MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 301 AM EDT MON MAR 21 2016 VALID MAR 21/0000 UTC THRU MAR 24/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE TROF EXITING EASTERN U.S. WITH ASSOCIATED DEEPENING SURFACE CYCLONE OFF U.S. EAST LIFTING INTO E CANADA MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE OVERALL MODEL GUIDANCE APPEARS TO HAVE COME TO A STRONGER AGREEMENT WITH GOOD ALIGNMENT THROUGH THE MAJORITY OF THE MASS FIELDS. THE 12Z UKMET IS THE ONLY MODEL OR ENSEMBLE MEAN THAT IS DISPLACED AS IT IS A BIT DEEPER AND BECOMES FAST WITH THE NEGATIVE TILT WHICH SUPPORTS THE RAPID DEEPENING OF THE SURFACE LOW OFF THE COAST. THE UKMET SURFACE REFLECTION IS BROAD AND ILL-DEFINED INITIALLY AND AFTER DEEPENING IS AN EASTERN OUTLIER. AS SUCH A NON-UKMET BLEND IS PREFERRED AT ABOVE AVERAGE CONFIDENCE. 07Z UPDATE: THE 00Z UKMET AS RESOLVED THE ISSUES PLAGUING THE 12Z RUN AND IS FAIRLY WELL MATCHED TO THE EARLIER PREFERENCE AND NEW 00Z ECMWF/CMC WHICH ALSO FOLLOW SUITE. AS SUCH AN OPERATIONAL MODEL BLEND IS PREFERRED AT ABOVE AVERAGE CONFIDENCE. SURFACE WAVE MOVING THROUGH NORTHERN CENTRAL PLAINS MONDAY/MIDWEST TUES/NEW ENGLAND WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: AVERAGE SHORTWAVE ENERGY CURRENTLY OVER E OR/WA WILL BE MOVING THROUGH A FAIRLY STRONG MEAN RIDGE AXIS ORIENTED OVER THE ROCKIES...MOST MODELS AGREE THAT THE ENERGY WILL QUICKLY MOVE THROUGH UNDER STRONG NORTHERN JET INFLUENCES ACROSS THE NORTHERN TIER OF THE US TUES AND CONTINUE TO STRETCH/SHEAR INTO THE CONFLUENT FLOW OVER THE GREAT LAKES/NEW ENGLAND BY WED...THIS RESULTS IN A WEAK SURFACE WAVE WITH THIS CLIPPER TO RACE ACROSS SOUTH DAKOTA MON/TUE...MI TUE/WED TO MAINE BY 12Z ON WED. MODELS ARE FAIRLY AGREEABLE WITH THE POSITION/TIMING FOR THE MOST PART; THE 12Z CMC REMAINS STRONGEST THROUGHOUT THE LIFE CYCLE AND GFS GENERALLY THE WEAKEST. OVERALL THE OFFSET OF EACH IS FAIRLY GOOD AS SUCH AN OPERATIONAL MODEL BLEND SHOULD BE SUFFICE HERE...BUT WITH THE SPREAD IN STRENGTH/QPF CONFIDENCE IS JUST AVERAGE. BY THE END OF THE FORECAST PERIOD THE PLACEMENT N-S OF THE FRONT WILL BE MORE HEAVILY INFLUENCED BY THE DEVELOPING STRONGER SURFACE WAVE/WARM ADVECTION OVER THE PLAINS...SO PLEASE REFER TO PREFERENCES BELOW FOR THAT SYSTEM AND QPF DISCUSSION AT QPFPFD FOR MORE DETAILS. 07Z UPDATE: THE 00Z CMC IS MUCH FLATTER WITH A WEAKER SURFACE WAVE AMPLIFICATION ACROSS THE GREAT LAKES MORE IN LINE WITH THE OTHER GUIDANCE...BUT DUE TO A WEAKER SOLUTION IT IS A BIT SLOWER WHICH NOW HIGHLIGHTS THE SLIGHTLY FASTER FRONTAL PASSAGE OF THE 00Z GFS ACROSS NEW ENGLAND. THIS IS NOT DRAMATIC AND WELL WITHIN THE REALM OF POSSIBILITIES AT THIS POINT TO CONTINUE AN OPERATIONAL MODEL BLEND AT AVERAGE CONFIDENCE. UPPER LOW MOVING MOVING INTO THE WEST MON/TUESDAY EJECTS INTO THE PLAINS WEDNESDAY WITH ASSOCIATED STRONG SURFACE RESPONSE HEADING TOWARD MIDWEST BY THURSDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z CMC/NAM BLEND TO REPRESENT ENSEMBLE AVERAGE CONFIDENCE: BELOW AVERAGE OVERALL THE PATTERN IS FAIRLY AGREEABLE THROUGH MON/TUESDAY AS THE UPPER LOW MOVES EASTWARD INTO THE INTERMOUNTAIN WEST. AFTER THIS POINT INTERACTION (OR LACK THEREOF) WITH WAVE ENERGY OUT OF THE NORTHERN STREAM AND/OR ENERGY (SEE SECTION ABOVE) THAT TRIES TO MOVE THROUGH THE MEAN RIDGE ACROSS THE S CANADIAN ROCKIES LINGERS AND DESCENDS/INTERACTS WITH THE LEADING EDGE OF THE UPPER LOW/SHORTWAVE LEADING TO INCREASING SPREAD OF EVOLUTION DIFFERENCES AS THE TROF EJECTS IN THE PLAINS. GIVEN THIS INTERACTION AND ITS ORIGIN POINT AT THE APEX OF THE MEAN RIDGE...PREDICTABILITY WILL BE DIFFICULT OVERALL. THE 00Z NAM IS MOST ROBUST/CONSOLIDATED WITH THE LINGERING ENERGY AND AS IT DESCENDS OUT OF CANADA INTO THE W DAKOTAS...THE LEADING SHORTWAVE ENERGY ELONGATES NORTHWARD TOWARD BETTER INTERACTION...AS SUCH THE NAM IS ON THE NORTHERN SIDE OF THE GUIDANCE SUITE. THE 00Z GFS ALSO FOLLOWS A NORTHERN TRACK LIKE THE NAM BUT IS A BIT MORE CONSOLIDATED AND THEREFORE IS A BIT LESS INFLUENCED BY THE WEAKER LINGERING SHORTWAVE AND DEVELOPS A MORE VIGOROUS COMMA HEAD ACROSS S MN/N IA/WI...ALSO ON THE NORTHERN SIDE OF GUIDANCE. ON THE OTHER SIDE OF THE SPECTRUM...THE 12Z ECMWF DOES NOT RESOLVE LINGERING SHORTWAVE ENERGY OR HAVE NORTHERN STREAM INFLUENCES...AND AS SUCH SLOWS/DEEPENS INTO A CUT-OFF LOW ACROSS KS BY WED EVENING...THOUGH THIS IS CONSISTENT WITH YESTERDAY'S 00Z RUN...BOTH THE 00Z AND 12Z ECENS MEANS WERE A BIT MORE PROGRESSIVE AND ILLUSTRATED THE AVERAGE/MIDDLE GROUND A BIT MORE THAN THE OPERATIONAL RUN. THE 12Z CMC LIKE THE ECMWF DOES NOT RESOLVE THE NORTHERN STREAM KICKER FEATURE...AND LIKEWISE IS A BIT SLOWER AND SOUTH THAN THE GFS/NAM BUT IS STILL A BIT NORTH OF THE ECENS MEAN WHICH PLACES IT MOST CENTRAL OF THE DETERMINISTIC RUNS. THE 12Z ENSEMBLE SPAGHETTI AND SURFACE LOW CLUSTERS...ALSO INDICATE THE CMC AND MUCH OF THE CMCE MEMBERS ARE NICELY BETWEEN THE BULK OF GEFS (NORTH AND EAST) AND ECMWF (SOUTH AND WEST). THE 12Z UKMET IS MOST UNIQUE IN THE DETERMINISTIC SUITE NOT RESOLVING SHORTWAVE ENERGY OUT OF THE RIDGE BUT DEVELOPING A VERY FAST NORTHERN STREAM SHORTWAVE THAT HELPS ACCELERATE THE NORTHERN PORTION OR LEADING ENERGY OF THE WAVE ACROSS THE MIDWEST BY THE END OF THE FORECAST PERIOD WHILE ALSO KEEPING A CONCENTRATED SHORTWAVE ROLLING THROUGH THE SOUTHERN RED RIVER VALLEY...WHICH SEEMS CLOSEST TO THE 00Z NAM BUT STILL DISTINCTLY DIFFERENT AND LEAST FAVORABLE SOLUTION OVERALL. GIVEN LOWER PREDICTABILITY...WOULD FAVOR GRAVITATING TOWARD A MIDDLE GROUND SOLUTION...NEAREST THE ENSEMBLE MEANS...PRESENTED BEST BY A NON-UKMET BLEND WEIGHTED TOWARD THE 12Z CMC. IF AVAILABLE A BLEND OF THE 12Z CMCE AND 12Z ECENS MEAN MAY RESULT IN BEST MIDDLE GROUND SOLUTION OVERALL. THE 12Z CMC IS A BIT WET OVERALL (TYPICAL OF BIAS)...PLEASE REFER TO QPFPFD AND QPFHSD FOR FURTHER DETAILS SPECIFIC TO QPF/SNOWFALL. 07Z UPDATE: THE 00Z ECMWF HAS TRENDED FASTER EVOLVING REMARKABLY SIMILAR TO THE 12Z ECENS MEAN THROUGH MUCH OF ITS DEPTH...THOUGH OVERALL IT IS THE SLOWEST AND MOST MATURE CYCLONE WITHIN THE 00Z DETERMINISTIC SUITE WITH A WELL EVOLVED COMMA HEAD (LIKELY A BIT TOO WET) BUT ALSO HAS FAIRLY STRONG BLOCKING HIGH ACROSS ONTARIO/QUEBEC BY THE END OF THE FORECAST PERIOD THAT IS BETTER SUPPORTED BY THE 21Z SREF/00Z GEFS/12Z ECENS MEAN THAN THE 00Z GFS IS...LIMITING ITS NORTHWARD TRACK A BIT. THE 00Z CMC ALSO REMAINS A SLOWER MORE MATURE SOLUTION THOUGH WITH A SLIGHTLY FASTER PROGRESSION THAN ITS 12Z RUN...MOVING TOWARD THE 00Z GEFS MEAN AND JUST EAST OF ITS 12Z CMCE MEAN...THOUGH ALSO STILL WITHIN CENTER OF THE ENSEMBLE MEANS WHICH IS PREFERRED AT HIGHEST WEIGHTING. THE 00Z UKMET EVOLVES SIMILARLY TO IS 12Z RUN BUT IS MORE PHASED IN THE NORTHERN STREAM AND LESS CONSOLIDATED/WRAPPED UP ACROSS THE RED RIVER...RESEMBLING THE 00Z NAM MUCH CLOSER AT THIS POINT BUT STILL ON THE NORTHEAST SIDE OF PACKING. WITHIN THE MASS FIELDS IT APPEARS THE ECMWF REMAINS A DEEP AND SLOW OUTLIER AND THE GFS IS A BIT TOO FAST...AS SUCH WILL CONTINUE TO PREFER A BLEND TOWARD THE 12Z CMCE/ECENS MEAN AND 00Z GEFS MEAN...WHICH IS BEST REPRESENTED BY THE 00Z CMC AND 00Z NAM. CONFIDENCE IN THIS SOLUTION IS BELOW AVERAGE GIVEN THE SPREAD. FRONT APPROACHING THE PACIFIC NORTHWEST WEDNESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/UKMET/CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE SMALL DIFFERENCES EXIST BY DAY 3 WITH RESPECT TO THE TIMING OF THE FRONTAL ZONE APPROACHING THE PACIFIC NORTHWEST AND ASSOCIATED SHORTWAVE SHED BY THE LARGER PARENT CLOSED LOW NEARING THE ALASKA PANHANDLE. THE 12Z ECMWF/UKMET AND 00Z NAM ARE A BIT FASTER AND ON THE SIDE OF THE RUN TO RUN TREND COMPARED TO THE 00Z GFS/12Z CMC...THOUGH THE 00Z GFS IS TRENDING FASTER TOO. GIVEN THE OVERALL TREND TOWARD A FASTER SOLUTION WILL FAVOR THE ONES LEADING THE TREND... AS SUCH A 12Z ECMWF/UKMET AND 00Z NAM IS PREFERRED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. 07Z UPDATE: THE 00Z NON-NCEP MODELS GENERALLY SLOWED A BIT TOWARD A MIDDLE GROUND BETWEEN THE FASTER 00Z NAM AND SLOWER 00Z GFS. GIVEN THE SPREAD IS NOT PARTICULARLY LARGE AND SENSIBLE WEATHER DIFFERENCES SEEM SMALL TO SUPPORT THESE MIDDLE GROUND SOLUTIONS SUPPORTED BY THE ENSEMBLE MEANS... 00Z ECMWF/UKMET/CMC BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA