020  
FXUS10 KWNH 110450  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1149 PM EST TUE DEC 10 2019  
 
VALID DEC 11/0000 UTC THRU DEC 14/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..LARGER SCALE CONUS (CONFIDENCE DISCUSSION)
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE BROAD GLOBAL TROF THAT HAS DOMINATED THE EASTERN HALF OF THE  
NA CONTINENT GIVES WAY TOWARD A MORE ZONAL PATTERN OVER THE NEXT  
FEW DAYS, LEAD BY SMALLER SHORTWAVE ENERGY PACKETS ALONG THE  
REMAINING NW-SE STRETCHED TROF CURRENTLY ENTERING THE WEST COAST  
(ONE NORTH ALONG THE VANCOUVER ISLAND/PUGET SOUND AND SOUTHERN  
NEAR CAPE MENDOCINO IN N CA). EVENTUALLY, THE LEAD NORTHERN AND  
SOUTHERN STREAM WAVES PROGRESS INTO THE PLAINS BEFORE GIVING FULL  
WAY TO A STRONG PACIFIC JET WITH NUMEROUS VERY SHORT  
WAVELENGTH/LOW AMPLITUDE WAVE PARADE INTO THE PACIFIC NORTHWEST,  
MIDDAY WED TO LATE FRIDAY WITH THE APPROACH OF A DEEPER LATITUDE  
SHORTWAVE TROF ENTERING SAT. HIGH CONFIDENCE IN GENERAL MODEL  
BLEND WILL EXIST FOR THE REMAINING GLOBAL SCALE TROF AND FRONTAL  
ZONE CROSSING THE EAST COAST/NORTHEAST TODAY, AFTERWARD HOWEVER,  
THE TIMING/SPACING OF NUMEROUS SMALLER SCALE FEATURES AND THEIR  
INTERACTIONS LEAD TO LARGE INTERNAL VARIATIONS, WITH MODERATE TO  
HIGH DIFFERENCES IN THE SENSIBLE WEATHER PREDICTABILITY EVEN  
THOUGH THE LARGE SCALE EVOLUTION OF A BROADLY NEGATIVE TILT TROF  
AND SOUTHEAST SURFACE LOW DEVELOPMENT IS AGREED UPON. SO  
BOTTOM-LINE, CONFIDENCE IS SLIGHTLY BELOW TO BELOW AVERAGE FOR THE  
INTERNAL PRECISE PLACEMENT OF IMPORTANT WEATHER ELEMENTS AS THE  
SYSTEM COMES TOGETHER BY THE WEEKEND.  
 
...NORTHERN STREAM SHORTWAVES ACROSS NORTHERN TIER INTO GREAT  
LAKES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~  
PREFERENCE: INITIALLY 00Z GFS/NAM AND 12Z ECMWF THRU 13.06Z  
18Z GEFS/00Z NAM AND 12Z ECMWF/ECENS AFTER  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE TO AVERAGE  
 
THE NORTHERN STREAM, STARTING WITH THE SHORTWAVE ENTERING THE  
PACNW AT THIS TIME, IS BETTER HANDLED THROUGH THE SHORT-RANGE  
PERIOD...WITH A SOLID CONSENSUS/GENERAL MODEL BLEND WORKING ACROSS  
THE NORTHERN TIER INTO THE GREAT LAKES BY FRI. ON ITS HEELS,  
THOUGH, THERE IS MORE VARIATION, MAINLY IN TIMING SPACING BETWEEN  
THE PACIFIC SHORTWAVE ENERGY AND THE DIGGING ARCTIC COLD AIR.  
HERE THE ECMWF, NAM AND GFS ARE SOLID IN TIMING, BUT THE GFS SHOWS  
A TYPICAL THOUGH MINOR TO MODERATE FAST BIAS WITH THE COLD AIR AND  
THEREFORE GREATER AMPLIFICATION. THE 00Z NAM, WHILE SPACED  
NICELY, SHOWS A GREATER REFLECTION OF THE WAVE IN THE HEIGHT  
FIELDS, BUT THAT SEEMS TO BE THE ONLY NEGATIVE IMPACT. SO WOULD  
BE SHIFTING MORE TOWARD A 18Z GEFS MEAN, 00Z NAM, 12Z ECMWF BLEND  
SOLUTION FOR THIS SYSTEM BUT AT AVERAGE TO SLIGHTLY ABOVE AVERAGE  
CONFIDENCE.  
 
   
..SOUTHERN STREAM/DEVELOPING SOUTHEAST SURFACE LOW FRI/SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM/12Z ECMWF (12Z ECENS MEAN)  
CONFIDENCE: SLIGHTLY BELOW TO BELOW AVERAGE  
 
THE SOUTHERN STREAM SYSTEMS/ENERGY ARE MORE UNCERTAIN, MAINLY  
DRIVEN BY THE UNCERTAINTY IN MODELS HANDLING THE INTERNAL WAVES OF  
THE ZONAL JET. INITIALLY THOUGH THE LEAD WAVE IS A BIT MORE  
CERTAIN IN ITS TIMING THROUGH THE 00Z GFS TRENDED A BACK TOWARD A  
STRONGER AND FURTHER SOUTH SOLUTION WHICH SHORTENS THE SPACING  
FROM THE NORTHWARD RETURNING SUBTROPICAL SHORTWAVE AND ASSOCIATED  
MOISTURE/INSTABILITY FLUX OUT OF THE GULF THURSDAY. THE TIGHTER  
SOLUTION OF THE GFS LEADS TO A LONGER RETENTION OF THE WAVE  
RELATIVE TO A MORE FAVORABLE 00Z NAM/12Z ECMWF AND CMC SOLUTIONS  
THAT FIT THE ENSEMBLE SUITE BETTER; THE UKMET REMAINS UNRESOLVED  
WITH THE WAVE (WELL TOO WEAK). GETTING THE INITIAL SETUP IS  
GOING TO BE CRITICAL TOWARD THE EVOLUTION/INTERNAL SENSIBLE  
WEATHER ACROSS THE SOUTHEAST UP THE EAST COAST BY 12Z  
SAT...BECAUSE THE SHORTWAVE EMERGING FROM THE 150KT 250H JET OUT  
OF THE PACIFIC/INTERMOUNTAIN WEST, INTERACT AND LEAD TO A GENERAL  
LARGER SCALE NEGATIVE TILT TO THE 5H PATTERN. THE GFS BEING  
STRONGER UPSTREAM, ENHANCES THE DEFORMATION ZONE ACROSS AL INTO TN  
GREATER THAN THE ECMWF WHICH IS WEAKER AND MORE PROGRESSIVE  
LEADING TO MORE MOISTURE/FLUX CONVERGENCE OUT OF THE GULF AND  
EASTERN ATLANTIC ACROSS THE CAROLINAS. THE 00Z NAM WHICH HAS  
INITIAL CONDITIONS A BIT MORE FAVORABLE INITIALLY THAN THE 00Z  
GFS; DOES EVOLVE A STRONGER MORE COMPACT UPSTREAM WAVE (THOUGH IN  
LINE WITH TYPICAL NEGATIVE DAY 3 BIAS), AND IS A SPLIT BETWEEN THE  
GFS AND ECWMF CAMPS. THE CMC IS UNCHARACTERISTICALLY PROGRESSIVE  
WITH THE ENTIRE LARGE SCALE TROF AND IS DISMISSED AS THE WAVE  
SHOULD BE WAITING FOR THE LARGER SCALE HEIGHT-FALLS EMERGING FROM  
THE STRONG UPSTREAM JET. SO ALL CONSIDERED, WILL BE FAVORING THE  
ECMWF/ECENS MEAN ACROSS THE SOUTHEAST BY THE LATE WEEK/SAT, THOUGH  
INCORPORATING THE NAM MAY HELP HEDGE THE MODERATE TO HIGH INTERNAL  
UNCERTAINTY.  
 
   
..WEST
 
 
~~~~~~~~~~~  
PREFERENCE: 00Z GFS/NAM AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
AS STATED IN CONUS DISCUSSION ABOVE, PARADE OF SMALL AMPLITUDE  
SHORTWAVES IN STRONG ZONAL JET MAKE DECIPHERING A PREFERENCE  
EXTREMELY DIFFICULT GIVEN THE SPACING TO WAVES MAY BE BELOW 6HRS  
AND WHERE SYNOPTIC FORCING HITS OROGRAPHIC FORCING ENHANCEMENT IS  
BEST HANDLED BY A GENERAL MODEL BLEND AND HIT HAZARDS AT LONGER  
TIME SCALES SUCH AS 12/24HR PACKS. STILL, TOWARD THE END OF THE  
TRAIN, A STRONGER/GREATER AMPLITUDE SHORTWAVE TRACKS THROUGH WITH  
SOME MODERATE NEUTRAL TO NEGATIVE TILT ORIENTATION LATE FRIDAY  
INTO EARLY MORNING SAT WITH AN ASSOCIATED SURFACE CYCLONE.  
REMARKABLY, THE GLOBAL GUIDANCE IS FAIRLY AGREEABLE WITH THE  
TIMING AND MASS FIELDS AS A WHOLE, PROVIDING SOME CONFIDENCE. THE  
LARGE DIFFERENCES ARE THE WIDTH OF THE UPPER LEVEL SYSTEM, WITH  
THE GFS A BIT MORE SLOWER AND BROADER SUPPORTED MORE BY THE CMC  
WHILE THE NAM/ECMWF ARE WELL PLACED/SHAPED BUT NARROWER AND THE  
UKMET IS MOST NARROW AND NEGATIVELY TILTED. WILL HEDGE MORE OF A  
COMPROMISE BETWEEN THE 00Z NAM/GFS AND 12Z ECWMF.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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