MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1214 PM EDT MON OCT 19 2015 VALID OCT 19/1200 UTC THRU OCT 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH FORECAST CONFIDENCE AND MODEL PREFERENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FLAT UPPER TROUGH/SURFACE COLD FRONT UPPER MIDWEST/GREAT LAKES BY MON/TUES...WITH THE FRONT STALLING ACROSS THE NORTHEAST AHEAD OF NEXT SURFACE WAVE (SEE BELOW) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF OPERATIONAL MODELS CONFIDENCE: ABOVE AVERAGE SOLID AGREEMENT CONTINUES WITH THE PLACEMENT AND TIMING OF A COLD FRONT CROSSING OUT OF MINNESOTA AND GENERALLY FLATTENING OVER THE LP OF MI AS THE MAIN UPPER LEVEL ENERGY SHIFTS THROUGH SE CANADA WITH THE 00Z CMC LAGGING THE MOST...TYPICAL OF ITS BIAS... BUT NOT SIGNIFICANTLY TO DISREGARD. SO WILL CONTINUE A BLEND OF THE OPERATIONAL MODELS...AND GIVEN STRONG ENSEMBLE SUPPORT FROM THE SREF/GEFS AND ECENS...CONFIDENCE IS ABOVE AVERAGE IN THE BLEND SOLUTION. NORTHERN STREAM SHORTWAVE AND ASSOCIATED SURFACE LOW CROSSING THE GREAT LAKES WED/THURS INTO NEW ENGLAND BY FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 12Z NAM/GFS AND 00Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN ELONGATED TROF JUST OFF THE NORTHWEST PACIFIC COAST IS DEPICTED WELL IN GOES-W WV LOOP...SOME OF THE ENERGY DROPS SOUTH INTO THE WESTERN HEMISPHERE OF THE WEAKENING UPPER LOW TO REINFORCE IT OVER THE SOUTHWEST. HOWEVER...THE NORTHERN PORTION OF THE TROUGH'S ENERGY REMAINS IN THE NORTHERN STREAM TRANSVERSING THE CANADIAN ROCKIES BEFORE CONSOLIDATING ACROSS THE CANADIAN PRAIRIES TUES INTO WED MORNING. IN THE WAKE OF THE CYCLONE DESCRIBED ABOVE...THE WAVE GRADUALLY AMPLIFIES...IN THE PROCESS GENERATING AN AREA OF LOW PRESSURE OVER THE CENTRAL PLAINS WHICH WILL THEN DEEPEN INTO THE GREAT LAKES AND SOUTHERN ONTARIO BY WED NIGHT AND THURS. THE 00Z UKMET QUICKLY BECOMES OUT OF PHASE...TRUE TO ITS BIAS...BECOMING FAST...INCLUDING THE FRONT ACROSS NEW ENGLAND THOUGH THERE IS MUCH BETTER AGREEMENT TOWARD THE BASE OF THE FRONT INTO OH/PA AND MID-ATLANTIC BY THURSDAY NIGHT/FRIDAY MORNING. THE 00Z CMC IS INITIALLY A BIT NORTH AND EAST OF BEST UPPER LEVEL CLUSTER AND REMAINS EAST THROUGHOUT THE FORECAST PERIOD. THIS ALLOWS THE SURFACE LOW TO INITIALLY TRACK WELL WITH THE CLUSTER INTO THE WESTERN LAKES BEFORE BECOMING A SOUTHERN OUTLIER AND EVENTUALLY A FAST/EASTERN ONE AS WELL. THE 12Z NAM HAS ENTERED A STRONG CLUSTERING WITH THE 12Z GFS/00Z ECMWF WITH VERY STRONG SUPPORT FROM THE 00Z/06Z GEFS AND 00Z ECENS MEAN...ALSO FITTING IN WITH A TIGHTENING 00Z ENSEMBLE SURFACE LOW CLUSTER. THIS BOLSTERS AN INCREASING CONFIDENCE IN A PREFERRED BLEND OF THE NAM/GFS/ECMWF TO SLIGHTLY ABOVE AVERAGE. UPPER TROUGH/CLOSED LOW DIGGING INTO THE SOUTHWEST U.S THROUGH MIDWEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN ELONGATED TROF JUST OFF THE NORTHWEST PACIFIC COAST IS DEPICTED WELL IN GOES-W WV LOOP...SOME OF THE ENERGY DROPS SOUTH INTO THE WESTERN HEMISPHERE OF THE WEAKENING UPPER LOW TO REINFORCE IT OVER THE SOUTHWEST. THIS ENERGY EVENTUALLY ROTATES THROUGH THE TROF WHILE INTERACTING WITH OTHER INTERNAL SMALLER SCALE SHORTWAVE CENTERS. EVENTUALLY THE BULK OF THE CUT-OFF LOW ENERGY LIFTS UNDER THE INFLUENCE OF THE APPROACHING UPSTREAM SHORTWAVE THURSDAY INTO FRIDAY (SEE SECTION BELOW). THE 00Z CMC REMAINS THE MAIN OUTLIER IN THE EVOLUTION OF THIS SCENARIO...AS BY DAY 3 IT A MUCH STRONGER SOLUTION OF THE KICKER WAVE ACROSS THE GREAT BASIN. THE 06Z GFS WAS GENERALLY FAST WITH THE INITIAL SHORTWAVE ENERGY ENTERING THE BASE WHICH LEAD TO LESS INTERACTION WITH THE OLDER CUT-OFF'S ENERGY...MAKING IT A NORTHERN SOLUTION OF THE REST OF THE OPERATIONAL MODELS. THIS WAS SUPPORTED BY THE 06Z GEFS AND 09Z SREF...THOUGH NOT THE 00Z GFS OR 00Z GEFS WHICH HAD STRONGER AGREEMENT WITH EARLIER THE 00Z ECMWF/UKMET SOLUTIONS. THE 12Z GFS KEPT WITH THIS FASTER SOLUTION BUT HAS TEMPERED A BIT TOWARD THE 00Z ECMWF/NAM. THE 00Z UKMET IS A BIT FASTER AND SO A AND IS IN GOOD AGREEMENT WITH THE 12Z GFS. THE 12Z NAM IS A BIT SLOWER THAN THE EARLIER 00Z CONSENSUS/PREFERENCE AS IT IS A BIT DEEPER AND MORE CONSOLIDATED WITH THE VORTICITY FEATURE OVER CO. STILL THESE ARE SUBTLE DIFFERENCES THAT AT THIS RANGE ARE NOT SIGNIFICANT ENOUGH TO NOT SUPPORT A BLEND OF THE 12Z NAM/GFS OR 00Z UKMET/ECMWF...PARTICULARLY GIVEN SUPPORT FROM THE OVERALL ENSEMBLE MEANS. AS SUCH A NON-CMC BLEND IS CONTINUE PREFERENCE AT SLIGHTLY ABOVE AVERAGE GIVEN THE HIGH AGREEMENTS UNTIL THE VERY END OF DAY 3...WHICH MAINLY SEEM TO BE MASS-FIELD DIFFERENCES AS QPF IS QUITE AGREEABLE (PLEASE SEE QPFPFD FOR MORE DETAILS) UPPER TROUGH AND COLD FRONT ENTERING THE PACIFIC NORTHWEST AND INTO THE NORTHERN ROCKIES WED/THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE A MODERATE RIDGE REMAINS ACROSS THE PACIFIC NORTHWEST THROUGH TUESDAY NIGHT BEFORE THE NEXT PACIFIC WAVE ENTERS THE PICTURE. WITH THE RIDGE IN PLACE THE BULK OF THE ENERGY LIFTS INTO CANADA WITH THE TROF BREAKING DOWN THE FLOW INTO MORE ONSHORE/ZONAL WITH WEAK TROF ENERGY ALLOWING TO KICK THE DEEPER CUT-OFF OUT OF THE SOUTHWEST. THE 00Z CMC IS A DISTINCT OUTLIER AS IT IS OVER-AMPLIFIED WHILE THE BULK OF THE ENSEMBLE SPAGHETTI PLOT IS BROADLY ZONAL...AND AS STATED IN SECTION ABOVE BEGINS TO DEEPEN IN ITS INTERACTION WITH THE LIFTING/OPENING SOUTHERN CUT-OFF LOW. THE 00Z NAM HAS SPED UP AND THOUGH STILL LAGS THE 00Z ECMWF AND UKMET ARE IN MUCH BETTER AGREEMENT. THE 12Z GFS IS IN LINE WITH THE 00Z UKMET/12Z NAM HAVING A STRONGER WAVE RESOLVED ACROSS THE GREAT BASIN INTO S CA BY DAY 3...COMPARED TO THE 00Z ECMWF BUT ALSO A BIT SLOWER/WEAKER ACROSS THE NORTHERN US ROCKIES LIKELY IN RESPONSE TO BEING A NORTHERN MEMBER OF HANDLING THE ENERGY LIFTING OUT OF THE SOUTHERN ROCKIES WITH THE OPENING CUT-OFF. GIVEN THE DIFFERENCES IN PLACEMENT OF ENERGY WITHIN THE ELONGATED TROF...OVERALL CONFIDENCE IS AVERAGE IN A NON-CMC BLEND. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA