MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 107 PM EDT FRI APR 11 2014 VALID APR 11/1200 UTC THRU APR 15/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...WEAK SHORTWAVE CROSSING LOWER NEW ENGLAND EARLY SATURDAY... ...DIFFUSE SURFACE LOW TRACKING THROUGH THE MID-ATLANTIC... PRELIMINARY PREFERENCE: A NON-00Z UKMET MODEL CONSENSUS FORECAST CONFIDENCE: ABOVE AVERAGE GUIDANCE IS IN AGREEMENT THAT A QUICK MOVING IMPULSE WILL EJECT FROM THE UPPER MIDWEST TOWARD LOWER NEW ENGLAND DURING THE NEXT 24 HOURS. THE 00Z UKMET IS SLIGHTLY AHEAD OF THE MODEL CONSENSUS THROUGH 12/0600Z WHICH LEADS TO A MORE NORTHEASTWARD POSITION OF THE WEAK SURFACE LOW CROSSING COASTAL NEW ENGLAND. GIVEN THIS ASSESSMENT...WILL FAVOR A NON-00Z UKMET SOLUTION. ...MID-LEVEL IMPULSE/ASSOCIATED SURFACE LOW AFFECTING THE NORTHERN PLAINS/UPPER MIDWEST ON SATURDAY... PRELIMINARY PREFERENCE: BLEND OF THE 00Z CMC/ECMWF FORECAST CONFIDENCE: AVERAGE AN ELONGATED AXIS OF ENERGY SLIPPING DOWN FROM WESTERN CANADA WILL SHIFT EASTWARD THROUGH THE DAKOTAS AND UPPER MIDWEST EARLY SATURDAY. THIS FLAT MID-LEVEL WAVE IS FORECAST TO ALLOW THE DEVELOPMENT OF A SURFACE LOW WITH LITTLE TO NO CHANGE IN STRENGTH EXPECTED. THE 12Z NAM/09Z SREF MEAN ARE CURRENTLY THE FASTEST SOLUTIONS WHILE THE 00Z CMC/UKMET/ECMWF AND 00Z ECMWF ENSEMBLE MEAN AGREEING ON A SLIGHTLY SLOWER PROGRESSION. THE 00Z GEFS MEMBERS VIA THE ENSEMBLE LOW PLOTS AGREE WITH THE NAM/SREF MEAN IDEA WHILE THE 00Z CMC/ECMWF ENSEMBLE MEMBERS FAVOR THE MORE WESTERN SOLUTION. THE PLOT SHOWS A STRONGER CONSOLIDATION OF SOLUTIONS WITH THE WESTERN CAMP SO THE PREFERENCE WILL LEAN TOWARD THE 00Z CMC/ECMWF. ...SHEARING WAVE MOVING ACROSS THE RED RIVER OF TX/OK BY 12/1200Z... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: AVERAGE A SHORTWAVE MINIMALLY VISIBLE ON WATER VAPOR IMAGERY IS FORECAST TO TRACK TOWARD THE FOUR CORNERS REGION EVENTUALLY REACHING THE RED RIVER BY EARLY SATURDAY. GUIDANCE ALL DEPICT THIS FEATURE SHEARING OUT DURING THIS EVOLUTION WITH SOME MODEL SPREAD EVIDENT BY 13/0000Z IN THE VICINITY OF THE MO VALLEY. WPC WILL FAVOR A GENERAL MODEL COMPROMISE TO AVERAGE OUT ALL THESE SMALLER-SCALE DIFFERENCES. ...SYSTEM SLIDING FROM THE UPPER INTERMOUNTAIN WEST TO THE SOUTHERN PLAINS SATURDAY THROUGH MONDAY... PRELIMINARY PREFERENCE: BLEND OF THE 00Z CMC/ECMWF WITH THE 00Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE AS THE INITIAL BATCH OF ENERGY TRACKS TOWARD THE NORTH-CENTRAL CONUS...ANOTHER SYSTEM IS FORECAST TO SLIDE SOUTHWARD FROM WESTERN CANADA INTO THE UPPER INTERMOUNTAIN WEST BY EARLY SATURDAY. MODELS INDICATE THIS SHORTWAVE WILL EVENTUALLY TURN SOUTHEASTWARD DURING THE WEEKEND REACHING THE SOUTHERN PLAINS BY MONDAY. THE GUIDANCE VARY WITH HOW FAR SOUTHWEST THE SYSTEM WILL TRACK ACROSS THE INTERMOUNTAIN WEST WITH THE 12Z GFS BEING PLACED THE FURTHEST EAST. THIS GFS SOLUTION CONTRADICTS ITS 06Z GEFS MEAN WHICH IS FURTHER WEST AND MORE ALONG THE LINES OF THE OTHER GUIDANCE. BY 14/0000Z...THE 00Z UKMET BECOMES QUICKER THAN THE ENSEMBLE MEANS WHICH IS SIMILAR TO ITS BEHAVIOR IN THE RUN YESTERDAY. MEANWHILE...THE 12Z GFS CONTINUES TO BECOME FASTER AND AHEAD OF ANY AVAILABLE PIECE OF GUIDANCE. THE 00Z CMC/ECMWF SHOW THE STRONGEST AGREEMENT WITH THE ENSEMBLE MEANS SO WILL FAVOR THEIR SOLUTIONS AND THROW IN THE ENSEMBLE MEAN GIVEN THE GROWING SPREAD LATE IN THE PERIOD. ...CLOSED LOW REACHING THE CA COAST BY 12/0000Z... ...STRONG COLD FRONT/SURFACE WAVES RACING THROUGH THE MS RIVER VALLEY... PRELIMINARY PREFERENCE: THROUGH DAY 2: BLEND OF THE 12Z NAM WITH THE 00Z ECMWF/UKMET...DAY 3...BLEND OF THE ENSEMBLE MEANS FORECAST CONFIDENCE: INITIALLY AVERAGE...BECOMING LOW A WELL PRONOUNCED CLOSED LOW WILL APPROACH THE SOUTHERN/CENTRAL CA COAST BY THIS EVENING WITH THE SYSTEM EVENTUALLY EVOLVING INTO MORE OF AN OPEN WAVE THEREAFTER. THERE APPEARS TO BE A BIT MORE SPREAD IN THE MODELS TODAY VERSUS THE CYCLES YESTERDAY WITH THE 12Z GFS BECOMING QUICKER BY LATER IN THE WEEKEND. LIKE PREVIOUS RUNS OF THE CMC...THE 00Z RUN TODAY REMAINS SLOWER THAN ALL OTHER MODELS. SITTING IN THE MIDDLE OF THE SPREAD ARE THE 12Z NAM AND 00Z ECMWF/UKMET. GIVEN THE FORECAST INVOLVES A CUT-OFF LOW EJECTING OUT OF THE SOUTHWESTERN U.S...WILL NOT FAVOR SOLUTIONS THAT ARE TOO QUICK GIVEN THE TENDENCY FOR THESE SYSTEMS TO COME OUT SLOWER. THIS DISMISSES THE 12Z GFS AT THIS POINT IN TIME. BY EARLY NEXT WEEK...THE SPEED OF THE FRONTAL BOUNDARY RACING THROUGH THE MS RIVER VALLEY AND INTO THE OH/TN VALLEYS BECOMES RATHER UNCERTAIN. THE 00Z UKMET CATCHES UP TO THE 12Z GFS WHILE THE 12Z NAM ENDS SLOWER THAN THE ALREADY SLUGGISH 00Z CMC. THROUGH DAY 2 A BLEND OF THE 12Z NAM WITH THE 00Z ECMWF/UKMET WILL SUFFICE. BEYOND THIS PERIOD...ENSEMBLE MEANS APPEAR TO BE THE WAY TO GO AS THEY ARE IN MUCH CLOSER AGREEMENT THAN THE DETERMINISTIC MODELS. ...MEAN UPPER TROF ANCHORING THE NORTHEASTERN PACIFIC BY EARLY NEXT WEEK... PRELIMINARY PREFERENCE: BLEND OF THE 06Z GEFS/09Z SREF/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: LOW WITH A BROAD UPPER TROF SETTING UP OVER THE CENTRAL TO EASTERN U.S. BY EARLY NEXT WEEK...A LARGE RIDGE WILL BE FEATURED ALONG THE WESTERN U.S. FURTHER UPSTREAM ANOTHER PACIFIC SYSTEM IS FORECAST TO AFFECT THE PACIFIC NORTHWEST ON MONDAY. THE MODEL SPREAD IS UNUSUALLY HIGH HERE WITH ALL ENSEMBLE MEANS BEING SIGNIFICANTLY SLOWER THAN THE FASTER DETERMINISTIC RUNS. THE 12Z NAM/GFS AND 00Z ECMWF AGREE SOMEWHAT WITH ONE ANOTHER WHILE THE 00Z CMC/UKMET ARE OFF TO THE RACES. HOWEVER...ALL THESE DETERMINISTIC RUNS ARE PROGRESSIVE COMPARED TO THE MORE WESTERN MEANS. GIVEN THE VAST SPREAD AT HAND...HAVE NO CHOICE BUT TO UTILIZE THE WELL CLUSTERED ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... RUBIN-OSTER