044  
FXUS10 KWNH 141619  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1118 AM EST SUN JAN 14 2018  
 
VALID JAN 14/1200 UTC THRU JAN 18/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
PAIR OF DEEP LAYER CYCLONES MOVING OFFSHORE PACIFIC NW  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
ALTHOUGH THERE IS A BIT OF DISPERSION WITH THE ACTUAL LOW CENTER,  
THE IMPACTS AROUND ITS EASTERN PERIPHERY ACROSS THE PACIFIC  
NORTHWEST APPEAR SIMILAR. A COMPROMISE OF THE 00Z CANADIAN, 00Z  
ECMWF, 00Z UKMET, 12Z NAM, AND 12Z GFS SHOULD WORK OUT FINE WITH  
CONFIDENCE ABOVE AVERAGE.  
 
MID-LEVEL CYCLONE MOVING BY WESTERN US/CAN BORDER WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GFS/ECMWF BLEND; CONFIDENCE SLIGHTLY ABOVE AVE  
 
THE GUIDANCE SHOWS A BIT A SPREAD WITH THE LATITUDE OF THIS  
SYSTEM. THE KEY FEATURE TO THIS SYSTEM'S TRACK APPEARS TO BE A  
LARGE POSITIVE ANOMALY SITTING OVER THE NORTHWEST  
TERRITORIES/WESTERN NUNAVUT WHICH FAVORS THE POSSIBILITY OF THE  
MID LEVEL CLOSED LOW 20 DEGREES TO ITS SOUTH NEAR THE 45TH  
PARALLEL. THIS FAVORS THE 12Z GFS/00Z ECMWF SOLUTIONS OVER THE  
MORE NORTHERLY 00Z CANADIAN/00Z UKMET GUIDANCE. THE 12Z NAM  
APPEARS WAY TOO WEAK. A COMPROMISE OF THE 12Z GFS/00Z ECMWF IS  
PREFERRED HERE WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
TROUGH MOVING THROUGH THE EAST WEDNESDAY  
SURFACE LOW SCOOTING BY NEW ENGLAND WEDNESDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND; CONFIDENCE AVERAGE  
 
THE 12Z NAM WAS DEEP/SLOW/SOUTHWEST WITH THIS SYSTEM WHEN COMPARED  
TO THE OTHER GUIDANCE, WHILE THE 12Z GFS WAS THE QUICKEST -- BOTH  
MODELS ARE DISPLAYING THEIR TYPICAL BIASES. NORMALLY DOWNSTREAM  
OF A RIDGE ONE WOULD FAVOR A SLOWER/DEEPER SOLUTION, BUT THE  
MID-LEVEL LOW EXPECTED TO MOVE ACROSS MT IS A WILD CARD AND COULD  
LEAD TO A LESS DUG IN AND MORE PROGRESSIVE SOLUTION. THIS RULED  
THE 12Z NAM OUT. OTHERWISE, THE 00Z ECMWF, 00Z UKMET, 00Z  
CANADIAN, 12Z GFS LIE WITHIN THE RANGE OF POSSIBLE SOLUTIONS  
ALOFT. A COMPROMISE OF THE ABOVE GUIDANCE IS PREFERRED WITH  
AVERAGE CONFIDENCE.  
 
SYSTEM MOVING ACROSS THE GREAT LAKES MONDAY/TUESDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS SYSTEM. A COMPROMISE  
OF THE 00Z ECMWF, 00Z UKMET, 00Z CANADIAN, 12Z GFS, AND 12Z NAM  
SHOULD WORK OUT WELL HERE. CONFIDENCE IS ABOVE AVERAGE IN THIS  
CHOICE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ROTH  

 
 
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