116  
FXUS10 KWNH 211646  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1245 PM EDT SAT MAR 21 2020  
 
VALID MAR 21/1200 UTC THRU MAR 25/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z INITIAL MODEL EVALUATION WITH LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PHASING STREAMS OVER THE MISSISSIPPI VALLEY MON, SUPPORTING EAST  
COAST/NORTHEAST STORM TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/UKMET BLEND WITH 12Z GFS ONLY THRU 23.12Z.  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
ACTIVE SOUTHERN STREAM IS EJECTING A SHORTWAVE ACROSS THE FOUR  
CORNERS REGION INTO THE PLAINS TODAY AND THIS WAVE WILL CONTINUE  
TO DRAW DEEP MOISTURE BOTH OFF THE GULF, BUT THE SUBTROPICAL  
PACIFIC TO SUPPORT AN INVERTED SURFACE TROF/WAVE THROUGH THE  
MISSISSIPPI VALLEY MONDAY. THE NORTHERN STREAM WILL ALSO BE  
DIGGING ACROSS CENTRAL CANADA INTO THE NORTHERN HIGH PLAINS TO  
HELP BROADEN A DEEPER LATITUDE/PHASED TROF ACROSS THE GREAT LAKES  
BY LATE MONDAY. TIMING AND INTERACTION BETWEEN STREAMS WITH THE  
INCLUSION OF LATENT HEAT RELEASE IN CERTAIN PORTIONS OF THE WAVE  
WILL CONTINUE TO BE LEAD TO LARGE UNCERTAINTY TO PRECISE IMPACTFUL  
SENSIBLE WEATHER. THIS INCLUDES THE DEVELOPMENT OF THE COASTAL  
SURFACE CYCLONE, BOTH IN LOCATION AND DEPTH BY TUESDAY. THE 12Z  
GFS CONTINUES TO BE SLIGHTLY FASTER IN THE NORTHERN STREAM AND SO  
DOES NOT DIG AS SHARPLY, YET ALSO SHOWS A BIAS NOTED THIS WINTER  
OF BEING A BIT TOO WARM WITH THE WARM CONVEYOR BELT/ISENTROPIC  
ASCENT CHANNEL WHICH HAS THE POTENTIAL TO LEAD TO GREATER  
UNCERTAINTY WITH PRECIPITATION TYPE ACROSS THE NORTHEAST. THE 12Z  
NAM CONTINUES TO SHOW A BIAS OF BEING A BIT TOO STRONG THROUGH THE  
DEPTH, LIKELY DUE TO INCREASED LATENT HEAT RELEASE IN THE  
MID-LEVEL COLUMN THROUGH THE MIDWEST/OHIO VALLEY, WHICH SUPPORTS A  
STRONGER CYCLONE AS WELL AS STRONGER TRAILING ANTI-CYCLONE. THIS  
IS A CLEAR OUTLIER IN MASS FIELDS; YET HAS SEEN THE ECMWF/UKMET  
TRENDING TOWARDS IT IN THE DEVELOPMENT OF THE SURFACE CYCLONE.  
THE 00Z CMC IS SLOW, EVEN MORE SO THAN NORMAL IN THE SOUTHERN  
STREAM. SO WITH REDUCED NORTHERN STREAM PHASING; THE NORTHERN  
STREAM EXITS FASTER ALLOWING FOR FAVORABLE UPPER LEVEL DIVERGENCE  
TO DEEPEN THE CYCLONE OVER SOUTHERN NEW ENGLAND ON TUESDAY. THE  
UKMET/ECWMF AND ECENS HAVE SEEN THE TREND NORTHWARD AND STRONGER  
WITH THE CYCLONE AS A WHOLE WHICH CONTINUES TO BE MOST CENTRAL IN  
THE EVOLUTION. GIVEN THE UNCERTAINTY INHERENT IN PHASING STREAMS;  
WILL GO WITH THE MORE CENTRAL EVOLUTION OF THE UKMET/ECWMF AS  
PREFERENCE; THOUGH INCLUSION OF THE GFS IS LIKELY SUPPORTIVE UNTIL  
AROUND 54HRS (23.12Z) WHEN THE NORTHERN STREAM/SOUTHERN STREAM ARE  
MOST DECOUPLED AND THE COASTAL CYCLONE DEVELOPS WELL SOUTH OF THE  
CLUSTER (THOUGH SUPPORTED BY THE 06Z GEFS). CONFIDENCE IS  
SLIGHTLY BELOW AVERAGE GIVEN THE LOWER PREDICTABILITY OF THE  
COMBINING STREAMS.  
 
CLOSED LOW OFF SW CA TODAY, TRACKS ACROSS SOUTHWEST INTO MID-MS  
VALLEY, MON AND TUES. RESPECTFULLY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS AND 00Z UKMET/12Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE LARGE CLOSED LOW CURRENTLY NEAR 35N135W WILL START TO ADVANCE  
EASTWARD IN THE NEXT THIS EVENING REACHING CENTRAL/SOUTHERN CA BY  
EARLY MONDAY. HOWEVER, EVEN BY THIS POINT THIS IS A SOLID  
DIFFERENCE IN THE MASS FIELDS, WITH THE 00Z CMC ALREADY  
SIGNIFICANTLY SLOWER, WHICH CONTINUES THROUGH THE REST OF THE  
SHORT-TERM FORECAST PERIOD. THE 12Z NAM IS ALSO A BIT STRONGER  
BUT ALSO FASTER. THE CONCERN THOUGH WITH THE NAM IS THE POOR  
DOWNSTREAM SETUP, AS THE OVER-STRONG PRECURSORY RIDGE LEADS TO  
STRONGER RETURN FLOW, FURTHER NORTH AND WHILE THE SURFACE LOW  
LEVEL MASS FIELDS JIVE WELL, THE EFFECTIVE BOUNDARIES/QPF ARE NOT,  
AND SO LIKE THE CMC IS NOT SUPPORTED. THE 12Z GFS SAW A SIZABLE  
SLOWING ESPECIALLY AS THE WAVE ENTERS THE PLAINS LATE MONDAY INTO  
TUESDAY, WHICH MAKES IT A TAD SLOWER THAN THE REMAINING GUIDANCE  
BUT IS STILL NOT AS SLOW/DEEP AS THE GEFS MEAN/BULK OF SOLUTIONS  
WHICH ALSO LAG THE UKMET/ECMWF. STILL THIS FAIRLY SMALL FOR DAY  
3...AND A 12Z GFS AND 00Z ECMWF/UKMET IS PREFERRED AT THIS TIME AT  
SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
PACIFIC NW CLOSED LOW, MON/TUES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM THROUGH 24.00Z  
12Z GFS AND 00Z UKMET/ECMWF BLEND THEREAFTER  
CONFIDENCE: SLIGHTLY ABOVE TO ABOVE AVERAGE  
 
THE NORTHERN STREAM STRONG SHORTWAVE BOWLING THROUGH BRISTOL  
BAY/AK PENINSULA WILL CONTINUE TO HUG THE AK PANHANDLE AND BC  
COAST CLOSING OFF INTO A SMALL BUT COMPACT CLOSED LOW REACHING THE  
PACIFIC NW BY MONDAY. ONLY THE 12Z NAM CONTINUES TO SHOW A  
BROADER INNER CORE/RING OF ENERGY, WHICH EVENTUALLY SLIDES  
EASTWARD RELATIVE TO THE OTHER GUIDANCE AS THE WAVE ELONGATES FROM  
THE UPSTREAM JET PULLING THE LARGER TROF PATTERN SOUTHWEST INTO  
THE PACIFIC BY 00Z TUESDAY; WHILE THE INNER CORE STRETCHES EAST OF  
THE COAST RANGE IN BC AND ACCELERATING FASTER/STRONGER INTO THE  
SOUTHERN CANADIAN PRAIRIES JUST NORTH OF THE US BORDER BY THE 00Z  
WED. THE CMC IS ONCE AGAIN ALSO SLOW, POSSIBLE DUE TO THE  
DOWNSTREAM BLOCKING/SLOWER EXITING WAVE. SO A NON-NAM BLEND  
PREFERENCE THROUGH 24/00Z BECOMES A 12Z GFS AND 00Z UKMET/ECMWF  
BLEND THEREAFTER AT SLIGHTLY ABOVE TO ABOVE AVERAGE CONFIDENCE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page