE THERE IS FAIRLY GOOD CLUSTERING OF THE LOW AND GOOD CONSENSUS WITH THE TRACK/TIMING OF THE WAVE AND TRANSFER TO THE COAST. AS SUCH A GENERAL MODEL BLEND IS SUPPORTED FOR THIS SYSTEM...THOUGH THE ECMWF/GFS MAY BE BEST TO USE INDIVIDUALLY AS NOT TO COMPLETELY WASH OUT THE SIGNAL IN SOME OF THE LOW TO MODEST SPREAD THAT REMAINS. GIVEN THIS TRAIT OF POTENTIALLY WASHING OUT THE SYSTEM TOO MUCH CONFIDENCE IN A GENERAL MODEL BLEND IS SLIGHTLY ABOVE AVERAGE. 19Z UPDATE: LITTLE SUBSTANTIAL CHANGE IN THE 12Z NON-NCEP SOLUTIONS AND THEREFORE NO CHANGES IN INITIAL THINKING/PREFERENCES. NORTHERN STREAM SHORTWAVES COMBINING ACROSS S CANADIAN ROCKIES EARLY SAT AND DEEPENING OVER GREAT LAKES LATE SUN...SUPPORTING PAIR OF SURFACE WAVES (US/CANADIAN BORDER/OHIO R VALLEY) THAT MELD ACROSS THE N MID-ATLANTIC AND RAPIDLY DEEPEN IN GULF OF MAINE MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE GOES MOSAIC WV LOOP INDICATES A REMAINING TIGHT/STRONG INNER CORE OF THE OVERALL NARROWING TROF ACROSS THE EASTERN NORTH PACIFIC THAT IS LIFTING AHEAD APPROACHING SHORTWAVE THAT IS ALSO ELONGATING ALONG THE BC COAST UNDER INFLUENCE OF STRONG JET OUT OF AK PENINSULA. THESE FEATURES SEEM TO MATCH INITIAL CONDITIONS OF THE 12Z GFS/NAM A BIT MORE THAN THE 00Z ECMWF AS THE NCEP SOLUTIONS PREFER THE STRENGTH IN THE NORTHERN PORTION OF THE LEAD TROF. STILL THE TWO SYSTEM WILL EFFECTIVELY MELD INTO A LARGER NORTHERN STREAM TROF THAT WILL AMPLIFY ON THE LEE OF THE ROCKIES INTO THE NORTHERN PLAINS INTO SUN. THIS WILL PROMOTE TWO SEPARATE SURFACE WAVES; ONE THAT WILL TRACK ALONG THE US/CANADIAN BORDER WEAKENING INTO THE EASTERN GREAT LAKES BY 00Z MON IN FAVOR OF THE LOW THAT FORMS IN W KS THEN TRACKS THROUGH MO AND UP THE OHIO RIVER SUNDAY. THE UPPER WAVE WILL MATURE AND SWING STRONG LOBE OF VORTICITY THROUGH THE BASE INTO MONDAY PROMOTING STRONG DEEPENING OF THE SURFACE WAVE JUST OFFSHORE LONG ISLAND INTO THE GULF OF MAINE INTO A FULL FLEDGED NOR'EASTER BY MORNING MON. MODELS AND ENSEMBLES HAVE BEEN SHIFTING TOWARD A GROWING CONSENSUS INCREASING CONFIDENCE OVERALL TOWARD FIRST NOTED BY THE ECMWF AS NOTED IN THE LAST 4 CYCLES OF ENSEMBLE SPAGHETTI ANALYSES. AGREEMENT IS FAIRLY SOLID WITHIN THE ENTIRE SUITE UNTIL SUNDAY AROUND 12Z. THE 00Z UKMET STARTS WITH A KNOWN NEGATIVE BIAS OF RESOLVING A STRONG FEATURE ACCELERATING A BIT TOO FAST INTO NEW ENGLAND...THIS LEAVES THE DEVELOPING CLOSED LOW AND SURFACE REFLECTION WELL EAST OF THE CONSENSUS. THE 00Z ECMWF ENTERS THE DEEPENING PHASE A BIT SLOWER THAN THE REST OF SUITE EVEN WITHIN ITS 00Z ECENS MEMBER SUITE...THIS ALLOWS A CLOSER PROXIMITY TO THE HEIGHT FALLS ALOFT AND GENERATES AN INCREASED RATE OF SURFACE DEEPENING IN COMPARISON TO THE 12Z GFS/NAM AND 00Z CMC THAT WERE A BIT EARLIER WITH THE SURFACE WAVE. THIS WOULD POSE SOME CONCERN OF USING THE ECMWF CARTE BLANCHE...BUT GIVEN ITS PROXIMITY AND SIMILARITY IN EVOLUTION ALLOWS FOR STRONG CONSIDERATION IN A BLEND WITH THE OTHER GUIDANCE. AS SUCH A NON-UKMET BLEND IS PREFERRED HOWEVER THERE REMAINS THE POTENTIAL FOR SMALL BUT SHIFTS THAT MAY LEAD TO GREATER IMPACT DIFFERENCE EVEN THOUGH THE SPREAD IS SMALL; THIS MAKES THE CONFIDENCE AVERAGE IN THIS BLEND. 19Z UPDATE: THE 12Z ECMWF TRENDED A BIT QUICKER WITH THE OHIO VALLEY SFC LOW...AND THEREFORE IS BETTER ALIGNED IN TIMING WITH RAPID DEEPENING ALONG THE SE NEW ENGLAND COAST WITH THE GFS/NAM. THOUGH THE ECMWF AND 12Z CMC CONTINUE TO BE A BIT MORE PROGRESSIVE IN THE MATURATION STAGE COMPARED TO THE GFS/NAM CONTINUING TO LEAD TO SENSIBLE WX DIFFERENCE BUT THE MASS SPREAD CONTINUES TO TIGHTEN TO A COMMON SOLUTION. THE 12Z UKMET ALSO TRENDED TOWARD THE OVERALL CONSENSUS AS IT IS MUCH DEEPER AND CLOSER TO THE COAST...HOWEVER DOES NOT STALL/WOBBLE THROUGH THE GULF OF MAINE BUT REMAINS EASTWARD MOVING LEADING IT TO BREAK FROM CONSENSUS TOWARD MONDAY EVENING. AS SUCH A NON-UKMET BLEND WILL BE PREFERRED BUT CONFIDENCE IS INCREASED TO SLIGHTLY ABOVE AVERAGE. SOUTHERN PORTION OF PACIFIC TROF MOVING INTO CALIFORNIA SATURDAY MORNING BECOMING A CLOSED LOW ACROSS THE SOUTHWEST/NW MEXICO SUN/MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/NAM/CMC BLEND CONFIDENCE: AVERAGE GOES MOSAIC WV LOOP ALREADY SHOWING THE FIRST STAGES OF THE EASTERN PACIFIC TROF BEGINNING TO SPLIT WITH THE SOUTHERN PORTION TO DIVE SOUTHEAST AND RECONSOLIDATE INTO A CLOSED UPPER LOW ALONG THE SW CA COAST BY LATE SATURDAY. INTERESTINGLY THE 00Z CMC/ECMWF HAVE INITIALIZED THIS SOUTHERN PORTION AS A FAIRLY STRONG AND COMPACT SYSTEM ALREADY WHICH IS NOT JUSTIFIED IN THE WV LOOP; PERHAPS SEEDING THE DEVELOPMENT STAGE TOO EARLY AND LEADING TO MORE AGGRESSIVE MASS/WIND FIELDS FOR S CA THAN THE 12Z GFS/NAM OR UKMET SUGGEST. STILL THERE IS FAIRLY SOLID CONSENSUS IN TIMING/STRENGTH BY LATE SUNDAY THOUGH THE PLACEMENT IS A BIT DIFFERENT LIKELY DRIVEN BY DIFFERENCES IN INTERNAL INTERACTIONS. THE 00Z ECMWF HAVING THE MOST CONSOLIDATED AND LEAST INTERACTIVE WITH OTHER EMBEDDED WAVES IN THE RECONSOLIDATION PROCESS...APPEARS UNCHECKED BY THESE INTERNAL WOBBLES ALLOWING FOR A FASTER ROUND OF THE BASE OF THE TROF TO EJECT NORTHEASTWARD FASTER THAN MUCH OF THE GUIDANCE...THIS AN A SLIGHTLY MORE AMPLIFIED NORTHERN STREAM (SEE SECTION BELOW) THAT DRAWS IT OUT...MAKING IT AND MANY OTHER ECENS MEMBERS APPEAR FAST. ON THE OPPOSITE SIDE OF THE SPECTRUM THE UKMET ENTERS THE CLOSED PHASE OFF SW CA...WITH MUCH GREAT ECCENTRICITY AND AS IT TRIES TO CONSOLIDATE IS SLOWED AND STRETCHED BY THIS INITIAL SETUP. THE 12Z GFS HAVING RESOLVED A WEAKER INITIAL CONDITION...LIKE THE UKMET...AS INCREASED ECCENTRICITY WHICH HAS LEAD IT TO EXHIBIT GREATER WOBBLES AND SLIGHTLY SOUTHWARD SHIFT COMPARED TO THE PRIOR RUNS. ALSO LIKE THE BULK OF THE GUIDANCE/ENSEMBLE MEMBERS THERE IS VERY LIMITED INTERACTION WITH THE NORTHERN STREAM AFTER MIDDAY SUNDAY ALLOWING FOR THE SOUTHERN TRACK. THE 12Z NAM/00Z CMC SEEM TO BE SIMILAR TO THE ECMWF BUT IN THE END WITHOUT INTERACTION WITH THE NORTHERN STREAM AND DEEP CONSOLIDATED UPPER LOWS DO NOT ACCELERATE NORTHEAST LIKE THE ECMWF. A GENERAL MODEL BLEND COULD BE SUPPORTED THROUGH 72HRS...BUT THE ECMWF/UKMET BECOME OUT OF PHASE AFTERWARD. STILL WILL PREFER A 12Z GFS/NAM AND 00Z CMC BLEND AS A COMPROMISE. CONFIDENCE IS FAIRLY HIGH IN THE OVERALL PATTERN BUT THE LARGE DIFFERENCES IN EVOLUTION AND INTERNAL INTERACTIONS LEAD TO A SLIGHT REDUCTION OVERALL AND AS SUCH IS AVERAGE OVERALL. 19Z UPDATE: THE 12Z ECMWF CONTINUED WITH THE SLIGHTLY FASTER TREND HAVING SLOWED EVER SO SLIGHTLY...THOUGH IT GAINED A PARTNER WITH THE 12Z UKMET THOUGH IT IS A MUCH WEAKER/LESS CONSOLIDATED WAVE FEATURE AS A WHOLE. THE CMC SHIFTED SLIGHTLY FASTER TOWARD THE GFS WHILE THE 12Z GEFS MEAN CONTINUES TO LAG THE OPERATIONAL ALMOST HALF WAY BETWEEN THE NAM AND GFS...PROVIDING SOME CONTINUED CONFIDENCE WITH INITIAL PREFERENCE. PHASED/NEGATIVE TILT TROF OF CANADIAN SHORTWAVES ENTERING WESTERN GREAT LAKES VERY LATE MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE LARGE SCALE RIDGING BEGINS TO DOMINATE WESTERN CANADA SAT INTO SUNDAY. SHEARED SHORTWAVE ENERGY AT THE SW EXTENT OF POLAR VORTEX OVER-TOPS THE RIDGE MONDAY AND COMBINED WITH A SHORTWAVE/SPEED MAX MOVING THROUGH THE MID-RIDGE...EVENTUALLY PHASE ON THE EASTERN SIDE OF THE RIDGE MIDDAY MONDAY ACROSS SASK/MANITOBA AND JUST START CLIPPING THE MN ARROWHEAD/WESTERN GREAT LAKES WITH FRONTAL PASSAGE. THIS WILL EVENTUALLY AMPLIFY/CLOSE OFF IN THE GREAT LAKES AFTER THE FORECAST PERIOD...PLEASE SEE MORE INFORMATION IN THE EXTENDED FORECAST DISCUSSION (PMDEPD) FOR FURTHER DETAILS. AT THIS POINT THE 00Z UKMET AND 00Z CMC SEEM A BIT TOO PROGRESSIVE WITH THE EMBEDDED MID-RIDGE SHORTWAVE MAKING THE HEIGHT FALLS A BIT TOO FAST COMPARED TO THE ENSEMBLE SUITE BY 00Z TUESDAY IN THE WESTERN GREAT LAKES. THE 12Z GFS/GEFS ARE MOST STUBBORN WITH THE PATTERN HAVING BEEN LESS PHASED AND MORE ROBUST WITH THE SHORTWAVE OVER-TOPPING THE RIDGE. WHILE NOT TO THE MAGNITUDE OF THE 12Z GFS...THE 12Z NAM AND 00Z ECMWF/ECENS MEAN ARE MORE SUPPORTIVE AND THEREFORE A 12Z GFS/NAM AND 00Z ECMWF BLEND REPRESENTS THE ENSEMBLES WELL AT THIS TIME. CONFIDENCE IS SLIGHTLY BELOW AVERAGE AS THERE ARE MANY MOVING PARTS STILL WELL UPSTREAM AND THIS PATTERN APPEARS TO BE HIGHLY INFLUENCED BY THE TIMING/PHASING OF SHORTWAVES WHICH MAY BE TOO DIFFICULT TO HAVE HIGH CONFIDENCE IN JUST YET BUT GUIDANCE APPEARS ON THE RIGHT TRACK TO RESOLVE THIS SO FAR. 19Z UPDATE: THE UKMET TRENDED A BIT WEAKER WITH THE LEADING SUBTLE MID-RIDGE SHORTWAVE LEADING TO AN OVERALL APPEARANCE OF SLOWER HEIGHT FALLS NEARER THE INITIAL PREFERENCE. THE 12Z CMC SLOWS A BIT COMPARED TO THE 00Z RUN BUT REMAINS A BIT FASTER AND MORE AMPLIFIED ENTERING THE WESTERN GREAT LAKES BY THE END OF THE FORECAST PERIOD. AS SUCH WILL SUPPORT A NON-CMC BLEND AT AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA