Prognostic Meteorological Discussion
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000
FXUS10 KWNH 220642
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
141 AM EST MON DEC 22 2014

VALID DEC 22/0000 UTC THRU DEC 25/1200 UTC

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

00Z MODEL EVALUATION AND FINAL MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ANY NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY
IMPACT THEIR SHORT RANGE FORECASTS.


NRN STREAM LOW IMPACTING THE NRN PLAINS AND UPR MS VALLEY TODAY/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM / 00Z CMC BLEND
CONFIDENCE: AVERAGE

THE 00Z GFS MADE A SIGNIFICANT SHIFT FROM ITS PREVIOUS CYCLES IN
HAVING STRONGER MID-LEVEL VORTICITY AT THE FRONT EDGE OF A NEWLY
DEVELOPED CLOSED LOW OVER THE UPPER MIDWEST MON NIGHT AND ITS
UPPER PATTERN DOES NOT FIT WELL WITH THE REMAINING MODEL
CONSENSUS. THE 00Z ECMWF/UKMET/CMC HAVE ADJUSTED IN THE DIRECTION
OF THE PREVIOUS PREFERENCE...AND STILL DO NOT SUPPORT THE 00Z GFS.
GIVEN THE LATEST ENSEMBLE SCATTER LOW PLOTS TUESDAY...THE TWO
CLOSEST DETERMINISITC MODELS ARE THE 00Z NAM AND CMC. THE 00Z
ECMWF/UKMET ARE CLOSE TO THIS IDEA...BUT PERHAPS STILL A BIT TOO
FAR EAST.


LONGWAVE TROUGH OVER THE CNTRL U.S. AND LOW PRESSURE MOVING ACROSS
THE OHIO RIVER VALLEY ON TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z CMC / 00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 00Z NAM IS QUICK TO STAND OUT AS WEAKER WITH SECONDARY
SHORTWAVE ENERGY DIVING SWD INTO THE SRN HIGH PLAINS TUE MORNING
AND IS LESS DEVELOPED WITH LOW PRESSURE ACROSS THE CNTRL GULF
COAST TUE NIGHT...ALL COMPARED TO THE REMAINING MODEL CONSENSUS.
THE 00Z NAM IS NOT LIKELY TO VERIFY.

THIS IS A TOUGH FORECAST WITH MANY DETAILS NOT HANDLED WELL IN ANY
SINGLE MODEL. CONSIDERING THE NON-NAM GUIDANCE...A 00Z ECWMF AND
00Z CMC BLEND COMPARE REASONABLY WITH THE LATEST ENSEMBLE
SPAGHETTI 500 MB HEIGHT TRENDS AT 540 AND 552 DM. THE 00Z GFS
LOOKS OKAY WITH THESE MODELS UNTIL AROUND 00Z/25...AT WHICH POINT
THE GFS SURFACE LOW ENDS UP ON THE EDGE OF THE ENSEMBLE SCATTER
LOW PLOTS. THE NEW 00Z ECMWF IS SIMILAR TO THE 00Z GFS BUT A TAD
FARTHER NORTH OR EAST BUT THE ENSEMBLE LOWS FAVOR A BLENDED
SOLUTION BETWEEN THE 00Z ECMWF/CMC. WHEN IT COMES TO THE COLD
FRONT SWINGING ACROSS THE EAST...THE 00Z ECMWF HAS SLOWED ENOUGH
TO INCLUDE IT WITH THE RELATIVELY UNCHANGED 00Z CMC IN A 50/50
BLEND. GIVEN THE AMPLIFIED PATTERN ALOFT AND SLOWING TRENDS IN THE
ENSEMBLE GUIDANCE...SLOWER IS BETTER. IT IS WORTH NOTING THAT THE
00Z GFSP SURFACE LOW IS ALSO BETWEEN THE 00Z ECMWF/CMC AT TIMES
BUT IS QUITE DEEP AND WRAPPED BACK TO THE WEST...AND UNSUPPORTED
AT THIS TIME IN TERMS OF STRENGTH.


WEAK FRONTAL LOW MOVING UP THE EAST COAST TODAY/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/CMC COMPROMISE
CONFIDENCE: ABOVE AVERAGE

DIFFERENCES ARE SMALL...BUT THE 00Z NAM CONTINUES TO STAND OUT AS
FARTHER NORTH WITH A WEAK SURFACE LOW ALONG THE EAST COAST LATER
TODAY AND TONIGHT. THE GFS/CMC REPRESENT A GOOD COMPROMISE IN THE
MIDDLE OF THE LATEST SPREAD WITH CLOSE AGREEMENT TO THE LATEST
ENSEMBLE MEANS...WHILE THE 00Z ECMWF/UKMET APPEAR TO BE FARTHER
SOUTH AND INLAND WITH THE LOW TRACK FOR BRIEF PERIODS OF TIME TUE
MORNING.


SHORTWAVE OVER THE WESTERN U.S. WED NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/ ECMWF BLEND
CONFIDENCE: BELOW AVERAGE

THE 00Z NAM / 00Z ECMWF BLENDED SOLUTION IS IN THE MIDDLE OF THE
LATEST SPREAD AND AGREES REASONABLY WELL WITH THE ENSEMBLE MEANS.
THE 00Z GFS IS DEEPER AND SLOWER...AND THE 00Z ECMWF TRENDED
DEEPER...BUT STILL A LITTLE FASTER THAN THE GFS. THE 00Z UKMET
ALSO TRENDED DEEPER WITH SIMILAR TIMING TO ITS 12Z RUN AND SIMILAR
TO THE 00Z ECMWF. LASTLY...THE 00Z CMC ALSO TRENDED DEEPER BUT NOT
TO THE EXTENT OF THE GFS/ECMWF/UKMET AND IS ON THE FASTER SIDE OF
THE GUIDANCE. ENSEMBLE SPREAD IS QUITE LARGE...LED BY THE DEEPER
ECMWF MEMBERS...WHILE THE GEFS MEMBERS ARE MUCH WEAKER/FLATTER.
THE PAST 3 CYCLES OF ENSEMBLE GUIDANCE SHOW NO CONVERGENCE TOWARD
THE DEEPER OR FLATTER TRACKS...BUT THE AMPLIFIED NATURE OF THE
UPPER PATTERN FAVORS TOWARD THE DEEPER END OF THE SPECTRUM ACROSS
THE WEST ON THU. THIS IS TOWARD THE 12Z/21 EC MEAN OR A 00Z
NAM/ECMWF BLEND.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...


OTTO

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