517  
FXUS10 KWNH 150549  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1248 AM EST MON JAN 15 2018  
 
VALID JAN 15/0000 UTC THRU JAN 18/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES WITH CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
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 12Z CANADIAN, 12Z  
ECMWF, 12Z 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 AVERAGE  
 
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/12Z CANADIAN SOLUTIONS OVER THE  
MORE NORTHERLY 12Z ECMWF GUIDANCE. TRENDS PLAY INTO THIS IDEA AS  
WELL AS THE CANADIAN HAS SHOWN MUCH BETTER CONTINUITY THAN THE  
ECMWF WITH THIS SYSTEM SINCE THEIR 00Z RUNS AND THE UKMET HAS  
TRENDED STRONGER SINCE ITS 00Z RUN, ALBEIT MORE TO THE NORTHEAST.  
THE 12Z NAM APPEARS WAY TOO WEAK. A COMPROMISE OF THE 12Z GFS/12Z  
CANADIAN IS PREFERRED HERE WITH CONFIDENCE NO BETTER THAN AVERAGE.  
 
TROUGH MOVING THROUGH THE EAST WEDNESDAY  
SURFACE LOW SCOOTING BY NEW ENGLAND WEDNESDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: CANADIAN/UKMET BLEND; CONFIDENCE AVERAGE  
 
THE 12Z NAM/12Z ECMWF WERE DEEP/SLOW/SOUTHWEST WITH THIS SYSTEM  
WHEN COMPARED TO THE OTHER GUIDANCE, WHILE THE 12Z GFS WAS THE  
QUICKEST -- BOTH THE NAM/GFS 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  
NEAR THE US/CANADIAN BORDER AND THE SHORTWAVE ACROSS THE SOUTHERN  
HIGH PLAINS ARE WILD CARDS WHICH SHOULD LEAD TO A LESS DUG IN AND  
MORE PROGRESSIVE SOLUTION. THIS RULED THE 12Z NAM/12Z ECMWF OUT.  
THE 12Z CANADIAN AND 12Z UKMET LIE CLOSEST TO THE MIDDLE OF THE  
RANGE OF POSSIBLE SOLUTIONS ALOFT, WHICH IS PREFERRED WITH AVERAGE  
CONFIDENCE.  
 
SYSTEM MOVING ACROSS THE GREAT LAKES MONDAY/TUESDAY  
SHORTWAVE MOVING ACROSS THE WEST INTO THE SOUTHERN PLAINS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE SYSTEMS. A  
COMPROMISE OF THE 12Z ECMWF, 12Z UKMET, 12Z 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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