Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8

000
FXUS10 KWNH 231630
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 AM 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 NAM/GFS EVALUATION WITH PRELIMINARY MODEL 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 COMPROMISE
CONFIDENCE: 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 00Z 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 00Z
ECMWF/00Z CANADIAN RUNS.  THE 12Z NAM/12Z GFS FIT THE
TELECONNECTION THE BEST AND HAVE THE SUPPORT OF THE 06Z GEFS MEAN
AND 09Z SREF MEAN, SO A COMPROMISE OF THE TWO IS PREFERRED WITH
AVERAGE CONFIDENCE.


SHORTWAVE MOVING TOWARDS THE GREAT LAKES WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: STRONGER THAN THE SREF MEAN
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
00Z 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 SHOWS SOME SHARPNESS WITH A SHORTWAVE
MOVING INTO THE LOWER OHIO VALLEY LATE WEDNESDAY, WHICH LIKELY
CAUSES ITS SURFACE LOW TO BE LOCATED AS FAR SOUTHEAST AS IT IS
WHEN COMPARED TO THE OTHER GUIDANCE.  THE 09Z SREF MEAN, THOUGH
WEAK, SPLITS THE DIFFERENCE WITH THIS SYSTEM -- IT 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 00Z ECMWF
IS THE SHARPEST OVERALL WITH THIS SYSTEM, WITH THE 00Z CANADIAN A
CLOSE SECOND, WHICH DOES NOT BEFIT THE BREADTH OF THE UPPER
TROUGH.  THE 00Z UKMET HAS ISSUES ALOFT WITH THIS SYSTEM WHICH
STEM FROM ITS MORE NORTHERLY DEEP CYCLONE OFFSHORE THE NORTHWEST
AND GREATER RIDGING ACROSS THE NORTHWEST, SO IT WAS NOT UTILIZED
EITHER.  THE 12Z NAM WAS THE WEAKEST AND BROADEST WITH THE OVERALL
UPPER TROUGH, 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 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 00Z CANADIAN IS DEEPER ALOFT WITH THIS SYSTEM -- ITS USUAL
BIAS -- WHICH APPEARS TO LEAD TO ITS SLOWER SURFACE LOW
PROGRESSION ACROSS MICHIGAN.  WITH THE REMAINDER OF THE GUIDANCE
IN GOOD AGREEMENT, PREFER A COMPROMISE OF THE 12Z NAM/12Z GFS/00Z
UKMET/00Z 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.