757  
FXUS10 KWNH 141834  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
233 PM EDT SAT OCT 14 2017  
 
VALID OCT 14/1200 UTC THRU OCT 18/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES INCLUDING CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SYSTEM MOVING INTO THE GREAT LAKES EARLY SUN/BY MAINE SUN NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 06Z NAM WAS A MUCH BETTER OVERALL EVOLUTION WITH THE GROWING  
CONSENSUS OF THE SHORTWAVE THAT CROSSES THE GREAT LAKES SUNDAY AND  
TRENDS INTO THE NORTHEAST US/SOUTHEAST CANADA BY EARLY MONDAY.  
HOWEVER THE 12Z NAM RUN HAS ONCE AGAIN BECOME A BIT MORE  
AGGRESSIVE IN WINDING UP THE CIRCULATION ENTERING THE GREAT  
LAKES...THIS SLOWS THE OVERALL TRANSLATION OF THE WAVE MAKING IT  
ONCE AGAIN A SIGNIFICANT OUTLIER TO THE OTHER DETERMINISTIC  
GUIDANCE INCLUDING THE LATEST 12Z RUN OF A FAIRLY STABLE GFS  
CONTINUITY. THE 00Z UKMET IS A BIT NORTH/FASTER IN A TYPICAL  
LOCATION BUT STILL WELL WITHIN THE CLUSTERING TO SUPPORT ITS  
REMAINING INCLUSION IN A NON-NAM PREFERENCE. CONFIDENCE IS  
SLIGHTLY ABOVE AVERAGE GIVEN THE SMALL REMAINING SPREAD AND SMALL  
RUN TO RUN VARIATION INHERENT IN THE GUIDANCE.  
 
19Z UPDATE: THE SMALL SHIFT SLOWER NOTED WITH THE 12Z GFS HAS BEEN  
SEEN WITH THE 12Z ECMWF/UKMET AND CMC TO KEEP A TIGHT CLUSTERING  
THROUGHOUT THE NON-NAM SOLUTION. AS SUCH WILL KEEP INITIAL  
PREFERENCE AND GIVEN THESE SMALL RUN TO RUN ADJUSTMENTS  
CONTINUING...CONFIDENCE ALSO REMAINS SLIGHTLY ABOVE AVERAGE.  
 
KICKER SHORTWAVE AMPLIFYING INTO THE GREAT LAKES SUNDAY NIGHT AND  
THROUGH THE NORTHEAST/MID-ATLANTIC MONDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A FAST MOVING FAIRLY COMPACT SHORTWAVE EMERGES FROM THE GULF OF AK  
TODAY AND RACES ACROSS CENTRAL/SOUTHERN CANADA ENTERING NORTH  
DAKOTA AND THE UPPER MIDWEST BY SUNDAY. THE WAVE EVENTUALLY  
REPLACES THE BASE OF THE LARGER SCALE TROF INTO MONDAY ACROSS THE  
GREAT LAKES INTO THE MID-ATLANTIC. IT IS AT THIS POINT THE 00Z  
CMC IS THE ONLY SIGNIFICANT OUTLIER HAVING SHORTENED THE DISTANCE  
FROM THE PRIOR WAVE AND EVOLVING A BIT QUICKER THOUGH IN A SIMILAR  
MANNER BY LATE SUN INTO MONDAY. EVEN THOUGH THE 12Z NAM HAS  
DOWNSTREAM SPEED ISSUES...THIS WAVE IS WELL TIMED/EVOLVES IN A  
SIMILAR MANNER AS THE 12Z GFS AND THE 00Z UKMET/ECMWF AS WELL AS  
THE FAIRLY TIGHT ENSEMBLE PACKING. AS SUCH WILL SUPPORT A NON-CMC  
BLEND AT ABOVE AVERAGE CONFIDENCE (GIVEN THE CMC EVOLVES SIMILARLY  
JUST UNCHARACTERISTICALLY FAST).  
 
19Z UPDATE: THE 12Z CMC HAS SLOWED ENOUGH FOR INCREASED SPACING  
WITH PRIOR WAVE AND IS NOW MATCHING THE REMAINING GUIDANCE ENOUGH  
TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
FRONT APPROACHING THE PACIFIC NORTHWEST MONDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS REMAIN PERSISTENT IN STRENGTH AND TIMING OF A SHORTWAVE  
AMPLIFICATION APPROACHING SOUTHEAST AK PANHANDLE INTO COASTAL BC  
EARLY MONDAY WITH A SURFACE WAVE. THE TRAILING TROF/HEIGHT FALLS  
WILL ALLOW FOR THE SOUTHWARD PUSH OF THE FRONTAL ZONE STARTING TO  
AFFECT VANCOUVER ISLAND INTO THE PACIFIC NORTHWEST TUESDAY INTO  
WED. THE 12Z NAM SHOWED A SLIGHT SLOWING TO CLUSTER BETTER WITH  
THE 12Z GFS AND 00Z ECMWF AND 00Z UKMET. THE 00Z UKMET IS A BIT  
FURTHER NORTH AND AFTER CROSSING THE CANADIAN ROCKIES A BIT  
QUICKER THAN THE NAM/GFS/ECMWF; THOUGH AS A WHOLE BUT NOT  
SIGNIFICANTLY TO REMOVE FROM ANY PREFERENCE. THE MAIN OUTLIER IS  
THE 00Z CMC WHICH WAS INITIALLY FAST WITH THE LEADING NORTHERN  
PORTION OF THE HEIGHT FALLS AND A WEAKER WAVE INCREASING  
SPACING/POSITIVE TILT TO THE OVERALL TROF/TRAILING HEIGHT FALLS.  
AS SUCH THE INCREASED SPACING ALLOWS FOR UPSTREAM AMPLIFICATION  
AND SLOWING OF FRONT WITH SECONDARY SURFACE WAVE DEVELOPMENT. AS  
SUCH WILL SUPPORT A NON-CMC BLEND AND GIVEN THE TIME RELATIVE  
SMALL SPREAD IN THE REMAINING GUIDANCE CONFIDENCE IS CONSIDERED  
SLIGHTLY ABOVE AVERAGE IN THE BLEND.  
 
19Z UPDATE: THE 12Z ECMWF TRENDED BACK TO SLIGHTLY FURTHER SOUTH  
AND MORE AMPLIFIED THAN THE 00Z RUN AS THE SHORTWAVE COMES ASHORE  
IN VANCOUVER ISLAND/S BC TUES...THIS MAKES IT A BIT SLOWER/DEEPER  
THAN THE 12Z GFS/NAM. THIS LEADS TO A SLIGHTLY WEAKER SURFACE  
REFLECTION (FURTHER NORTH) AND STRONGER FRONTAL ZONE/CONVERGENCE  
RESPONSE...BUT STILL FAIRLY CLOSE TO THE 12Z NAM/GFS. THE 12Z  
UKMET TRENDED VERY SIMILARLY TO THE ECMWF ESPECIALLY WITH THE  
STRONGER MORE SOUTHERN AMPLIFICATION...AND OVERALL SEEMS TO BE A  
GOOD BRIDGE BETWEEN THE NAM/GFS AND ECMWF. THE 12Z CMC WHILE  
TRENDING A BIT BETTER (WEAKER AND FASTER) STILL IS A CLEAR OUTLIER  
TO KEEP SUPPORT IN A NON-CMC BLEND.  
 
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