MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 248 AM EDT MON APR 18 2016 VALID APR 18/0000 UTC THRU APR 21/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TROUGH/FRONT MOVING INTO THE NORTHEAST LATE MON/TUES WITH SURFACE CYCLOGENESIS OFF NEW ENGLAND TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE TIMING/PLACEMENT OF THE WAVE CONTINUES TO BE WELL ALIGNED WITH THE WAVE AND EVENTUAL DEEPENING OF THE UPPER LEVEL TROF OFF THE NORTHEAST COAST INCLUDING THE SURFACE REFLECTION. THE 12Z ECMWF/00Z UKMET BOTH REMAIN A BIT MORE AMPLIFIED PARTICULARLY IN THE LOWER LEVELS 7H TO SFC...AND AS SUCH RESULT IN A BIT HIGHER QPF/DEEPER SURFACE REFLECTION THAT DEVELOPS OFF THE COAST. STILL THIS APPEARS SMALL IF BLENDED WITH THE SLIGHTLY WEAKER 00Z NAM/GFS AND 12Z CMC. AS SUCH WILL FAVOR AN OPERATIONAL MODEL BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE GIVEN THERE REMAINS THIS SMALL DIFFERENCE IN MAGNITUDE. 07Z UPDATE: LITTLE CHANGE SEEN IN THE 00Z CMC/ECMWF OVERALL THOUGH THE ECMWF DID TREND AWAY FROM THE MORE AMPLIFIED 7H FLOW LIKE THE UKMET...AND RESOLVED A WEAKER SURFACE LOW OFF THE SE COAST. OVERALL THE CHANGES ARE SMALL ENOUGH TO KEEP AN OPERATIONAL BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. INTERMOUNTAIN WEST CUTOFF UPPER LOW SHIFTING INTO THE PLAINS WED AND UPPER MIDWEST BY THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/UKMET/ECMWF BLEND CONFIDENCE: AVERAGE THERE CONTINUES TO BE FAIRLY STRONG AGREEMENT IN THE OVERALL PATTERN WITH THE CLOSED LOW AND ITS EVOLUTION...ALTHOUGH THERE REMAIN SMALL DIFFERENCES IN PLACEMENT/TIMING WITH THE INTERNAL SHORTWAVES ROTATING OUT OF THE BASE OF THE TROUGH WHICH IS NOT UNEXPECTED FOR A GENERALLY FILLING UPPER LEVEL LOW. THIS MAKES PREDICTABILITY OF THE INTERNAL WAVES/CONVECTIVE FEATURES TO VARY WITH EACH MODEL ITERATION...HAVING LESS CONFIDENCE IN ONE PARTICULAR RUN OVER ANOTHER. AS SUCH WILL GRAVITATE TOWARD THE ENSEMBLE MEANS...WHICH ARE FAIRLY TIGHTLY ALIGNED...THOUGH THE ECENS MEAN IS A BIT SLOWER/DEEPER BY THE END OF THE PERIOD WHICH IS FAIRLY TYPICAL WHEN COMPARED TO THE GEFS/GFS. THE 12Z CMC REMAINS GENERALLY SOUTH AND SLOWER THAN MUCH OF THE REST OF THE GUIDANCE. THE 00Z NAM THOUGH FEELING SOME INFLUENCE FROM THE DEEP NORTHERN CANADA CYCLONE BY WED EVENING...THE INNER CORE REMAINS VERY CONSOLIDATE AND WELL SOUTH OF MUCH OF THE GUIDANCE. THE 00Z GFS ON THE OTHER HAND IS QUICKER TO PHASE WITH THIS NORTHERN STREAM TROF...DRAWING NORTHEAST INTO THE WESTERN GREAT LAKES EVEN FASTER THAN THE 18Z GEFS; THOUGH PLAUSIBLE WITHOUT MUCH OTHER SUPPORT A BIT HESITANT TO KEEP IT FULLY WEIGHTED IN A BLEND. THE 00Z UKMET LOOKS LIKE A VERY NICE COMPROMISE OF THE 00Z GFS/12Z ECMWF AND LIES WITHIN THE CENTER OF THE ENSEMBLE SUITE...GIVING IT HIGHER WEIGHTING. ALL CONSIDERED PREFERENCE TOWARD 00Z GFS/UKMET AND 12Z ECMWF BLEND BUT ONLY AVERAGE CONFIDENCE GIVEN THE INTERNAL DETAIL DIFFERENCES ARE LOWER CONFIDENCE THOUGH THE LARGER SCALE MASS FIELDS ARE HIGHER. 07Z UPDATE: THE 00Z ECMWF FOLLOWED A TREND OF OPENING UP BY THE END OF DAY 3 LIKE THE 00Z UKMET AND GFS...BUT TYPICAL OF ITS BIAS...WAS MUCH SLOWER OVERALL. THE 00Z CMC MADE A POSITIVE SHIFT TOWARD THE CONSENSUS AND MATCHES ITS FAVORABLE 12Z CMCE MEAN...BUT ALSO RETAINS A VERY STRONG SOUTHERN INTERNALLY SHORTWAVE TO FULLY INCORPORATE IT IN THE BLEND. AS SUCH WILL FAVOR A 00Z UKMET/ECMWF/GFS BLEND. PERIPHERAL SHORTWAVE OF LARGE DEEP NORTHERN CANADA UPPER LOW MOVING TOWARD NW GREAT LAKES BY THURS WITH ASSOCIATED SURFACE FRONT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z UKMET/ECMWF BLEND CONFIDENCE: AVERAGE COMPARED TO ENSEMBLE SPAGHETTI PLOTS...THE 00Z GFS APPEARS TO BE A BIT QUICKER WITH THE SHORTWAVE DESCENDING OUT OF NORTHERN CANADA WHICH AS MENTIONED ABOVE...IS LESS FAVORABLE DUE TO QUICKER PHASING WITH THE REMNANT INNER CORE OF THE UPPER LOW ACROSS THE UPPER MIDWEST THURSDAY. THIS SUPPORTS A FASTER FRONTAL PASSAGE AND FURTHER/DEEPER SURFACE REFLECTION ACROSS THE U.P. OF MI BY THE END OF THE FORECAST PERIOD. THE 00Z NAM IS A BIT SLOWER WITH THE LARGER SCALE UPPER LOW ACROSS HUDSON BAY MAKING THE ORIENTATION OF THE SURFACE FRONT A BIT SHARPER THAN MUCH OF THE OTHER GUIDANCE...WHILE THE 12Z CMC IS ALIGNED WITH THE THE 12Z ECMWF/UKMET WITH THE UPPER LOW BUT IS SLOWER WITH THE SHORTWAVE MAKING THE FRONTAL ZONE LAG AND ORIENT MORE E-W. ALL CONSIDERED WILL FAVOR A 00Z UKMET/12Z ECMWF BLEND AT AVERAGE CONFIDENCE. 07Z UPDATE: A SLIGHTLY SLOWER 00Z ECMWF ADDED A BIT OF SPREAD WITH THE 00Z UKMET ACROSS THE ARROWHEAD OF MN BY THE END OF DAY 3...BUT OVERALL THE CHANGE WAS MINOR TO KEEP A UKMET/ECMWF BLEND AT AVERAGE CONFIDENCE. UPPER LOW ENTERING CENTRAL WEST COAST WED MORNING AND SHEARING OUT ALONG W WA/OR BY WED EVENING/THURS MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/ECMWF/UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE CUT-OFF LOW NEARS THE CA COAST TUES BUT WILL BE WEAKENING INTO A FAIRLY STRONG RIDGE OVER THE NORTHWEST DAMPENING IT AS IT LIFTS BY COASTAL WA/OR BY THURS MORNING. SEEN A SLIGHTLY FASTER TREND BY WED IN THE LAST FEW ITERATIONS OF MOST MODELS EXCLUDING THE VERY SLOW CMC. THE 00Z NAM IS NOW QUICKEST BOTH IN SPEED AS WELL AS IN THE WEAKENING TREND. THIS IS COUNTER TO THE 12Z ECMWF WHICH IS NEXT FASTEST BUT IS A BIT MORE AMPLIFIED IN SOLID LOCK STEP WITH THE 12Z ECENS MEAN. THE 00Z GFS IS A BIT FASTER TOWARD THE 12Z ECMWF BUT IS A BIT SLOWER...A GOOD COMPROMISE BETWEEN THE 12Z ECENS MEAN/18Z GEFS. THE 00Z UKMET ALSO SHIFTED A BIT FASTER TOO BUT BY THURS SEEMS TO LINGER A BIT MORE THAN SUPPORTED BY THE ENSEMBLES...AS SUCH WILL FAVOR A 12Z ECMWF/00Z GFS BLEND TO BEST REPRESENT THE ENSEMBLE SUITE. GIVEN THE SPREAD IN WEAKENING TREND SEEMS TO BE INCREASING INCLUDING A BIT MORE TIMING SPREAD TOO...MAKES CONFIDENCE A BIT LOWER THAN THE LAST FEW DAYS BUT STILL MODERATE OR AVERAGE OVERALL IN THIS BLEND. 07Z UPDATE: THE 00Z CMC HAS ONCE AGAIN SHIFTED FASTER BUT REMAINS THE SLOWEST OVERALL...THOUGH MUCH BETTER OVERALL. THE SHIFT TOWARD A SLOWER TIMING OF THE TROF WITH THE 00Z ECMWF MATCHES THE TIMING BETWEEN THE 00Z GFS/UKMET AND VERY SIMILAR TO THE 00Z GEFS TO HAVE SLIGHTLY INCREASED CONFIDENCE IN THIS BLEND. AS SUCH PREFERENCE IS 00Z GFS/UKMET/ECMWF BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA