MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 204 AM EST SAT DEC 06 2014 VALID DEC 06/0000 UTC THRU DEC 09/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/GEM AND THE ECMWF ...SHORTWAVE AND ATTENDANT SURFACE LOW CROSSING THE APPALACHIANS/MID-ATLANTIC ON SAT... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THE MODELS ARE IN REASONABLY GOOD AGREEMENT WITH THE SHORTWAVE TROUGH AND ATTENDANT SURFACE LOW THAT CROSSES OUT OF THE OH VALLEY AND MOVES THROUGH THE MID-ATLANTIC REGION ON SAT. THE LOW MOVES OFFSHORE AND IS EXPECTED TO WEAKEN ON SUN. A GENERAL MODEL COMPROMISE WILL BE PREFERRED TO RESOLVE THE SMALLER SCALE DIFFS SEEN AS IT CROSSES THROUGH THE MID-ATLANTIC STATES. ...UPPER TROUGH ADVANCING ACROSS THE NORTHWEST THROUGH SAT... ...ENERGY AMPLIFYING OVER THE GREAT LAKES AND OH VALLEY... PREFERENCE: BLEND OF THE 00Z GFS AND 00Z ECMWF CONFIDENCE: AVERAGE THE MODELS ARE GENERALLY IN GOOD AGREEMENT AT LEAST OVER THE NEXT COUPLE OF DAYS WITH THE SHORTWAVE ENERGY TRAVERSING THE NORTHWEST AND THEN EJECTING EAST-SOUTHEAST THROUGH THE NORTHERN PLAINS AND INTO THE MIDWEST. ALTHOUGH THE 00Z NAM DOES TEND TO APPEAR A LITTLE STRONG WITH ITS HEIGHT FALLS. MUCH MORE SIGNIFICANT DIFFERENCES APPEAR THOUGH BY DAY 3 OVER THE GREAT LAKES AND OH VALLEY. THE 00Z UKMET AND 00Z BECOME QUITE AGGRESSIVE WITH THEIR HEIGHT FALLS DIGGING SOUTHEASTWARD...WITH THE GEM ACTUALLY FAVORING A CLOSED LOW OVER THE UPPER OH VALLEY AND LOWER GREAT LAKES. THE UKMET FAVORS A CLOSED LOW A BIT FARTHER WEST MORE INTO THE LOWER OH VALLEY. THE 00Z GFS/00Z ECMWF AND ESP THE 00Z NAM ARE WEAKER BY COMPARISON...BUT NEVERTHELESS SHOW SHORTWAVE ENERGY AMPLIFYING TOWARD THE OH VALLEY. THE 00Z UKMET IS THE SLOWEST SOLN OVERALL. THE LATEST GEFS MEAN AND ECENS MEAN ARE SUPPORTIVE OF THE DETERMINISTIC GFS/ECMWF CAMP. ACCOUNTING FOR THE DEEPER UKMET/GEM SOLNS ALOFT...AND THE NAM WHICH IS WEAKEST...WILL PREFER A BLEND OF THE GFS AND ECMWF WITH THIS ENERGY THROUGH THE DAY 3 PERIOD. ...SHORTWAVE TRACKING ACROSS THE SOUTHERN TIER OF THE U.S. THROUGH MON... ...SURFACE LOW EVOLUTION OFF THE SOUTHEAST/MID-ATLANTIC COASTS MON AND TUES... PREFERENCE: 00Z ECMWF CONFIDENCE: BELOW AVERAGE THERE IS RELATIVELY SMALL MODEL SPREAD SEEN THROUGH DAY 1 WITH THE SOUTHERN STREAM SHORTWAVE THAT CROSSES THE SOUTHWEST U.S. AND THEN EJECTS OUT ACROSS THE SOUTHERN PLAINS. THE 00Z UKMET THOUGH IS A TAD SLOWER/DEEPER WITH THE SHORTWAVE...WITH THE 00Z NAM A TAD FASTER. HOWEVER...THESE DIFFS MAGNIFY QUITE SIGNIFICANTLY IN THE DAY 2 AND DAY 3 PERIOD AS THE ENERGY CROSSES THE LOWER MS VALLEY AND MOVES TO THE MID-ATLANTIC AND SOUTHEAST COASTAL PLAIN BY THE END OF DAY 3. UNFORTUNATELY...THE MASS FIELD DIFFS ALOFT WILL DRIVE SERIOUS MASS FIELD DIFFS AT THE SURFACE WITH A DEVELOPING LOW THAT IS EXPECTED TO EVOLVE OFF THE SOUTHEAST AND MID-ATLANTIC COAST. IT SHOULD BE NOTED THAT ALL OF THE MODELS ACTUALLY INDICATE THAT THE INITIAL LOW OFFSHORE THE EAST COAST IS RELATED TO THE SHORTWAVE AND ATTENDANT LOW CENTER THAT WILL CROSS THE MID-ATLANTIC ON SAT. THIS LOW CENTER WEAKENS OFFSHORE THE MID-ATLANTIC ON SUN...AND THEN SINKS SOUTH TO OFF THE SOUTHEAST COAST MON IN RESPONSE TO VERY STRONG SURFACE RIDGING/HIGH PRESSURE THAT ADVANCES OVER THE NORTHEAST AND NORTHWEST ATLANTIC. THE ARRIVAL OF THE AFOREMENTIONED UPSTREAM SOUTHERN STREAM ENERGY THEN ESSENTIALLY CAPTURES THE LEFTOVER LOW OFFSHORE THE SOUTHEAST...RE-INTENSIFIES IT...AND THEN LIFTS IT NORTH-NORTHWEST BACK TOWARD THE MID-ATLANTIC STATES ON DAY 3/TUES. THE 00Z NAM IS A ROBUST OUTLIER WITH THE SOUTHERN STREAM ENERGY AND DRIVES THIS LOW CENTER BODILY TOWARD THE DELMARVA EARLY TUES. THE 00Z GEM IS QUITE EXTREME AS IT SHOWS THE STRONGER NORTHERN STREAM HEIGHT FALLS OVER THE OH VALLEY BASICALLY ABSORBING THE SOUTHERN STREAM SHORTWAVE AND FAVORING MUCH QUICKER RE-INTENSIFICATION AND A RAPID TRACK NORTH OFF THE MID-ATLANTIC COAST AND INTO SOUTHERN NEW ENGLAND BY EARLY TUES. THE 00Z GFS FLATTENS OUT THE SOUTHERN STREAM ENERGY MORE SO THAN ANY OTHER MODEL WHICH ALLOWS THE SURFACE LOW OFF THE SOUTHEAST COAST TO STAY FARTHER OFFSHORE WHILE GRADUALLY LIFTING NORTHWARD. THE 00Z ECMWF IS STRONGER THAN THE 00Z GFS...BUT NOT AS STRONG AS THE 00Z NAM AND IS JUST A LITTLE WEAKER THAN THE 00Z UKMET. THE UKMET DOES FAVOR A BIT MORE BACKING OF THE MID LEVEL FLOW ALONG THE EAST COAST THROUGH EARLY TUES VERSUS THE ECMWF. REGARDING THE SURFACE LOW TRACK AND DEPTH...THE ECMWF OFFERS A NICE COMPROMISE BETWEEN THE NAM AND GFS. THE GEM IS TOO FAR NORTH AND FAST...WITH THE UKMET LIKELY A LITTLE TOO SLOW. THE LATEST GEFS MEAN FAVORS THE DETERMINISTIC GFS...WITH THE ECENS MEAN NOW CLOSEST TO THE 00Z UKMET. THE SREF MEAN SUPPORTS THE ECENS MEAN. THE MASS FIELD SPREAD IN THE MODELS IS SEEN DRIVING VERY SERIOUS QPF DIFFS...BUT BASED ON THE 00Z MODEL SUITE AND LATEST TRENDS/CLUSTERING...THE 00Z ECMWF DOES APPEAR TO BE A REASONABLE STARTING POINT FOR THIS SYSTEM REGARDING MASS FIELDS. CONFIDENCE HOWEVER REMAINS QUITE LIMITED. ...SHORTWAVE TROUGH APPROACHING THE WEST COAST LATE SUN... PREFERENCE: NON-GFS CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z GFS IS THE SLOWEST SOLN WITH THIS SHORTWAVE IMPACTING THE WEST COAST BY LATER SUN AND SUN NIGHT. THE REMAINING MODELS AND ESP THE 00Z ECMWF ARE A BIT MORE PROGRESSIVE. THE ENSEMBLE MEANS INCLUDING THE GEFS MEAN AND ECENS MEAN ARE MORE PROGRESSIVE AWAY FROM THE DETERMINISTIC GFS. GIVEN THE FAST PACIFIC FLOW UPSTREAM OVER THE PACIFIC OCEAN...A MORE PROGRESSIVE SOLN WOULD MAKE MORE SENSE. THEREFORE...A NON-GFS CONSENSUS WILL BE PREFERRED. ...SHORTWAVE ENERGY/ONSHORE FLOW IMPACTING THE NORTHWEST MON AND TUES... PREFERENCE: NON-GFS CONSENSUS CONFIDENCE: AVERAGE THE MODELS DEPICT DEEP LAYER SOUTHWEST FLOW IMPACTING THE NORTHWEST BY LATER MON INTO TUES...WITH EMBEDDED WEAK SHORTWAVE ENERGY AIMING FOR THE COASTAL RANGES. ALL OF THE MODELS DEPICT A ROBUST INCREASE IN SOUTHWEST ONSHORE FLOW INTO THE WA/OR COASTAL RANGES BY THE END OF THE PERIOD AS A RESULT. THE MODEL DIFFS ARE MORE CENTERED ON THE SHORTWAVE/JET MAX THAT SURGES EAST ALONG 40N AND AMPLIFIES OFF THE WEST COAST OF BRITISH COLUMBIA. THE GUIDANCE INDICATES A VERY INTENSE SURFACE LOW DEVELOPING OVER THE NORTHEAST PACIFIC IN RESPONSE TO THE POWERFUL JET AND SHORTWAVE AMPLIFICATION. THE 00Z GFS APPEARS TO BE A LITTLE TOO FAR SOUTH WITH ITS CLOSED LOW DEVELOPMENT AND SURFACE LOW REFLECTION. THE MULTI-MODEL CONSENSUS AWAY FROM THE GFS...COUPLED WITH THE LATEST GEFS MEAN AND ECENS MEAN FAVOR A CLOSED LOW DEVELOPMENT A LITTLE FARTHER NORTH INTO NORTHEAST PACIFIC OCEAN. WILL FAVOR A NON-GFS CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON