MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 221 AM EST SUN JAN 31 2016 VALID JAN 31/0000 UTC THRU FEB 03/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 0Z GUIDANCE EVALUATION INCLUDING FINAL MODEL PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MID-LEVEL SHORTWAVE MOVING INTO THE GREAT LAKES DEVELOPING SURFACE LOW INTO THE GREAT LAKES REGION TODAY AND ASSOCIATED FRONTAL PASSAGE THROUGH THE EAST COAST MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL CONSENSUS CONFIDENCE: ABOVE AVERAGE MODELS CONTINUE TO WOBBLE BACK AND FORTH BETWEEN A WEAKER SOLUTION SOME RUNS AND A SLIGHTLY DEEPER TROUGH MOVING ACROSS THE GREAT LAKES ON OTHERS. AT THIS POINT APPEARS TO BE JUST SUBTLE DIFFERENCES IN HOW THE GUIDANCE IS HANDLING THE STRUNG OUT NORTHERN STREAM SHORTWAVE ENERGY AS IT MOVES EAST. VERY LITTLE TO POINT TO AT THIS TIME IN TRYING TO DETERMINE THE MORE LIKELY SOLUTION. TEND TO BELIEVE A SOLUTION SOMEWHERE BETWEEN THE TWO EXTREMES IS MOST LIKELY. THE 12Z GEM REMAINS THE SLOWEST/DEEPEST AND THE 12Z UKMET THE FLATTEST AND MOST PROGRESSIVE SOLUTION. BOTH OF THESE SOLUTIONS APPEAR OUTSIDE THE MORE PROBABLE SOLUTIONS...WITH SOMEWHERE BETWEEN THE 0Z GFS AND 12Z ECMWF SEEMING TO REPRESENT A PLAUSIBLE MIDDLE GROUND SOLUTION. THE OZ NAM ALSO APPEARS WITHIN REASON. THUS WILL FAVOR A BLEND OF THE 0Z GFS/NAM AND 12Z ECMWF WITH THIS SYSTEM AS IT MOVES ACROSS THE GREAT LAKES TODAY. THIS BLEND ALSO SEEMS TO WORK FAIRLY WELL WITH THE FRONTAL PROGRESSION TOWARDS THE EAST COAST ON MONDAY. ALTHOUGH AS A WAVE INTERACTS WITH THE FRONT AND A WEAK SURFACE REFLECTION MOVES INTO THE MID ATLANTIC...THE GFS REMAINS AN OUTLIER. AND GIVEN ITS DRY BIAS IN THESE CASES IT LIKELY BECOMES A LESS USEFUL SOLUTION ACROSS THE MID ATLANTIC BY THIS PERIOD...WITH MORE OF A NAM/ECMWF BLEND MORE LIKELY. 07Z UPDATE: FINALLY SEEING A GOOD CLUSTERING IN THE GUIDANCE WITH REGARDS TO THE DEEPNESS OF THE TROUGH AND THE ASSOCIATED SURFACE LOW AS IT MOVES ACROSS THE GREAT LAKES TODAY. THUS WILL CHANGE THE WPC PREFERENCE TO A GENERAL MODEL BLEND. PREFER A NON GFS SOLUTION (DRY BIAS) BY DAY 2 AS THE WAVE INTERACTS WITH THE FRONT ACROSS THE MID ATLANTIC...WITH THE NAM/GEM/ECMWF/UKMET IN BETTER AGREEMENT. LONGWAVE TROUGH MOVING THROUGH THE SOUTHWEST U.S. INTO EARLY NEXT WEEK SURFACE LOW TRACKING THROUGH THE SOUTHWEST INTO THE THE SOUTHERN PLAINS MONDAY EVENING NORTHEAST INTO THE GREAT LAKES BY TUESDAY EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND THROUGH DAY 2...AND A NON NAM SOLUTION BY DAY 3 CONFIDENCE: SLIGHTLY ABOVE AVERAGE LARGE SCALE AGREEMENT CONTINUES WITH THE DEEPENING LONGWAVE TROUGH ACROSS THE SOUTHWEST AS WELL AS THE RESULTANT SURFACE LOW FORMATION ON SUNDAY MOVING THROUGH THE FOUR CORNERS...EVENTUALLY TRANSFERRING TO THE LEE LOW DEVELOPMENT OVER NE NEW MEXICO ON MONDAY AFTERNOON. WHILE THIS OVERALL LARGER SCALE PATTERN SEEMS WELL ESTABLISHED AND CONFIDENCE IS HIGH ON THIS SYSTEM HAVING SIGNIFICANT IMPACTS...SUBTLE SHIFTS IN THE GUIDANCE OVER THE COMING DAYS WILL RESULT IN LOWER CONFIDENCE IN THE FINER INTERNAL DIFFERENCES/DETAILS WHICH MOSTLY BEGINS TO EXPAND MONDAY EVENING INTO TUESDAY IN THE EJECTION ACROSS THE GREAT PLAINS. VERY GOOD CLUSTERING IS SEEN AMONG THE GUIDANCE THROUGH MONDAY NIGHT WITH THE LOW TRACK. THE 0Z GFS REMAINS A BIT FURTHER NORTH THAN THE OTHER GUIDANCE...BUT IS SLIGHTLY SOUTH OF ITS 18Z RUN. THIS IS SOMETHING TO WATCH...BUT NOT YET CLEAR IF THIS IS A RELIABLE TREND OR IF THE GFS IS JUST AN OUTLIER. IT IS INTERESTING THAT BOTH THE 18Z AND 0Z RUNS OF THE GFS HAVE THE LOW SLIGHTLY FURTHER NORTH THAN ANY OF THE GEFS MEMBERS FROM 12Z...WHICH ARE GENERALLY MUCH MORE CLUSTERED WITH THE OZ NAM AND 12Z ECMWF/GEM/UKMET. THINK THE 0Z RUNS OF THE OTHER GLOBAL GUIDANCE WILL GIVE A STRONG HINT AS TO WHETHER THIS NORTHWARD TREND IS REASONABLE OR NOT. FOR NOW THE GFS WOULD APPEAR TO REPRESENT A LESS LIKELY SOLUTION THROUGH DAY 2...ALTHOUGH NOT AN IMPOSSIBLE SOLUTION. THE 12Z GEM IS A BIT SLOW WITH THE PROGRESSION OF THE SYSTEM THROUGH MONDAY NIGHT...ALTHOUGH THIS DOES NOT APPEAR TO SIGNIFICANTLY IMPACT ITS SENSIBLE WEATHER. THUS THE WPC PREFERENCE THROUGH MONDAY NIGHT IS A GENERAL MODEL CONSENSUS GIVEN THE RELATIVELY GOOD AGREEMENT. THIS TYPE OF BLEND WOULD DOWNPLAY THE GFS SOLUTION...BUT STILL INCORPORATE SOME OF IT GIVEN THE UNCERTAINTY. AS WE HEAD THROUGH TUESDAY THE LOW WILL MOVE TOWARDS THE GREAT LAKES. BY THIS TIME THE 0Z NAM BECOMES A FLAT AND WEAK OUTLIER...AND IS THUS NOT PREFERRED GIVEN IT LIES OUTSIDE THE REASONABLE DETERMINISTIC AND ENSEMBLE ENVELOPE. WITH REGARDS TO THE NORTHWARD EXTENT...THE REMAINDER OF THE GUIDANCE ARE IN VERY GOOD AGREEMENT NOW THAT THE 0Z GFS HAS TRENDED SOUTHEAST. THUS THE ONLY REAL DIFFERENCES ARE WITH TIMING...WITH THE 0Z GFS THE QUICKEST SOLUTION AND THE 12Z ECMWF/GEM THE SLOWEST...AND THE UKMET IN BETWEEN. NOT UNCOMMON TO SEE THE GFS FAST AND ECMWF SLOW WITH SYSTEMS...AND MORE OFTEN THAN NOT A SOLUTION IN BETWEEN SEEMS TO VERIFY BEST. THUS SOMETHING CLOSER TO THE 12Z UKMET...WHICH IS BETWEEN THE 0Z GFS AND 12Z ECMWF IS PROBABLY THE MOST LIKELY SOLUTION WITH REGARDS TO TIMING. 07Z UPDATE: THE 0Z ECMWF AND UKMET JOINED THE GFS WITH A NORTHWARD TREND THROUGH 12Z TUESDAY...ALTHOUGH NOT AS FAR NORTH AS THE GFS. BASED ON THESE TRENDS WOULD APPEAR THAT THE 0Z GEM AND NAM ARE LIKELY A BIT TOO SUPPRESSED WITH THIS SYSTEM. ENSEMBLE MEANS ARE A BIT SOUTH OF THE DETERMINISTIC GFS/ECMWF THOUGH...AND KEEPING THE NAM/GEM IN THE FAVORED BLEND WILL HELP HEDGE FOR THE SOUTEHRN POTENTIAL AND KEEP SOME CONTINUITY FROM PREVIOUS FORECASTS. THUS WILL CONTINUE WITH A GENERAL MODEL BLEND PREFERENCE THROUGH 12Z TUESDAY...WITH CONFIDENCE INCREASING SOME FOR THE TREND NORTH CLOSER TO THE 0Z ECMWF/GFS/UKMET SOLUTIONS. AFTER 12Z TUESDAY GUIDANCE REMAINS IN PRETTY GOOD AGREEMENT. THE 0Z GEM REMAINS A BIT SLOWER THAN THE BEST CLUSTERING...BUT ITS TRACK STILL SEEMS WITHIN THE RANGE OF POSSIBILITY. WITH THE LATEST ECMWF TRENDING SLIGHTLY SOUTHEAST...THE 0Z ECMWF/GEM ARE NOW A BIT FURTHER SOUTHEAST WITH THE LOW TRACK AND THUS NORTHWARD EXTENT OF THE SYSTEM THAN THE GFS. THE NEW 0Z GEFS MEAN SUPPORTS A SOLUTION BETWEEN THE ECMWF AND GFS...PRETTY CLOSE TO THE 0Z UKMET. THUS A MIDDLE GROUND CONSENSUS CONTINUES TO BE PREFERRED...WHICH CAN BE BEST REPRESENTED BY THE OZ UKMET...OR BY A CONSENSUS OF THE NORTHWEST GFS AND SOUTHEAST ECMWF/GEM. SHORTWAVE SHEARING THROUGH THE MEAN PACIFIC RIDGE TOWARD THE NORTHWEST TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 0Z DETERMINISTIC NON NAM CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE A HIGHLY ELONGATED TROUGH MOVES THROUGH A WELL ESTABLISHED/STRONG MEAN PACIFIC RIDGE MONDAY INTO TUESDAY...AND GENERALLY SHEARS OUT WITH LITTLE IMPACT TO SIGNIFICANT WEATHER...HOWEVER THE SOUTHERN AND CENTRAL ENERGY OF THE WAVE SLIDE ALONG THE EASTERN SIDE OF THE RIDGE TO HELP REINFORCE THE BASE (AND WESTERN SIDE) OF THE LARGER SCALE TROUGH ACROSS THE SOUTHWEST BY TUE EVENING. THE 0Z GFS AND 12Z ECMWF APPEAR TO BE HANDLING THIS FEATURE VERY SIMILARLY...WHICH IS USUALLY A GOOD SIGNAL TO LEAN THE PREFERENCE IN THAT DIRECTION. 07Z UPDATE: IN GENERAL THE GUIDANCE HAS COME INTO GOOD AGREEMENT WITH THIS SYSTEM. THE 0Z NAM IS A SLOW OUTLIER WITH THIS FEATURE...AND 0Z GFS MAY NOW ALSO BE A BIT OF A SLOW OUTLIER. HOWEVER THE GFS SOLUTION STILL SEEMS WITHIN THE ENSEMBLE SPREAD...AND WILL THUS PREFER A NON NAM SOLUTION AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... CHENARD