Prognostic Meteorological Discussion
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000
FXUS10 KWNH 220516
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 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 NAM/GFS EVALUATION AND PRELIMINARY 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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PRELIMINARY PREFERENCE: 00Z NAM / 21Z SREF MEAN 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 12Z ECMWF/UKMET/CMC ARE EITHER WEAKER OR TOO FAR
WEST WITH MID-LEVEL ENERGY AND THE CORRESPONDING SURFACE LOW GIVEN
ENSEMBLE SCATTER PLOT LOW PLACEMENT TUE MORNING. THE SREF/GEFS/EC
MEANS SHOW GOOD AGREEMENT TO BE BETWEEN THE NAM AND THE ECMWF.
GIVEN THE ECMWF IS WEAKER AND HAS MORE EMPHASIS ON A SECONDARY LOW
NEAR SIOUX FALLS ALONG AN INVERTED SURFACE TROUGH...THIS IDEA DOES
NOT FIT IN WITH REMAINING MODEL GUIDANCE...SO A BLEND OF THE 00Z
NAM...LIKELY A BIT TOO FAR EAST...AND THE 21Z SREF MEAN...WHICH IS
FARTHER WEST...SEEMS BEST WARRANTED.


LONGWAVE TROUGH OVER THE CNTRL U.S. AND LOW PRESSURE MOVING ACROSS
THE OHIO RIVER VALLEY ON TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 70% 12Z CMC / 30% 12Z 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 12Z ECWMF AND
12Z 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 ENSEMBLE LOWS FAVOR A BLENDED SOLUTION BETWEEN THE
12Z ECMWF/CMC. HOWEVER...WHEN IT COMES TO THE COLD FRONT SWINGING
ACROSS THE EAST...THE 12Z ECMWF IS FAST...WHICH IS LESS FAVORABLE
GIVEN THE AMPLIFIED PATTERN ALOFT AND SLOWING TRENDS IN THE
ENSEMBLE GUIDANCE. THEREFORE...WHILE A BLENDED SURFACE LOW
POSITION BETWEEN THE 12Z ECMWF/CMC APPEARS BEST AT THIS TIME...A
COLD FRONT SPEED CLOSER TO THE 12Z CMC IS PREFERRED. IT IS WORTH
NOTING THAT THE 00Z GFSP SURFACE LOW IS ALSO BETWEEN THE 12Z
ECMWF/CMC 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 / 12Z ECMWF 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/ECMWF REPRESENT A GOOD COMPROMISE IN
THE MIDDLE OF THE LATEST SPREAD WITH CLOSE AGREEMENT TO THE LATEST
ENSEMBLE MEANS.


SHORTWAVE OVER THE WESTERN U.S. WED NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM / 12Z ECMWF BLEND
CONFIDENCE: BELOW AVERAGE

THE 00Z NAM / 12Z ECMWF BLENDED SOLUTION IS IN THE MIDDLE OF THE
LATEST SPREAD AND AGREES WELL WITH THE ENSEMBLE MEANS. THE 00Z GFS
IS DEEPER AND SLOWER...WHILE THE 12Z UKMET IS FASTER. THE 12Z CMC
IS MUCH WEAKER BY LATE WED INTO THU WITH THE UPPER TROUGH. DESPITE
WHAT APPEARS TO BE A STRAIGHT FORWARD SOLUTION TO THE MODEL
SPREAD...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.

...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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