MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 305 PM EDT THU AUG 18 2016 VALID AUG 18/1200 UTC THRU AUG 22/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING FINAL PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ AMPLIFYING TROF CROSSING SE QUEBEC CLIPPING MAINE/SE CANADA THUR/FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE GUIDANCE REMAINS TIGHTLY AGREED TO A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE. EXITING SHORTWAVE IN NEW ENGLAND AND LINGERING TROUGH/SHEAR AXIS STRETCHING FROM THE MID-ATLANTIC THROUGH THE LOWER MS VALLEY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE SHEARING SHORTWAVE CAN BE SEEN CROSSING NEW ENGLAND CURRENTLY IN WV WITH REMAINING ELONGATED SHEAR AXIS/CONFLUENCE TROF BACK TROUGH THE S MID-ATLANTIC/TN VALLEY TOWARD N TX AT THIS TIME. THE 12Z NAM REMAINS A BIT DEEPER WITH THE WAVE AS IT EXITS BUT ALSO CONTINUES TO ROLL UP THE SHEAR AXIS INTO MORE CONCENTRIC VORT CENTERS THAN THE REST OF THE GUIDANCE THOUGH THE ORIENTATION APPEARS CORRECT...THIS VORTEX ROLL UP LEADS TO DIFFERENCES IN TIMING WITH THE MORE CONSISTENT GFS/ECMWF/UKMET. THIS INCLUDES THE TRACK/SHAPE/STRENGTH OF A WAVE MOVING THROUGH THE TN VALLEY FRIDAY AND N CAROLINAS SAT. THE 00Z CMC IS GENERALLY WEAK AND DOES NOT RESOLVE MUCH WAVE ACTIVITY ALONG THE BOUNDARY TO SUPPORT LARGER QPF DIFFERENCES AS WELL. AS SUCH WILL SUPPORT A 12Z GFS AND 00Z ECMWF/UKMET BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE GIVEN SUPPORT OF THE ENSEMBLE MEANS. 19Z UPDATE: THE DIFFERENCES SEEM MINOR OVERALL THOUGH THE UKMET HAS TRENDED TO A WEAKER CMC SOLUTION...SO WITH BEST AGREEMENT BETWEEN THE GFS/ECMWF WILL SUPPORT THIS BLEND GIVEN BEST CONTINUITY. DEVELOPING TROUGH ACROSS ACROSS ROCKIES/N PLAINS BY FRIDAY INCLUDING ENERGY FROM CENTRAL ROCKIES WITH SURFACE LOW TRACKING FROM CENTRAL PLAINS THROUGH GREAT LAKES SAT-SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/CMC BLEND CONFIDENCE: AVERAGE WEAK TROUGHING CURRENTLY EXISTS ACROSS THE INTERMOUNTAIN WEST...WITH MULTIPLE PIECES OF EMBEDDED SHORTWAVE ENERGY. SOME OF THIS ENERGY WILL EJECT EAST INTO THE NORTHERN PLAINS AND UPEPR MS VALLEY THURSDAY INTO FRIDAY. A STRONGER SHORTWAVE IS EXPECTED TO DIVE SOUTHEAST OUT OF BRITISH COLUMBIA INTO ID/MT BY 00Z FRIDAY WHICH IN TURN CARVE OUT A DEEPER TROUGH AS IT EJECTS INTO THE PLAINS/MS VALLEY ON SATURDAY. THIS INCLUDES A SURFACE LOW TRACKING INTO THE GREAT LAKES ON SATURDAY. THE 12Z NAM QUICKLY BREAKS FROM MODEL CONSENSUS AS THE MAIN SHORTWAVE DROPS OUT OF THE ROCKIES... MUCH DEEPER AND EVENTUALLY SLOWER. THIS DEEPENING/SLOWING PLACES IT SIGNIFICANTLY OUT OF PHASE AND ROBUST MORE LIKE AN OCTOBER/NOVEMBER PATTERN ACROSS THE GREAT LAKES RESULTING IN A 989MB LOW IN THE UP OF MI. BASED ON OTHER GUIDANCE/ENSEMBLE TRENDS AND CLUSTER...THE 12Z NAM IS SIGNIFICANT OUTLIER. THE 12Z GFS CONTINUES A SLIGHTLY DEEPER AND TAD FASTER TREND BY DAY 3 ACROSS THE GREAT LAKES BUT MATCH LOCATION AND STRENGTH OF THE 00Z UKMET AND A BIT WEAKER THAN THE 00Z ECMWF ESPECIALLY AT THE SURFACE. THE REMARKABLE AGREEMENT OF THE 3 MODELS AS WELL AS THE 06Z GEFS/00Z ECENS MEAN PROVIDES STRENGTHENING CONFIDENCE OVERALL IN THE TROF EVOLUTION AS WELL AS THE SURFACE LOW AND FRONTAL ZONE TRACKING THROUGH THE GREAT LAKES/OHIO VALLEY TOWARD THE EAST COAST BY THE END OF DAY 3. THE 00Z CMC IS MORE ALIGNED THAN IT HAS BEEN WITH RESPECT TO PRIOR RUNS/DAYS...BUT REMAINS JUST MISALIGNED GIVEN THE TIGHT AGREEMENT ELSEWHERE TO INCLUDE IT IN THE PREFERENCE. ALL CONSIDERED A SLIGHTLY ABOVE AVERAGE CONFIDENCE IN A 12Z GFS AND 00Z ECWMF/UKMET BLEND IS PREFERENCE. 19Z UPDATE: THE 12Z UKMET TRENDED SLOWER/DEEPER WHICH PRESENTED ITSELF CLOSER TOWARD THE UNFAVORABLE 12Z NAM...HOWEVER THE 12Z CMC TRENDED FAVORABLY TOWARD A CONSENSUS WITH THE 12Z GEFS/00Z ECENS MEAN/12Z GFS AND THE SIMILAR 12Z ECMWF...THIS KEEPS FAIRLY HIGH CONFIDENCE IN THE GFS/ECMWF COMPROMISE AND COULD INCLUDE THE 12Z CMC TO PROVIDE SOME ADDITIONAL STABILITY AS WELL. AS SUCH WILL PREFER THE 00Z UKMET AND/OR 12Z CMC INTO THE BLEND WITH THE 12Z ECMWF/GFS AT AVERAGE CONFIDENCE. CONVECTIVELY INDUCED SHORTWAVE FROM WESTERN MEXICO MOVING NE TOWARD TX SAT INTO SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/UKMET BLEND CONFIDENCE: AVERAGE TROPICAL INFLUENCE/UPSCALE GROWTH OCCURS ACROSS WESTERN MEXICO (S SINALOA/N NAYARIT) AT THE WESTERN APEX OF THE SUBTROPICAL RIDGE NEAR THE WESTERN EXTENTS OF THE LINGERING TROF/ATMOSPHERIC RIVER THAT HAS DOMINATED THE TX/MS RIVER VALLEY OVER THE LAST WEEK OR SO. MODEL AGREEMENT (EVEN WITHIN ENSEMBLE SPREAD) IS FAIRLY STRONG EVEN WITH RESPECT TO CONVECTIVELY DRIVEN PROCESS AS A WHOLE. THE 12Z NAM IS GENERALLY A BIT FASTER AND MORE ROBUST WITH THE SYSTEM CROSSING THE BIG BEND OF TX FRI INTO SAT... COMPARED TO THE MORE MODERATELY TIMED GFS/ECMWF AND UKMET. WHILE DIFFERENCES IN ELONGATION/CONSOLIDATION (GFS TO ECMWF TO UKMET RESPECTFULLY) OF THE WAVE REMAIN ALONG WITH STRENGTH DIFFERENCES (WEAK TO STRONG: ECMWF TO GFS TO UKMET) THE TIMING/PLACEMENT OF THE WAVE AS A WHOLE IS FAIRLY STRONG GIVEN THE TIME UNTIL THE EVENT AS WELL AS THE CONVECTIVE PROCESSES. AT THIS TIME A 12Z GFS AND 00Z ECMWF/UKMET BLEND SEEMS REASONABLE AND THOUGH CONFIDENCE IS HIGHER THAN NORMAL FOR SUCH A SETUP...VARIATION/PREDICTABILITY ARE TIED HEAVILY TO LOCAL/MESOSCALE EFFECTS TO BE TOO CONFIDENT AT THIS POINT...AND ONLY AVERAGE OVERALL. PLEASE SEE WPC QPFPFD FOR ADDITIONAL QPF DETAILS/PREFERENCES. BOTH THE 12Z UKMET/ECMWF TRENDED A BIT FASTER AWAY FROM THE GFS BUT MORE ELONGATED LIKE THE GFS...THIS INCREASES SOME SPREAD (WHICH WOULD BE EXPECTED GIVEN INFLUENCE OF CONVECTIVE PROCESSES). WHILE THE 00Z CMC REMAINS WEAKEST...THE TIMING/PLACEMENT TO THE GFS IS A POSITIVE TREND. WITH THIS SLIGHT DIFFERENCES IN TIMING WILL SUPPORT A NON-NAM BLEND BUT REDUCING CONFIDENCE OVERALL TOWARD AVERAGE TO SLIGHTLY BELOW AVERAGE. MID-LEVEL TROF ENTERING SW BC/NW WA BY LATE SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE VARIATION IN DEVOLUTION OF CLOSED LOW OVER THE WESTERN AK PENINSULA FRI INTO SAT PLAYS A CRITICAL ROLE IN THE MODEL SPREAD. THE NCEP MODELS ARE MORE AGGRESSIVE IN EJECTING LEAD SHORTWAVE ENERGY TOWARD THE TOP OF THE RIDGE WHICH EFFECTIVELY STALLS AND KEEPS AN ELONGATED TROF ORIENTATION ACROSS N BC AND BOREAL ALB/SASK COMPARED TO THE ECWMF ECMWF (AND LESSER SO THE UKMET/CMC) THAT MAINTAIN THE AMPLIFIED RIDGE AND ALLOW THE LEADING SHORTWAVE ENERGY TO ELONGATE/SHEAR INTO THE WESTERN SIDE OF THE RIDGE INTO CENTRAL CANADA. THIS RESULTS IN THE NAM/GFS DEVELOPING SLOWER AND SOUTHWARD AS THE SYSTEM TRIES TO CLOSE OFF AGAIN TOWARD CENTRAL BC AND PUGET SOUND BY SUN EVENING...WHILE THE ECMWF BEING A BIT MORE CONSOLIDATED DEVELOPS THE CLOSED LOW SOONER AND FURTHER NORTH...LIMITING THE AFFECTS INTO THE NORTHWEST. THE UKMET/CMC ARE MIDDLE GROUND SOLUTIONS BUT AS SUCH ARE A BIT FASTER BUT ALSO A BIT SOUTH WITH GREATEST AFFECTS NEARING NW WA BY 00Z MONDAY. OVERALL THE PLAUSIBILITY OF THE NAM/GFS SEEMS LESS LIKELY TOWARD DEVELOPING A MORE CONSOLIDATED TROF THAT STALLS AT THE APEX OF THE RIDGE...BUT THE ECMWF IS ON THE NORTHERN EDGE OF THE ENSEMBLE GUIDANCE AND QUITE STRONG. THE 00Z CMC SHOWED HIGH RUN TO RUN VARIABILITY WITH A FLAT PATTERN TRANSITIONING INTO A DEEP TROF...THE UKMET SHOWED SOME CONSISTENCY BUT ALSO HINTED OF SOME OF ITS KNOWN BIAS BEING FAST. A GENERAL MODEL BLEND MAY BE BEST AS IT RESULTS IN A CENTRAL CONSENSUS THOUGH CONFIDENCE IS BELOW AVERAGE AT THIS TIME. 19Z UPDATE: THE 12Z ECMWF TRENDED SOUTHWARD TOWARD BETTER CONSENSUS THOUGH CONTINUES TO KEEP THE AMPLIFIED RIDGE DOWNSTREAM COMPARED TO THE GFS/NAM. HOWEVER...THE 12Z UKMET TRENDED TOWARD THE NCEP SOLUTIONS PROVIDING SOME ADDITIONAL SUPPORT OF THEIR SLOWER/DEEPER SOLUTIONS. THE 00Z CMC REMAINED FAIRLY SIMILAR TO ITS PRIOR RUN. ALL CONSIDERED THE OVERALL SPREAD HAS REDUCED AND THOUGH THE EXACT EVOLUTION REMAINS DIFFERENT...THERE IS ENOUGH SIMILARITY NEAR THE NW PACIFIC REGION TO CONTINUE A GENERAL MODEL BLEND AT INCREASED CONFIDENCE BUT REMAINING SLIGHTLY BELOW AVERAGE. GALLINA www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...