417  
FXUS10 KWNH 231837  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
236 PM EDT MON SEP 23 2019  
 
VALID SEP 23/1200 UTC THRU SEP 27/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..CONUS
 
 
~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
EXCEPTION: WEIGHT TOWARD 12Z GFS/ECMWF/CMC IN SOUTHWEST ON DAY 3.  
CONFIDENCE: ABOVE AVERAGE  
 
19Z UPDATE: WITH LITTLE INITIAL SPREAD, THE THE 12Z ECMWF/CMC AND  
UKMET SHOWED LITTLE DIFFERENCES IN THE MASS FIELDS FROM THEIR 00Z  
RUNS. ONLY SLIGHTLY STRONGER/DEEPER REFLECTIONS ON DAY 3 THROUGH  
THE UPPER OHIO VALLEY INTO THE NORTHEAST/MID-ATLANTIC (GIVEN  
INCREASED MOISTURE/QPF ALONG THE FRONT) WERE NOTED WITH THE 12Z  
UKMET/CMC. THIS WAS OPPOSED TO A SLIGHT DRYING IN THE ECMWF.  
STILL THIS APPEARS MINOR AT DAY 3 TO KEEP WITH INITIAL PREFERENCE.  
 
SIMILARLY, IN THE SOUTHWEST, THE UKMET LIFTS OUT A BIT FASTER THAN  
EVEN THE 00Z RUN, BUT STILL WELL WITHIN THE REALM OF MODERATE  
ENSEMBLE SPREAD TO HAVE HIGH CONFIDENCE IN A GENERAL MODEL BLEND  
HERE AS WELL, JUST WEIGHTED A BIT LOWER THAN THE 12Z ECMWF/CMC/GFS  
 
---PRIOR DISCUSSION---  
THE SHORT RANGE PATTERN WILL BE DOMINATED BY A VERY STRONG 150+KT  
250MB JET CURRENTLY CROSSING THE GULF OF AK, THAT CROSSES THE  
CANADIAN ROCKIES AND DIGS OUT A BROAD CLOSED LOW THAT SUPPORTS A  
FAST MOVING SURFACE WAVE ALONG THE US/CANADIAN BORDER WITH A FRONT  
THAT DROPS SOUTH THROUGH THE PLAINS TUESDAY INTO THE GREAT LAKES  
BY WED AND INTO THE NORTHEAST/MID-ATLANTIC BY THURSDAY. THE MASS  
FIELDS ARE QUITE AGREEABLE WITH ONLY THE 12Z NAM/GFS CONTINUING A  
BIAS OF BEING A BIT TOO DRY RELATIVE TO THE ECMWF/UKMET AND CMC.  
FOR THE MASS FIELDS, A GENERAL MODEL BLEND WILL WORK WELL AND WITH  
MINOR SPREAD EVEN INTERNALLY, THE CONFIDENCE IS HIGH FOR THIS  
PORTION OF THE WEATHER. HOWEVER, THE UNCERTAINTY IN MOISTURE  
RETURN BEGS SOME REDUCTION IN OVERALL CONFIDENCE TO SLIGHTLY BELOW  
AVERAGE.  
 
AHEAD OF THIS STRONG WAVE, A CLOSED LOW CONTINUES TO TRACK ACROSS  
THE GREAT LAKES INTO THE NORTHEAST WITH LITTLE MODEL DISAGREEMENT,  
WITH ONLY MODERATE SPREAD ON HOW THIS TROF COLLECTS THE REMAINS OF  
TROPICAL STORM JERRY, WHICH IS WELL OFF COAST TO BE AN AFFECT TO  
THE CONUS. AS SUCH A GENERAL MODEL BLEND CAN BE EMPLOYED AT ABOVE  
AVERAGE CONFIDENCE.  
 
GOES-W WV DENOTES A SHORTWAVE STARTING TO BREAK FROM THE NORTHERN  
STREAM INTO A CLOSED LOW ACROSS THE SOUTHERN SIERRA MOUNTAINS.  
THIS WAVE WILL CONTINUE TO DEEPEN AND DROP INTO THE LOWER COLORADO  
RIVER BASIN. GUIDANCE IS VERY AGREEABLE WITH THIS EVOLUTION AS  
WELL, BUT EVENTUALLY, AN ANTICYCLONIC LOOP WILL OCCUR AND THE 12Z  
NAM AND 00Z UKMET START TO LIFT BACK NORTHEAST A BIT FASTER THAN  
THE REMAINING GUIDANCE IS EXPECTING AT THE END OF THE FORECAST  
PERIOD. WHILE, A BIT FAST, IT IS NOT OUT OF THE REALM OF  
POSSIBILITY AND WITH CONVECTIVE INFLUENCE OVER TERRAIN IN CENTRAL  
AZ INTO NM, THIS EVOLUTION/TIMING MAY BE CORRECT. HOWEVER, WILL  
FAVOR (WEIGHT HEAVIER) A BLEND CLOSER TO THE 00Z ECMWF/CMC AND 12Z  
GFS ON DAY 3 IN A GENERAL MODEL BLEND. CONFIDENCE IS ABOVE  
AVERAGE IN THIS BLEND.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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