095  
FXUS10 KWNH 181633  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1133 AM EST THU JAN 18 2018  
 
VALID JAN 18/1200 UTC THRU JAN 22/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SOUTHERN STREAM WAVE EJECTING NORTHEAST FROM THE GULF OF  
MEXICO...  
 
PREFERENCE: NON GFS SOLN WEIGHTED SOMEWHAT FASTER THAN THE ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE NUMERICAL GUIDANCE GENERALLY HANDLED THIS SYSTEM COMPARABLY AS  
IT SLOWLY MAKES ITS WAY EAST AND NORTH FROM THE WESTERN GULF OF  
MEXICO AND STRADDLES THE GULF COAST STATES THROUGH DAY 2. THE  
REAL DIFFERENCES BEGIN TO OPEN UP BETWEEN THE GFS AND THE OTHER  
MODELS ON DAY 3...SATURDAY. THE 18/00Z AND 18/06Z GFS DEEPENED  
THE MID LEVEL SYSTEM AND BEGAN TO SHOW REFLECTIONS OF THE WAVE  
CLOSER TO THE SURFACE. IT DOES THIS IN A REGION WHERE MID/UPPER  
LEVEL HEIGHTS TO ITS NORTH AND EAST ARE RISING...NOT GENERALLY A  
FAVORABLE ENVIRONMENT FOR A SYSTEM TO BECOME REINVIGORATED. THE  
18/00Z ECMWF WAS SLOWER AND WEAKER...WHILE THE 18/12Z NAM AND EVEN  
THE 18/00Z UKMET WERE CLUSTERED TOGETHER BETWEEN THE FASTER AND  
SLOWER SOLN. THE NAM WAS EVEN A TAD STRONGER THAN THE  
ECMWF/UKMET. THOSE DIFFERENCES WERE PRETTY SMALL...LEAVING THE  
GFS AS A FAST/STRONG STRONG OUTLIER. AT THIS POINT...WOULD THINK  
A NON GFS SOLN WOULD BE BEST. OF THE REMAINING MODELS...SLIGHTLY  
FAVOR A FASTER SOLN THAN THE ECMWF.  
 
...SHORTWAVE INITIALLY OVER UPPER MIDWEST MOVING ACROSS NEW  
ENGLAND FRIDAY AFTERNOON...  
 
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A WAVE MAKING ITS WAY ALONG THE INTERNATIONAL BORDER THIS MORNING  
WILL CROSS THE GREAT LAKES AND THEN CLIP PARTS OF THE NORTHEASTERN  
U.S. STATES BY FRIDAY AFTERNOON. THE NUMERICAL GUIDANCE TENDED TO  
HANDLE THIS FEATURE IN A SIMILAR FASHION...BOTH IN TERMS OF  
STRENGTH AND FORWARD SPEED. A GENERAL MODEL COMPROMISE SHOULD  
TAKE CARE OF ANY SMALL DIFFERENCES WHICH LINGER.  
 
...SLOW MOVING MID/UPPER LEVEL SYSTEM MOVING OFF THE MID ATLANTIC  
REGION DAY 1...  
 
PREFERENCE: 18/00Z ECMWF...18/12Z NAM/GFS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MID/UPPER LEVEL CIRCULATION OF A SYSTEM WHICH IMPACTED THE  
EASTERN STATES STILL LINGERED OVER THE CAROLINAS AND FAR SOUTHEAST  
VA EARLY THIS MORNING...WHILE THE SURFACE REFLECTION WAS LOCATED  
OUT AT SEA. THE 18/00Z ECMWF AND THE 18/12Z NAM/GFS HANDLED THE  
DEPARTURE OF THE SYSTEM IN A SIMILAR WAY.  
   
..DEEPENING TROUGH MOVING INLAND
 
WITH SOUTHERN STREAM ENERGY  
EMERGING OVER THE PLAINS SUNDAY...  
 
PREFERENCE: 17/12Z ECMWF/UKMET BLEND  
CONFIDENCE: ABOVE AVERAGE ON DAYS 1/2...AVERAGE AT BEST ON DAY 3  
 
THE MODELS TEND TO BE IN PRETTY GOOD AGREEMENT WITH A CLOSED LOW  
INITIALLY OFF THE COAST OF BRITISH COLUMBIA THIS MORNING AS IT  
WEAKENS THROUGH FRIDAY MORNING. EVEN THE DETAILS WITH THE LARGER  
SCALE TROUGH WERE IN PRETTY GOOD AGREEMENT AS A SHORTWAVE HELPS  
CARVE OUT A SOUTHERN STREAM THAT COMES ONSHORE OVER CA LATE FRIDAY  
AND THEN PROGRESSES ACROSS THE SOUTHERN INTERMOUNTAIN REGION BY  
SATURDAY AFTERNOON/EVENING.  
 
THE REAL DIFFERENCES OPEN UP STARTING ABOUT 21/00Z AND PERSIST  
BEYOND THE END OF THE DAY 3 PERIOD AT 22/00Z. THE 12Z NCEP  
GUIDANCE HAS SHIFTED TO A STRONGER...MORE DEVELOPED SOLUTION AS A  
MID/UPPER LEVEL LOW DEVELOPS OVER THE WESTERN HIGH PLAINS. THE  
18/00Z ECMWF WAS SLOWER AND WEAKER BY THE END OF DAY 3. THIS IDEA  
HAD SUPPORT FROM THE 18/00Z UKMET AND A NUMBER OF THE GEFS  
MEMBERS. THE 18/12Z GFS WAS DEEPER AND ON THE EASTERN SIDE OF THE  
GUIDANCE. INITIAL THINKING WAS TO FAVOR A SOLN BETWEEN THE  
FASTER/DEEPER GFS AND THE SLOWER/WEAKER ECMWF...ALTHOUGH THE WAY  
THE 18/12Z NAM BEGAN TO ALIGN ITS THINKING WITH THAT OF THE GFS  
MAY BE A SIGN THAT MORE 12Z GUIDANCE COMES IN FASTER/DEEPER.  
EITHER WAY...THE FAST AND GENERALLY FLAT FLOW UPSTREAM OF THIS  
REGION ARGUES AGAINST THE EC IDEA OF A SLOWER EJECTION. INCLUSION  
OF THE UKMET SHOULD HELP IN PULLING THE SYSTEM EAST OF THE ECMWF  
WHILE SHOWING MORE DEPTH/DEVELOPMENT THAN THE EC.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
BANN  
 

 
 
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