MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1248 AM EDT THU APR 24 2014 VALID APR 24/0000 UTC THRU APR 27/1200 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. ...STRONG CLOSED LOW EXITING INTO THE CANADIAN MARITIMES MIDDAY THURSDAY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: HIGH A BROAD NEGATIVELY-TILTED TROF CURRENTLY ANCHORING THE NORTHEASTERN CONUS WILL SHIFT EASTWARD EARLY THIS MORNING AND DEVELOP INTO A CLOSED LOW OFFSHORE. IN GENERAL THE MODELS ARE VERY CLOSE TO ONE ANOTHER SO WILL FAVOR A GENERAL MODEL COMPROMISE FOR THIS SYSTEM. ...PAIR OF SYSTEMS MOVING IN TANDEM TOWARD THE UPPER GREAT LAKES/OH VALLEY...RESPECTIVELY... ...ASSOCIATED SURFACE LOWS MARCHING EASTWARD... PRELIMINARY PREFERENCE: BLEND OF THE 00Z NAM/GFS WITH THE 12Z ECMWF ENSEMBLE...MORE TOWARD THE 00Z NAM FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE MODELS DEPICT SPLIT FLOW IN PLACE WITH A PAIR OF OF SYSTEMS SLIDING EASTWARD WHILE BEING NEARLY IN TANDEM. WITH THE NORTHERN STREAM UPPER TROF...THE 12Z ECMWF IS A BIT SLOWER THAN THE CONSENSUS NOTED FURTHER DOWNSTREAM. EVENTUALLY THIS SYSTEM DEVELOPS A CLOSED LOW ACROSS SOUTHERN ONTARIO BY 26/0000Z WHILE THE OTHER BATCH OF ENERGY SHEARS AND MOVES THROUGH THE MID-ATLANTIC FRIDAY EVENING. ENSEMBLE SURFACE LOW PLOTS AGREE THAT A PAIR OF SURFACE WAVES WITH ACCOMPANY THIS SYSTEM WITH THE SOUTHERN MOST LOW DOMINATING. CURRENTLY THE 12Z CMC/21Z SREF MEAN DISAGREE WITH THE STRONGER CLUSTERING IN THE VICINITY OF UPSTATE NY FRIDAY EVENING. EVENTUALLY MODELS DEVELOP A WAVE OFF THE DELMARVA COAST WITH THE 00Z GFS A BIT TOO AGGRESSIVE WITH THE INTENSITY WITH ONLY A FEW 12Z GEFS MEMBERS SUPPORTING SUCH A SOLUTION. INTERESTINGLY THE 12Z ECMWF DIVERGES SIGNIFICANTLY FROM ITS OWN MEAN AS THE LOW MOVES OFFSHORE. THROUGHOUT THE FORECAST PERIOD THE 00Z NAM/GFS APPEAR TO FOLLOW THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS MOST CLOSELY. HOWEVER...WILL WEIGHT AWAY FROM THE 00Z GFS GIVEN ITS AFOREMENTIONED STRONGER SURFACE SOLUTION. ...DEEP UPPER TROF CROSSING THE DESERT SOUTHWEST/FOUR CORNERS REGION THIS WEEKEND... ...POWERFUL SURFACE CYCLONE ACROSS THE MIDDLE OF THE U.S... PRELIMINARY PREFERENCE: BLEND OF THE 12Z CMC/ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE THE FLOW REALLY BEGINS TO AMPLIFY ACROSS THE SOUTHWESTERN CONUS BY EARLY IN THE UPCOMING WEEKEND. THE 00Z NAM/GFS ARE QUICKER EJECTING THIS SYSTEM TOWARD THE FOUR CORNERS REGION WITH CORRESPONDING SUPPORT FROM THE 18Z GEFS/21Z SREF MEANS. MEANWHILE...THE 12Z CMC IS DECIDEDLY SLOWER WITH THE 12Z ECMWF/UKMET SIT SOMEWHERE IN THE CENTER OF THE SPREAD. THE PAST COUPLE OF RUNS OF THE GUIDANCE SHOW THE NCEP MODELS HAVE CONSISTENTLY BEEN ON THE FURTHER EAST SIDE OF THE MODEL ENVELOPE. THE SEPARATION IS ALSO WELL ESTABLISHED IN THE PAST FOUR SPAGHETTI PLOTS ALTHOUGH THE DIFFERENCES HAVE DECREASED. PER COORDINATION WITH WPC MEDIUM RANGE ALONG WITH THE TENDENCY OF MODELS TO BE TOO QUICK TO EJECT CLOSED LOWS OUT OF THE SOUTHWESTERN U.S...WILL FAVOR THE SLOWER SOLUTIONS HERE. THE 12Z ECMWF/CMC FIT THAT BILL AND WILL THROW IN THE 12Z ECMWF ENSEMBLE MEAN TO ACCOUNT FOR THE GROWING MODEL UNCERTAINTY. ...NEXT PACIFIC SYSTEM REACHING THE PACIFIC NORTHWEST BY EARLY SUNDAY... PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE AS THE INITIAL UPPER TROF TRACKS TOWARD THE SOUTHERN HIGH PLAINS BY EARLY SUNDAY...ANOTHER SYSTEM IS EXPECTED TO APPROACH THE PACIFIC NORTHWEST COAST AT THE SAME TIME. THE 540-DM SPAGHETTI PLOT SHOWS ENOUGH SPREAD IN THE GUIDANCE THAT A COMBINATION OF THE MEANS WILL BE PREFERRED. WILL TAKE A SPLIT BETWEEN THE 18Z GEFS MEAN AND 12Z ECMWF ENSEMBLE MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... RUBIN-OSTER