MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 247 PM EDT MON OCT 17 2016 VALID OCT 17/1200 UTC THRU OCT 21/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SYSTEM MOVING ACROSS THE PLAINS/GREAT LAKES MON/TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 12Z NAM HAS SHIFTED EVER SO SLIGHTLY FASTER BUT ALONG WITH THE 12Z CMC REMAINS A BIT SLOW PARTICULARLY AS THE SFC CYCLONE CROSSES WI EARLY TUES...THOUGH THE LAG IS PRESENT THROUGH MUCH OF THE LOWER ATMOSPHERE. THE 12Z GFS DID NOT VARY MUCH FROM THE 00Z/06Z RUNS OR THE 06Z GEFS SOLUTION TO PROVIDE FURTHER CONFIDENCE IN IT ALONG WITH THE 00Z ECMWF/ECENS MEAN AND 00Z UKMET. GIVEN THE TIGHTER PACKING OVERALL INCLUDING TIMING/STRENGTH OF THE FRONT ACROSS NEW ENGLAND ON WED; THE PREFERENCE WILL BE A 12Z GFS AND 00Z ECMWF/UKMET BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: THE 12Z CMC SHOWED SOME SLIGHT SHIFT FASTER TOWARD TIGHTER OVERALL CONSENSUS. THIS LEAVES THE 12Z NAM ALONE...SLOW ACROSS N WI/U.P. OF MI ON TUESDAY. MINUS THIS SMALL DEVIATION CONFIDENCE IS ABOVE AVERAGE IN BLENDING ALL GUIDANCE (THOUGH LESSER WEIGHTING OF THE NAM IS PREFERRED THROUGH TUESDAY). UPPER TROUGH CROSSING THE WEST COAST EARLY TUE AND REACHING THE CNTRL ROCKIES WED MORNING WITH EVENTUAL SURFACE LOW NEAR THE OHIO VALLEY THU MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: BELOW AVERAGE (MAINLY AFTER 20/00Z) FAST MOVING SHORTWAVE CURRENTLY APPROACHING PACIFIC COAST APPEARS WELL TIMED AND PLACED WITHIN THE GUIDANCE SUITE THROUGH THE EARLY PART OF THE FORECAST PERIOD CROSSING THE WEST INTO THE CENTRAL ROCKIES. AFTER 20/00Z (THURS) AS THE WAVE EJECTS INTO THE CENTRAL PLAINS...TIMING AND AMPLIFICATION DIFFERENCES EMERGE TOWARD A MUDDLE ENSEMBLE CLUSTER DAY 3 INTO THE MID-MS VALLEY AND OHIO VALLEY. SOME OF THE DIFFERENCE IN THE GUIDANCE APPEARS TIED TOWARD THE STRENGTH OF THE SUB-TROPICAL RIDGING ACROSS THE SOUTHEAST (UPSTREAM OF TUTT/DEVELOPING CYCLONE). THE 00Z UKMET IS MOST AGGRESSIVE IN BREAKING DOWN THE RIDGE WHICH SEEMS A BIT OVER ZEALOUS GIVEN FAIRLY GOOD AGREEMENT OF DOWNSTREAM DEVELOPMENT NEAR THE BAHAMAS...AND WHILE IT DOES NOT SEEM TO AFFECT THE SURFACE LOW POSITIONING ACROSS THE OHIO VALLEY...IT SEEMS A BIT SUSPECT OVERALL. THE 00Z ECMWF IS LESS AMPLIFIED AND LIFTS SHORTWAVE ENERGY NORTHEAST FASTER THAN THE REST OF THE GUIDANCE EVEN SLIGHTLY FASTER THAN THE MAJORITY OF ITS ENSEMBLE SOLUTIONS...CASTING SOME DOUBT. THIS SOLUTION IS SUPPORTED BY A 00Z CMC BUT THE CMC LEAVES A BULK OF THE MID-LEVEL ENERGY FURTHER SOUTH IN THE LOWER OHIO VALLEY BY LATE THURS...AND FASTER THAN THE CMCE. THE 00Z NAM AND GFS CONTINUE TO BE THE SLOWER AND MOST AMPLIFIED SOLUTIONS WITH THE NAM SLIGHTLY OUTPACING THE GFS SOLUTION. THE 00Z GFS HAS TRENDED FURTHER EAST TOWARD A MORE COMMON SOLUTION AWAY FROM SLOWER LESS LIKELY SOLUTIONS SUCH AS THE 06Z GFS AND A BULK OF 06Z GEFS MEMBERS. WHILE NO DETERMINISTIC OR ENSEMBLE MEAN SEEM THE MOST IDEAL AT THIS TIME (GIVEN DOWNSTREAM STRENGTH UNCERTAINTIES) A NON-UKMET BLEND SEEMS A MIDDLE GROUND COMPROMISE. CONFIDENCE IN THE BLEND IS HIGH THROUGH WED, BUT GIVEN THE LARGE SPREAD AND LITTLE EVIDENCE TOWARD ONE SIDE OF THE SPREAD OVER THE OTHER AT THIS TIME... CONFIDENCE AFTER WED IS BELOW AVERAGE 19Z UPDATE: THE 12Z ECMWF TRENDED A BIT SLOWER WITH SHORTWAVE ENERGY ROUNDING THE BASE ALLOWING FOR SOME INCREASED AMPLIFICATION BY DAY 3 ACROSS THE MS RIVER/LOWER OHIO RIVER VALLEY SUPPORTING A SLOWING BUT DEEPENING OF THE SURFACE WAVE. THIS WAS MATCHED BY THE 12Z CMC BRINGING A BIT CLOSER AGREEMENT WITH THE SLOWER/MORE AMPLIFIED GFS/NAM CAMP. THE 12Z UKMET CONTINUES TO BE FASTEST EVEN STEPPING FORWARD A BIT MORE AWAY FROM THE ECMWF/CMC SOLUTION. THINKING SOMEWHERE IN THE MIDDLE BETWEEN THE GFS/NAM AND ECMWF/CMC SEEMS MORE LIKELY GIVEN BOTH CAMPS TRENDING THIS DIRECTION. AS SUCH WILL CONTINUE TO FAVOR A NON-UKMET BLEND AND THOUGH CONFIDENCE IS INCREASING IT REMAINS BELOW AVERAGE GIVEN THE SPREAD. DEEP UPPER LEVEL LOW IN THE GULF OF AK THROUGH THU MORNING WITH ONSHORE FLOW INTO THE PACIFIC NORTHWEST AHEAD OF E-PAC COLD FRONT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE A DEEP GLOBAL SCALE UPPER LEVEL LOW DEVELOPS ACROSS THE GULF OF ALASKA BY WED WITH TIGHT PACKING/SOUTHWESTERLY ONSHORE FLOW TO DOMINATE THE PACIFIC NORTHWEST UNTIL A LEAD SHORTWAVE WITH ASSOCIATED WARM FRONT REACHES SW BRITISH COLUMBIA WED NIGHT SWITCHING LOW LEVEL FLOW MORE SOUTHERLY IN ADVANCE OF STRONGER COLD FRONT WITH WEAK TRIPLE POINT LOW NEARING VANCOUVER ISLAND MIDDAY THURSDAY. THERE ARE SLIGHT TIMING/ORIENTATION DIFFERENCES...AS THE ECMWF IS A BIT FURTHER SOUTH AND THEREFORE IN DEEPER FASTER FLOW LEADING TO A FLATTER JET/ONSHORE PATTERN THURSDAY COMPARED TO THE REST OF THE GUIDANCE FOLLOWED BY THE 00Z UKMET. THE 12Z GFS HAS BACKED OFF A MORE AMPLIFIED SOLUTION WITH THE INNER CORE OF THE UPPER LOW...DEPRESSING THE DOWNSTREAM RIDGING SLIGHTLY COMPARED TO PRIOR RUNS. HOWEVER THE GFS IS STILL FURTHEST SOUTH. THE 00Z NAM IS A BIT FASTER WITH THE INNER CORE OF THE UPPER LOW AND SHOWS SOME INCREASED AMPLIFIED FLOW TOO TO SUPPORT THE GFS. THE 00Z CMC/UKMET ARE BOTH SLOWER AND FURTHER NORTH THAN THE ECMWF WITH THE INNER CORE AWAY FROM BEST ENSEMBLE CLUSTERING (INCLUDING CMCE MEMBERS0. ALL CONSIDERED A BLEND OF THE 12Z GFS/NAM AND 00Z ECMWF SEEM TO BEST REPRESENT THE ENSEMBLE SOLUTIONS. CONFIDENCE IS ONLY AVERAGE GIVEN DIFFERENCES IN TIMING CONTINUE TO VARY FROM RUN TO RUN. PLEASE REFER TO QPFPFD FOR ADDITIONAL PREFERENCES WITH RESPECT TO QPF IMPACTS THURSDAY. 19Z UPDATE: THE 12Z UKMET TRENDED A BIT DEEPER WITH THE LEAD SHORTWAVE AND MATCHES WELL IN TIMING WITH THE 12Z ECMWF (WHICH CONTINUES TO BE GENERALLY FLATTER GOING INTO THURS). WHILE THE UKMET CONTINUES TO REMAIN STRONGER WELL NORTH WITH THE UPPER LOW ITSELF...THIS SEEMS TO BE MINOR COMPARED TO THE OVERALL BLEND. THE 12Z CMC TRENDED SLOWER WEAKENING THE LEAD SHORTWAVE IN FAVOR OF A SLOWER DEEPER SECONDARY PUSH ON THURSDAY...SLOWER THAN THE 12Z GFS. AS SUCH A NON-CMC BLEND IS PREFERRED AT AVERAGE CONFIDENCE. SHORTWAVE TROUGH MOVING TOWARD THE BAHAMAS THIS MORNING MID-LEVEL LOW CLOSING OFF NEAR THE BAHAMAS TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF BLEND CONFIDENCE: AVERAGE WESTERLY FLOW AIDS TUTT DEVELOPMENT ACROSS THE BAHAMAS IN THE NEXT COUPLE DAYS WITH FAIRLY PERSISTENT CONVECTIVE ENVIRONMENT INSPIRING SURFACE DEVELOPMENT...PLEASE CONTINUE TO SEE NHC TROPICAL WEATHER OUTLOOKS FOR STATUS CHANGES AND PROBABILITY OF DEVELOPING INTO A TROPICAL CYCLONE. THE 12Z NAM CONTINUES TO BE DEEPER LEADING TO A FURTHER SOUTH AND WESTWARD DEVELOPMENT OF THE TUTT AND EVENTUAL SURFACE REFLECTION...WHILE THE 12Z GFS SHOWS LITTLE CHANGE AND MATCHES THE 00Z ECMWF/GEFS MEAN AND ECENS MEAN THROUGH MUCH OF THE EVOLUTION. INTERESTINGLY...THE GFS/ECMWF AND 12Z NAM BECOME ALIGNED THROUGH MUCH OF THE DEPTH OF THE SYSTEM NORTHEAST OF THE NORTHEASTERN BAHAMIAN CHAIN BY 00Z FRIDAY. THE 00Z UKMET/CMC ARE DISPLACED FURTHER NORTH AWAY FROM THIS BETTER ALIGNMENT. ALL CONSIDERED A PREFERENCE MATCHES A 12Z GFS/00Z ECMWF BLEND (INFUSED WITH GEFS/ECENS MEAN WEIGHTING) AT AVERAGE CONFIDENCE THOUGH MUCH OF THE IMPACTS ARE NOT TO AFFECT THE CONUS THROUGH THIS FORECAST PERIOD. 19Z UPDATE: THE 12Z ECMWF TRENDED A BIT SLOWER AND THEREFORE A BIT FURTHER NORTH NOW ON THE NORTHERN SIDE OF THE 00Z ECENS MEAN. THE 12Z GEFS HOWEVER SHIFTED TOWARD VERY STRONG AGREEMENT WITH THE ECENS MEAN...WITH THE 12Z GFS ON THE SW SIDE OF THE CLUSTER. THE 12Z UKMET WHILE A BIT WEAKER OVERALL STILL REMAINS THE NORTHERN MOST OF THE GLOBAL GUIDANCE WHILE THE 12Z CMC WAS DEEPER AND FURTHER NORTH THAN THE 00Z RUN BUT ALSO MUCH FASTER THAN THE GFS/ECMWF CONSENSUS. AS SUCH WILL CONTINUE TO PREFER A 12Z GFS/ECMWF BLEND TO BEST REPRESENT THE ENSEMBLE CLUSTER. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA