Prognostic Meteorological Discussion
Issued by NWS

000
FXUS10 KWNH 210448
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1247 AM EDT TUE MAY 21 2013

VALID MAY 21/0000 UTC THRU MAY 24/1200 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...


00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


DEEP CYCLONE MOVING INTO THE NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  NON-NAM COMPROMISE
CONFIDENCE:  ABOVE AVERAGE

OUTSIDE THE SLOW/MORE WESTWARD 00Z NAM, THE GUIDANCE SHOWS
EXCELLENT AGREEMENT WITH THIS SYSTEM`S PROGRESSION.  USING THE
NAM`S LONG-STANDING SLOW BIAS WITH SYSTEMS PROGRESSING THROUGH THE
WESTERLIES AS A GUIDE, PREFER A NON-NAM COMPROMISE HERE WITH ABOVE
AVERAGE CONFIDENCE CONSIDERING ITS SLOW MOVEMENT AND AMPLIFIED
NATURE.  THE 21Z SREF MEAN SHOULD BE OF SOME UTILITY IN THIS
REGION.


SYSTEM MOVING ACROSS THE MIDWEST AND EAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z ECMWF/12Z UKMET/12Z CANADIAN
CONFIDENCE:  AVERAGE

THE 00Z NAM/00Z GFS/18Z GEFS MEAN ARE SLOWER AND SHARPER WITH THIS
SYSTEM AS IT MOVES THROUGH THE OHIO VALLEY INTO THE EAST.  THE
FLOW PATTERN IT IS EMBEDDED WITHIN FEATURES A BROAD UPPER/POLAR
VORTEX ACROSS EASTERN CANADA WITH A BROAD RIDGING ACROSS THE
CENTRAL PLAINS.  BOTH THESE FEATURES WOULD FAVOR A BROADER AND
MORE PROGRESSIVE SYSTEM THAN ADVERTISED BY THE NAM/GFS SOLUTIONS.
THE LONG-RUNNING NAM SLOW BIAS ALSO ARGUES FOR A SOLUTION QUICKER
THAN THE NAM.  THE MODEL PREFERENCE IS FOR A 12Z ECMWF/12Z
UKMET/12Z CANADIAN WITH AVERAGE CONFIDENCE DUE TO ITS PROGRESSIVE
AND DEAMPLIFYING NATURE.  THE 21Z SREF MEAN SHOULD BE OF SOME
UTILITY WITH THIS SYSTEM.


UPPER TROUGH OVER FLORIDA
~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  00Z GFS
CONFIDENCE:  ABOVE AVERAGE

THE 12Z UKMET/21Z SREF MEAN ARE THE WEAKEST WITH THIS SYSTEM`S
DEPICTION WHILE THE 00Z NAM IS THE STRONGEST.  MODEL BIAS OF THE
ECMWF WHICH USUALLY CAUSE WEAKER MID-LEVEL SYSTEMS TO BE FORECAST
AS TOO WEAK AND OF THE NAM WHICH NORMALLY DEPICTS MID-LEVEL
SYSTEMS TOO STRONGLY ARGUE FOR A SOLUTION IN BETWEEN THE
TWO...CLOSEST TO THE 00Z GFS.  THE 00Z GFS IS PREFERRED WITH ABOVE
AVERAGE CONFIDENCE CONSIDERING ITS VERY SLOW PROGRESSION.


...MODEL TREND GRAPHICS AT
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML...
...500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML...

ROTH
$$