MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 AM EDT WED MAY 22 2013

VALID MAY 22/0000 UTC THRU MAY 25/1200 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 OVER THE NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  NON-CANADIAN COMPROMISE
CONFIDENCE:  ABOVE AVERAGE

THE GUIDANCE IS IN VERY GOOD AGREEMENT THAT A DEEP CYCLONE CENTER
MOVING ASHORE INTO THE NORTHWEST WILL MEANDER NORTHWARD TOWARDS
THE WESTERN US/CANADIAN BORDER, SENDING SHORTWAVES UNDER ITS BASE
THROUGH THE GREAT BASIN INTO THE NORTHERN HIGH PLAINS. 
DETAIL-WISE, THE 12Z ECMWF HAS A BONUS MID-LEVEL LOW IT MOVES
THROUGH MONTANA, WHICH IS LIKELY TOO STRONG.  THE 12Z UKMET HAS AN
EXTRA MID-LEVEL CYCLONE ACROSS THE NORTHWEST PACIFIC, WHICH IS
POSSIBLE IF THE NORTHWESTERN SYSTEM ENDS UP A LITTLE MORE
EASTWARD.  THE 12Z CANADIAN IS SOUTHEAST OF THE OTHER GUIDANCE,
WHICH IS ITS BIAS WITH CLOSED LOWS, SO IT IS PROBABLY TOO
EQUATOR-WARD WITH THIS SYSTEM.  THE 00Z NAM LOOKS USABLE THROUGH
SATURDAY.   THE PREFERENCE HERE IS FOR A NON-CANADIAN COMPROMISE
TO DEAL WITH THE LINGERING DETAIL ISSUES WITH ABOVE AVERAGE
CONFIDENCE CONSIDERING ITS AMPLIFIED NATURE AND SLOW MOVEMENT.


LARGE SYSTEM MOVING FROM THE MIDWEST TO THE EAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  18Z GFS/21Z SREF MEAN/12Z ECMWF COMPROMISE
CONFIDENCE:  AVERAGE

THE 00Z NAM/00Z GFS ARE SLOW AND SHARP WITH THE BASE OF THE MAIN
UPPER TROUGH PROGRESSING THROUGH THE MID-ATLANTIC STATES, WITH THE
00Z GFS GIVING THE GIFT OF A CLOSED LOW NEAR THE VIRGINIA CAPES
FRIDAY NIGHT.  WITH A SHORTWAVE DROPPING DOWN THROUGH SOUTHEAST
CANADA AND A BROAD UPSTREAM RIDGE -- WHICH IS SLOWLY BUILDING -- A
BROADER UPPER TROUGH SHOULD MATERIALIZE, WHICH DECREASES THE
CHANCES OF A CLOSED LOW AT ITS BASE.  THE 12Z GLOBAL ENSEMBLE
GUIDANCE FAVORS A COMPROMISE OF THE 18Z GFS/12Z ECMWF, WHICH IS
ALSO CLOSE TO THE 21Z SREF MEAN WITH THIS SYSTEM'S EVOLUTION. 
THIS CLUSTER OF SOLUTIONS IS PREFERRED WITH AVERAGE CONFIDENCE
CONSIDERING ITS PROGRESSIVE NATURE.


UPPER LOW/TROUGH OVER FLORIDA INTO THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  GENERAL MODEL COMPROMISE
CONFIDENCE:  HIGH

THE GUIDANCE IS IN EXCELLENT AGREEMENT WITH THIS SYSTEM'S
EVOLUTION.  TO DEAL WITH ANY LINGERING DETAIL ISSUES, A GENERAL
MODEL COMPROMISE IS PREFERRED WITH HIGH CONFIDENCE.


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

ROTH