Prognostic Meteorological Discussion
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FXUS10 KWNH 200644
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 AM EST SAT DEC 20 2014

VALID DEC 20/0000 UTC THRU DEC 23/1200 UTC

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

00Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


SRN STREAM SHORTWAVE EXITING OFF OF THE MID-ATLANTIC COAST TODAY
WEAK SURFACE LOWS IN THE NRN GULF OF MEXICO AND OFF THE SE COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z GFS COMPROMISE
CONFIDENCE: ABOVE AVERAGE

MODELS SHOW SIMILARLY WITH THESE SYSTEMS...BUT THE 00Z GFS IS
CLOSER TO THE SOUTHEAST COASTLINE LATER TODAY WITH A WEAK FRONTAL
WAVE COMPARED TO THE REMAINING DETERMINISTIC/ENSEMBLE GUIDANCE.
OUTSIDE OF THAT SMALL DETAIL...THERE ARE NO MAJOR DIFFERENCES
BETWEEN THE LATEST GUIDANCE.


UPPER TROUGH AXIS OVER NEW ENGLAND SUN AFTERNOON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


LOW AMPLITUDE SHORTWAVE PASSING THROUGH THE NRN PLAINS TODAY/SUN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

MINOR MODEL DIFFERENCES CAN BE RESOLVED WITH A GENERAL MODEL
COMPROMISE.


SERN U.S. FRONT AND POSSIBLE WEAK WAVE OFF OF THE EAST COAST ON MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z GFS...00Z ECMWF...00Z UKMET
CONFIDENCE: AVERAGE

DETERMINISTIC AND ENSEMBLE TRENDS SINCE YESTERDAY BEST SUPPORT THE
00Z ECMWF WHICH IS CLOSE TO THE 00Z GFS AND 00Z UKMET. IT APPEARS
THAT THE 00Z NAM IS TOO FAR NORTH AND THE 00Z CMC IS MUCH FARTHER
OUT TO SEA CONCERNING A WEAK SURFACE LOW ALONG A FRONT PROGGED
JUST OFF THE EAST COAST THIS MON.


EVOLVING LONGWAVE TROUGH OVER THE MIDDLE OF THE COUNTRY
SURFACE LOW MOVING INTO THE N-CNTRL U.S. ON MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET BLEND
CONFIDENCE: A LITTLE BELOW AVERAGE

THE ECMWF HAS HELD GOOD CONTINUITY SINCE ITS 12Z/18 CYCLE...AND
THE 00Z UKMET HAS ADJUSTED SLOWER FOR THIS CYCLE...TOWARD THE
ECMWF. THERE HAS BEEN A SLOWING TREND SEEN IN THE ENSEMBLE
SPAGHETTI HEIGHT PLOTS WHICH IS ALSO RELFECTED IN SOME OF THE
DETERMINISTIC GUIDANCE. THIS IS TRUE WITH THE EVOLVING UPPER
TROUGH AND SURFACE LOW EXPECTED TO MOVE OUT OF THE WEST AND ACROSS
THE N-CNTRL U.S. ON MON. ENSEMBLE SPREAD IS SHRINKING BUT ENOUGH
OF A SPREAD REMAINS TO KEEP CONFIDENCE A BIT BELOW AVERAGE.
CURRENTLY A BLEND OF THE ECMWF/UKMET REPRESENTS THE BEST FIT TO
THE EVOLVING PATTERN.


POTENTIAL SHORTWAVE NEARING BRITISH COLUMBIA MON NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS...00Z ECMWF
CONFIDENCE: BELOW AVERAGE

DESPITE SOME RECENT CONVERGENCE...IT IS UNCLEAR WHAT DEGREE OF
SHORTWAVE ENERGY WILL MAKE IT OVER A STRONG E-PAC RIDGE BY TUE
MORNING. CURRENTLY...A BLENDED SOLUTION OF THE 00Z GFS AND 00Z
ECMWF FITS BEST WITH THE MIDDLE OF THE LATEST SPREAD AND CLOSEST
TO THE ENSEMBLE MEANS. THERE WAS ONLY SMALL ADJUSTMENTS TOWARD THE
GFS MADE BY BOTH THE 00Z ECMWF/UKMET WHICH APPEAR SIMILAR.


...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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