Prognostic Meteorological Discussion
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000
FXUS10 KWNH 250444
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 PM EST WED DEC 24 2014

VALID DEC 25/0000 UTC THRU DEC 28/1200 UTC

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

...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...FULL-LATITUDE TROF EXITING THE EASTERN U.S. BY CHRISTMAS
EVENING...
...ASSOCIATED COLD FRONT/STRONG AREA OF LOW PRESSURE...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

A LONGWAVE TROF EXTENDING FROM THE GREAT LAKES DOWN TO THE LOWER
MS VALLEY WILL QUICKLY TRANSLATE EASTWARD BEFORE EXITING THE U.S.
CHRISTMAS EVENING. ULTIMATELY ANY MAJOR DIFFERENCES WITH THIS
SYSTEM OCCUR AFTER IT DEPARTS FROM THE EAST COAST. THUS...A
GENERAL MODEL COMPROMISE IS WARRANTED HERE.


...INITIAL SHORTWAVE ENERGY MOVING UP TOWARD THE UPPER MIDWEST BY
FRIDAY MORNING...

PRELIMINARY PREFERENCE: NON-00Z NAM SOLUTION
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

HEIGHT FALLS SLIDING FROM THE CENTRAL GREAT BASIN TOWARD THE ROCKY
MOUNTAIN CHAIN WILL QUICKLY EVOLVE INTO A CLOSED LOW ACROSS THE
COMPLEX TERRAIN OF UT BY 25/1800Z. MODELS SUGGEST THIS SYSTEM WILL
GRADUALLY DRAG SOUTHWARD WITH SHORTWAVE ENERGY LIFTING TOWARD THE
MIDDLE MS VALLEY/UPPER MIDWEST. THE 00Z NAM SEEMED TO BE A TAD
QUICKER THAN OTHER SOLUTIONS AT THE VALID TIME. WILL REJECT THIS
SOLUTION AND FAVOR A NON-00Z NAM APPROACH.


...POSITIVELY-TILTED TROF MOVING THROUGH THE CENTRAL U.S...
...ADVANCING BAROCLINIC ZONE...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z NAM/12Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

MODELS SEEM TO VARY WITH THE PLACEMENT OF THIS UPPER TROF AS IT
CONGREGATES OVER THE FOUR CORNERS REGION EARLY FRIDAY. AT THAT
POINT IN TIME...THE 12Z CMC/UKMET ARE WEST OF THE GENERAL
CONSENSUS. ON THE OTHER SIDE OF THE SPECTRUM IS THE 00Z
GFS-PARALLEL WHICH IS MUCH QUICKER ALOFT. SPREAD CONTINUES TO GROW
AS THE UPPER TROF COMES OUT IN TWO PARTS. AN INITIAL BATCH OF
SHORTWAVE ENERGY EJECTS TOWARD THE MIDDLE MS VALLEY WITH THE
AFOREMENTIONED TIMING DIFFERENCES APPLYING HERE AS WELL. REGARDING
THE SOUTHERN EXTENT OF THE UPPER TROF...THERE IS A GREATER AMOUNT
OF SPREAD WITH THIS SECTOR...PARTICULARLY LATE IN THE PERIOD. AS
WAS THE CASE PREVIOUSLY...THE 12Z CMC/UKMET DIVERGE MOST
SIGNIFICANTLY FROM THE PACK AND CANNOT BE DISMISSED AS OUTLIER
SOLUTIONS. GENERALLY SPEAKING...THE 00Z NAM/12Z ECMWF OFFERS A
REASONABLE SOLUTION WHICH FITS CLOSER TO THE CENTER OF THE
ENSEMBLE SPREAD.


...UPPER TROF DIGGING INTO THE PACIFIC NORTHWEST BY MID-WEEKEND...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECWMF...WEIGHTED
2/3 TOWARD THE ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE HIGH AMPLITUDE PATTERN WILL CONTINUE INTO THE WEEKEND WITH A
MEAN UPPER RIDGE ANCHORING THE EAST PACIFIC WHILE A LONGWAVE TROF
EXTENDS FROM THE PACIFIC NORTHWEST EASTWARD TO THE GREAT LAKES
REGION. A PRONOUNCED SHORTWAVE WILL BE SEEN DIGGING INTO THE
PACIFIC NORTHWEST BY THE MIDDLE OF THE WEEKEND WITH A SLEW OF
TIMING DIFFERENCES NOTED. ON OPPOSITES OF THE SPECTRUM ARE THE 12Z
CMC/UKMET WITH THE LATTER BEING DECIDEDLY FASTER. MULTI-DAY
SPAGHETTI PLOTS SUGGEST A TREND IN THE SLOWER DIRECTION BUT
DEFINITELY NOT AS SLOW AND FLAT AS THE 12Z CMC. AT THE CENTER OF
THE SPREAD ARE THE 00Z GFS/12Z ECMWF WHICH FIT WELL WITH THE
ENSEMBLE CLUSTERING. WILL GIVE A SLIGHT EDGE TO THE 12Z ECWMF AS
IT LEANS ON THE MORE AMPLIFIED SIDE AS SUGGESTED BY A VAST
MAJORITY OF THE 12Z ECMWF ENSEMBLE MEMBERS.



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

RUBIN-OSTER

$$




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