398   
FXUS10 KWNH 041900  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 PM EST SAT JAN 04 2020  
  
VALID JAN 04/1200 UTC THRU JAN 08/0000 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..UPPER TROUGH CROSSING FROM THE MIDWEST TO THE EAST COAST  
   
..SURFACE LOW NEAR NEW ENGLAND TODAY/TONIGHT  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
  
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM. NO SIGNIFICANT CHANGES  
WERE NOTED WITH THE 12Z ECMWF/UKMET/CMC COMPARED WITH THEIR  
PREVIOUS 00Z CYCLES.  
  
...SHORTWAVE EJECTING OUT ACROSS THE PLAINS, REACHING THE GREAT  
LAKES BY SUN NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
  
THERE REMAIN SOME MINOR PLACEMENT DIFFERENCES WITH THE MID-LEVEL  
SHORTWAVE AS IT NEARS THE GREAT LAKES. THE 12Z CMC REMAINS FARTHER  
SOUTH WITH THE 500 MB TROUGH AXIS BUT THE 12Z UKMET ADJUSTED  
NORTHWARD ENOUGH TO BE INCLUDED IN THE REMAINING DETERMINISTIC  
CONSENSUS. THE ENSEMBLE MEANS SUPPORT A NON 12Z CMC BLEND.  
  
   
..SPLIT-FLOW TROUGH NEAR THE PACIFIC NORTHWEST BY SUN  
   
..CLIPPER TYPE LOW APPROACHING THE GREAT LAKES BY TUE  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/12Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
  
TIMING AND LATITUDINAL DIFFERENCES SHOW UP WITH THE NORTHERN  
PORTION OF A MID-LEVEL TROUGH AMPLIFYING THROUGH THE CENTRAL TO  
EASTERN U.S. MONDAY NIGHT. THE 12Z NAM AND 12Z CMC ARE SLOWER  
WHILE THE 12Z UKMET IS DISPLACED SLIGHTLY NORTHWARD WITH THE  
VORTICITY MAXIMA COMPARED TO THE ENSEMBLE MEANS AND REMAINING  
DETERMINISTIC GUIDANCE. THE 12Z GFS AND 12Z ECMWF ARE THOUGHT TO  
BE CLOSER TO THE MIDDLE OF THE MODEL SPREAD AND ARE PREFERRED AT  
THIS TIME, WITH THE 12Z ECMWF SHIFTING A LITTLE NORTH OF ITS  
PREVIOUS 00Z CYCLE.  
  
   
..SOUTHERN STREAM TROUGH/LOW NEAR THE TN VALLEY BY TUES  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
  
THE SOUTHERN PORTION OF A BROADENING MID-LEVEL TROUGH OVER THE  
EASTERN TWO THIRDS OF THE NATION MONDAY NIGHT INTO TUESDAY IS  
EXPECTED TO COINCIDE WITH A WEAK SURFACE LOW TO CROSS THE  
TENNESSEE VALLEY. THE 12Z GFS BECOMES SIGNIFICANTLY FASTER BY  
TUESDAY MORNING WHILE THE 12Z CMC SHOWS SLOWEST OF THE  
DETERMINISTIC GUIDANCE. THE 12Z NAM AND 12Z ECMWF SHOW CLOSEST TO  
THE ENSEMBLE MEANS BUT THE 12Z UKMET ADJUSTED A BIT FASTER WITH  
ITS 500 MB TROUGH TAKING ITS SURFACE LOW AWAY FROM THE FAVORED  
CONSENSUS.  
  
   
..SHORTWAVE/FRONTS APPROACHING THE PACIFIC NORTHWEST TUE  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z NAM BLEND  
CONFIDENCE: AVERAGE  
  
MODERATE SPREAD CONTINUES TO EXIST WITH A SHORTWAVE TROUGH TO  
APPROACH THE PACIFIC NORTHWEST LATE MONDAY INTO TUESDAY. A WARM  
FRONT IS FORECAST TO REACH WESTERN BRITISH COLUMBIA AND COASTAL  
WASHINGTON MONDAY MORNING AS A LOW NEARS JUST NORTH OF VANCOUVER  
ISLAND. THERE ARE SOME MINOR PLACEMENT DIFFERENCES WITH THE  
SURFACE LOW, THE 12Z UKMET IS TOWARD THE SOUTHERN SIDE OF THE  
DETERMINISTIC SPREAD WHILE THE 12Z NAM IS FARTHER NORTH. A BLEND  
TOWARD THE MIDDLE (LESS 12Z UKMET INFLUENCE) WILL ALIGN BEST WITH  
THE LATEST ENSEMBLE SCATTER LOW PLOTS.  
  
HOWEVER, LARGER DIFFERENCES SHOW UP DUE TO THE APPROACHING  
SHORTWAVE TO THE WEST. WITH THIS FEATURE, THE 00Z ECMWF WAS FASTER  
BUT THE 12Z ECMWF SLOWED DOWN. THE 12Z NAM WAS WEAKEST WITH THE  
TROUGH AND CONSIDERED THE LEAST LIKELY TO VERIFY. TIMING  
ADJUSTMENTS FROM THE 12Z ECMWF/UKMET/CMC COMPARED WITH THEIR  
PREVIOUS 00Z CYCLES ALLOW FOR THEIR INCLUSION AS PART OF THE  
PREFERENCE, EXCLUDING THE 12Z NAM. OF THE NON 12Z NAM GUIDANCE,  
THE 12Z CMC WAS SLOWEST, BUT JUST WITHIN TOLERANCE GIVEN THE  
LATEST ENSEMBLE SPREAD. THEREFORE, A NON 12Z NAM BLEND WILL BE  
PREFERRED WITH THIS SYSTEM GIVEN DIFFERENCES FROM THE 12Z UKMET'S  
SURFACE LOW INFLUENCE IS FELT FARTHER NORTH AWAY FROM WASHINGTON.  
  
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
  
OTTO  
  
  
 
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