MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1229 AM EDT MON MAY 20 2013

VALID MAY 20/0000 UTC THRU MAY 23/1200 UTC

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

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


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

OTHER THAN THE SLOW AND DEEP 00Z NAM/21Z SREF MEAN, THE REMAINDER
OF THE GUIDANCE IS IN GOOD AGREEMENT CONCERNING THIS SYSTEM'S
EVOLUTION.  THE AFOREMENTIONED PIECES OF GUIDANCE ARE LIKELY SLOW
DUE TO THE WRF PHYSICS THEY INCLUDE, AND IN THE CASE OF THE NAM,
THIS IS A WELL-KNOWN BIAS THAT HAS EXISTED FOR SEVERAL YEARS. 
WITH THE 18Z GEFS MEAN CLOSER TO THE QUICKER/MORE EASTWARD 12Z
ECMWF ENSEMBLE MEAN SOLUTION, THE NON-NAM/NON-SREF MEAN EASTERN
CONSENSUS IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE DUE TO ITS
INCREASINGLY AMPLIFIED AND SLOW-MOVING NATURE.


SYSTEM MOVING THROUGH THE GREAT LAKES/NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z CANADIAN
CONFIDENCE:  AVERAGE

THERE IS RELATIVELY GOOD AGREEMENT ON THE LARGE SCALE WITH THIS
SYSTEM.  THE NAM BECOMES A LITTLE DEEP WITH A LOW MOVING THROUGH
THE GREAT LAKES/SOUTHEAST CANADA EARLY WEDNESDAY, WHICH LEADS TO A
QUICKER MOVING WARM FRONT ACROSS NEW ENGLAND.  THE 00Z GFS BECOMES
QUICK WITH THE NEW ENGLAND WARM FRONT DUE TO SLIGHTLY MORE
PROGRESSION ALOFT.  IN ADDITION, THERE ARE DETAIL ISSUES IN
REGARDS TO A SECONDARY COLD FRONT/POSSIBLE PNEUMONIA FRONT
DROPPING OUT OF LAKE MICHIGAN INTO ILLINOIS AND INDIANA, WITH THE
12Z ECMWF THE SLOWEST WITH ITS PROGRESSION AND THE 00Z GFS/00Z
NAM/12Z UKMET THE QUICKEST.  CONSIDERING THE ABOVE, THE 12Z
CANADIAN IS A REASONABLE COMPROMISE WITH ITS MASS FIELDS, AND IS
PREFERRED WITH AVERAGE CONFIDENCE CONSIDERING THE SYSTEM'S
PROGRESSIVE NATURE.  THIS DOES NOT NECESSARY TRANSLATE TO THE QPF
PREFERENCE, AS THE CANADIAN HAS A WELL-KNOWN AND LONG-STANDING
HIGH BIAS WITH PRECIPITATION AMOUNTS AND COVERAGE.  SEE THE
QUANTITATIVE PRECIPITATION DISCUSSION -- QPFPFD -- FOR MORE
DETAILS ON THE RAINFALL FORECAST.


SHORTWAVE TROUGH MOVING THROUGH CAROLINAS
WEAK UPPER LEVEL LOW/TROUGH STUCK ACROSS FLORIDA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z ECMWF/00Z GFS COMPROMISE
CONFIDENCE:  ABOVE AVERAGE

THE 00Z NAM IS SLOW WITH ITS SHORTWAVE PROGRESSION ACROSS THE
CAROLINAS -- WHICH HAS BEEN ITS HISTORY WITH THIS SYSTEM.  ACROSS
FLORIDA, THE ECMWF HAS TRENDED STRONGER WITH THE LINGERING UPPER
LOW/TROUGH SINCE THIS TIME YESTERDAY, IN THE DIRECTION OF THE MORE
CONSISTENT GFS,  WHILE THE 12Z CANADIAN/12Z UKMET SHOW A WEAKER
SYSTEM.  AS THE ECMWF TENDS TO HAVE A WEAK BIAS WITH WEAK ENERGY
IN THE SUBTROPICS, USED THIS AS A GUIDE TOWARDS A 12Z ECMWF/00Z
GFS PREFERENCE OVERALL, WITH CONFIDENCE ABOVE AVERAGE IN THIS
CHOICE DUE TO THE OVERALL SYSTEM'S SLOW PROGRESSION.


...MODEL TREND GRAPHICS AT www.wpc.ncep.noaa.gov/html/model2.shtml

ROTH