MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1154 AM EST SUN FEB 15 2015 VALID FEB 15/1200 UTC THRU FEB 19/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ POWERFUL UPPER LOW AND SURFACE LOW DEPARTING THE CANADIAN MARITIMES THROUGH EARLY MON MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS NOW SHOW SIMILARLY WITH THIS SYSTEM. PAIR OF SHORTWAVES DIGGING DOWN THROUGH THE WESTERN U.S. TODAY/MON BAJA ENERGY SHEARING OUT TO THE EAST ACROSS THE GULF COAST TUE A.M. SURFACE LOW ACROSS THE GULF COAST STATES ON MON SURFACE LOW TRACKING OFF THE NORTHEAST COAST ON TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z UKMET AND 00Z ECMWF CONFIDENCE: BELOW AVERAGE AFTER SEVERAL ENSEMBLE CYCLES OF A WEAKENING TREND TOWARD THE FLATTER ENSEMBLE CONSENSUS...A MARKED SHIFT IN THE 00Z/15 ENSEMBLE PACKAGE HAS SHIFTED BACK TO THE PREVIOUS EDGE OF THE ENSEMBLE SPREAD REGARDING A SHORTWAVE NEAR THE FOUR CORNERS REGION. THE CURRENT ENSEMBLE SPAGHETTI PLOTS SHOW SIMILAR SPREAD TO YESTERDAY...BUT THEY ARE JUST DISPLACED TOWARD THE MORE AMPLIFIED SIDE OF THE CURRENT MODEL SPREAD. LOOKING AT THE 500 MB SHORTWAVE FORECAST TO BE TRACK FROM THE FOUR CORNERS TO THE TX/OK PANHANDLES TONIGHT...THE 12Z NAM/GFS ARE A BIT FLATTER THAN EVEN SHORT TERM FORECASTS FROM THE 00Z NMM/ARW...13Z HRRR...14Z RAP. HOWEVER...THESE SHORT TERM MODELS SUPPORT A 00Z ECMWF/UKMET BLEND THROUGH THE BEGINNING OF THE DAY 1 PERIOD. **ALL** OF THE DETERMINISTIC GUIDANCE HAS TRENDED SHARPER WITH THIS FEATURE SINCE YESTERDAY...AND MAY STILL BE TRYING TO CATCH UP TO CURRENT OBSERVATIONS. DUE TO THE CHANGES SEEN AND TRENDS...WE WILL BE LEANING TOWARD THE MORE AMPLIFIED CAMP...BEST SUPPORTED BY THE 00Z ECMWF/UKMET...WHICH IS AGREED UPON BY THE 00Z ECMWF MEAN. CONFIDENCE REMAINS LOW GIVEN THE INSTABILITY IN THE MODELS AND SIGNIFICANT RUN TO RUN CHANGES. SURFACE LOW TRACKING NWD OFF THE MID-ATLANTIC COAST ON WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z UKMET AND 00Z ECMWF CONFIDENCE: BELOW AVERAGE THE GUIDANCE IS SHOWING YET ANOTHER SURFACE LOW TRACKING NWD THROUGH THE WRN ATLANTIC ON WED...BUT THE LATEST ENSEMBLE SCATTER LOW PLOTS HAVE THIS LOW ANYWHERE BETWEEN 100 AND 500 MILES EAST OF CAPE HATTERAS 12Z/18...WED MORNING. THIS WAVE IS PARTIALLY TIED TO A MID-LEVEL SHORTWAVE MENTIONED ABOVE...WHICH IS FORECAST TO BE NEAR THE SOUTHEAST U.S. WED MORNING. SIMILAR TO THE FIRST SHORTWAVE REFERENCED IN THE ABOVE SECTION...THIS WAVE HAS BEEN TRENDING SLOWER/SHARPER BY WED MORNING OFF OF THE SOUTHEAST COAST. IT IS EXPECTED THIS LOW SHOULD TRACK FAR ENOUGH AWAY FROM THE COAST TO NOT HAVE MUCH IMPACT ON LAND...BUT A 00Z ECMWF/UKMET BLEND WILL BE PREFERRED FOR NOW...STAYING CONSISTENT WITH THE ABOVE SECTION. AGAIN...GIVEN SIGNIFICANT RUN TO RUN CHANGES IN THE MODELS AND HIGH MODEL SPREAD...CONFIDENCE IS LOW. SHORTWAVE TROUGH REACHING THE NORTHWEST ON WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM...12Z GFS...00Z ECMWF COMPROMISE CONFIDENCE: AVERAGE THE MODELS DEPICT A PACIFIC SHORTWAVE BREAKING DOWN THE STRONG RIDGE OFFSHORE THE WEST COAST BY TUE AND THEN MOVING TOWARD THE NORTHWEST U.S. BY WED. THE 00Z CMC IS A SLOW OUTLIER SOLUTION. THE 00Z UKMET TRENDED A LITTLE SLOWER BUT IS STILL A BIT AHEAD OF THE WELL CLUSTERED NAM/GFS/ECMWF...WITH THE LATEST ENSEMBLE MEANS AGREEING WITH THE MIDDLE GROUND NAM/GFS/ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO