171  
FXUS10 KWNH 161832  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
131 PM EST THU NOV 16 2017  
 
VALID NOV 16/1200 UTC THRU NOV 20/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES WITH CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SYSTEM LEAVING NEW ENGLAND TODAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 00Z UKMET ONCE AGAIN LAGS THE OVERALL CONSENSUS AS THE  
SURFACE/STACKED LOW LIFTS INTO SE CANADA FRI. OTHERWISE...THERE  
REMAIN SOME LINGERING DEPTH DISCONTINUITIES (2-3 MB AT THE  
SURFACE) THE PLACEMENT/SHAPE LOOK STRONG ENOUGH TO SUPPORT A  
NON-UKMET BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
19Z UPDATE: 12Z UKMET RUN WHILE STILL A BIT SLOWER THAN THE OTHER  
GUIDANCE IS NOW WELL WITHIN THE TIGHT CLUSTERING TO SUPPORT A  
GENERAL MODEL BLEND.  
 
NORTHERN STREAM S/W AND CYCLONE LIFTING ACROSS SOUTHERN CANADA  
WITH COLD FRONT MOVING THROUGH NORTHERN TIER TODAY TO SAT MORNING  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE LEAD SHORTWAVE/HEIGHT FALLS FROM THE MAIN UPPER LOW ALONG THE  
WEST COAST IS CURRENTLY CROSSING INTO THE US/CANADIAN BORDER  
ROCKIES OUT OF E WA...MODELS HAVE COME INTO A NEAR CONSENSUS WITH  
ITS FUTURE EVOLUTION INCLUDING THE LEE SURFACE CYCLONE. THIS WAVE  
WILL TRACK FROM S ALBERTA TODAY TO NE MANITOBA BY LATE FRIDAY  
BEFORE SHOWING ANY REAL DIFFERENCES/DEPARTURES. THIS INCLUDES  
THE TIMING OF THE FRONTAL ZONE CROSSING INTO THE GREAT LAKES AND  
CONNECTING BACK TO THE DEVELOPING CENTRAL PLAINS LOW. AS SUCH  
WILL SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.  
 
19Z UPDATE: NO SIGNIFICANT CHANGE NOTED IN THE 12Z UKMET/CMC/ECMWF  
OR GEFS MEAN TO SUGGEST CHANGE TO THE GENERAL MODEL BLEND  
PREFERENCE.  
 
CYCLONE MOVING FROM CENTRAL PLAINS TO GREAT LAKES TO NEW ENGLAND  
FRI...SAT...SUN WITH ATTENDANT FRONTAL ZONE THROUGH THE SOUTH  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: AVERAGE  
 
OVERALL EVOLUTION OF THE BASE OF THE LARGE WESTERN TROF CONTINUES  
TO CONSOLIDATE BUT SMALL BUT IMPORTANT DIFFERENCES CONTINUE TO  
LEAD TO MODERATE SPREAD PARTICULARLY TOWARD THE PRECISE  
LOCATION/TRACK OF THE SURFACE WAVE AND THE TIMING OF THE ATTENDANT  
COLD FRONT ESPECIALLY ON SUN. THE 12Z NAM AND GFS BOTH SHIFTED  
SOUTH WITH THE TRACK WHILE BROADENING THE OVERALL WAVELENGTH OF  
THE TROF (BEGINNING TO BE ROUNDER AS IT LIFTS OUT OF THE OH/TN  
VALLEY INTO NEW ENGLAND. THIS IS OPPOSED BY A MORE ELONGATED  
EMERGENCE LIFTING NORTH BY THE ECWMF/CMC AND UKMET. THE 00Z CMC  
LOOKS MOST OF OF PLACE IS COMPARISON PLOTS BEING A BIT TOO FAST  
ESPECIALLY IN TIMING OF THE COLD FRONT THROUGH THE SOUTH AND AS  
SUCH WILL BE REMOVED FROM ANY PREFERENCE AT THIS TIME. A NON-CMC  
BLEND SHOULD SUFFICE AT THIS TIME BUT MODEST MASS SPREADS WITH THE  
LOW TRACK CONFIDENCE IS AVERAGE IN THIS BLEND.  
 
19Z UPDATE: THE 12Z CMC SLOWED THE INNER CORE OF THE UPPER LOW BUT  
CONTINUES TO PRESENT A STRONG COLD CONVEYOR/JET THAT PRESSES THE  
COLD FRONT A BIT TOO FAST THROUGH THE MID-ATLANTIC/CAROLINAS AND  
SOUTHEASTERN TIER STATES. THE 12Z ECMWF SLOWED A BIT...LIKE THE  
GFS/NAM ALLOWING FOR ADDITIONAL TIME TO TIGHTEN/AMPLIFY ACROSS THE  
GREAT LAKES...TRACK FURTHER SOUTH AND SLOW THE FRONTAL TIMING A  
SHADE. STILL THIS IS QUITE CLOSE TO THE GFS. THE 12Z UKMET IS  
THE LONE GUIDANCE MEMBER TO NOT MAKE THE SLIGHT SOUTHWARD  
SHIFT...YET STILL REMAINS CLOSE/CLUSTERED AND TIMED WELL WITH THE  
GFS/NAM/ECMWF TO KEEP A NON-CMC BLEND.  
 
TROUGH AND SURFACE WAVE APPROACHING VANCOUVER ISLAND LATE SAT WITH  
FRONTAL ZONE SLIPPING INTO NW BY LATE SUN  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
BY FRIDAY A SHORTWAVE BEGINS TO AMPLIFY ACROSS THE GULF OF AK AND  
DRAW SOME SOUTHERN ENERGY INTO IT BROADENING THE TROF BY SAT AS IT  
SLOWLY DROPS TOWARD THE PACIFIC NORTHWEST. CORRALLED BY A SURFACE  
WAVE LIFTING NORTHEAST INTO CENTRAL BC BY 00Z SUN...THE MOISTURE  
TONGUE WILL BEGIN TO PULL NORTHWARD AS WELL AND BY SUNDAY WILL BE  
DIRECTED TOWARD VANCOUVER ISLAND. IT IS IN THE INTERACTION TIMING  
AND STRENGTH OF THE SOUTHERN WAVE THAT GENERALLY LEADS TO MODEST  
MODEL SPREAD TOWARD SAT/SUN AND HOW FAST/STRETCHED IT BECOMES AS  
IT PROGRESSES SOUTHEAST. THE BULK OF ENSEMBLE SOLUTIONS ARE  
TRENDING TO A SHARPER SOLUTION WITH MODEST POSITIVE TILT  
ORIENTATION. THE 00Z CMC IS A BIT MORE AGGRESSIVE/STRONG IN THE  
SOUTHERN PORTION OF THE TROF BY SUNDAY AND PRESSES THE BASE'S  
HEIGHT FALLS FORWARD FASTER. THE GFS WHICH HAD BEEN LAGGING  
SIGNIFICANTLY HAS TRANSITIONED FASTER TO BECOME MUCH CLOSER TO THE  
OTHERWISE AGREEABLE 12Z NAM AND 00Z ECMWF/UKMET REPRESENTING THE  
THE MIDDLE OF THE MODEST ENSEMBLE SPREAD. A SLIGHT EASTWARD SHIFT  
AT THE NORTHERN PORTION OF THE TROF BY 00Z MON WAS NOTED IN THE  
12Z NAM RUN RELATIVE TO THE GFS/UKMET/ECMWF BUT SEEMS MINOR IN FOR  
A DAY 3 TO KEEP IT WITHIN THE OVERALL PREFERENCE. AS SUCH A  
NON-CMC BLEND IS SUGGESTED WITH GREATEST WEIGHTING TOWARD THE  
ECWMF. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE.  
 
19Z UPDATE: THE 12Z CMC WHILE STILL A SHADE FASTER AND LESS  
ELONGATED TOWARD THE SOUTHWEST TOWARD LATE SUNDAY IS CLOSE ENOUGH  
TO FURTHER TIGHTEN THE GUIDANCE CLUSTER/EVOLUTION. LITTLE  
VARIATION IN THE ECMWF FURTHER SOLIDIFIES AND INCREASES CONFIDENCE  
IN A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE AT THIS TIME  
OUT INTO THE FUTURE.  
 
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