MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1151 AM EST SAT JAN 18 2014 VALID JAN 18/1200 UTC THRU JAN 22/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...SYSTEM DIVING TOWARD THE SOUTHEAST U.S. THIS EVENING... PREFERENCE: NONE LOW PRESSURE OVER THE MIDWEST STATES WILL FILL...BUT THE ASSOCIATED FRONTAL SYSTEM AND MID LEVEL WAVE WILL CONTINUE FORWARD...SWEEPING OFF THE EAST COAST BY SUNDAY EVENING. MODEL SOLUTIONS FOR THIS SYSTEM HAVE BEEN FAIRLY CONSISTENT. ALOFT THE GFS TENDS TO FASTEST AND THE CANADIAN TENDS TO BE SLOWEST...BUT THESE DIFFERENCES ARE MINOR AND ARISE ONLY AFTER THE SYSTEM MOVES OFFSHORE. ...SYSTEM IN BRITISH COLUMBIA THIS EVENING MOVING TO THE EAST COAST BY TUESDAY... PREFERENCE: 12Z GFS A SHORT TO MEDIUM WAVELENGTH TROUGH ENTERED WESTERN CANADA SATURDAY MORNING. IT WILL GLIDE QUICKLY THROUGH THE LARGE SCALE EASTERN U.S. TROUGH AND START TO LIFT NORTHEASTWARD ALONG THE EAST COAST BY TUESDAY NIGHT. THIS WAVE IS VERY LIKELY TO PRODUCE BROAD CYCLOGENESIS AS IT REACHES THE COAST. THE MAJORITY OF THE 00Z GUIDANCE PLACED THIS CYCLOGENESIS WELL OFF THE COAST. ALTHOUGH A LARGE BUILD UP OF POLAR AND ARCTIC AIR WILL PUSH THE LARGEST LOW LEVEL THERMAL GRADIENTS OUT TO SEA...THERE IS A TREND IN THE 12Z NAM AND GFS TO BRING CYCLOGENESIS CLOSER TO THE COAST. THE NAM MAY BE TOO SHARP ALOFT...AND CERTAINLY IS AN OUTLIER IN THE DEPTH OF COLD AIR THAT IT HAS SUPPORTING THIS FEATURE WHEN IT DIGS INTO THE SOUTHEAST U.S. ON DAY 3. THE POTENTIAL DOES EXIST...HOWEVER...FOR AN OVERALL TREND IN THE DIRECTION OF WHAT THE NAM IS DEPICTING...GIVEN THAT WE WILL SEE A WELL DEFINED SHORTWAVE DROPPING INTO THE BASE OF AN ESTABLISHED LONGWAVE. THEREFORE...LATCHING ONTO THE TREND...BUT DOING SO IN A MORE CONSERVATIVE WAY...WE RECOMMEND THE 12Z GFS. ...SYSTEM APPROACHING THE PACIFIC NORTHWEST LATE TUESDAY... PREFERENCE: BLEND OF 12Z NAM WITH 06Z GFS THIS SYSTEM IS MORE LIKELY TO AFFECT THE PACIFIC NORTHWEST ON DAY 4 OR 5 IN THE MEDIUM RANGE...BUT THERE IS SOME SIGNIFICANT MODEL SPREAD REGARDING ITS POSITION ON DAY 3. RECENT RUNS OF THE UKMET AND CANADIAN HAVE LEANED TOWARD THE FAST SIDE OF THE SPREAD...AND THE 12Z GFS HAS JOINED THEM. OVER THE PAST FEW CYCLES DATING BACK TO THE 17/00 CYCLE...HOWEVER...THE GEFS MEAN HAS BEEN STEADY WITH A SOLUTION MORE LIKE THE 00Z GFS AND ECMWF. THE ECMWF ENSEMBLE MEAN WAS INITIALLY MUCH SLOWER...BUT SEEMS ALSO TO HAVE SETTLED IN NEAR THE 00Z GFS AND ECMWF. WITH THE 12Z NAM AND 06Z GFS FALLING CLOSE TO THAT SAME POSITION...WE PREFER THE LARGE CLUSTER OF SLOWER SOLUTIONS RATHER THAN THE 12Z GFS. THIS ALSO KEEPS CONSISTENCY WITH THE WPC MEDIUM RANGE FORECAST. ...WEAK SYSTEM SHOWING UP IN THE SOUTHERN PLAINS/ROCKIES LATE SUNDAY INTO MONDAY... PREFERENCE: ANY OF 12Z NAM/GFS OR 00Z CANADIAN THIS SYSTEM IS DEFINED MAINLY ALOFT...ALTHOUGH A PRE-FRONTAL TROUGH RELATED TO THE LARGER SCALE FLOW WILL ALSO PUSH THROUGH THIS REGION AT THE SAME TIME. THE GFS AND ECMWF HAVE BEEN CONSISTENT...RESPECTIVELY...WITH THE GFS TENDING TO BE A LITTLE SLOWER THAN THE ECMWF. ONE COULD EASILY RECOMMEND A SIMPLE BLEND OF ALL THE OPERATIONAL MODELS...BUT WE WILL SIDE WITH THE MORE RECENTLY INITIALIZED 12Z NAM AND GFS...WHICH HAVE SUPPORT FROM THE 00Z CANADIAN. WE NOTE ALSO THAT TRENDS IN THE 12Z GUIDANCE ARE STARTING TO MAKE THE 00Z ECMWF LOOK FAST WITH THE SYSTEM DROPPING THROUGH THE MIDWEST MONDAY. THIS GIVES US MORE CONFIDENCE IN STEERING AWAY FROM ITS QUICK SOLUTION DOWN SOUTH. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE