524  
FXUS10 KWNH 020501  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
100 AM EDT SAT MAY 02 2020  
 
VALID MAY 02/0000 UTC THRU MAY 05/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES AND  
CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE/SURFACE LOW TRACKING NEAR THE U.S./CANADIAN BORDER  
THROUGH SUNDAY, FRONTAL ZONE THROUGH OHIO VALLEY; NORTHEAST  
REINFORCEMENT/SURFACE REDEVELOPMENT SUNDAY TO MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z GFS BLEND, LED BY 00Z NAM/12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE IN FAIR AGREEMENT WITH TIMING, BUT THE 00Z GFS  
BECOMES FASTER WITH THE SHORTWAVE AS IT NEARS THE NORTHEAST. THIS  
IS REFLECTED IN ENSEMBLE SPAGHETTI PLOTS AND COMPARISONS OF THE  
00Z GFS TO THE LATEST DETERMINISTIC CONSENSUS. WHILE THERE ARE  
SOME DIFFERENCES WITH FRONTAL PLACEMENT ACROSS THE MS VALLEY AND  
TO THE WEST...WITH THE 12Z UKMET SLOWER IN THE SOUTHERN PLAINS, A  
NON-00Z GFS BLEND OF GUIDANCE APPEARS REASONABLE AT THIS POINT IN  
TIME.  
 
...DEEP TROUGH OFFSHORE THE WEST COAST TODAY WITH REMNANT  
SHORTWAVE ENERGY MOVING THROUGH THE NORTHERN ROCKIES SUNDAY  
MORNING, NORTHERN HIGH PLAINS SURFACE LOW...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/CMC/ECMWF MEAN  
CONFIDENCE: BELOW AVERAGE  
 
LARGE SPREAD AND POOR RUN TO RUN CONSISTENCY MAKE FOR BELOW  
AVERAGE FORECAST CONFIDENCE. INITIALLY, THERE IS GOOD AGREEMENT  
WITH THE UPPER TROUGH AXIS REACHING WASHINGTON AND OREGON BUT  
DIFFERENCES GROW THROUGH SUNDAY WITH THE REMNANT SHORTWAVE AS IT  
MOVES INLAND ACROSS THE NORTHERN ROCKIES AND SOUTHWESTERN CANADA.  
THERE ARE ALSO EMBEDDED SHORTWAVES WITHIN ZONAL FLOW ACROSS THE  
INTERMOUNTAIN WEST WITH POOR MODEL AGREEMENT.  
 
THE PREFERENCE IS TO STAY NEAR THE MIDDLE, AWAY FROM OUTLIERS,  
WHILE CONSIDERING TRENDS. THIS TAKES OUT THE 00Z NAM AND 00Z GFS  
WHICH ARE FASTER WITH THE UPPER TROUGH INTO SOUTHERN  
ALBERTA/SASKATCHEWAN. THE 12Z ECMWF IS SLIGHTLY MORE ELONGATED  
WITH THE TROUGH AXIS TOWARD THE EAST BY MONDAY MORNING, BUT THE  
12Z ECMWF MEAN IS MORE IN LINE WITH A MIDDLE GROUND. THE 12Z UKMET  
IS ALSO MIDDLE GROUND BUT IT LACKS A MORE ROBUST SHORTWAVE TO THE  
SOUTH AS SEEN IN THE ENSEMBLES. THE 12Z CMC IS ALSO A REASONABLE  
SOLUTION NEAR THE ECMWF AND ITS MEAN.  
 
...NEXT EMBEDDED SHORTWAVE IN GULF OF AK GYRE, CLIPPING NW  
MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/ECMWF MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
ENSEMBLE SPAGHETTI HEIGHTS SHOW THE 12Z UKMET AS A FAST OUTLIER  
WITH THE TROUGH AXIS CLIPPING THE PACIFIC NORTHWEST MONDAY NIGHT.  
THE 12Z CMC ALSO APPEARS A BIT FAST WHILE THE 00Z NAM/GFS APPEAR  
SLOW. OVERALL TRENDS IN THE ENSEMBLES OVER THEIR PAST FOUR 12/00Z  
CYCLES SUPPORT SOME SLOWING VALID TUESDAY MORNING WHICH WOULD  
LEAVE THE FASTER GUIDANCE OUT OF THE PREFERENCE. WHILE THERE IS  
SOME POTENTIAL FOR FURTHER SLOWING, PREFER TO STAY TOWARD THE  
MIDDLE OR THE 12Z ECMWF/ECMWF MEAN. THIS SOLUTION IS ALSO  
CONSISTENT WITH OTHER SYSTEMS DOWNSTREAM ACROSS THE CONUS.  
 
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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