MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 234 AM EDT SAT APR 11 2015 VALID APR 11/0000 UTC THRU APR 14/1200 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. ...PRONOUNCED UPPER TROF CROSSING THE NORTHEASTERN U.S. EARLY SATURDAY... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE A DEEP UPPER TROF CURRENTLY MOVING TOWARD THE LOWER GREAT LAKES WILL CONTINUE MARCHING EASTWARD WITH HEIGHT FALLS EXPECTED TO EXIT THE NORTHEASTERN CONUS. THE 00Z CMC HAS ADJUSTED ITS SOLUTION ACCORDINGLY TO MATCH THE OTHER GUIDANCE. THUS...A GENERAL MODEL COMPROMISE IS WARRANTED. ...WEAK SHORTWAVE MOVING THROUGH THE DAKOTAS ON SATURDAY MORNING... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE WATER VAPOR IMAGERY TONIGHT SHOWED A VERY WEAK SHORTWAVE MOVING TOWARD THE NORTHERN HIGH PLAINS. THERE IS FAIRLY STRONG AGREEMENT WITH THE SYSTEM REACHING SOUTHWESTERN ONTARIO BY 12/0000Z SO A GENERAL MODEL COMPROMISE IS RECOMMENDED. ...STRONG CLOSED LOW TRACKING FROM BAJA CA TO THE SOUTHERN PLAINS... PRELIMINARY PREFERENCE: A COMPROMISE BETWEEN THE 00Z NAM/GFS/ECMWF FORECAST CONFIDENCE: AVERAGE A COMPACT UPPER LOW INITIALLY IN THE VICINITY OF 30N/130W WILL RACE EASTWARD REACHING THE CENTRAL COAST OF BAJA CA BY LATE SATURDAY NIGHT. A MAJORITY OF THE MODELS KEEP THE SYSTEM AS A STRONG CLOSED LOW BARRELING TOWARD FAR WEST TX BY SUNDAY EVENING. AS WAS THE CASE YESTERDAY...THE BIGGEST OUTLIER IS THE 00Z UKMET WHICH IS MUCH SLOWER. LIKEWISE...THE 21Z SREF MEAN SUPPORTS THIS SLOWER SOLUTION BUT PLAN ON STAYING AWAY FROM THESE IDEAS. ON THE OTHER SIDE OF THE ENVELOPE IS THE 00Z CMC WHICH IS QUICKER AND LOOKS QUITE SIMILAR TO THE 00Z RUN THE NIGHT PREVIOUS. OVERALL...THERE IS SUFFICIENT AGREEMENT AMONG THE 00Z NAM/GFS/ECMWF. WILL FAVOR A COMPROMISE BETWEEN THESE SOLUTIONS HERE. ...AMPLIFIED FLOW MOVING ALONG THE NORTHERN TIER OF THE CONUS THROUGHOUT THE PERIOD... ...ASSOCIATED COLD FRONT/SURFACE CYCLONE... PRELIMINARY PREFERENCE: BLEND OF THE 00Z NAM/12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE THE NORTHERN BRANCH OF THE JET WILL CONTINUE TO FAVOR AMPLIFIED/PROGRESSIVE FLOW DURING THE NEXT FEW DAYS. A STRONG BAND OF HEIGHT FALLS WILL MIGRATE EASTWARD FROM THE PACIFIC NORTHWEST TOWARD THE UPPER MIDWEST CARRYING A PRONOUNCED COLD FRONT INTO THE CENTER OF THE COUNTRY. THE 00Z GFS/UKMET SEEM TO BE THE FASTEST PLAYERS HERE WITH THE UKMET KEEPING ITS THEME FROM THE PREVIOUS NIGHT. ENSEMBLE MEANS CLUSTER WELL AND SUGGEST THE 00Z GFS/UKMET ARE INDEED TOO QUICK. THE 00Z NAM/12Z ECMWF OFFERS SUPPORT FOR THE 12Z ECMWF ENSEMBLE MEAN WHILE THE 00Z ECMWF TRENDED MORE AMPLIFIED LEADING TO THE DEVELOPMENT OF A SURFACE WAVE BY MONDAY MORNING. NOT COMPLETELY SOLD ON THIS TREND YET SO WILL MAINTAIN THE PREVIOUS PREFERENCE HERE. ...NEXT PACIFIC SYSTEM REACHING THE PACIFIC NORTHWEST BY EARLY NEXT WEEK... ...ACCOMPANYING STRONG SURFACE LOW... PRELIMINARY PREFERENCE: BLEND OF THE 00Z NAM/ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE AN AREA OF THE MAP WHICH CONTINUES TO EXHIBIT THE GREATEST AMOUNT OF UNCERTAINTY. A SERIES OF SURFACE SOLUTIONS ARE NOTED ACROSS THE EASTERN PACIFIC WITH SIGNIFICANT DIFFERENCES IN THE INTENSITY OF LOW PRESSURE THERE. DETERMINISTIC MODELS SHOW A LOT OF VARIABILITY WITH THE 00Z GFS CONTINUING TO BE THE DEEPEST AS IT PHASES A PAIR OF SHORTWAVES UPSTREAM. THERE IS EVEN DISAGREEMENT AMONG THE ENSEMBLE MEANS AS THE 12Z ECMWF ENSEMBLE MEAN HAS TRENDED SLOWER RELATIVE TO YESTERDAY. LOOKING ALOFT...BY 14/1200Z...ALL MODELS SHOW PRONOUNCED HEIGHT FALLS WORKING THEIR WAY TOWARD THE CENTRAL GREAT BASIN. THE INITIALLY MORE AMPLIFIED SOLUTIONS IN THE 00Z GFS/12Z UKMET HAVE BEEN JOINED BY A MAJORITY OF THE 00Z GUIDANCE. SUCH TRENDS HAVE NOW MOVED AWAY FROM THE FLATTER ENSEMBLE MEANS. THERE ARE PLENTY OF ENSEMBLE MEMBERS WITHIN THE SPAGHETTI PLOTS SO SUPPORT SUCH AMPLIFICATION. HOWEVER...GIVEN THE HIGH AMOUNT OF UNCERTAINTY...WILL AT LEAST INCLUDE SOME ENSEMBLE MEAN INTO THE MIX. WILL CONTINUE THE PREVIOUS PREFERENCE EXCEPT THIS WILL FEATURE THE 00Z ECMWF RATHER. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER