011  
FXUS10 KWNH 131635  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1235 PM EDT MON APR 13 2020  
 
VALID APR 13/1200 UTC THRU APR 17/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
OVERALL CONUS PATTERN  
~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/00Z ECMWF BLEND (NAM INCLUSION, OK IN WEST)  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
AVERAGE TO SLIGHTLY BELOW AVERAGE OFF WEST COAST DAY 3  
 
EASTERN HALF OF CONUS  
-----------------------  
EXTREMELY DEEP SURFACE CYCLONE IS LIFTING OUT OF THE NORTHERN  
GREAT LAKES WITH CENTROID OF DEEPER GLOBAL SCALE TROF WITH IT.  
THE EXTREMELY STRONG WARM CONVEYOR BELT AND COLD FRONT WILL PRESS  
THROUGH THE NORTHEAST WITHOUT SIGNIFICANT DIFFERENCE IN THE MASS  
FIELDS TO SUPPORT A GENERAL MODEL BLEND; THOUGH THE TRAILING  
FRONTAL ZONE THROUGH THE SOUTHEAST WILL BECOME STATIONARY BY  
TUESDAY.  
 
A SUBTLE SHORTWAVE OUT OF THE WEST IN FAST MOVING WESTERLY FLOW  
WILL EVENTUALLY SUPPORT A WEAK SURFACE WAVE IN GA/SC OR ALONG THE  
GULF STREAM BY LATE TUES/EARLY WED. AS THE SHORTWAVE REACHES THE  
CONFLUENT REGION OF THE EASTERN PORTION OF THE LARGE SCALE TROF,  
THERE IS SOME AMPLIFICATION AS IT LIFTS NORTH ALONG THE GULF  
STREAM AND EVENTUALLY TOWARD CAPE RACE BY LATE THURSDAY. THERE IS  
SIZABLE MODEL DIFFERENCES WITH ITS TIMING/PLACEMENT ALONG THE  
FRONT WITH THE UKMET LAGGING AND THE NAM A BIT LEFT OF ENSEMBLE  
SUITE, ENOUGH TO SUGGEST LESS PREFERENCE THERE.  
 
IN THE NORTHERN STREAM, REINFORCING SHORTWAVES ROUND AND HELP TO  
ELONGATE THE GLOBAL TROF BEFORE IT SLIDES EASTWARD THROUGH THE  
GREAT LAKES WED BEFORE SWINGING THROUGH THE NORTHEAST THURSDAY.  
THE 12Z NAM IS A BIT STRONGER/AMPLIFIED, IN LINE WITH DEEPENING  
THE AFOREMENTIONED OFFSHORE SURFACE LOW. THE 00Z CMC ALSO APPEARS  
TO BE VERY COMPACT STRONG WITH THIS WAVE TOO, BUT ALSO A TAD  
SLOWER...SO WILL PUSH A BIT FURTHER AWAY FROM THIS SOLUTION TOO.  
 
WESTERN US/ROCKIES  
--------------------  
A HIGHLY AMPLIFIED RIDGE EXISTS IN THE EASTERN PACIFIC THROUGH THE  
GULF OF AK... THIS BLOCK PRESENTS A LOWER PREDICTABILITY FORECAST  
FOR A COMPACT SHORTWAVE THAT WILL PLOW THROUGH THE NORTHERN  
PORTION OF IT ON TUES BEFORE DESCENDING SOUTH JUST OFF SHORE.  
WEAK FLOW AND SMALL VARIATION CAN LEAD TO LARGER DOWNSTREAM  
DIFFERENCES. THIS IS CLEARLY THE CASE WITH THE 00Z UKMET, WHICH  
IS SMALLER/MORE COMPACT AND SLOWER GETTING THROUGH THE RIDGE. THE  
CMC ALSO IS COMING OUT IN FRACTIONAL PIECES WHICH DOESN'T LOOK  
CORRECT AS WELL.  
 
A NORTHERN STREAM TROUGH CURRENTLY IN CENTRAL AK WILL ALSO DROP  
BETWEEN THE RIDGE AND THE LARGER SCALE TROF AND ENTER THE US  
ROCKIES WED. THE WAVE IN THE GENERAL WEAKNESS BETWEEN THE LARGER  
SCALE TROF BEGINS TO BROADEN/AMPLIFY ACROSS THE GREAT BASIN BY THE  
END OF THE FORECAST PERIOD. THIS WILL BRING IT CLOSER TO  
INTERACTING WITH THE AFOREMENTIONED OFF-SHORE LOW. THE ENSEMBLE  
SUITE IS SOLID WITH THE PLACEMENT BETWEEN THE TWO, AND THE 12Z GFS  
(THOUGH A TAD FAST) AND THE 00Z ECMWF (THOUGH A TAD SLOW) ARE THE  
BEST REPRESENTATIONS WITHIN THE GUIDANCE SUITE.  
 
ALL TOGETHER, WILL SUGGEST A 12Z GFS/00Z ECMWF BLEND, THOUGH THE  
NAM MAYBE USEFUL IN THE WEST/ROCKIES. CONFIDENCE IS SLIGHTLY  
ABOVE AVERAGE WITH EXCEPTION TO THE CLOSED LOW OFF THE WEST COAST  
WHICH IS AVERAGE TO SLIGHTLY BELOW AVERAGE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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