557  
FXUS10 KWNH 031825  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
224 PM EDT FRI JUL 03 2020  
 
VALID JUL 03/1200 UTC THRU JUL 07/0000 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
19Z UPDATE: NO SIGNIFICANT CHANGES NOTED WITH THE REST OF THE 12Z  
GUIDANCE AND NO CHANGES NEEDED TO THE MODEL BLEND PREFERENCE.  
 
TROUGH OVER THE NORTHEAST U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND DAY 1/2; GFS/ECMWF BLEND DAY 3  
CONFIDENCE: ABOVE AVERAGE  
 
A PAIR OF SHORTWAVE TROUGHS ARE EXPECTED TO MOVE THROUGH THE  
NORTHEAST OVER THE NEXT FEW DAYS, THE FIRST ARRIVING LATE TONIGHT  
INTO SATURDAY. A WEAK AND QUICK MOVING SHORTWAVE TROUGH PUSHES OUT  
OF THE LONGWAVE TROUGH OVER EASTERN CANADA, AND DIVES ACROSS NEW  
YORK STATE. TIMING AND POSITION IS RELATIVELY GOOD THROUGH 24-36  
HOURS IN THE GLOBAL DETERMINISTIC MODELS, THE MAIN DIFFERENCES  
BEING SOME SPATIAL SPREAD SEEN BY 12Z SATURDAY, WHERE THE ECMWF IS  
A BIT FURTHER NORTH WHILE THE UKMET AND THE NAM TO SOME DEGREE ARE  
A BIT FURTHER SOUTH/SOUTHWEST. NONETHELESS, A GENERAL MODEL BLEND  
FOR MASS FIELD PURPOSES IS SUFFICIENT. A SECOND SHORTWAVE TROUGH  
THEN ARRIVES LATER IN THE PERIOD, DURING DAY 3, AND IS EXPECTED TO  
CLIP THE NORTHERN AREAS OF THE NORTHEAST AND ACROSS NEW ENGLAND.  
HERE, MORE TIMING DIFFERENCES ARE NOTED WHERE THE GFS IS FASTER  
AND THE ECMWF/UKMET ARE SLOWER. THE UKMET IS ALSO MORE AMPLIFIED  
WHILE THE GFS IS A FLATTER. LOOKING AT THE ENSEMBLE MEANS, A BLEND  
OF THE GFS/ECMWF WOULD BE A GOOD CONSENSUS APPROACH FOR DAY 3.  
 
TROUGH OVER THE GULF COAST REGION  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GFS/ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
A SLIGHT WEAKNESS IN THE UPPER LEVEL RIDGE ANCHORED OVER THE  
CENTRAL/SOUTHERN PLAINS EXPANDS FURTHER DURING THE COURSE OF THE  
PERIOD AS SEVERAL CONVECTIVELY ENHANCED MCVS SETTLE OVER THE LOWER  
MS RIVER VALLEY AND GULF COAST REGION (WHILE THE RIDGE UPSTREAM  
RETREATS TO THE SOUTHWEST US). THE SYNOPTIC PATTERN IS LARGELY  
AGREEABLE THOUGH THE CMC/UKMET TAKE THE SHORTWAVE ENERGY FURTHER  
SOUTH INTO THE MOISTURE/THERMAL RIDGE ALONG THE GULF COAST  
COMPARED TO THE NAM/ECMWF/GFS. THE LATTER MAKES MORE SENSE GIVEN  
THE HIGHER MOISTURE IN PLACE WHICH SHOULD HELP SUPPRESS ITS  
SOUTHWARD MOVEMENT. THEREFORE A BLEND OF THE GFS/ECWMF IS  
PREFERRED.  
 
DEEP UPPER TROUGH/CLOSED LOW ACROSS THE PACIFIC NORTHWEST AND  
WESTERN CANADA  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GFS/ECMWF BLEND  
CONFIDENCE: MODERATE  
 
SHORTWAVE TROUGHING OVER THE PACIFIC NORTHWEST LIFTS NORTHEAST  
INTO THE CANADIAN ROCKIES DURING THE DAY 1/2 PERIOD. THE GFS AND  
UKMET ARE SLOWER WITH THE SHORTWAVE AND ALSO MORE AMPLIFIED WHILE  
THE NAM/ECMWF/CMC ARE FLATTER AND FASTER. THEN ON DAY 3, ANOTHER  
SHORTWAVE DROPS FROM WESTERN CANADA TOWARD THE PACIFIC NW. HERE  
MORE TYPICAL MODEL BIASES ARE SEEN, WITH THE GFS FASTER THAN THE  
OTHER DETERMINISTIC GUIDANCE WHILE THE UKMET IS SLOWER/AMPLIFIED.  
AS A COMPROMISE AND CONSENSUS, A BLEND OF THE GFS/ECMWF 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  
 
TAYLOR  
 

 
 
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