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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0501Z Dec 21, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 AM EST SUN DEC 21 2014

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

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

00Z NAM/GFS EVALUATION AND PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS TO NOT APPEAR TO BE SUFFICIENTLY
LARGE TO IMPACT THEIR FORECASTS.


MID-UPPER LEVEL TROUGH AXIS REACHING THE APPALACHIANS BY MON A.M.
WEAK SURFACE FRONTAL WAVE OFF OF THE SOUTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS / 12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

WHILE THE 00Z GFS IS SLIGHTLY FASTER WITH THE UPPER WAVE AS IT
REACHES THE APPALACHIANS...THE 00Z NAM IS ON THE SLOW SIDE...AND A
COMPROMISE OF THE FASTER/SLOWER SOLUTIONS SEEMS BEST GIVEN THE
SHORTER TIME SCALE BEING CONSIDERED. A WEAK COASTAL LOW IS
FORECAST ALONG A FRONT DRAPED ALONG THE SOUTHEAST COAST AND THE
GFS IS SLIGHTLY EAST OF THE CONSENSUS WHILE THE 00Z NAM REMAINS
NORTH OF THE PACK. GIVEN THE WEAK NATURE OF THIS SYSTEM...AND
MULTIPLE WEAKER LOWS DEPICTED IN THE GUIDANCE ACROSS THE WESTERN
ATLANTIC...MAINLY IN THE UKMET/CMC...PREFER TO STAY CLOSE TO THE
ENSEMBLE MEANS...BEST REPRESENTED BY A 00Z GFS / 12Z ECMWF BLEND.


CLOSED UPPER LOW FORMING OVER SOUTH DAKOTA BY MON EVENING
CORRESPONDING SURFACE LOW MOVING THROUGH THE DAKOTAS ON MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM / 12Z ECMWF BLEND
CONFIDENCE: AVERAGE

BOTH THE 00Z NAM/GFS HAVE SHOWED A SIMILAR AND CLEAR TREND TO
CLOSE OFF A MID-LEVEL LOW OVER SOUTH DAKOTA EARLIER THAN THE
ECMWF/UKMET/CMC. THE ECMWF HAS BEEN RATHER CONSISTENT BUT IS ALSO
ON THE EDGE OF THE ENSEMBLE SPREAD AND NORTH OF ITS OWN ENSEMBLE
MEAN. IT IS LIKELY UNWISE TO IGNORE THE NAM/GFS TRENDS...BUT ALSO
UNWISE TO JUMP ON BOARD 100 PERCENT. THEREFORE...GIVEN THE
ENSEMBLE DISTRIBUTION...THE PREFERENCE IS TO GO BETWEEN THESE
EXTREMES...BEST REPRESENTED BY THE 00Z NAM AND 12Z ECMWF.


MID-LEVEL SHORTWAVES PASSING THROUGH SRN BRITISH COLUMBIA TODAY
DOWNSTREAM SURFACE LOW DEVELOPMENT ACROSS THE LOWER MISS VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: CLOSEST TO 12Z UKMET OR 00Z GFS PARALLEL
CONFIDENCE: BELOW AVERAGE

GIVEN THE CONNECTION TO WHAT HAPPENS ACROSS THE DAKOTAS WITH A
CLOSED LOW REFERENCED IN THE ABOVE SECTION...IT APPEARS THIS NEXT
WAVE FOLLOWS SUIT...WITH THE 00Z GFS MORE AMPLIFIED WITH SHORTWAVE
ENERGY DIVING SWD TOWARD TEXAS...WHILE THE 12Z ECMWF IS ON THE
WEAKER SIDE...AND THE 12Z CMC IS MORE FRAGMENTED WITH THE
SHORTWAVE ENERGY DIVING EAST OF A LARGE E-PAC RIDGE. IT APPEARS
THE 00Z GFSP IS A PREFERRED BLEND BETWEEN THE ECMWF/GFS. THE 12Z
UKMET MATCHES CLOSEST TO THE GFSP...AND IS LIKELY THE BEST
OPERATIONAL PIECE OF GUIDANCE AT THIS POINT...ALTHOUGH NO SINGLE
MODEL SHOWS A PREFERRED EVOLUTION AT THIS TIME.


SHORTWAVE REACHING THE BRITISH COLUMBIA COAST TUE MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z UKMET...OR SLIGHTLY WEAKER VERSION OF 12Z UKMET
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE PRESENCE OF SUCH A STRONG RIDGE IN THE EAST PAC WOULD TEND TO
FAVOR LESS SHORTWAVE ENERGY PUSHING INTO THE RIDGE AXIS AS HAS
BEEN SEEN IN RECENT RUNS OF THE ECMWF BY TUE MORNING. THE 00Z
GFS/UKMET ARE SIMILAR WITH A STRONG AND COMPACT CLOSED LOW NEARING
BRITISH COLUMBIA...BUT ARE ON THE STRONGER SIDE OF THE GUIDANCE.
THE 12Z CMC IS THE ODD MAN OUT WITH A RELATIVELY WEAK STORM. THE
ENSEMBLE MEANS SHOW GOOD AGREEMENT...TOWARD THE 12Z UKMET...WHICH
IS A LITTLE FASTER THAN THE 00Z GFS...SO THAT IS WHERE THE
PREFERENCE WILL LEAN AS OF NOW. ENSEMBLE SPREAD IS LARGE IN
STRENGTH AND TIMING WHICH LOWERS CONFIDENCE FOR THIS SYSTEM.

www.wpc.ncep.noaa.gov/html/model2.shtml...
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...


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