MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 PM EDT WED AUG 12 2015 VALID AUG 12/1200 UTC THRU AUG 16/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...QUASI-STATIONARY UPPER LOW SPINNING OFF THE NORTHERN CA COAST... ...EVOLVING INTO AN OPEN WAVE SOLUTION LATE IN THE PERIOD... FINAL PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET FORECAST CONFIDENCE: AVERAGE WATER VAPOR IMAGERY THIS AFTERNOON SHOWED A BROAD CYCLONIC CIRCULATION ANCHORING ROUGHLY 40N/130W. ENHANCED MOISTURE IN ADVANCE OF THIS CLOSED LOW HAS SPARKED NUMEROUS SHOWERS AND THUNDERSTORMS JUST OFFSHORE OF THE PACIFIC NORTHWEST ALONG WITH INTERIOR LOCATIONS. MODELS AGREE ON THIS SYSTEM BEING NEARLY CUT OFF IN NATURE BEFORE A NORTHERN STREAM KICKER SYSTEM NUDGES IT FORWARD. AT THIS POINT THE UPPER LOW WILL EVOLVE INTO MORE OF AN OPEN WAVE SOLUTION. AS THIS OCCURS...THE GUIDANCE BEGIN TO DIVERGE WITH HOW QUICKLY THIS OCCURS WHICH HAS BEEN A FORECAST ISSUE IN RECENT DAYS. THE DIFFERENT ENSEMBLE SUITES DISAGREE ON THE TIMING WITH THE GEFS/SREF SOLUTIONS BEING QUICKER. THE 12Z NAM/GFS SUPPORT THIS FASTER CAMP BUT THE MULTI-DAY SPAGHETTI PLOT TRENDS FAVOR A MUCH SLOWER IDEA. THE 12Z UKMET DID SEEM TO SPEED UP A TAD AFTER BEING ONE OF THE SLOWER SOLUTIONS IN RECENT MODEL CYCLES. THIS BRINGS THE 12Z UKMET IN MUCH CLOSER AGREEMENT TO THE 12Z ECMWF. PLAN ON FOLLOWING THIS TREND IN THE GUIDANCE AND REMOVE THE 00Z ECMWF ENSEMBLE MEAN FROM THE PREVIOUS SOLUTION GIVEN THE SPREAD HAS NOW DECREASE SOME. WILL RAISE THE CONFIDENCE ACCORDINGLY. ...UPPER TROUGH OVER THE NORTHEASTERN U.S. THROUGH THURSDAY... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A NEGATIVE HEIGHT HEIGHT ANOMALY POSITIONED OVER THE NORTHEASTERN U.S. AND INTO EASTERN CANADA WILL REMAIN IN PLACE FOR THE NEXT COUPLE OF DAYS. THE FORWARD PROGRESSION SHOULD BE STUNTED BY THE BLOCKING DOWNSTREAM RIDGE ACROSS THE OPEN ATLANTIC WITH SHORTWAVES LIFTING INTO THE CANADIAN MARITIMES. AS A WHOLE...THE MODELS ARE CONSISTENT WITH ONE ANOTHER ON THE LARGER SCALE WITH SOME VARIABILITY ON THE FINER SCALES. THE RECOMMENDATION HERE IS A GENERAL MODEL COMPROMISE. ...STALLED MID/UPPER TROUGH ACROSS THE SOUTHEASTERN U.S... ...FRONTAL ZONE/EMBEDDED WAVES... FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE AS THE SYNOPTIC SCALE UPPER TROUGH ACROSS THE NORTHEASTERN U.S. GRADUALLY LIFTS NORTH AND EAST...AN ELONGATED WEAKNESS WILL SETTLE AND STALL IN THE VICINITY OF THE SOUTHEASTERN CONUS. LIKE YESTERDAY...THE 12Z NAM SHOWS MORE AMPLIFICATION IN THE 588-DM HEIGHT CONTOUR WHICH DRAGS SHORTWAVES INTO SOUTHERN FL ON THURSDAY EVENING. ITS DIFFERENCES ALOFT REFLECT AT THE SURFACE WITH THE LOW-LEVEL CONVERGENCE MAXIMA MUCH CLOSER TO THE SOUTHEASTERN U.S. COAST. AS THE SLOW MOVING TROUGH GENTLY LIFTS TOWARD THE NORTHEAST...THE 12Z/00Z CMC/UKMET SHOW A MORE PRONOUNCED SURFACE CIRCULATION OFF THE GA COAST ON 15/0000Z. ENSEMBLE SCATTER LOW PLOTS GENERALLY SHOW THIS BEING A LOW PROBABILITY SOLUTION. WITH THAT SAID...WILL STAY AWAY FROM THE AFOREMENTIONED MODELS AND LEAN IN THE DIRECTION OF THE 12Z GFS/ECMWF. ...SERIES OF MESOSCALE IMPULSES TRAVERSING THE PROMINENT UPPER RIDGE ACROSS THE CENTRAL U.S... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A BROAD UPPER RIDGE CURRENTLY POSITIONED OVER THE SOUTHERN/CENTRAL PLAINS WILL ALLOW A SERIES OF IMPULSES AND ENHANCED MONSOONAL MOISTURE TO WORK ITS WAY NORTHWARD ALONG THE WESTERN FLANK OF THE ANTICYCLONIC FLOW. THESE FEATURES EVENTUALLY WILL SLIDE EAST AND SOUTHEAST AROUND THE UPPER RIDGE. ONE OF THE MORE POTENT DISTURBANCES IS FORECAST TO MOVE FROM NE/SD TOWARD THE MIDDLE MS VALLEY ON THURSDAY EVENING...POTENTIALLY AS A CONVECTIVE COMPLEX. WHAT REMAINS OF THIS SYSTEM SHOULD CROSS THE OZARKS BY 15/0000Z WITH MODEL DIFFERENCES QUITE SMALL. A GENERAL MODEL COMPROMISE APPEARS SUITABLE HERE. ...MID-LEVEL WEAKNESS CENTERED SOMEWHERE BETWEEN THE GULF COAST AND TN VALLEY BY THE WEEKEND... FINAL PREFERENCE: BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE TOWARD THE END OF THE PERIOD...MODELS AGREE ON AN ARRAY OF SHORTWAVES...POSSIBLY AS A CLOSED LOW...MEANDERING ABOUT THE SOUTHERN U.S. AND POINTS NORTHWARD. UNCERTAINTY IS RATHER HIGH WITH EXACTLY WHERE THIS SETS UP SO WILL LEAN TOWARD AN ENSEMBLE MEAN DRIVEN SOLUTION. WILL FAVOR A COMBINATION OF THE 12Z GEFS/00Z ECMWF ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER