MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 253 PM EDT SUN MAR 19 2017 VALID MAR 19/1200 UTC THRU MAR 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE INTERVALS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ UPPER LOW AND ASSOCIATED SURFACE REFLECTION OFF NORTHEAST US COAST LIFTING NORTHEAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/UKMET CONFIDENCE: ABOVE AVERAGE EFFECTS REMAINING IN THE CONUS WITH RESPECT TO THIS SYSTEM ARE STRONG ENOUGH TO SUPPORT A GENERAL MODEL BLEND. HOWEVER EFFECTS IN THE SHIPPING LANES UP THROUGH THE ENTRANCE TO THE ST. LAWRENCE SEAWAY STILL HAVE SOME VARIANCE WITHIN THE MODEL SUITE TO SUGGEST REMOVAL OF A SOLUTION OR TWO IN THE PREFERENCE. THE NAM SHIFTED A BIT IN THE EVOLUTION OF THE UPPER LOW DEEPENING FURTHER SOUTH AND WEST OF THE BEST CONSENSUS HAVING RETAINED A STRONGER CONSOLIDATED PORTION OF THE WAVE IN A LIKELY HIGH SHEARING/ELONGATING ENVIRONMENTAL SETUP BY MIDDAY MONDAY..WHICH IS A KNOWN NEGATIVE BIAS IN THE NAM. LIKEWISE THE 00Z CMC LOADS THE TROF A BIT NORTH AND SUPPORTS A SURFACE REFLECTION THAT WOBBLE QUITE CLOSE TO THE NOVA SCOTIA COASTLINE COMPARED TO REMAINING TIGHT AGREEMENT AND CONSISTENCY IN THE ENSEMBLE CLUSTER THROUGH MIDDAY TUESDAY. AS SUCH FOR MARINE CONCERNS...A PREFERENCE TOWARD A 12Z GFS AND 00Z UKMET/ECMWF BLEND IS PREFERRED AT ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: THE 12Z CMC HAS SHIFTED ITS TRACK TOWARD THE COMMON SOLUTION THROUGH 21/00Z AWAY FROM THE SE NOVA SCOTIA COAST...BUT NOW UNDER INFLUENCE OF A FASTER/STRONGER UPSTREAM SHORTWAVE (SECTION BELOW) DEEPENS AND LIFTS INTO S NEWFOUNDLAND WITH LITTLE SUPPORT IN OTHER GUIDANCE OR ENSEMBLE PACKING. LITTLE CHANGE IN THE UKMET OR ECMWF THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD AND AS SUCH WILL STAY WITH INITIAL PREFERENCE OF THE GFS/UKMET/ECMWF BLEND AT ABOVE AVERAGE CONFIDENCE. BROADENING UPPER LOW ACROSS CANADA WITH INITIAL WAVE THROUGH NORTHEAST TUES...COLD FRONT SWEEPS THROUGH UPPER MIDWEST/GREAT LAKES MONDAY AND MID-ATLANTIC/CAROLINAS EARLY TUES (DRAPED BACK TO CENTRAL PLAINS SFC WAVE)...SURFACE WAVE DEVELOPING IN THE CAROLINAS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: ABOVE AVERAGE WV LOOP SHOWS POTENT WAVE ENTERING CENTRAL BC AT THIS TIME ON THE WESTERN SIDE OF A WELL FORECAST BROAD GLOBAL SCALE TROF EVOLVING ACROSS NORTH CENTRAL CANADA CURRENTLY. THIS POTENT WAVE WILL SWING AROUND THE BASE OF THE DEVELOPING GLOBAL SCALE LOW LATE MON/TUESDAY ACROSS THE S CANADIAN PRAIRIE AND MELD WITH TRAILING SHORTWAVE TROF ENERGY ACROSS E ONTARIO/S QUEBEC INTO FAR NORTHERN NEW ENGLAND LATE TUESDAY PRODUCING SOME NEGATIVE TILT OF THE GLOBAL TROF AT THE TIME. WHILE THE MAIN EFFECTS OF THIS WAVE WILL BE FELT NORTH OF THE BORDER...AN ASSOCIATED SURFACE FRONT DRAPED FROM THE DEEP LOW IN CANADA WILL TRANSLATE ACROSS THE NORTHERN TIER/GREAT LAKES AND NORTHEAST WHILE A LEE SFC CYCLONE IN KS/OK WILL ANCHOR THE BASE OF THE FRONTAL ZONE AS IT REMAINS STATIONARY. BY EARLY TUESDAY THE FRONTAL ZONE WILL BE EAST-WEST FROM THE S VA/N NC BACK TO THIS STATIONARY LEE LOW. WHILE THERE ARE SOME MODEST 5H HEIGHT DIFFERENCES WITH THE WAVE THROUGH NEW ENGLAND THE AFFECTS ON THE FRONTAL ZONE AND SENSIBLE WX ARE MINOR. WEAK REINFORCEMENT/HEIGHT FALL OF NEXT WAVE (SEE BELOW) IS SUFFICIENT TO FOCUS SURFACE CYCLOGENESIS ACROSS THE CAROLINAS BETWEEN 22/00-06Z WED. WHILE THERE ARE SOME SLIGHT TIMING DIFFERENCES...IN THE RELATIVE QUICK FLOW/SETUP THE SPREAD IS REMARKABLY SMALL FOR DAY 3...TO SUGGEST HIGHER PREDICTABILITY OVERALL WITH HIGHER CONFIDENCE. THROUGH THE ENTIRE EVOLUTION OF THE FRONTAL ZONE THERE IS ENOUGH TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: THE 12Z CMC HAS TRENDED FASTER/STRONGER WITH THE LEAD SHORTWAVE ENERGY ACROSS SE CANADA IN A SIMILAR VAIN TO THE 12Z NAM. WHILE THE NAM DOES NOT HAVE MUCH IMPACT IN THE LOWER LEVELS AND SURFACE...THIS IS NOT THE CASE WITH THE CMC; DEEPENING THE DOWNSTREAM SURFACE WAVE NEAR NEWFOUNDLAND (SEE SECTION ABOVE) AS WELL AS LEADING TO INCREASED HEIGHT FALLS ACROSS THE NORTHEAST ATLANTIC SPURRING A FASTER AND MUCH DEEPER SURFACE LOW DEVELOPING OUT OF THE CAROLINAS WED. WITH LITTLE CHANGE FOR THE 12Z UKMET/ECMWF...A PREFERENCE OF A NON-CMC BLEND IS SUGGESTED AT ABOVE AVERAGE CONFIDENCE. KICKER SHORTWAVE AMPLIFYING ACROSS GREAT LAKES LATE TUE/EARLY WED WITH ARCTIC FRONT THROUGH NORTHERN NEW ENGLAND ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS/CMC BLEND CONFIDENCE: AVERAGE ON THE HEELS OF THE MAIN HEIGHT FALLS...AN ADDITIONAL ARCTIC KICKER WAVE DESCENDS OUT OF CENTRAL CANADA AND IN COMBINATION WITH UPSTREAM RIDGE PUMPING...FOCUSES HEIGHT FALLS ACROSS THE GREAT LAKES WED MORNING LEADING TO A SHARPENING OF THE GLOBAL TROF ACROSS THE NORTHEAST/MID-ATLANTIC BY THE END OF THE FORECAST PERIOD. AS THE WAVE DEEPENS IN THE GREAT LAKES THE ARCTIC SHORTWAVE/BUILDING SURFACE HIGH/COLD PUNCH SHARPENS THE ARCTIC FRONT ACROSS NORTHERN NEW ENGLAND. OVERALL THE EVOLUTION OF THE WAVE IS IN STRONG AGREEMENT (PLACEMENT/STRENGTH TIMING) WITH EXCEPTION OF THE 00Z UKMET WHICH SHOWS SIMILARITY BUT COMES TO THE TROF IN A DIFFERENT MANNER AND LEADS TO A DEEP SURFACE WAVE ALONG THE ARCTIC BOUNDARY THAT MOVES THROUGH MAINE BY 22/12Z WED. AT THE SURFACE THE UKMET SOLUTION APPEARS SUPPORTED BY THE ECMWF GIVEN A DEEPER CLOSED WAVE; THIS IS FURTHER SUPPORTED BY THE NUMEROUS ECENS MEMBERS. THE ODDITY IS IN THE ENSEMBLE CLUSTER IS THE COMPLETE DEARTH OF CMCE/GEFS MEMBERS LEADING TO SOME CONCERN. IT IS NOTED THAT THE ECMWF HAS A UNIQUE BIAS OF DEEP/STRONG SHORTWAVES ORIGINATING FROM ABOVE THE ARCTIC CIRCLE AND 5H VORTICITY FEELS SEEM TO CONFIRM THIS AND LIKELY ACCOUNT FOR THE DEEPER INTERACTION/SURFACE REFLECTION. WHILE THE 12Z NAM/GFS AND 00Z CMC MAY BE TOO FAST/WEAK...WILL PREFER THIS TEMPERED SOLUTION AT THIS TIME...THOUGH CONFIDENCE IS AVERAGE AS THE UKMET/ECMWF CANNOT SOLUTION CANNOT BE FULLY RULED OUT AS A POSSIBILITY JUST YET. 19Z UPDATE: THE 12Z ECMWF HAS TRENDED A BIT SLOWER BUT RETAINS THE STRENGTH OF THE DEEPER ARCTIC WAVE WITH EARLIER/WESTWARD SHIFT OF THE CLOSING OF THE SURFACE WAVE ALONG THE ARCTIC FRONT. WHILE THE 12Z GEFS SUPPORTS THE GFS TOWARD EVENTUAL CYCLOGENESIS AROUND MAINE/NEW BRUNSWICK THIS SEEMS MORE METEOROLOGICALLY SOUND GIVEN THE WAVE IS PASSING THE MEAN GLOBAL TROF AXIS INTO MORE FAVORABLE DPVA AND SFC DEEPENING. THE 12Z UKMET CONTINUES TO SHOW A DIFFERENT EVOLUTION TO THE OVERALL PATTERN BUT HAS SHIFTED THE AXIS OF THE ARCTIC BOUNDARY FURTHER NORTH EVEN FURTHER FROM THE ECMWF AND OTHER GUIDANCE MEMBERS. AS SUCH WILL CONTINUE TO FAVOR A 12Z GFS/NAM AND CMC BLEND. PRECURSORY HEIGHT FALLS ALONG CENTRAL WEST COAST ON MON BEFORE MAIN DEEP TROF AND ASSOCIATED SURFACE REFLECTION AFFECT THE WEST COAST TUES INTO EARLY WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM BLEND CONFIDENCE: ABOVE AVERAGE CONFIDENCE GOES-W WV LOOP DENOTES SUBTLE SHORTWAVE FEATURES LIFTING NORTH OUT OF SUBTROPICS TOWARD CENTRAL CALIFORNIA IN ADVANCE OF DEVELOPING DEEP WAVE WEST OF 140W. THE CONFLUENCE OF THESE FEATURES APPEARS WELL AGREED UPON THROUGH THE VERY SHORT RANGE SUPPORTING A WEAK SURFACE WAVE LIFTING NORTH ALONG 130W AND DIFFLUENT FLOW/MST TRANSPORT TO AFFECT N CA THROUGH MONDAY. HOWEVER AS THE MAIN HEIGHT FALLS START TO OVER WASH THE WEST COAST SOME INCREASED MODEL SPREAD IS DENOTED. THE 12Z NAM IS THE MAIN CULPRIT OF DISSENSION AS THE INNER CORE OF THE INNER CORE OF THE UPPER LOW CLOSES THE 540DM LINE...AS IT RESOLVES A DEEPER MORE CONSOLIDATED VORT CENTER A TYPICAL NEGATIVE NAM BIAS...WHICH COMPOUNDS AFTER 21/12Z LEADING TO SLOWER AND DEEPER EVOLUTION THROUGH OUT THE WAVE NEARING THE COAST. THE REMAINING GUIDANCE HAVE MORE SUBTLE DIFFERENCES THAT WOULD BE EXPECTED BY DAY 2 INTO 3 WHICH SHOULD RESOLVE ITSELF IN BLEND SUPPORTED BY THE ENSEMBLE MEANS. AS SUCH A NON-NAM BLEND IS PREFERRED (MAINLY AFTER 21/12Z) AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: SMALL ADJUSTMENTS WERE NOTED WITH 12Z ECMWF/UKMET/CMC AND 12Z GEFS MEAN WITH RESPECT TO TIMING/STRENGTH AND SHAPE OF THE EVOLUTION OF THIS WAVE. STILL THIS WAS WELL WITHIN TOLERANCE TO KEEP A NON-NAM BLEND AT INCREASING CONFIDENCE. STRONG GULF OF ALASKA SHORTWAVE DIGGING SOUTH TO REPLACE PRIOR WAVE AS CORE OF MEAN GLOBAL TROF NEARING THE PACIFIC NORTHWEST LATE WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THOUGH COMPARISON FIELDS MAY SUGGEST A PHASED SOLUTION GIVEN THE LARGE/DEEP LATITUDINAL TROF TRACKING INTO THE ENTIRE WEST COAST BY LATE WED...THERE DOES NOT APPEAR TO BE MUCH INTERACTION/CONNECTION BETWEEN THE NORTHERN AND SOUTHERN STREAMS. AS THE PRIOR SYSTEM LIFTS NORTH(SEE SECTION ABOVE) ON TUES WITHIN THE MEAN DEEPER GLOBAL SCALE TROF...INCREASED INTERACTION OCCURS DRAWING SHORTWAVE ENERGY OUT OF THE GULF OF AK SOUTHWARD. CYCLE TO CYCLE ENSEMBLE SPAGHETTI ANALYSIS DENOTES THE OPERATIONAL ECMWF HAS BEEN LOCKED IN DRAWING A STRONGER/WOUND UP WAVE FURTHER SOUTH AND RETAINING ITS INTENSITY DOMINATING THE PRIOR SYSTEM BEFORE ROLLING TOWARD VANCOUVER ISLAND/WA BY 00Z THURS AND THE 00Z ECMWF IS EXTENDS THIS TREND EVEN FURTHER. HOWEVER THERE HAS BEEN LITTLE SUBSTANTIAL SUPPORT WITH THE EXCEPTION OF A FEW ECENS MEMBERS UNTIL THE 00Z GFS MATCHED IT FAIRLY WELL. SUBSEQUENT 06Z/12Z GFS RUNS HAVE ONCE AGAIN BACKED OF SUPPORTING A MORE ELONGATED TROF THAT REMAINS CONNECTED TO THE MAIN GULF OF AK LOW...THIS IS SUPPORTED BY THE BULK OF THE ENSEMBLES AS WELL AS THE 12Z NAM AND 00Z UKMET. THE 00Z CMC SUGGESTS A DEEPER MORE CONSOLIDATED LOW BUT MUCH FURTHER NORTH THAN THE ECMWF OR EVEN THE CORE OF THE WAVE IN THE 12Z GFS/NAM ELONGATED TROF. AS SUCH WPC PREFERENCE IS THE 12Z GFS/NAM AND 00Z UKMET...HOWEVER WITH A COMPLEX EVOLUTION LIKELY TO UNFOLD CONFIDENCE REMAINS AVERAGE EVEN WITH GENERAL ENSEMBLE SUPPORT IN THE GEFS/ECENS AND CMCE. 19Z UPDATE: THE 12Z ECMWF HAS BACKED OFF THE STRONG/WOUND UP WAVE DESCENDING OUT OF THE GULF OF AK...SHEARING/ELONGATING THE MEAN TROF TOWARD A SLIGHT NEGATIVE TILT LOOKING QUITE COMPARABLE TO THE 12Z GFS. LIKEWISE THE CMC TRENDED THIS DIRECTION AS WELL. THIS ALLOWS FOR INCREASED CONFIDENCE OVERALL AS WELL AS FURTHER ASSESSMENT WITH RESPECT TO TIMING/PLACEMENT OF THE WAVE; WHICH LEADS TO SOME QUESTIONING OF INCLUSION OF THE 12Z NAM BEGIN A BIT SLOWER/DEEPER WITH THE TROF PARTICULARLY TOWARD THE WA/OR COAST BY 00Z THURS...IN LINE WITH THE KNOWN SLOWER/DEEPER BIAS AND THE CMC IS GENERALLY WEAKER IN THE BASE AS WELL AS FAST. ALL CONSIDERED A SLIGHTLY ABOVE AVERAGE CONFIDENCE BLEND BETWEEN THE 12Z GFS/ECMWF SEEMS LOOKS MORE FAVORABLE WITHIN THE OVERALL TIGHTER PACKING. CENTRAL PACIFIC SHORTWAVE CARVES OUT THE BASE OF EASTERN PACIFIC TROF AFFECTING CENTRAL AND SOUTHERN CALIFORNIA LATE WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE WITH THE WAVE JUST WET OF 140W CURRENTLY BEING DRAW NORTH TUESDAY...THE NEXT SET OF UPSTREAM SHORTWAVES AMPLIFIES THE BASE OF THE TROF VACATED BY THE LEAD SYSTEM NEARING THE SOUTHERN CALIFORNIA COAST LATE WED BRINGING THE CHANCE FOR HEAVY RAINFALL/MST TRANSPORT (PLEASE SEE QPFPFD AND DAY 3 EXCESSIVE RAINFALL OUTLOOK FOR ADDITIONAL DETAILS). THERE IS SOLID MODEL AGREEMENT IN THE TIMING OF THE PAIR OF SHORTWAVES AND THE MEAN TROF AS A WHOLE. HOWEVER THE SPREAD REMAINS IN THE STRENGTH AND SPACING OF SAID SHORTWAVES. THE 00Z CMC IS THE GREATEST SPACED AND HAS THE WEAKEST REFLECTIONS INCLUDING WELL UNDER REPRESENTED JET STREAK MAGNITUDES. WHILE THE 12Z GFS MEAN TROF LOCATION IS TIMED WELL WITH THE OTHER GUIDANCE...THERE IS A FASTER SPEED BIAS NOTED AS THE LEAD WAVE IS ALREADY LIFTING NORTHWARD INTO S NV BY 23/00Z LEADING TO A FASTER SECOND WAVE NARROWING THE TROF WAVELENGTH. KNOWING THE GFS BIAS OF BEING FAST...THIS DEEPENING/NARROWING WAVE MAY BE A BIT TOO AGGRESSIVE WITHIN GRAND SCHEME. NOT SURPRISINGLY THE 12Z NAM IS NOT FAR BEHIND THE GFS FOLLOWED BY THE 00Z UKMET AND THE 00Z ECMWF. WHILE THE ECMWF MAY SHOW SOME TYPICAL SLOW BIAS...A BLEND OF THE 12Z NAM/00Z UKMET WITH IT MAY ALLOW FOR NICE COMPROMISE THIS FAR OUT. THERE IS CONFIDENCE GIVEN THE ENSEMBLE CONSISTENCY AND OVERALL SHAPE/FEATURES INTERNAL TO THE WAVE BUT ALSO ENOUGH SPREAD TO SUGGEST CONFIDENCE IS AVERAGE IN THIS BLEND AT THIS TIME. 19Z UPDATE: BOTH THE 12Z ECMWF/UKMET TRENDED A BIT FASTER TOWARD THE 12Z GFS/NAM SOLUTION ALSO NARROWING THE WIDTH OF THE WAVE AS IT APPROACHES THE WEST COAST...THE ECMWF A BIT MORE THAN THE UKMET IN BOTH ASPECTS. ONLY THE 00Z CMC CONTINUING TO BE GENERALLY WEAKER WITH THE SHORTWAVES OVERALL IS MOST OF AN OUTLIER. WITH FASTER TIMING...THE 12Z GFS MAY BE A BIT MORE FAVORABLE OVERALL... AND WILL SUPPORT ITS INCLUSION IN THE FINAL PREFERENCE BUT AT LOWER WEIGHTING. AS SUCH WPC SUPPORTS A NON-CMC BLEND AT AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA