853  
FXUS10 KWNH 181610  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1110 AM EST SAT NOV 18 2017  
 
VALID NOV 18/1200 UTC THRU NOV 22/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL ASSESSMENT INCLUDING PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
LARGE STORM SYSTEM OVER THE EASTERN U.S. THIS WEEKEND  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z NAM HAS SHIFTED SLIGHTLY NORTH TO FURTHER CONSOLIDATE THE  
MASS FIELDS TOWARD A COMMON SOLUTION THOUGH THE DEPTH OF THE FULL  
LATITUDE CYCLONE. SOME SMALL DIFFERENCES NEAR THE INNER CORE  
ESPECIALLY MONDAY/TUESDAY SHIFTING INTO CANADA; YET A GENERAL  
MODEL BLEND IN THIS CASE WILL SOLIDIFY THIS MINOR VARIATIONS AND  
PROVIDE ABOVE AVERAGE CONFIDENCE IN THIS SOLUTION MOVING FORWARD.  
 
NORTHERN PORTION OF TROF TRACKING EASTWARD ACROSS SOUTHERN CANADA  
EVENTUALLY AMPLIFYING OVER THE GREAT LAKES TUES INTO WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/00Z CMC BLEND  
CONFIDENCE: AVERAGE  
 
GOES-W WV SHOWS TROF IN EASTERN GULF OF AK BEGINNING TO ELONGATE  
TOWARD THE SSW AS IT SINKS SW TOWARD PACIFIC NORTHWEST. A SUBTLE  
SHORTWAVE LIFTING NORTHEAST AHEAD OF THE MAIN TROF AXIS SPURRING A  
SURFACE WAVE THAT REACHES THE CENTRAL BC COAST LATER TODAY INTO  
SUN. THIS ENERGY TRANSLATES ACROSS THE CANADIAN ROCKIES SPURRING  
A STRONG LEE CYCLONE WHILE CONCURRENTLY DRAWING THE NORTHERN  
POTION OF THE UPPER TROF ALONG WITH IT; EVENTUALLY SEVERING FROM  
THE REMAINING TROF ENERGY ACROSS THE NORTHERN US ROCKIES MONDAY.  
AS IT DOES SO...THE WAVE STRENGTHENS AND AMPLIFIES ACROSS SOUTHERN  
CANADA INTO THE WESTERN GREAT LAKES TUES. THE 00Z UKMET  
CONTINUES TO BE GREATEST PHASED/CONNECTED TO THE BASE OF THE  
TROF...AND IN DOING SO LAGS THE MAIN SUITE OF GUIDANCE/ENSEMBLES  
ACROSS SOUTHERN CA. THE 12Z NAM SHOWS A BIT OF KNOWN BIAS WITH A  
STRONGER YET VERY CONSOLIDATED INNER CORE OF THE WAVE CROSS INTO  
THE GREAT LAKES WHILE THE BULK OF GUIDANCE SHOWS SOME SOUTHWARD  
EXTENSION OF THE TROF...MAKING IT A BIT LESS DESIRABLE. THE 00Z  
ECMWF ON THE OTHER SIDE OF THE SPECTRUM...WHILE STRONG WITH THE  
SHORTWAVE ENTERING THE WESTERN GREAT LAKES...HAS A STRONG BASE/JET  
STREAK CROSSING THE MIDWEST INTO THE OHIO VALLEY BY THE END OF THE  
FORECAST PERIOD. THIS SOUTHWARD EXTENSION IS A BIT MORE DRAMATIC  
THAN EVEN THE BULK OF ECENS MEMBERS. THE 00Z CMC IS QUITE SIMILAR  
BUT DOES NOT MANIFEST THE DEEPER TROF THROUGH THE GREAT LAKES.  
THE 12Z GFS WHILE INITIALLY FINE THROUGH THE CANADIAN ROCKIES BUT  
START TO SHOW SOME TYPICAL FAST SPEED BIAS ALLOWING FOR A SLIGHT  
NEGATIVE TILT TROF THROUGH THE GREAT LAKES BY TUES. WHILE NO  
DETERMINISTIC MODEL SEEMS IDEAL TOWARD THE OVERALL ENSEMBLE MEAN  
SOLUTIONS...A COMBINATION OF THE 00Z ECMWF AND CMC SEEMS  
APPROPRIATE AT AVERAGE CONFIDENCE.  
 
BASE OF TROUGH APPROACHING THE PACIFIC NORTHWEST SUNDAY/SLIDING  
SOUTHEAST THROUGH ROCKIES INTO PLAINS TUES FILLING OUT BASE OF  
TROF IN GULF WED  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/NAM AND 00Z ECMWF BLEND  
CONFIDENCE: BELOW AVERAGE  
 
THE BASE OF AN ELONGATED TROF WILL BE TRAPPED UNDER STRONG LARGER  
SCALE SOUTHWESTERLY PUMPING OF RIDGING LATE SUN/MON WITH THE RAPID  
APPROACH OF THE BROAD/CLOSED LOW THAT WILL DOMINATE THE  
NORTHEASTERN PACIFIC/GULF OF AK BY EARLY NEXT WEEK. THIS WILL  
LEAVE THE REMAINING ENERGY UNDER WEAK STEERING FLOW BUT ALSO AN  
ENVIRONMENT WITH THE POTENTIAL FOR THE SYSTEM TO CONSOLIDATE/WIND  
UP INTO A DEEPER CYCLONE. THIS STRONGER CONSOLIDATED SOLUTION  
CONTINUES TO BE PRESENTED BY THE 00Z CMC. HOWEVER...THE  
ECMWF/ECENS MEAN ALONG WITH 12Z AND 00Z/06Z GFS/NAM SOLUTIONS  
CONTINUED A SLOWER EASTWARD SHIFT SHOWING GREATER STRETCHING OF  
THE WAVE AT THE APEX OF THE BUILDING RIDGE...LEADING TO A SPLIT OF  
THE WAVE ENERGY...SOME DOWN THE EASTERN SIDE OF THE TROF TO START  
CARVING OUT THE BASE OF THE LARGER SCALE TROF ACROSS THE GULF ON  
MONDAY (NAM) OR SOME SLOWER LIFTING NORTH WEST OF THE RIDGE AXIS  
INTO BC/ALBERTA BEFORE STARTING THE SLIDE INTO THE ROCKIES/GREAT  
PLAINS (ECMWF/GFS). THE 00Z UKMET IS MUCH TOO PHASED WITH THE  
NORTHERN STREAM AND NOT REPRESENTED WELL IN OTHER ENSEMBLE  
GUIDANCE SCENARIOS OR WITHIN THE RUN TO RUN TRENDS TO SUPPORT IT.  
THE 12Z NAM MAY BE A BIT TOO FAST/GREAT WITH THE STRENGTH OF THE  
WAVE LATE TUES BUT ALSO KEEPS WITH SOME CONTINUITY FROM THE PRIOR  
RUNS YESTERDAY.  
 
THIS REMAINS A VERY LOW PREDICTABILITY ENVIRONMENT ESPECIALLY IN  
TIMING AND THEREFORE CONFIDENCE REMAINS BELOW AVERAGE. SOMEWHERE  
BETWEEN THE 00Z ECMWF AND 12Z GFS SEEMS APPROPRIATE GIVEN THE  
OVERALL ENSEMBLE TRENDS/LONGER TERM RELIABILITY IN THESE GUIDANCE  
MEMBERS BUT INCLUDE A LOW PERCENTAGE OF THE 12Z NAM FOR CONTINUITY  
TO HELP ACCOUNT FOR THE SLIGHTLY FASTER SOLUTIONS IN THE ENSEMBLE  
SUITE.  
 
BROAD/DEEP CLOSED DOMINATING THE NORTHEASTERN PACIFIC...SOUTHWEST  
FLOW INTO THE PACIFIC NORTHWEST BY LATE TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-GFS BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
AS MENTIONED IN PRIOR TWO SECTIONS...THE INFLUENCE OF THIS  
DEVELOPING LARGE SCALE DEEP CYCLONE ALREADY HAS AN IMPACT TO THE  
PACIFIC NORTHWEST EVEN BEFORE ITS DIRECT INFLUENCE. THE STRONG  
SOUTHWEST PUMPING OF THE RIDGE MON/TUES WILL USHER IN SMALLER  
SHORTWAVE VORT CENTERS FROM THE SUBTROPICAL EASTERN PACIFIC WITH  
THE STRONGEST TUESDAY DEVELOPING A SURFACE WAVE BETWEEN 130-140W  
BUT ALSO DIRECT ADDITIONAL MOISTURE ALONG THE WARM FRONT SETTING  
UP THE NEXT SURGE IN THE ATMOSPHERIC RIVER; HOWEVER THERE REMAINS  
A FAIRLY LARGE SPREAD IN TIMING...THE NAM/GFS HAD BEEN LEADING THE  
CMC/ECMWF/UKMET ABOUT 6-9HRS FASTER. HOWEVER THE 12Z NAM HAS  
TRENDED MUCH SLOWER THOUGH STILL OUTPACES THE SLOWER NON-NCEP  
SOLUTIONS. THE 00Z UKMET MAY PRESS THE WARM FRONTAL TROF A BIT  
FURTHER EAST THAN THE OTHER GUIDANCE BUT STILL REMAINS WITHIN THE  
REALM OF PROBABILITY GIVEN THE CURRENT ENSEMBLE SPREAD. THE 12Z  
GFS DID NOT MAKE THE SLOWING SHIFT THAT THE NAM DID BUT HAD SLOWED  
SLIGHTLY THOUGH STILL REMAINS THE OUTLIER. AT THIS POINT...THERE  
IS LOWER CONFIDENCE DUE TO THE TIMING AND INTERACTION OF THESE  
SMALL WAVES ON THE EASTERN SIDE OF THE DEEPER CYCLONE...HOWEVER  
WILL FAVOR THE SLOWER GUIDANCE THAT HAS A BIT GREATER  
ENSEMBLE/CONTINUITY SUPPORT. AS SUCH A NON-GFS BLEND IS SUPPORTED  
BUT AT SLIGHTLY BELOW AVERAGE CONFIDENCE.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page