Prognostic Meteorological Discussion
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000
FXUS10 KWNH 250637
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
136 AM EST THU DEC 25 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 MODEL GUIDANCE ALONG WITH FINAL
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...

FINAL 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...

FINAL 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...

FINAL PREFERENCE: BLEND OF THE 00Z NAM/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. THE
FORECAST SPREAD HAS DECREASED RATHER MARKEDLY GIVEN THE ARRIVAL OF
00Z GUIDANCE. THE 00Z CMC/UKMET HAVE MOVED EASTWARD BRINGING THEM
CLOSER TO THE MODEL CONSENSUS. MEANWHILE...THE 00Z GFS-PARALLEL
CONTINUES TO BE THE QUICKEST SOLUTION WITH THE 00Z GFS SOMEWHAT
FOLLOWING THIS SOLUTION. 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. THE 00Z CMC REMAINS THE
CLOSEST ATTEMPTING TO CLOSE OFF AN UPPER LOW OVER MX BY 28/1200Z.
ADDITIONALLY...THE 00Z ECMWF HAS SPED UP BRINGING IT MUCH CLOSER
TO THE QUICKER 00Z UKMET SOLUTION. THIS ALSO CARRIES ITS FORECAST
EAST OF ITS 12Z ECMWF ENSEMBLE MEAN. CHOOSE TO MAINTAIN THE
PREVIOUS BLEND WHILE INCORPORATING THE LATEST 00Z ECMWF. THIS
SHOULD HOPEFULLY ALLOW FOR THE POSSIBLE FASTER TREND WHILE ALSO
UTILIZING THE SLOWER 00Z NAM.


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

FINAL PREFERENCE: BLEND OF THE 00Z GFS/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. THE SPREAD HAS DIMINISHED WITH THE
LATEST GUIDANCE AVAILABLE AS THE 00Z UKMET TRENDED SLOWER WHILE
THE 00Z CMC CAME IN QUICKER AND A BIT MORE AMPLIFIED THAN
PREVIOUSLY SEEN. THIS CARRIES THESE SOLUTIONS CL0SEE TO THE
INITIAL PREFERENCE. SEE NO REASON TO SHIFT COURSE NOW SO WILL KEEP
THE PREVIOUS PREFERENCE IN PLACE. THAT IS...A BLEND OF THE 00Z
GFS/ECMWF. AGAIN WILL GIVE A SLIGHT EDGE TO THE 00Z 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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