858  
FXUS10 KWNH 161844  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
244 PM EDT MON OCT 16 2017  
 
VALID OCT 16/1200 UTC THRU OCT 20/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE MOVING QUICKLY EAST IN ZONAL FLOW ALONG THE  
U.S.-CANADA BORDER TUESDAY THROUGH THURSDAY...   
..ASSOCIATED DEEPENING SURFACE LOW AND COLD FRONT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF / CMC / UKMET  
CONFIDENCE: ABOVE AVERAGE  
 
A SHORTWAVE EMBEDDED IN ZONAL FLOW WILL MOVE RAPIDLY EAST ALONG OR  
JUST NORTH OF THE CANADIAN BORDER IN THE NEXT 48 HOURS...MOVING  
ABOUT 50 DEGREES LONGITUDE (150W TO 100W) BY WEDNESDAY MORNING.  
MODELS ALSO SHOW RELATIVELY STRONG LEE CYCLOGENESIS TO THE EAST OF  
THE CANADIAN ROCKIES (DEEPENING RATE OF SURFACE LOW NOT QUITE 1  
BERGERON BUT CLOSE) AND OCCLUDE THE CYCLONE IN THE VICINITY OF  
NORTHERN MANITOBA AND HUDSON BAY BY WEDNESDAY NIGHT. THE 12Z NAM  
AND GFS ARE SLOWER THAN THE OTHER GLOBAL MODELS...AND THE GFS HAS  
A STRONGER MID-LEVEL VORT MAX DISPLACED ABOUT 1-2 DEGREES LATITUDE  
FURTHER SOUTH THAN THE OTHER MODELS. WITH ZONAL FLOW...THE  
PREFERENCE IS FOR THE MODEL CAMP THAT IS MORE PROGRESSIVE WITH THE  
WAVE AND LESS AMPLIFIED. OVERALL THE 12Z NAM AND GFS DIFFERENCES  
ARE NOT LARGE...BUT ENOUGH AT SUCH SHORT TIME RANGES THAT A  
ECMWF...CMC...UKMET BLEND IS RECOMMENDED.  
 
CHANGE FROM PRELIMINARY PREFERENCE: NONE.  
 
...TROUGH DIGGING INTO THE PACIFIC NORTHWEST LATE WEDNESDAY INTO  
THURSDAY ASSOCIATED WITH AN ATMOSPHERIC RIVER EVENT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A DEEPER TROUGH (COMPARED TO THE TUESDAY SYSTEM) WILL DIG INTO THE  
PACIFIC NORTHWEST LATE WEDNESDAY INTO THURSDAY...WITH A STRONG  
SURFACE CYCLONE APPROACHING BRITISH COLUMBIA BY THE END OF THE  
WORK WEEK. AN ATMOSPHERIC RIVER WILL BE PUSHING INTO THE PACIFIC  
NORTHWEST JUST AHEAD OF THE TROUGH. MODEL DIFFERENCES WITH THIS  
SYSTEM ARE FAIRLY SMALL. NORMALIZED STANDARD DEVIATION OF MSLP AND  
500MB HEIGHTS ON THE 00Z ECMWF ENSEMBLES SHOWED GENERALLY NEAR OR  
SLIGHTLY BELOW NORMAL AMOUNT OF SPREAD OVER THE NORTHWEST FROM  
WEDNESDAY INTO THURSDAY. ONE EXCEPTION CONTINUED TO BE THE 12Z CMC  
WHICH SHOWED A FLATTER WAVE ACROSS THE EASTERN PACIFIC WITH HIGHER  
HEIGHTS THROUGH MOST OF THE MID-LATITUDES (30-60N)...AS MUCH AS  
60M HIGHER THAN ENSEMBLE MEANS AT 500MB IN SOME LOCATIONS.  
THEREFORE...A GENERAL MODEL BLEND THAT EXCLUDES THE 00Z CMC IS  
PREFERRED.  
 
CHANGE FROM PRELIMINARY PREFERENCE: NONE. THE CANADIAN MODEL  
CONTINUED TO BE THE OUTLIER...AS IT WAS ON THE 00Z RUN. OTHER  
MODELS CONTINUE TO BE IN FAIRLY GOOD AGREEMENT.  
 
...PROGRESSIVE TROUGH MOVING FROM THE EASTERN GREAT LAKES TODAY TO  
THE CANADIAN MARITIMES TUESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A BROAD TROUGH OVER THE NORTHEASTERN CONUS WILL GRADUALLY  
DEAMPLIFY AND QUICKLY EXIT OVER THE ATLANTIC DURING THE NEXT 24  
HOURS...WITH THE SURFACE COLD FRONT GENERALLY ALREADY OFFSHORE.  
MODELS SHOW NO SUBSTANTIAL DISAGREEMENT IN THE MASS FIELDS WITH  
THIS SYSTEM SO A GENERAL MODEL BLEND IS RECOMMENDED WITH HIGH  
CONFIDENCE.  
 
   
..LINGERING BROAD TROUGH OVER THE SOUTHEAST STATES
 
   
..STALLING COLD FRONT IN THE VICINITY OF FLORIDA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
ALTHOUGH THE COMPONENT OF THE EASTERN CONUS WAVE TIED MORE CLOSELY  
TO THE NORTHERN STREAM JET SHOULD BE PROGRESSIVE...A BROAD TROUGH  
IS LIKELY TO LINGER OVER THE SOUTHEAST THROUGH THE REMAINDER OF  
THE WEEK. INITIALLY THIS WILL LIKELY BE RELATED TO THE SOUTHERN  
PORTION OF THE INITIAL TROUGH...HOWEVER SEVERAL REINFORCING  
SHORTWAVES CURRENTLY NEAR THE NORTHWESTERN U.S. ARE LIKELY TO  
ARRIVE OVER THE NEXT SEVERAL DAYS. AT THE SURFACE...A COLD FRONT  
WILL STALL OUT NEAR THE SOUTHERN PERIPHERY OF THE LOW-LEVEL MID  
ATLANTIC ANTICYCLONE.  
 
IN GENERAL...THE 12Z ECMWF AND 12Z GFS ARE CLOSEST TO THE ENSEMBLE  
MEANS (00Z ECMWF ENS AND 12Z GEFS) IN THEIR DEPICTION OF THE MASS  
FIELDS. BOTH MAINTAIN SLIGHTLY LOWER HEIGHTS ALOFT THROUGH THE  
REGION...WHICH IS GENERALLY PREFERRED GIVEN THE PROMINENT  
SOUTHWARD EXTENSION OF THE TROUGH NOTED ON WATER VAPOR SATELLITE  
AT THE MOMENT...AS WELL AS SOME CONVECTION OVER THE CENTRAL GULF  
THAT MAY BE TIED TO A WEAK MID-LEVEL LOW. THE CMC...UKMET...AND  
NAM (TO A SLIGHTLY LESSER EXTENT) TEND TO DEAMPLIFY THE TROUGH AND  
BUILD HEIGHTS FASTER...AND DEPICT A STRONGER SUBTROPICAL RIDGE /  
SURFACE HIGH ACROSS THE EASTERN CONUS OVERALL. GIVEN THE SUPPORT  
FROM THE ENSEMBLE MEANS...PREFER A BLEND OF THE 12Z GFS AND 12Z  
ECMWF IN THIS REGION.  
 
CHANGE FROM PRELIMINARY PREFERENCE: NONE. ALTHOUGH THERE WERE SOME  
MINOR TRENDS FROM THE 00Z MODEL CYCLE...OVERALL THE DIFFERENCES  
BETWEEN THE MODELS REMAIN RELATIVELY SIMILAR.  
 
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