MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 AM EDT THU MAR 12 2015 VALID MAR 12/0000 UTC THRU MAR 15/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z MODEL GUIDANCE ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...SLOW MOVING UPPER LOW LIFTING OUT OF THE SOUTHERN PLAINS... ...SURFACE WAVE CROSSING THE OZARKS BY MIDDAY FRIDAY... FINAL PREFERENCE: BLEND OF THE 00Z ECMWF/UKMET FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE AN ELONGATED UPPER LOW STRETCHING FROM THE SOUTHERN PLAINS DOWN ACROSS THE LOWER RIO GRANDE AND INTO EASTERN MX IS COMPROMISED OF A NUMBER OF SMALLER-SCALE SHORTWAVES. THE SYSTEM WILL CONTINUE TO HAVE ACCESS TO ABUNDANT GULF MOISTURE WITH THE BLENDED-TPW PRODUCT SHOWING ORIGINS TO SOUTH OF 20N. A MULTI-DAY HEAVY RAINFALL EPISODE IS IN THE FORECAST ACROSS THE LOWER MS VALLEY UP INTO THE TN/OH RIVER VALLEYS. THE OVERALL FORECAST IS NOT TRIVIAL GIVEN THE MULTITUDE OF SMALL-SCALE FEATURES INTERACTING WITH ONE ANOTHER IN THE SYNOPTIC PATTERN. INSTEAD OF FOCUSING ON THE COMPLEX MID-LEVEL PATTERN...WILL FOLLOW THE PATH OF THE SURFACE WAVE AND THE ASSOCIATED FRONTAL ZONE. AS OF THE 03Z WPC SURFACE ANALYSIS...A 1014-MB LOW WAS LOCATED IN THE WEST-CENTRAL GULF OF MX. MODELS FORECAST THIS CYCLONE TO LIFT NORTHWARD IN TIME SPREADING THE AXIS OF HEAVY RAINFALL FARTHER INLAND. THE TREND IN THE 00Z GUIDANCE IS TO STRENGTHEN THIS LOW CENTER WITH THE 00Z ECMWF/UKMET NEARLY IN STRIDE WITH ONE ANOTHER. MEANWHILE...THE 00Z GFS HAS TRENDED A BIT TO THE EAST WHICH CARRIES ITS STRONGER AXIS OF LOW-LEVEL CONVERGENCE TO A POSITION EAST OF THE STRONGER CONSENSUS. WILL SLIGHTLY ADJUST THE PREFERENCE TO ACCOUNT FOR THESE TRENDS AND RECOMMEND UTILIZING THE 00Z UKMET OVER THE 00Z NAM. THIS LEADS TO A BLEND OF THE 00Z ECMWF/UKMET WITH CONFIDENCE REMAINING SOMEWHAT BELOW AVERAGE GIVEN THE SLEW OF MESOSCALE FEATURES TO CONTEND WITH. ...PROGRESSIVE SHORTWAVE MOVING THROUGH MAINE IN THE NEXT FEW HOURS... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: HIGH WATER VAPOR IMAGERY EARLY THIS MORNING SHOWED A WELL-DEFINED SHORTWAVE CURRENTLY APPROACHING THE ST. LAWRENCE RIVER VALLEY. THE PROGRESSIVE NATURE OF THIS SYSTEM WILL CARRY IT QUICKLY EASTWARD AND EXITING INTO THE CANADIAN MARITIMES BY 12/1800Z. MODELS ARE IN SUFFICIENT AGREEMENT WHICH WARRANTS A GENERAL MODEL COMPROMISE. ...PACIFIC SYSTEM CURRENTLY MOVING THROUGH THE INTERMOUNTAIN WEST... ...EVENTUAL LOBE OF ENERGY DROPPING DOWN TO MX FRIDAY ONWARD... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE HEIGHT FALLS CURRENTLY CROSSING THE WESTERN U.S. IS SPREADING A BROAD AREA OF LIGHT PRECIPITATION TO THE REGION. THIS BROAD UPPER TROF IS EXPECTED TO SPLIT WITH SOME OF THE SHORTWAVE ENERGY MOVING TOWARD THE NORTHERN HIGH PLAINS WHILE A BULK OF THE SYSTEM DROPS DOWN TOWARD THE MEXICAN BORDER. WHILE VARYING SOMEWHAT WITH TIMING...ALL OF THE DETERMINISTIC MODELS AGREE WITH THE ENSEMBLES SUGGESTING THE SYSTEM WILL CLOSE OFF AROUND 25N LATITUDE OVER WESTERN MX. DEPENDING UPON THE MODEL...THIS UPPER LOW REALLY GETS PINCHED OFF FROM THE PREVAILING WESTERLIES AS IT SPINS SOUTH OF BAJA CA. AS MODELS AGREE ON THE GENERAL PROGRESSION OF THIS FEATURE...A GENERAL MODEL COMPROMISE IS A REASONABLE PREFERENCE HERE. ...STRONG SYSTEM CROSSING THE GREAT LAKES ON SATURDAY... ...ASSOCIATED SURFACE CYCLONE AND FRONTAL ZONE... FINAL PREFERENCE: BLEND OF THE 00Z ECMWF/12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE THE GUIDANCE SHOW A SYSTEM GRADUALLY AMPLIFYING ACROSS THE NORTHERN TIER OF THE COUNTRY WITH THE SHORTWAVE BECOMING PARTICULARLY WRAPPED UP OVER THE UPPER GREAT LAKES BY 14/1200Z. IT APPEARS THE MODELS HAVE BEGUN TRENDING TOWARD A MORE DEVELOPED SYSTEM WHICH STUNTS THE EASTWARD PROGRESSION OF THE SURFACE LOW WHILE MAINTAINING A DEEPER SOLUTION. DEFINITELY NOT IN FAVOR OF THE FASTER 21Z SREF MEAN WHICH SHOWS MORE OF AN OPEN WAVE QUICKLY RACING EASTWARD. THE OVERALL PATTERN ALOFT...WHILE AMPLIFIED...SHOWS QUITE A BIT OF SPREAD IN TIMING PER THE 552-DM SPAGHETTI PLOTS. THE 12Z ECMWF ENSEMBLE MEMBERS AT LEAST SHOW A BIT MORE CLUSTERING IN THEIR SOLUTIONS RELATIVE TO OTHER ENSEMBLES WHICH SHOW MORE SPREAD ON THE SPAGHETTI PLOT. CONSIDERING THE 00Z MODEL TRENDS...FORTUNATELY THE 00Z CMC/UKMET HAVE STAYED THE COURSE FAVORING DEEPER SOLUTIONS WHICH SUPPORTS THE IDEA OF THE 00Z ECMWF AND 12Z ECMWF ENSEMBLE MEAN. RATHER THAN COMPLICATE THE PREFERENCE WITH ADDITIONAL SOLUTIONS...WILL MAINTAIN THE PREVIOUS SUGGESTION WHILE INCORPORATING THE LATEST ECMWF. HOWEVER...PLAN ON GIVING A LITTLE MORE WEIGHT TO THE ENSEMBLE MEAN GIVEN THE SPREAD IN THE ENSEMBLE LOW PLOTS OFF THE NEW ENGLAND COAST. SOME OF THE SOLUTIONS ARE QUITE INTENSE WITH SURFACE PRESSURES IN MILLIBARS WELL INTO THE 990S. ...SERIES OF LOW-AMPLITUDE IMPULSES AFFECTING THE PACIFIC NORTHWEST LATE IN THE PERIOD... FINAL PREFERENCE: BLEND OF THE 00Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: LOW THE FLOW BECOMES A BIT MORE ZONAL IN NATURE ACROSS THE NORTHWESTERN U.S. BY FRIDAY AND INTO THE WEEKEND. MODELS SHOW A COMPLEX ARRAY OF SHORTWAVES MOVING TOWARD THE COASTLINE ON SATURDAY WITH THE GUIDANCE SCATTERED ABOUT. THIS UNCERTAINTY SHOWS UP QUITE WELL IN THE 552-DM SPAGHETTI PLOT. THE LOW CONFIDENCE FORECAST CONTINUES AFTER SEEING ALL OF THE 00Z MODEL GUIDANCE. LITTLE TO NO DEFINABLE TREND ARE NOTED WITH SOLUTIONS SHOWING A VARIETY OF TIMING/AMPLITUDE DIFFERENCES. REGARDLESS OF THE MODEL...STRONG ONSHORE FLOW WILL MAKE FOR QUITE THE HEAVY PRECIPITATION EVENT OVER THE PACIFIC NORTHWEST AND UPPER INTERMOUNTAIN WEST. THE SAFE BET IS TO COMBINE THE 00Z GEFS/12Z ECMWF ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER