204  
FXUS10 KWNH 110638  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
237 AM EDT WED OCT 11 2017  
 
VALID OCT 11/0000 UTC THRU OCT 14/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...INCLUDING PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...TROUGH DEAMPLIFYING AND ACCELERATING TO THE NORTHEAST U.S.  
COAST BY THURSDAY AND ACCOMPANYING WEAK SURFACE LOW IN THE UPPER  
MIDWEST / OHIO VALLEY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
IN GENERAL...THERE IS EXCELLENT MODEL AGREEMENT WITH THIS SYSTEM.  
THE EXCEPTION IS THE 12Z CMC WHICH SHOWS HIGHER HEIGHTS THROUGH  
THE DEPTH OF THE RIDGE OVER MUCH OF THE EASTERN CONUS. THIS LEADS  
TO A FASTER EJECTION AND DEAMPLIFICATION OF THE WAVE THAN ALMOST  
ALL OTHER MODELS...AND THE RIDGE BUILDING IN ACROSS THE EASTERN  
U.S. FASTER. THEREFORE...A NON-CMC BLEND IS RECOMMENDED FOR THIS  
SYSTEM WITH ABOVE AVERAGE CONFIDENCE.  
 
CHANGE FROM PRELIMINARY PREFERENCE: NONE. THE 00Z CMC DID TREND  
TOWARD THE MODEL CONSENSUS...BUT STILL DEAMPLIFIES THE WAVE FASTER  
THAN OTHER AVAILABLE MODELS AND BUILDS THE RIDGE IN SLIGHTLY  
FASTER IN THE EASTERN U.S.  
 
...UPPER TROUGH ARRIVING IN THE NORTHWESTERN U.S. WITH LEAD  
SHORTWAVE EJECTING TO HUDSON BAY BY THE WEEKEND...  
...ATTENDANT SURFACE CYCLONE DEVELOPING INTO CANADA AND ASSOCIATED  
COLD FRONT CROSSING THE NW REACHING NRN PLAINS ON THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
IN GENERAL...MODELS HAVE CONTINUED TO COME INTO BETTER AGREEMENT  
WITH THIS SYSTEM...AND ARE VERY CLOSE IN THE PLACEMENT OF THE  
SURFACE CYCLONE...TIMING OF THE WAVE AS IT EJECTS...AND THE COLD  
FRONT.  
 
CHANGE FROM PRELIMINARY PREFERENCE: REMOVE 00Z NAM FROM BLEND.  
TRENDS FROM ALL THE 00Z MODELS HAVE PLACED THE NAM AS A BIT OF AN  
OUTLIER NOW...PRIMARILY RELATED TO THE STRENGTH OF THE DEEPENING  
CYCLONE OVER SOUTHERN CANADA BEYOND 48 HOURS. THE EFFECTS FROM  
THIS ARE ALSO SEEN IN THE NORTHERN TIER OF STATES IN THE U.S. WITH  
SLIGHTLY LOWER HEIGHTS AND THICKNESSES.  
 
...SECONDARY SHORTWAVE DIGGING SOUTH INTO THE WESTERN U.S. FROM  
LATE THURSDAY INTO FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
WHILE THERE IS SLIGHTLY LESS MODEL AGREEMENT WITH THIS SYSTEM AS  
COMPARED TO THE OTHERS...THE MODELS ARE STILL FAIRLY CONSISTENT  
WITH THEIR MASS FIELDS. THEY ALL HAVE A SIMILAR TIMING FOR THIS  
WAVE AS IT DROPS SOUTH ON THE BACK PERIPHERY OF THE WESTERN U.S.  
TROUGH...A SIMILAR STRUCTURE TO THE TROUGH AS IT AMPLIFIES IN  
RESPONSE TO THE DIGGING WAVE ON FRIDAY...AND EVEN SIMILAR  
PLACEMENT OF VORT MAXES ALOFT.  
 
CHANGE FROM PRELIMINARY PREFERENCE: INCLUDE THE 00Z CMC. THE 12Z  
CANADIAN WAS EXCLUDED FOR HIGHER HEIGHTS AND SLIGHTLY FASTER  
MOTION OF THE TROUGH THROUGH THE WEST...BUT HAS SINCE MOVED CLOSER  
TO THE OTHER MODELS. THEREFORE...A GENERAL MODEL BLEND IS NOW  
RECOMMENDED.  
 
...TROPICAL WAVE CURRENTLY NEAR HISPANIOLA MOVING WEST TO NEAR  
FLORIDA BY FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
FOR THE CURRENT DEPICTION OF HEIGHT FIELDS ACROSS THE GULF OF  
MEXICO...CARIBBEAN SEA...AND SW ATLANTIC OCEAN...THE 12Z CANADIAN  
SHOWS A STRONGER SUBTROPICAL RIDGE AND WEAKER MID-UPPER LEVEL LOW  
ASSOCIATED WITH THE WAVE. THIS EVENTUALLY LEADS TO A SLOWER  
WESTWARD PROGRESSION OF THE WAVE BY FRIDAY. THE CANADIAN ALSO  
DEVELOPS A SURFACE LOW FAR TO THE NORTHWEST (NEAR 28N/74W BY 12Z  
FRIDAY) WHICH IS A SIGNIFICANT OUTLIER FROM THE OTHER MODEL  
SOLUTIONS. OTHERWISE...THERE ARE SOME DETAIL DIFFERENCES BETWEEN  
THE MODELS BUT THEY ARE ALL CLOSE ENOUGH TO BE USED IN A GENERAL  
BLEND OTHERWISE. THEREFORE...A NON-CMC BLEND IS RECOMMENDED FOR  
THIS SYSTEM.  
 
CHANGE FROM PRELIMINARY PREFERENCE: NONE. ALTHOUGH THE 00Z CMC HAS  
TRENDED A BIT IN THE DIRECTION OF THE OTHER MODELS...PARTICULARLY  
ALOFT...IT STILL GENERATES A SURFACE LOW FAR FURTHER TO THE  
NORTHEAST IN THE ATLANTIC THAN THE OTHER MODELS AND STILL HAS A  
WEAKER LOW ALOFT WITH THIS WAVE.  
 
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