769  
FXUS10 KWNH 100634  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
133 AM EST FRI NOV 10 2017  
 
VALID NOV 10/0000 UTC THRU NOV 13/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH LATEST MODEL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..LEAD SHORTWAVE CURRENTLY NEAR THE IDAHO PANHANDLE
 
EJECTING  
EAST ALONG THE US-CANADA BORDER THROUGH THE WEEKEND...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z ECMWF / 00Z UKMET / 00Z GFS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THIS SHORTWAVE IS AN INITIAL WAVE GETTING KICKED OUT OF THE  
BROADER TROUGH NEAR THE PACIFIC NORTHWEST COAST CURRENTLY. THERE  
IS EXCELLENT MODEL AGREEMENT ON THE TIMING AND LOCATION OF THE  
SHORTWAVE THROUGH AROUND 36 HOURS. MINOR DIFFERENCES APPEAR AFTER  
THAT...PRIMARILY RELATED TO HOW FAST THE WAVE DEAMPLIFIES WITH THE  
VORT MAX GETTING SHEARED OUT AND ABSORBED IN THE NORTHERN STREAM  
FLOW AROUND THE GREAT LAKES ON SUNDAY. THE 00Z GFS HAS ONE OF THE  
STRONGER DEPICTIONS OF THE SHORTWAVE AND THUS MAINTAINS A MORE  
COHERENT SHORTWAVE THROUGH NORTHERN MAINE BY SUNDAY NIGHT. NONE OF  
THE OTHER MODELS SHOW THIS. THE 00Z NAM ALSO HAS A STRONGER VORT  
MAX ALOFT...BUT IT ATTEMPTS TO SLOW IT DOWN AND PHASE IT WITH THE  
TRAILING SHORTWAVE (DISCUSSED BELOW). AS THE GFS AND NAM ARE THE  
FIRST 00Z MODELS ARRIVING...WE WILL HAVE TO SEE IF THIS  
ESTABLISHES A TREND. THE REMAINING GLOBAL MODELS (ECMWF, UKMET,  
CMC) SEEM FAIRLY SIMILAR SO THEY WILL BE INCLUDED IN THE  
PREFERENCE.  
 
06Z UPDATE: ADD GFS TO THE PREFERENCE AND REMOVE THE CMC. THE 00Z  
ECMWF AND 00Z UKMET HAVE TRENDED TOWARD THE GFS IN SHOWING A MORE  
COHERENT SHORTWAVE CONTINUING TO PROGRESS EAST ALL THE WAY THROUGH  
MAINE BY SUNDAY NIGHT. THE 00Z CMC STILL SHOWS THIS TO A CERTAIN  
EXTENT...BUT DIGS THE SHORTWAVE MORE INTO SOUTHERN NEW ENGLAND AS  
IT PHASES WITH THE TRAILING SHORTWAVE. THIS IS MORE SIMILAR TO THE  
NAM...BUT APPEARS TO BE THE LESS LIKELY SOLUTION. THEREFORE...THE  
PREFERENCE IS NOW TO LEAN TOWARD A BLEND OF THE  
ECMWF...UKMET...AND GFS.  
 
...CLOSED LOW JUST OFFSHORE OF THE PACIFIC NORTHWEST OPENING INTO  
A TROUGH AND MOVING ONSHORE TODAY...   
..BROAD TROUGH REACHING THE NORTHERN PLAINS SATURDAY
 
AND THE  
GREAT LAKES BY SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z GFS / 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS SHOW VERY GOOD SIMILARITY...AS WITH THE LEAD  
SHORTWAVE...THROUGH 36 HOURS. DIFFERENCES EMERGE AROUND THAT POINT  
WHEN THE BROAD SHORTWAVE BEGINS TO REACH THE EASTERN SLOPES OF THE  
ROCKIES AND KICK OUT INTO THE PLAINS ON SATURDAY. THE 00Z NAM AND  
12Z CMC SHOW A FASTER PROGRESSION BY PERHAPS 6-12 HOURS. THIS  
LEADS TO DIFFERENCES IN INTERACTIONS WITH THE LEAD SHORTWAVE...AND  
BOTH MODELS ALSO SHOW THE VORTICITY MAX BECOMING CONCENTRATED  
FORWARD ON THE LEADING EDGE OF THE TROUGH. THE OTHER GLOBAL MODELS  
SHOW THE VORT MAX MORE CONCENTRATED IN THE BASE OF THE  
TROUGH...AND THESE DIFFERENCES DO HAVE SOME IMPACT ON OTHER MASS  
FIELDS AND EVEN SENSIBLE WEATHER. THE 12Z UKMET...DESPITE ITS  
INITIAL SIMILARITIES TO THE GFS AND ECMWF...EVENTUALLY SHOWS A  
MUCH SHARPER TROUGH THAN ANY OF THE OTHER MODELS...AND IT WAS A  
CLEAR OUTLIER BY MONDAY ON THE 12Z ENSEMBLE SPAGHETTI PLOTS.  
THEREFORE...THE PREFERENCE IS FOR A BLEND THAT INCORPORATES THE  
GFS AND ECMWF AS THIS IS ALSO VERY CLOSE TO THE GEFS AND ECMWF  
ENSEMBLE MEANS.  
 
06Z UPDATE: NO CHANGE FROM THE PRELIMINARY PREFERENCE. THE 00Z CMC  
HAS...IF ANYTHING...TRENDED CLOSER TO THE NAM WHICH DOES APPEAR TO  
BE THE LESS LIKELY SOLUTION AT THIS POINT. THE 00Z UKMET DOES NOT  
SHOW AS SHARP OF A SHORTWAVE IN THE EASTERN CONUS LATE THIS  
WEEKEND AND INTO MONDAY...BUT IT IS NOW SLOWER THAN THE ECMWF AND  
GFS. GIVEN THE CONSISTENCY OF THE ECMWF AND GFS...PREFER THOSE  
SOLUTIONS.  
 
...UPPER TROUGH DROPPING SOUTH TO OFFSHORE THE PACIFIC NORTHWEST  
THIS WEEKEND AND INTO MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ALTHOUGH THERE ARE DETAIL DIFFERENCES BETWEEN THE MODELS...THEY  
ARE QUITE SIMILAR WITH THIS SYSTEM THROUGH 72-84 HOURS. THE 00Z  
NAM SHOWS A STRONGER TROUGH AND UPPER LEVEL LOW THAN THE OTHER  
MODELS...BUT THIS IS THE ONLY MODEL WITH A NOTEWORTHY AND  
CONSISTENT BIAS RELATIVE TO THE REST OF THE MODELS. THEREFORE...A  
NON-NAM BLEND IS PREFERRED.  
 
06Z UPDATE: NO CHANGE FROM THE PRELIMINARY PREFERENCE. THERE ARE  
STILL DETAIL DIFFERENCES IN THE MODELS...BUT NONE THAT ARE  
SYSTEMATIC IN SUCH A WAY AS TO EXCLUDE THEM FROM THE BLEND (OTHER  
THAN THE NAM, AS DESCRIBED ABOVE).  
 
...POWERFUL OCCLUDING CYCLONE OVER EASTERN CANADA TODAY AND  
SATURDAY WITH ACCOMPANYING COLD FRONT SURGING THROUGH THE  
NORTHEASTERN US...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS SHOW VERY GOOD AGREEMENT WITH THIS SYSTEM WITH ALL OF THE  
MASS FIELDS...AND THE PRIMARY DIFFERENCES ARE RELATED TO TIMING  
DIFFERENCES ON THE ORDER OF AN HOUR OR TWO. THEREFORE...A GENERAL  
MODEL BLEND IS PREFERRED WITH HIGH CONFIDENCE.  
 
06Z UPDATE: NO CHANGE FROM THE PRELIMINARY PREFERENCE.  
 
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