MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 100 AM EDT THU MAY 14 2015 VALID MAY 14/0000 UTC THRU MAY 17/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...CLUSTER OF SHORTWAVES LIFTING ACROSS THE GREAT PLAINS EARLY ON... ...RESULTANT VORTICITY CENTERS CROSSING THE GREAT LAKES BY FRIDAY MORNING... PRELIMINARY PREFERENCE: NON-12Z CMC MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A DISORGANIZED AXIS OF SHORTWAVE ENERGY CURRENTLY SITUATED OVER THE GREAT PLAINS WILL LIFT IN UNISON TOWARD THE UPPER MIDWEST/GREAT LAKES REGION DURING THE NEXT 24 HOURS. EVENTUALLY THIS SHEARING IMPULSE WILL MIGRATE EASTWARD PUSHING INTO NEW ENGLAND BY EARLY SATURDAY. THE MODELS ARE IN FAIRLY GOOD AGREEMENT AS A WHOLE. THE EXCEPTION TO THIS RULE IS THE 12Z CMC WHICH SHOWED A NORTHWARD DISPLACEMENT MOVING INTO DAY 3. A NON-12Z CMC MODEL COMPROMISE SEEMS REASONABLE. ...BROAD/ANOMALOUS CLOSED LOW EJECTING FROM THE SOUTHWESTERN U.S. TOWARD THE PLAINS... PRELIMINARY PREFERENCE: BLEND OF THE 12Z ECMWF/ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN IMPRESSIVE UPPER LOW DROPPING SOUTHWARD ALONG THE WEST COAST WILL CONSIST OF A VERY BROAD CIRCULATION WITH 500-MB HEIGHT ANOMALIES APPROACHING 3 TO 3.5 STANDARD DEVIATIONS BELOW NORMAL. THIS ROBUST UPPER CYCLONE WILL WORK ITS WAY EASTWARD CARRYING A SERIES OF SMALLER-SCALE SHORTWAVES ROTATING ABOUT THE BASE OF THE TROF. THESE FEATURES WILL BE THE IMPETUS FOR PRECIPITATION...ESPECIALLY ACROSS THE COMPLEX TERRAIN OVER THE WESTERN U.S. LOOKING AT THE GUIDANCE...THE MODEL SPREAD IS NOT TOO SIGNIFICANT ALTHOUGH THERE IS SOME VARIATION BETWEEN THE CAMPS. MULTI-DAY SPAGHETTI PLOTS HAD BEEN SHOWING A TREND IN THE FASTER DIRECTION FOR A WHILE BEFORE THE LAST MODEL CYCLE SUGGEST A MOVE TOWARD A SLOWER SOLUTION. THE STRONGEST CLUSTERING WAS THE IN 12Z ECMWF ENSEMBLE MEMBER GROUPING WITH A LITTLE MORE SCATTER IN THE OTHER MEMBERS. THE 12Z ECMWF/ECMWF ENSEMBLE MEAN SEEMS TO OFFER A RATHER STABLE SOLUTION WHICH FOLLOWS THE RECENT TRENDS. WILL LEAN SLOWER AS SUCH WHICH ALSO SEEMS TO BE MORE FAVORED IN A SYNOPTIC SITUATION FEATURING A SLOW MOVING UPPER LOW. ...UPPER TROF CROSSING NORTHERN NEW ENGLAND BY EARLY SUNDAY... PRELIMINARY PREFERENCE: BLEND OF THE 00Z NAM/GFS FORECAST CONFIDENCE: AVERAGE WITHIN THE NORTHERN BRANCH OF THE JET STREAM...AN AXIS OF HEIGHT FALLS IS EXPECTED TO GAIN AMPLITUDE ACROSS UPPER NEW ENGLAND BY EARLY SUNDAY. THIS AMPLIFICATION IN THE HEIGHTS INDUCES A WEAK AREA OF LOW PRESSURE JUST OFFSHORE OF ME. WHILE THE 00Z GFS HAS TRENDED A BIT MORE AMPLIFIED WHICH IS IN THE DIRECTION OF THE 12Z ECMWF...THIS LATTER MODEL APPEARS TO BE A TAD OVERDONE. IT SHOWS A CLOSED 570-DM LOW OVER NORTHERN ME WITH SUPPORT FROM ITS ENSEMBLE MEAN. HOWEVER...NOT READY TO BUY INTO THEIR SOLUTIONS YET AND WILL PREFER MORE CONSERVATIVE...BUT CLUSTERED 00Z NAM/GFS. ...BROAD CYCLONIC CIRCULATION OFF THE WEST COAST OVER THE WEEKEND... PRELIMINARY PREFERENCE: FORECAST CONFIDENCE: TOWARD THE END OF THE PERIOD...ANOTHER BROAD UPPER LOW WILL DESCEND ON THE COASTAL WATERS OF THE WESTERN U.S. THIS ULTIMATELY PLACES TWO LARGE CIRCULATIONS IN CLOSE PROXIMITY TO ONE ANOTHER FOR LATTER HALF OF THE WEEKEND. GIVEN DOWNSTREAM TIMING WILL INFLUENCE THE POSITION OF THIS UPPER LOW...WILL LEAN IN THE DIRECTION OF WHAT WAS EARLIER RECOMMENDED. THAT IS...A BLEND OF THE 12Z ECMWF/ECMWF ENSEMBLE MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER