866   
FXUS10 KWNH 260514  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1214 AM EST WED FEB 26 2020  
  
VALID FEB 26/0000 UTC THRU FEB 29/1200 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..EASTERN HALF OF NORTH AMERICA  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z CMC BLEND  
CONFIDENCE: AVERAGE  
  
A CLOSED LOW OVER THE SOUTHERN/CENTRAL GREAT PLAINS WILL OPEN UP  
INTO A MID-LEVEL TROUGH DURING THE DAY ON WEDNESDAY AND TRACK  
TOWARD THE NORTHEAST FOR THURSDAY WITH A NEGATIVELY TITLED AXIS IN  
THE MIDDLE AND UPPER LEVELS. AN UPSTREAM NORTHERN STREAM TROUGH  
WILL MOVE ACROSS THE UPPER GREAT LAKES AND PHASE WITH THE ENERGY  
MOVING INTO NEW ENGLAND. A CORRESPONDING SURFACE LOW WILL RAPIDLY  
DEEPEN AS IT TRACKS THROUGH PENNSYLVANIA AND NEW YORK WEDNESDAY  
NIGHT, WITH SECONDARY LOW DEVELOPMENT LIKELY ALONG THE NORTHERN  
NEW ENGLAND COAST ON THURSDAY. AFTER THE SYSTEM REACHES MATURITY  
AND BEGINS TO WEAKEN, A DEEP 500 MB LOW WILL ANCHOR OVER SOUTHERN  
QUEBEC, SETTING UP A FAVORABLE LAKE EFFECT SNOW EVENT DOWNWIND OF  
LAKE ERIE AND ONTARIO.  
  
THE MODELS HAVE BEEN FLIP FLOPPING WITH THE TIMING OF THE LEAD  
SHORTWAVE CROSSING THE APPALACHIANS LATE WEDNESDAY INTO THURSDAY  
MORNING FOR THE PAST FEW DAYS. THE DIFFERENCES ARE RELATIVELY  
MINOR THROUGH THURSDAY MORNING, BUT THE 12Z CMC BEGINS TO DEPART  
FROM THE REMAINING CONSENSUS ON THURSDAY. THE 12Z CMC ENDS UP WITH  
A LARGER 500 MB LOW COMPARED TO THE LATEST ENSEMBLE CONSENSUS AND  
IS ALSO WEAKER WITH 850 MB FLOW ACROSS NEW YORK. THE POSITION OF  
THE 12Z CMC 850-500 MB LOW CENTER ALSO DIFFERS FROM THE REMAINING  
MODEL CONSENSUS, SO A NON 12Z CMC BLEND IS PREFERRED.  
  
THE NON 12Z CMC GUIDANCE IS NOT IDENTICAL, BUT A BLEND OF THE  
REMAINING GUIDANCE SHOULD HELP TO SMOOTH OUT SMALLER SCALE  
DIFFERENCES. THIS BLEND HOLDS TRUE FOR A PAIR OF WEAK MID-LEVEL  
SHORTWAVES DIVING SOUTHEASTWARD THROUGH THE GREAT PLAINS AND INTO  
THE SOUTHERN U.S. WHERE A NON 12Z CMC BLEND REPRESENTS THE MIDDLE  
OF THE TIMING/POSITION DIFFERENCES NOTED.  
  
   
..WESTERN U.S  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z CMC BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
  
A SOMEWHAT SHARP MID-LEVEL SHORTWAVE WILL REACH THE PACIFIC  
NORTHWEST COAST SOMETIME LATE ON FRIDAY, TRACKING INTO THE  
NORTHERN U.S. ROCKIES AND SOUTHERN CANADIAN ROCKIES BY SATURDAY  
MORNING. THE ENSEMBLE MEANS ARE IN RELATIVELY GOOD AGREEMENT WITH  
THE TIMING OF THE TROUGH BUT ENSEMBLE SPREAD IS MODEST. NO CLEAR  
TRENDS HAVE BEEN IDENTIFIED REGARDING TIMING, BUT THERE HAS BEEN  
GENERAL CONVERGENCE TOWARD THE MIDDLE OVER THE PAST 4 12/00Z  
CYCLES.  
  
THE 12Z CMC IS SLOWER THAN THE MEANS, WHILE THE 00Z GFS IS  
SLIGHTLY AHEAD. NO MODEL IS AN OUTLIER WITH RESPECT TO THE  
INDIVIDUAL ENSEMBLE MEMBERS, BUT THE 12Z CMC STANDS OUT THE  
GREATEST. A BLEND OF THE REMAINING MODELS REGARDING TIMING AND  
STRENGTH 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  
  
OTTO  
  
  
 
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