596  
FXUS10 KWNH 061845  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
144 PM EST WED DEC 06 2017  
 
VALID DEC 06/1200 UTC THRU DEC 10/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..STALLED FRONT ACROSS THE SOUTHERN CONUS
 
   
..DIGGING SHORTWAVE FROM THE ROCKIES INTO TEXAS BY THU NGT
 
AND  
ROUNDING THE BASE OF THE TROUGH THROUGH THE SOUTHEAST...   
..WEAK SURFACE WAVES DEVELOPING OFF THE SE ATLANTIC COAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z ECMWF  
MOST WEIGHT TOWARD THE 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
FOR THE INITIAL ELONGATED TROUGH OVER THE SOUTHERN CONUS AND THE  
DIGGING SHORTWAVE DOWN THE EASTERN EXTENT OF THE ROCKIES...MODELS  
DO SHOW A FAIR AMOUNT OF SIMILARITY (THROUGH 08/00Z...FIRST 36  
HOURS OF THE FORECAST). DIFFERENCES EMERGE AS THE SHORTWAVE BEGINS  
TO KICK EAST ALONG THE GULF COAST STATES AND EVENTUALLY TO THE  
EASTERN SEABOARD. THE 00Z CMC AND 12Z NAM OFFER THE MOST AMPLIFIED  
SOLUTIONS OF THE OPERATIONAL MODELS BY FAR...HAVE THE STRONGEST  
WAVE AS IT REACHES THE ATLANTIC COAST...AND ARE THE SLOWEST WITH  
PROGRESSION ALONG THE GULF COAST. THERE IS VERY LITTLE SUPPORT  
AMONG NAEFS (GEFS+CMC) AND ECMWF ENSEMBLE MEMBERS FOR SUCH AN  
AMPLIFIED SOLUTION. WHEN EXAMINING THE ISOHEIGHTS AT THE BASE OF  
THE TROUGH (AROUND 558-564 DKM) IN A SPAGHETTI FORMAT...THE NAM  
AND CMC ARE GENERALLY MORE AMPLIFIED THAN ALL AVAILABLE ENSEMBLE  
MEMBERS. EVEN THE 00Z CMC ENSEMBLE MEAN IS CLOSELY CLUSTERED WITH  
OTHER AVAILABLE GLOBAL MODELS AND ENSEMBLE MEANS. THE OTHER MODELS  
ARE IN BETTER AGREEMENT...BUT THE 12Z GFS IS SLIGHTLY FASTER AND  
LESS AMPLIFIED THAN THE ECMWF AND UKMET. THE MAJORITY OF THE  
MULTI-MODEL ENSEMBLE CLUSTERS ARE IN BETTER AGREEMENT WITH THE  
INTERMEDIATE ECMWF/UKMET SOLUTION...AND THEREFORE GREATER WEIGHT  
WILL BE PLACED ON THAT. BASED ON THE THICKNESS FIELDS...THEIR  
TEMPERATURE PROFILES SEEM TO BE MORE REASONABLE AS WELL...AS THERE  
IS NOT A STRONG PERSISTENT FETCH OF ARCTIC AIR AVAILABLE FOR  
SUBSTANTIAL COOLING (WESTERLY COMPONENT TO THE LOW-LEVEL FLOW  
THU-FRI OVER MUCH OF CENTRAL AND EASTERN CONUS; STRONGEST SFC HIGH  
WELL WEST IN THE ROCKIES) AND THUS THE CMC/NAM APPEAR TO BE MUCH  
COOLER PRIMARILY THROUGH DYNAMIC COOLING WITH THE STRONGER WAVE  
ALONG THE GULF COAST. GIVEN THAT THE OTHER OPERATIONAL MODELS AND  
ALL OF THE MULTI-MODEL ENSEMBLE CLUSTERS SHOW A DISTINCTLY  
POSITIVE TILT TO THE WAVE...THE ECMWF TEMPERATURE PROFILES ALSO  
SEEM MORE REASONABLE.  
 
18Z UPDATE: REMOVE THE UKMET FROM THE PREFERENCE. THE 12Z UKMET  
TRENDED MORE SUBSTANTIALLY TOWARD THE CMC (12Z RUN FAIRLY  
CONSISTENT WITH PREVIOUS RUN) AND NAM...WHICH NOW SHOWS A  
SLOWER...SHARPER...AND STRONGER WAVE TRANSLATING ACROSS THE GULF  
COAST. THIS STILL EXISTS ON THE MORE AMPLIFIED EXTREME OF ENSEMBLE  
MEMBERS. THE 12Z ECMWF DID TREND SLIGHTLY MORE AMPLIFIED AND  
SLOWER...BUT NOT TO THE EXTREME OF THE OTHER MODELS. THE ECMWF IS  
STILL ABOUT 40-70 METERS HIGHER WITH ITS HEIGHTS IN THE CENTRAL  
GULF COAST AT THE CORE OF THE WAVE AROUND 09/12Z AS COMPARED TO  
THE CMC/UKMET/NAM. THE 12Z GFS REMAINS ON THE LESS AMPLIFIED END  
OF MODELS...BUT THE 12Z GEFS MEAN CAME IN EVEN LESS AMPLIFIED. FOR  
THIS REASON...WILL PREFER A BLEND OF THE GFS AND ECMWF AS THAT  
CONTINUES TO BE A RELATIVELY CONSISTENT AND INTERMEDIATE SOLUTION.  
HOWEVER...GIVEN THE TRENDS IN THE UKMET AND ECMWF...IT WILL HAVE  
TO BE MONITORED WHETHER THESE TRENDS BECOME MORE PRONOUNCED.  
FURTHER UP THE EAST COAST...THE CMC AND UKMET NOW SHOW A MUCH  
STRONGER LOW CLOSER TO THE COAST (LIKELY DUE TO INITIAL TRENDS OF  
A STRONGER WAVE). THESE ARE OUTLIERS RELATIVE TO OTHER MODELS SO  
AGAIN THE PREFERENCE OF GFS/ECMWF BLEND SEEMS PREFERABLE.  
 
...SEVERAL CLIPPER SYSTEMS ROTATING THROUGH THE GREAT LAKES AROUND  
DEEP CYCLONE IN HUDSON BAY REGION...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS ALL CAPTURE THE GENERAL IDEA OF SEVERAL CLIPPER SYSTEMS  
MOVING THROUGH THE GREAT LAKES...AND HAVE GENERALLY SIMILAR  
PATTERNS IN THE MASS FIELDS. WITH THE BROAD TROUGH IN THE EASTERN  
CONUS AND BROAD RIDGE IN THE WESTERN CONUS IN A RELATIVELY STABLE  
CONFIGURATION...THE BIG PICTURE SHOULD BE IN FAIRLY GOOD  
AGREEMENT. HOWEVER...SOME OF THE DETAIL DIFFERENCES MAY MAKE AN  
IMPACT ON WIND FIELDS AND THUS LAKE EFFECT PATTERNS IN THE GREAT  
LAKES REGION. THE 00Z UKMET WAS A BIT OF AN OUTLIER WITH THE  
INITIAL SHORTWAVE CROSSING FROM THE WESTERN LAKES TODAY TO THE  
EASTERN LAKES THURSDAY. IT MOVED THE SHORTWAVE MUCH FASTER THAN  
OTHER MODELS AND THIS DIFFERENCE CONTINUES THROUGH THE TRAIN OF  
SHORTWAVES THAT PUSH THROUGH THE REGION. THEREFORE...IT IS  
EXCLUDED FROM THE PREFERENCE AT THIS TIME. THE 00Z CMC IS A LITTLE  
FLATTER AND WEAKER WITH THE SERIES OF WAVES OVERALL. IT SHOWS  
HIGHER HEIGHTS THAN THE OTHER MODELS THROUGH MUCH OF THE AREA NEAR  
THE DEEPER CYCLONE...AND THIS IS A BIAS THAT OCCURS ALMOST  
IMMEDIATELY. FOR THIS REASON IT IS ALSO EXCLUDED FROM THE  
PREFERENCE. OTHERWISE...THE 12Z NAM...12Z GFS...AND 00Z ECMWF  
ADVERTISE SIMILAR TIMING AND PLACEMENT OF THE SHORTWAVE  
TROUGHS...AND PLACEMENT OF ASSOCIATED MID-LEVEL VORTICITY MAXIMA.  
 
18Z UPDATE: REMOVE THE NAM FROM THE PREFERENCE. THERE WERE NOT  
SUBSTANTIAL CHANGES TO THE MODELS IN THE GREAT LAKES  
REGION...ALTHOUGH THE 12Z NAM NOW SEEMS SLOWER THAN THE GFS/ECMWF  
AND SLIGHTLY OUT OF PHASE WITH THE THIRD CLIPPER WAVE THAT MOVES  
INTO THE REGION ON SATURDAY. THEREFORE...THE PREFERENCE IS A BLEND  
OF THE GFS AND ECMWF.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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