MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 314 AM EDT WED APR 16 2014 VALID APR 16/0000 UTC THRU APR 19/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ============================================== 00Z MODEL EVALUATION AND PREFERENCES ============================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ============================================== ...UPPER MIDWEST STORM LATER APPROACHING THE NORTHEAST IN A WEAKENED STATE... MIDWEST PREFERENCE: BLEND OF 00Z NAM/GFS/ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE NORTHEAST PREFERENCE: BLEND OF 00Z NAM/ECMWF/UKMET CONFIDENCE: SLIGHTLY BELOW AVERAGE THE NAM/GFS/ECMWF FORM A STRONG CLUSTER OF OPERATIONAL MODELS...SUPPORTED BY THE ENSEMBLE MEANS...PARTICULARLY DURING THE EARLY LIFE OF THIS SYSTEM WHEN IT WILL PRODUCE IMPACTFUL SNOWFALL ACROSS THE UPPER MIDWEST. SEE THE HEAVY SNOW DISCUSSION...QPFHSD FROM THE WPC WINTER WEATHER DESK FOR SNOWFALL DETAILS. 00Z RUNS TRENDED DEEPER ALOFT ON DAY 1. THIS HELPED PULL THE NAM/GFS SURFACE TROUGH BACK WEST AND INTO BETTER AGREEMENT WITH THE MORE CONSISTENT ECMWF. IN PLAN VIEW 850-700 MB PLOTS THERE APPEARS TO BE STRONG CONSENSUS REGARDING THERMAL PROFILES. FOLLOWING THIS INITIAL LEAD SHORTWAVE EVENT...A LARGER SCALE TROUGH WILL HAVE BECOME ESTABLISHED ALONG THE INTERNATIONAL BORDER...AND WILL THEN SINK/SWING EAST TO SOUTHEASTWARD. AT THE SURFACE THERE ARE RELATIVELY MINOR BUT NOTICEABLE DIFFERENCES BETWEEN THE NAM/GFS/ECMWF. ALOFT...DIFFERENCES ARE MAGNIFIED. THE GFS IS CERTAINLY ONE OF THE DEEPEST SOLUTIONS AT 500 MB. THE 00Z ECMWF TRENDED MUCH MORE FLAT AND PROGRESSIVE...AND IS SUPPORTED BY THE UKMET AT THE SURFACE AND ALOFT. THE NAM IS SLOW/DEEP AS THE GFS...AND MAY STILL BE BLENDED REASONABLY WITH THE MORE PROGRESSIVE SOLUTIONS. ...SOUTHERN STREAM WAVE AMPLIFYING ALONG THE GULF COAST... PREFERENCE: BLEND OF 12Z ECMWF/UKMET CONFIDENCE: SLIGHTLY BELOW AVERAGE A SHORTWAVE DIPPING INTO THE SOUTHERN PLAINS ON DAY 1 WILL PHASE WITH AN ACTIVE SUB-TROPICAL JET TO ALLOW THE FORMATION OF A BROAD BUT ORGANIZED BAROCLINIC SYSTEM IN THE GULF OF MEXICO. THERE IS AN INCREASING MODEL SIGNAL FOR HEAVY RAIN IN FLORIDA THURSDAY AND FRIDAY. THE MODELS VARY IN THEIR DEGREE OF PHASING AND THE DEPTH THAT THE GULF SYSTEM ATTAINS. GENERALLY THE ECMWF/UKMET/CANADIAN FORECAST A SIMILAR SYSTEM CONCEPTUALLY...ALTHOUGH THE CANADIAN IS ON THE WEAK SIDE. THE PAST FEW RUNS OF THE NAM HAVE HANDLED THIS SYSTEM IN A REASONABLE FASHION...BUT ITS SOLUTION IS ONE OF THE DEEPEST AMONG OPERATIONAL MODELS AND THE ENSEMBLES. THE PERFORMANCE OF THE NAM REGARDING LARGE SCALE SYSTEMS AT THIS LATITUDE IS NOT USUALLY THE BEST...SO WE WILL NOT YET INCLUDE IT IN OUR PREFERENCE HERE...BUT WILL NOT RULE IT OUT EITHER...ESPECIALLY WITH THE ECMWF TRENDING STRONGER. RECENT GFS RUNS HAVE BEEN FAST AND UNDER-DEVELOPED. ...TROUGH CROSSING THE NORTHWEST AND REACHING THE NORTHERN PLAINS THU/FRI... PREFERENCE: BLEND OF 00Z ECMWF/UKMET/CANADIAN CONFIDENCE: AVERAGE THE MODELS PREDICT SIMILAR STRENGTH FOR THIS PROGRESSIVE SHORTER WAVELENGTH SYSTEM. GIVEN TRENDS IN THE UKMET AND CANADIAN...THEY NOW CLUSTER FAIRLY WELL WITH RESPECT TO THE LATITUDE AT WHICH THE EMBEDDED VORTICITY MAXIMUM WILL FORM...ALTHOUGH THE NAM DOES NOT FORM A CLOSED CIRCULATION. THE MAIN DIFFERENCE NOW IS TIMING...WITH THE GFS/NAM BEING ON THE SLOW SIDE. THE SLOWER NCEP SOLUTIONS ARE LIKELY RELATED IN PART TO THEIR DEEPER SOLUTION DOWNSTREAM OVER THE GREAT LAKES WHICH PROPS UP SHORTWAVE RIDGING FARTHER WEST ACROSS THE PLAINS ON THU/FRI. ...SYSTEM ENTERING THE SOUTHWEST U.S... PREFERENCE: BLEND OF THE OPERATIONAL MODELS CONFIDENCE: AVERAGE THE MODELS WILL NOT APPEAR COMPLETELY IN PHASE WITH ONE ANOTHER AT 500 MB...GIVEN THE BROAD WAVELENGTH AND WEAK GRADIENTS. DIFFERENCES AT THE SURFACE TO 700 MB ARE MUCH LESS PRONOUNCED. THE UKMET AND CANADIAN TRENDED TOWARD OUR FAVORED SOLUTION BASED ON THE ENSEMBLE SPREAD AND MORE CONSISTENT GFS/ECMWF. THERE IS NOW NO STRONG PREFERENCE...ALTHOUGH SOME MEANINGFUL SMALL SCALE DIFFERENCES MAY STILL ARISE IN FUTURE MODEL CYCLES. ...PACIFIC NORTHWEST LATE FRIDAY... PREFERENCE: BLEND OF THE OPERATIONAL MODELS...EXCLUDING THE 00Z ECMWF CONFIDENCE: AVERAGE THE IMPACTS FROM THIS SYSTEM WILL LIKELY HOLD OFF UNTIL DAY 4. THROUGH DAY 3 THERE IS STRONG MODEL AGREEMENT ON THE LARGE SCALE. WITH ITS 00Z RUN THE CANADIAN IMPROVED UPON ITS TRACK OF THE SURFACE LOW/FRONT. THE ECMWF...ON THE OTHER HAND...TRENDED FASTER ALOFT...WITH A MORE STRONGLY PRONOUNCED NEGATIVE TILT BY DAY 3. THIS IS A SLIGHT DIFFERENCE...BUT FOR NOW WE WILL KEEP OUR PREFERENCE TIED TO THE NAM AND GLOBAL MODEL CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE