380   
FXUS10 KWNH 171658  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1157 AM EST MON FEB 17 2020  
  
VALID FEB 17/1200 UTC THRU FEB 21/0000 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
12Z MODEL EVALUATION WITH LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..PAIR OF SHORTWAVES CROSSING THE GREAT LAKES/NORTHEAST  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
  
A SHORTWAVE AND ASSOCIATED SURFACE LOW WILL CROSS THE GREAT LAKES  
REGION ON TUESDAY AND THEN ADVANCE EAST-NORTHEAST AND CLIP  
PORTIONS OF NORTHERN NEW ENGLAND THROUGH EARLY WEDNESDAY. IN THE  
WAKE OF THIS INITIAL SHORTWAVE, THERE WILL BE ANOTHER NORTHERN  
STREAM SHORTWAVE THAT WILL FOLLOW WITH ABOUT 12 HOURS WORTH OF  
SEPARATION. ALL OF THIS ENERGY BY LATE WEDNESDAY WILL BE EXITING  
NORTHERN NEW ENGLAND AND LIFTING THROUGH EASTERN CANADA. THE  
MODELS AT THIS POINT SHOW MINIMAL MASS FIELD SPREAD AT THE SURFACE  
AND ALOFT, SO A GENERAL MODEL BLEND WILL BE PREFERRED WITH BOTH  
SHORTWAVES.  
  
   
..BROAD LONGWAVE TROUGH OVER THE PLAINS/MIDWEST WEDNESDAY  
   
..ENERGY REACHING THE GREAT LAKES/NORTHEAST BY THURSDAY  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: AVERAGE  
  
AS A TRANSIENT DEEP LAYER RIDGE MOVES INTO SOUTHWEST CANADA AND  
ACROSS THE PACIFIC NORTHWEST BY WEDNESDAY, THERE WILL BE A  
POSITIVELY TILTED AND BROAD LONGWAVE TROUGH DOWNSTREAM THAT WILL  
CROSS THE NORTHERN PLAINS AND A LARGE AREA OF THE MIDWEST. BY  
THURSDAY, THIS TROUGHING WILL CROSS THE GREAT LAKES AND NORTHEAST.  
THE 00Z CMC BECOMES A BIT OF A SLOWER AND DEEPER OUTLIER WITH THE  
TROUGH AS IT MOVES INTO THE EASTERN U.S. BY THURSDAY. THE 00Z  
ECMWF AND 00Z ECENS MEAN ARE ALSO SOMEWHAT ON THE SLOWER SIDE OF  
THE GUIDANCE, BUT FOR NOW, WILL SUGGEST A NON-CMC BLEND GIVEN THAT  
THERE IS SOME SUPPORT FOR THE SLOWER ECMWF-LED GUIDANCE FROM THE  
06Z GEFS ENSEMBLE SUITE.  
  
   
..LINGERING ENERGY OVER THE CENTRAL ROCKIES/HIGH PLAINS  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF  
CONFIDENCE: AVERAGE  
  
THE GUIDANCE SUGGESTS A TRAILING TAIL OF ENERGY ASSOCIATED WITH  
THE AFOREMENTIONED LONGWAVE TROUGH BECOMING DETACHED AND LINGERING  
OVER THE CENTRAL ROCKIES AND HIGH PLAINS LATE WEDNESDAY INTO  
THURSDAY. THE 12Z GFS, 00Z ECMWF AND 00Z CMC AGREE IN TAKING THIS  
ENERGY MORE PROGRESSIVELY DOWNSTREAM. HOWEVER, THE 12Z NAM AND 00Z  
UKMET HOLD BACK A CONSIDERABLE AMOUNT OF ENERGY BY COMPARISON. ON  
WEDNESDAY, THE NAM IS THE STRONGEST SOLUTION WITH ITS ENERGY OVER  
WY/CO, BUT THEN BY THURSDAY THE UKMET SUGGESTS A CLOSED LOW  
PUSHING EAST ACROSS SD/NE. THE BETTER ENSEMBLE SUPPORT AND  
DETERMINISTIC CLUSTERING WOULD FAVOR A SOLUTION TOWARD THE GFS AND  
ECMWF, SO A BLEND OF THOSE TWO SOLUTIONS WILL BE PREFERRED.  
  
   
..SHORTWAVE CLIPPING THE PACIFIC NORTHWEST THURSDAY  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM AND 00Z ECMWF  
CONFIDENCE: BELOW AVERAGE  
  
A NORTHERN STREAM SHORTWAVE MAY CLIP THE PACIFIC NORTHWEST ON  
THURSDAY AS THE PATTERN TRANSITIONS TO VERY STRONG PACIFIC FLOW  
CROSSING FROM THE GULF OF AK THROUGH MUCH OF WESTERN AND CENTRAL  
CANADA. THE GUIDANCE IS A BIT SPLIT ON WHETHER THIS SHORTWAVE WILL  
SEPARATE OUT FROM THE STRONG NORTHERN STREAM FLOW. THE 12Z GFS AND  
00Z CMC FAVOR THE ENERGY DIGGING SOUTH OFFSHORE THE PACIFIC  
NORTHWEST AND ATTEMPTING TO CLOSE OFF. THE 12Z NAM AND ESPECIALLY  
THE 00Z UKMET ARE MORE PROGRESSIVE AND SHOW THE SYSTEM REMAINING  
MORE CLOSELY DOMINATED BY THE STRONG PACIFIC FLOW FARTHER NORTH.  
THE 00Z ECMWF GENERALLY SPLITS THE DIFFERENCE BETWEEN THE SLOWER  
AND FASTER CAMPS. THE ENSEMBLE MEANS ARE GENERALLY SPLIT AS WELL,  
WITH THE GEFS SLOWER AND MORE OFFSHORE WITH THE ENERGY, AND THE  
ECENS SUITE FASTER AND CLOSE TO A BLEND OF THE NAM AND ECMWF. THE  
00Z CMCE SUITE IS ALSO VERY CLOSE TO THIS CAMP AS WELL, SO A BLEND  
OF THE NAM AND ECMWF WILL BE PREFERRED. CONFIDENCE IS LIMITED  
GIVEN THE COLLECTIVE MASS FIELD SPREAD WITH THE GUIDANCE.  
  
   
..UPPER TROUGH/CLOSED LOW OFFSHORE CALIFORNIA BY THURSDAY  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
  
THE MODELS SHOW A STRONG SPLIT IN THE UPPER FLOW PATTERN BY  
THURSDAY WITH A SUBSTANTIAL SOUTHERN STREAM TROUGH AND CLOSED LOW  
FOCUSING OFFSHORE OF CALIFORNIA AS STRONG NORTHERN STREAM PACIFIC  
FLOW ADVANCES THROUGH WESTERN CANADA. OVERALL, THERE IS DECENT  
MODEL AGREEMENT WITH THE SOUTHERN STREAM ENERGY AS ALL OF THE  
MODELS SHOW A NEGATIVE HEIGHT ANOMALY ASSOCIATED WITH A CLOSED LOW  
JUST OFFSHORE OF CENTRAL CALIFORNIA BY THE END OF THE PERIOD. THE  
00Z CMC IS A BIT FARTHER EAST WITH THE PLACEMENT OF THE CLOSED LOW  
AND IS GENERALLY AN OUTLIER COMPARED TO THE SUITE OF DETERMINISTIC  
AND ENSEMBLE GUIDANCE. SO, A NON-CMC BLEND WILL BE PREFERRED WITH  
THIS SOUTHERN STREAM TROUGHING ON THURSDAY.  
  
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
  
ORRISON  
  
  
 
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