MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1210 AM EST TUE DEC 16 2014 VALID DEC 16/0000 UTC THRU DEC 19/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...TROUGH DEVELOPING TOWARD THE SOUTHERN ROCKIES/PLAINS... PREFERENCE: BLEND OF 12Z ECMWF/UKMET OPERATIONAL MODELS CONTINUE TO EXHIBIT A LOT OF SPREAD CONCERNING THE DEPTH OF THE TROUGH EXPECTED TO REACH TEXAS BY FRIDAY MORNING. THE ECMWF ENSEMBLE MEAN...ON THE OTHER HAND...HAS BEEN VERY CONSISTENT...AND IS DEEPER THAN MANY OF THE OPERATIONAL MODELS. THE EXCEPTION IS THE UKMET WHICH IS TYPICALLY DEEP BIASED OVER THE SOUTHWEST U.S. SEE NO REASON TO STRAY FROM THE PREVIOUS PREFERENCE OF A 12Z ECMWF/UKMET BLEND. THE NAM AND GFS ARE GETTING CLOSE...AND FEATURE REASONABLE TIMING...BUT ARE STILL LESS DEEP THAN DESIRED. THE OPERATIONAL ECMWF IS ALSO JUST SLIGHTLY LESS DEEP THAN THE ENSEMBLE MEAN. BLENDING THE ECMWF WITH THE DEEPER UKMET SHOULD YIELD A GOOD CONSENSUS...INCLUDING AT THE SURFACE...WHERE THERE SHOULD BE GREATER RESPONSE AND FALLING PRESSURES ACROSS CENTRAL TEXAS. THE 12Z ECMWF WAS LIKELY TOO SUPPRESSED IN KEEPING THE FRONTAL ZONE OVER SOUTH TEXAS WITH HIGH PRESSURE STRONGLY INTACT TO THE NORTH. ...SOUTHERN/CENTRAL PLAINS LEAD SHORTWAVE... PREFERENCE: 12Z ECMWF AHEAD OF THE DEEPENING SOUTHERN ROCKIES/PLAINS SYSTEM A LEAD SHORTWAVE WILL EJECT ON WED/THU. THE MODELS ARE MORE UNIFORMLY MAINTAINING A WEAK REFLECTION OF THIS WAVE...WHEREAS EARLIER CYCLES FEATURED SOME MODELS THAT WERE DAMPENING THE WAVE ENTIRELY. STILL...THE DEPTH OF THE WAVE IS IN QUESTION...AND THE ECMWF IS PREFERRED AS ITS OVERALL HEIGHT PATTERN IN THE SOUTHERN STREAM IS CLOSEST TO THAT OF OUR PREFERRED SOLUTION. ...MIDWEST/GREAT LAKES/NORTHEAST... PREFERENCE: BLEND OF 00Z GFS MODELS AGREE THROUGH THE TIME WHEN A CYCLONE LIFTING INTO THE GREAT LAKES MERGES WITH A LOW DROPPING DOWN FROM ONTARIO. THEN A SMALL SCALE SHORTWAVE WILL ROTATE AROUND THE BASE OF THE RESULTING LOW. THE MODELS ARE HANDLING THIS SHORTWAVE WITH VARIOUS SPEED AND INTENSITY. CONFIDENCE IS LOW AS TO THE SMALL SCALE DETAILS...BUT THERE IS GOOD EVIDENCE THAT THIS WAVE WILL BE SUFFICIENT TO FORCE ADDITIONAL HEIGHT FALLS AND INTENSIFICATION ALONG THE EASTERN EXTENSION OF THE BROAD UPPER LOW. THE ECMWF IS LIKELY TOO SLOW TO EMPHASIZE THIS EFFECT...AS IT WAS EVEN SOWER THAN THE ECMWF ENSEMBLE MEAN. THE TREND IN THE NAM/GFS AND THE 00Z UKMET IS TOWARD A LITTLE MORE EMPHASIS ON THIS DEVELOPMENT ON THE EAST SIDE OF THE BROAD LOW...THUS PULLING THE CENTER OF LOWER HEIGHTS FARTHER OFF OF MAINE ON DAY 3. ...PACIFIC NORTHWEST... PREFERENCE: BLEND OF 00Z NAM/12Z ECMWF MODELS ARE CONVERGING ON THE PRESENCE OF A DEEP LOW IN THE GULF OF ALASKA...WITH AN ATTENDANT JET DIVING TOWARD THE WA/OR COAST. THE ECMWF MAINTAINS BEST CONTINUITY OF THESE FEATURES. THE UKMET RUNS HAVE BEEN SOMEWHAT QUICK AND FLAT WITH THE MID LEVEL FLOW ACCOMPANYING THE JET. THE NAM AND GFS LIFT THE GULF OF ALASKA LOW NORTHWESTWARD WITHOUT ANY OBVIOUS FORCING FOR THIS TO OCCUR...YET THEIR FORECASTS DOWNSTREAM TOWARD WA/OR ARE A CLOSE MATCH TO THE ECMWF. THE NAM IS A LITTLE SHARPER AT 700-500 MB...AND SERVES AS AN EVEN BETTER MATCH THAN THE GFS. ...NORTHERN ROCKIES/NORTHERN PLAINS... PREFERENCE: BLEND OF 00Z GFS/UKMET SEVERAL SMALLER SCALE AND RELATIVELY WEAK VORTICITY MAXIMA WILL INTERACT WITHIN A GENERAL WEAKNESS IN THE MID LEVEL HEIGHT FIELD OVER THE NORTHERN ROCKIES/PLAINS. BY FRIDAY MORNING SOME CONSOLIDATION OF THIS ENERGY SHOULD OCCUR DOWNSTREAM OF A SHARPENING SHORTWAVE RIDGE AXIS...YIELDING A LOOSELY DEFINED TROUGH OVER EASTERN MT/WY INTO THE DAKOTAS AND NEBRASKA. DESPITE GOOD PERFORMANCE UPSTREAM IN THE PACIFIC...THE ECMWF APPEARED TOO WEAK AND PROGRESSIVE WITH THE NORTHERN ROCKIES/PLAINS ENERGY. THE NAM WAS WEAK AND SLOW HERE...PRODUCING AN UNREALISTIC WAVELENGTH BETWEEN THE PACIFIC NORTHWEST AND NORTHERN PLAINS TROUGHS. THE 00Z GFS AND UKMET BETTER FIT THE ENSEMBLE MEANS...AND SHOW GOOD AGREEMENT WITH ONE ANOTHER. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE