Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9
000
FXUS10 KWNH 231833
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
132 PM EST SUN NOV 23 2014

VALID NOV 23/1200 UTC THRU NOV 27/0000 UTC

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

12Z MODEL EVALUATION WITH PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


DEGREE OF RIDGING ACROSS THE PACIFIC NW WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/NAM/ECMWF COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

BETWEEN A DEEP CYCLONE WELL OFFSHORE OREGON AND A COMPLEX UPPER
TROUGH ACROSS THE MIDWEST, RIDGING IS EXPECTED ACROSS THE WEST.
BUT TO WHAT DEGREE?  THE 12Z UKMET IS THE MOST EMPHATIC WITH
MID-LEVEL RIDGING, BUT ITS POSITION OF A DEEP CYCLONE WELL
OFFSHORE THE PACIFIC NORTHWEST IS WELL NORTH OF THE OTHER GUIDANCE
(ITS RIDGING IS LIKELY TOO STRONG).  THE GUIDANCE SOMETIMES BREAKS
DOWN THE TOP OF RIDGES PREMATURELY, WHICH IS SEEN ON THE 12Z
CANADIAN RUN.  THE 12Z NAM/12Z GFS/12Z ECMWF FIT THE
TELECONNECTION THE BEST AND HAVE THE SUPPORT OF THE 06Z/12Z GEFS
MEANS AND 09Z SREF MEAN, SO A COMPROMISE OF THE THREE IS PREFERRED
WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE.


SHORTWAVE MOVING TOWARDS THE GREAT LAKES WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: SREF MEAN/ECMWF COMPROMISE
CONFIDENCE: LOW

THE DETERMINISTIC AND 00Z GLOBAL ENSEMBLE GUIDANCE SHOWS THE
LARGEST SPREAD WITH THIS SYSTEM.  THE OVERALL UPPER TROUGH IS
DISJOINTED, COMPOSED OF AT LEAST THREE SOMEWHAT OUT OF PHASE
STREAMS ACROSS HUDSON BAY, NEAR THE CENTRAL US/CANADIAN BORDER,
WITH A SOUTHERN STREAM SYSTEM ENTERING THE EAST WEDNESDAY.  THE
12Z ECMWF SHOWS THE GREATEST SHARPNESS ALOFT WITHIN THE VARIOUS
STREAMS, WHICH DOES NOT MAKE SENSE CONSIDERING THE BREADTH OF THE
UPPER TROUGH.  THE 12Z GFS/12Z UKMET SHOW SOME SHARPNESS WITH A
SHORTWAVE MOVING INTO THE LOWER OHIO VALLEY/MID-SOUTH LATE
WEDNESDAY, WHICH LIKELY CAUSES THEIR SURFACE LOWS TO BE LOCATED
THAT FAR SOUTH.  THE 09Z SREF MEAN, THOUGH WEAK, SPLITS THE
DIFFERENCE WITH THIS SYSTEM.  THE 12Z ECMWF SURFACE LOW SOLUTION
IS REASONABLY SIMILAR TO THE SREF MEAN.  A COMPROMISE OF THE TWO
IS PREFERRED WITH LOW CONFIDENCE CONSIDERING THE SIGNIFICANT
SPREAD SEEN IN THE GUIDANCE AND THE UNCERTAINTY INHERENT WHEN AN
UPPER TROUGH CONSISTS OF THREE OF MORE STREAMS OF THE WESTERLIES.


SYSTEM MOVING FROM THE NORTHWEST THROUGH THE SOUTH
LOW MOVING OFFSHORE THE EAST COAST WEDNESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS
CONFIDENCE: AVERAGE

LIKE THE NORTHERN PLAINS/UPPER MIDWESTERN SHORTWAVE, THE 12Z
ECMWF/12Z UKMET ARE THE SHARPEST OVERALL WITH THIS SYSTEM, WHICH
DOES NOT BEFIT THE BREADTH OF THE UPPER TROUGH.  THE 12Z NAM WAS
THE WEAKEST AND BROADEST WITH THE OVERALL UPPER TROUGH -- WITH THE
12Z CANADIAN A CLOSE SECOND -- SHOWING A BROADER SOLUTION THAN THE
00Z ECMWF/06Z GEFS/09Z SREF MEAN, WHICH SAILS A WEAK FRONTAL WAVE
WELL OUT TO SEA.  OVERALL, FEEL THE 12Z GFS/09Z SREF MEAN/00Z
ECMWF ENSEMBLE MEAN SPLIT THE DIFFERENCE THE BEST (THOUGH THE 09Z
SREF MEAN IS LIKELY TOO WEAK ALOFT AND AT THE SURFACE).  A
SOLUTION CLOSE TO THE 12Z GFS IS PREFERRED WITH AVERAGE
CONFIDENCE.  THIS SOLUTION KEEPS GOOD CONTINUITY WITH THE MORNING
MEDIUM RANGE FORECAST AND WAS COORDINATED WITH THE DAY 2/3 QPF AND
WINTER WEATHER DESKS.


LOW MOVING THROUGH THE GREAT LAKES SUN/MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CANADIAN COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE 12Z CANADIAN IS DEEPER ALOFT WITH THIS SYSTEM -- ITS USUAL
BIAS -- WHICH APPEARS TO LEAD TO ITS SLOWER SURFACE LOW
PROGRESSION ACROSS MICHIGAN.  THE CANADIAN IS TRENDING WEAKER
ALOFT AND QUICKER WITH ITS SURFACE LOW SOLUTION SINCE ITS 00Z RUN.
 WITH THE REMAINDER OF THE GUIDANCE IN GOOD AGREEMENT, PREFER A
COMPROMISE OF THE 12Z NAM/12Z GFS/12Z UKMET/12Z ECMWF WITH ABOVE
AVERAGE CONFIDENCE.


...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
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.