746  
FXUS10 KWNH 101831  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 PM EST WED JAN 10 2018  
 
VALID JAN 10/1200 UTC THRU JAN 14/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...INITIAL TROUGH OVER FOUR CORNERS REGION WITH ASSOCIATED +PV  
ANOMALY EJECTING NORTHEAST INTO THE UPPER MISS VLY THURSDAY...   
..WEAK SURFACE LOW OR FRONTAL WAVE IN WESTERN GREAT LAKES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
---18Z UPDATE---  
NO CHANGE TO THE PRELIMINARY PREFERENCE FOR A GENERAL MODEL BLEND  
AS MODELS APPEAR TO STILL BE IN FAIRLY GOOD AGREEMENT WITH THE  
MASS FIELDS.  
 
---PREV. DISCUSSION---  
INITIAL MODEL DIFFERENCES WITH THE TROUGH OVER THE SOUTHWEST ARE  
FAIRLY MINOR...AND DESPITE SOME DETAIL DIFFERENCES OVER THE GREAT  
LAKES BY THURSDAY THEY REMAIN FAIRLY SIMILAR OVER THE NEXT 36  
HOURS. GIVEN THIS...A GENERAL MODEL BLEND IS PREFERRED.  
 
...SHEARED VORT MAX DIGGING FROM WA/OR COASTS TO SRN PLAINS BY THU  
MORNING...LEADING TO FURTHER TROUGH AMPLIFICATION...  
...EJECTING WAVE AND ASSOCIATED CYCLOGENESIS TO THE NORTHEAST ON  
FRIDAY AND INTO EARLY SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z NAM / 12Z UKMET  
CONFIDENCE: AVERAGE  
 
---18Z UPDATE---  
WITH THE 12Z MODEL CYCLE FINISHING UP...THE CMC AND ECMWF HAVE  
TRENDED IN THE DIRECTION OF OTHER MODELS...SO OVERALL THERE IS  
BETTER AGREEMENT THAN PREVIOUS CYCLES. THE 12Z CMC IS LESS  
AMPLIFIED AND FASTER WITH THE TROUGH...WHILE THE 12Z ECMWF IS A  
LITTLE SLOWER WITH THE TROUGH AND HAS A WEAKER SURFACE LOW.  
HOWEVER...BOTH MODELS CONTINUE TO HAVE SOME OF THE STRONGER  
SURFACE LOWS RELATIVE TO ALL THE OPERATIONAL MODELS IN THE  
NORTHEAST REGION. THE TRENDS ARE IN THE DIRECTION OF THE  
PRELIMINARY PREFERENCE...BUT WILL SIMPLY MAINTAIN THAT PREFERENCE  
FOR NOW RATHER THAN ADDING IN ANY MORE MODELS. THIS WILL ALSO HELP  
MAINTAIN BETTER CONTINUITY WITH THE PREVIOUS WPC FORECAST.  
CONFIDENCE HAS BEEN INCREASED TO AVERAGE GIVEN BETTER MODEL  
AGREEMENT.  
 
---PREV. DISCUSSION---  
AVAILABLE MODELS DEPICT A SIMILAR EVOLUTION WITH AN EJECTING  
TROUGH INDUCING SOME SURFACE CYCLOGENESIS INTO THE EASTERN  
CONUS...BUT GENERALLY NOT CONCENTRATED ENOUGH TO DEVELOP INTO A  
STRONG CYCLONE. THE RESULT IS A BROAD FRONTAL ZONE WITH WEAK LOW  
PRESSURE CENTERS AND SEVERAL HANDOFFS FROM ONE WEAK LOW TO THE  
NEXT ALONG STRENGTHENING BAROCLINIC ZONES (E.G. THE COASTAL FRONT  
AS THE TROUGH APPROACHES THE NORTHEAST). THEREFORE...ALTHOUGH THE  
MODELS DO NOT HAVE WILDLY DIFFERENT SOLUTIONS...THERE ARE  
IMPORTANT DETAIL DIFFERENCES THAT WILL IMPACT PRECIPITATION TYPES  
AND AMOUNTS ACROSS A BROAD SWATH OF THE COUNTRY EAST OF THE  
MISSISSIPPI RIVER. FOR MORE ON THE QPF AND WINTER WEATHER  
FORECASTS...PLEASE REFERENCE THOSE DISCUSSIONS.  
 
THERE APPEAR TO BE TWO NOTABLE TRENDS IN THE 12Z MODEL CYCLE WITH  
RESPECT TO THE EJECTING TROUGH. FIRST...MANY OF THE MODELS ARE  
REDUCING THE AMPLIFICATION OF THE TROUGH AT A GIVEN FORECAST HOUR  
RELATIVE TO PREVIOUS MODEL RUNS. THE 12Z UKMET...FOR  
EXAMPLE...PREVIOUSLY HAD A CLOSED UPPER LEVEL LOW OVER TEXAS ON  
THURSDAY NIGHT BUT NOW SHOWS MORE OF AN OPEN WAVE. THIS MAY ALSO  
RELATE TO THE SECOND TREND...WHICH IS THAT THE MODELS HAVE  
GENERALLY SPED UP THE PROGRESSION OF THE WAVE (ALBEIT SLIGHTLY FOR  
NOW).  
 
PREVIOUS WPC FORECAST CYCLES HAVE PREFERRED THE SLOWER END OF THE  
MODEL SPREAD...
SO TO MAINTAIN SOME CONTINUITY THE PREFERENCE WILL  
NOT BE TO TREND TO ONLY THE FASTER MODELS. GIVEN CONTINUED  
UNCERTAINTY...A BROADER-BASED BLEND IS PREFERRED TO ENCOMPASS MORE  
OF RANGE OF POSSIBILITIES IN A REASONABLE COMPROMISE SOLUTION.  
HOWEVER...FOR NOW THE 00Z ECMWF WAS EXCLUDED FROM THE PREFERENCE  
AS ITS SURFACE LOW IS MUCH STRONGER AND THAN OTHER MODELS...EVEN  
AT EARLIER FORECAST HOURS OVER THE SOUTH. THIS AFFECTS THE  
ORIENTATION OF THE PRECIPITATION FIELD AND LIKELY OTHER MASS  
FIELDS AND SENSIBLE WEATHER IMPACTS. THE 00Z CMC ALSO SHOWS A MORE  
AMPLIFIED TROUGH...AND THE 12Z RUN IS NOT YET AVAILABLE TO  
EVALUATE WHETHER THE CMC WILL ALSO HAVE THE LESS AMPLIFIED TREND  
THAT WAS PREVIOUSLY MENTIONED. ALTHOUGH THIS DOES NOT AFFECT THE  
SURFACE LOW AS MUCH INITIALLY...IT DOES EVENTUALLY LEAD TO A  
STRONGER SURFACE LOW THAT TRACKS FURTHER INLAND OVER THE  
NORTHEAST. THE OTHER MODELS (NAM/GFS/UKMET) SHOW A WEAKER SURFACE  
LOW THAT DOES EVENTUALLY REFOCUS CLOSE TO THE COAST OVER THE  
NORTHEAST.  
 
   
..SHORTWAVE ARRIVING IN THE PACIFIC NORTHWEST ON THURSDAY
 
   
..DEAMPLIFYING OVER THE NORTHERN ROCKIES ON FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND  
CONFIDENCE: AVERAGE  
 
---18Z UPDATE---  
THE 12Z CMC IS IN MUCH BETTER AGREEMENT WITH THE DEPICTION OF THE  
DOWNSTREAM RIDGE AND HAS ALSO BECOME MORE SIMILAR WITH THE TROUGH  
AS IT APPROACHES THE PACIFIC NORTHWEST. THEREFORE...THE UKMET  
CONTINUES TO HAVE THE STRONGEST AND MOST AMPLIFIED TROUGH...AND  
FOR REASONS STATED EARLIER IT IS EXCLUDED FROM THE PREFERENCE. THE  
CMC HAS BEEN ADDED.  
 
---PREV. DISCUSSION---  
OVER THE EASTERN PACIFIC...THE 00Z CMC HAS HIGHER HEIGHTS THAN  
OTHER AVAILABLE MODELS THROUGH THE RIDGE DOWNSTREAM FROM THE  
APPROACHING TROUGH...BUT DOES NOT SEEM TO HAVE A CORRESPONDING  
AMPLIFICATION TO THE TROUGH. IT IS ONE OF THE LESS AMPLIFIED  
SOLUTIONS FOR THE TROUGH AND ALSO HAS THE SURFACE LOW PLACEMENT  
FURTHER NORTH. THE 12Z UKMET...BY CONTRAST...HAS A SHARPER TROUGH  
WITH GREATER AMPLIFICATION AS IT APPROACHES THE COAST.  
HOWEVER...WITH AN EASTERLY PROGRESSION INTO A LARGER RIDGE...THE  
CURRENT PREFERENCE IS FOR A SOLUTION IN BETWEEN THE CMC AND  
UKMET...WHICH IS BEST REPRESENTED BY A BLEND OF THE GFS...NAM AND  
ECMWF. THESE THREE MODELS ARE IN FAIRLY GOOD AGREEMENT AND THIS  
BLEND WILL PRODUCE A TROUGH THAT IS NOT AS AMPLIFIED AS THE  
UKMET...WITH A SURFACE LOW POSITION AND TIMING THAT IS NOT AS FAR  
NORTH AND SLOW AS THE 00Z CMC IS PRODUCING.  
 
...BROAD INITIAL TROUGH OVER FLORIDA DEAMPLIFYING WITH THE  
APPROACH OF STRONGER HEIGHT FALLS FROM THE WEST ON THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS DO SHOW SOME MINOR VARIATION IN THE MASS FIELDS WITH THIS  
SYSTEM...BUT OVERALL SHOW SIMILAR PLACEMENT OF THE TROUGH AND  
TIMING OF THE DEAMPLIFICATION WITH THE APPROACH OF THE TROUGH FROM  
THE WEST. WITH TIME ITS INFLUENCE WILL WANE AS THE CENTRAL U.S.  
TROUGH BEGINS TO EJECT NORTHEAST. GIVEN THE RELATIVELY SMALL  
DIFFERENCES...A GENERAL MODEL BLEND IS PREFERRED.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page