Prognostic Meteorological Discussion
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FXUS10 KWNH 171644
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1144 AM EST WED DEC 17 2014

VALID DEC 17/1200 UTC THRU DEC 21/0000 UTC

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

==============================================
12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==============================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==============================================

...PACIFIC SHORTWAVES REACHING THE PLAINS THU...

PREFERENCE: 12Z GFS/00Z ECMWF/UKMET
CONFIDENCE: ABOVE AVERAGE

THE 12Z NAM IS SLOWER THAN THE CONSENSUS WITH THE SHORT WAVE THAT
TRACKS FROM THE SOUTHWEST STATES INTO THE CENTRAL AND SOUTHERN
PLAINS DURING DAY 1 AND EARLY DAY 2. OTHERWISE...THERE IS GOOD
MODEL CLUSTERING WITH RESPECT TO THE SHORT WAVE THROUGH 20/00Z.
AFTER THAT TIME...THE 00Z CANADIAN DEAMPLIFIES A BIT TOO
QUICKLY...AND THE 12Z NAM CONTINUES TO REMAIN THE SLOW OUTLIER.


...DEVELOPING LONG WAVE TROUGH ACROSS THE OH VALLEY BY DAY 3...

PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF
CONFIDENCE: AVERAGE

THE 12Z NAM IS SLOWER AND DEEPER WITH THE MID LEVEL SHORT WAVES
THAT EVENTUALLY TRIES CARVING OUT A LONG WAVE TROUGH EXTENDING
FROM THE OH VALLEY INTO THE SOUTHEAST STATES BY DAY 3. GIVEN THE
SPEED OF THE UPSTREAM FLOW...THIS OUTCOME APPEARS UNLIKELY. THE
12Z GFS/00Z ECMWF OFFER THE MORE AMPLIFIED SOLUTION...WHILE
MAINTAINING SOME OF THE MOMENTUM OF THE MID LEVEL FLOW....WHILE
THE 00Z UKMET/CANADIAN APPEAR TO BE TOO FLAT WITH THE MID LEVEL
FLOW.

GIVEN THE THE 12Z GFS/00Z ECMWF BLEND OFFER THE BEST TEMPORAL AND
SPATIAL CONTINUITY WITH THEIR RESPECTIVE SOLUTIONS (AS WELL AS
WITH THEIR ENSEMBLE MEAN POSITIONS)...THIS BLEND IS THE PREFERRED
SOLUTION. THE SURFACE REFLECTIONS DEGENERATES FROM A WEAK CLOSED
SYSTEM ALONG THE WESTERN GULF COAST TO MORE OF AN OPEN WAVE OVER
THE EASTERN GULF...AND THIS TREND IS SEEN IN JUST ABOUT ALL
SOLUTIONS.



...SHORT WAVE ENERGY ACROSS THE WESTERN UNITED STATES DAYS 2/3...

PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF
CONFIDENCE: AVERAGE

THE FAST MID FLOW ENTERING THE PACIFIC NORTHWEST AND NORTHERN CA
MAKES IDENTIFYING INDIVIDUAL SHORT WAVES IN THE FLOW DIFFICULT IN
THE DAY 2 AND 3 TIME FRAME. THE NORTHERN STREAM CONTAINS THE MORE
AMPLIFIED SHORT WAVE DURING THE DAY 1/2 TIME FRAME...AS IT TRACKS
FROM THE PACIFIC NORTHWEST INTO THE NORTHERN PLAINS. THE 12Z GFS
AND 00Z ECMWF BOTH OFFER THE BETTER SPATIAL CONSISTENCY WITH THIS
SHORT WAVE (AS WELL AS WITH THEIR RESPECTIVE ENSEMBLE MEANS).
BECAUSE OF THIS...THE PREFERENCE HERE IS THE 12Z GFS/00Z ECMWF
BLEND.

THE SOUTHERN SHORT WAVE BECOMES MORE AMPLIFIED WITH TIME DURING
THE DAY 2 AND 3 TIME FRAME ACROSS THE SOUTHWEST. THE 12Z NAM IS
WITHIN THE MODEL SPREAD CONCERNING THE PLACEMENT OF THE SHORT WAVE
BY THE END OF DAY 3...AND IS CLOSE TO A 12Z GFS/00Z ECMWF BLEND.


...GREAT LAKES/NORTHEAST...

PREFERENCE: BLEND OF 00Z ECMWF/UKMET INITIALLY...FAVORING THE 12Z
GFS/00Z UKMET BY DAY 3
CONFIDENCE: AVERAGE

THE 12Z NAM CONTINUES TO BE THE WESTERNMOST MEMBER OF THE SOLUTION
ENVELOPE (THE 09Z SREF MEAN POSITION OF THE SURFACE LOW WAS
FURTHER EAST) ACROSS NORTHERN NEW ENGLAND AND THE GULF OF ME ON
DAYS 1 AND 2. THE 12Z NAM THEN BECOMES SLOWER THAN THE CONSENSUS
(MUCH LIKE THE 00Z ECMWF) ON DAY 3 ACROSS THE MARITIMES. THE 12Z
GFS PRESENTS THE EASTERNMOST MEMBER OF THE ENVELOPE WITH RESPECT
TO SURFACE LOW POSITION ON DAY 1. HOWEVER...THE LOW DEEPENS AS IT
INTERACTS WITH THE MID LEVEL CLOSED LOW OVER THE GULF OF ME...AND
FALLS INTO THE MIDDLE OF THE SURFACE LOW POSITION BLEND (ALONG
WITH THE 00Z ECMWF AND 00Z UKMET). BY DAY 3...THE 00Z ECMWF LOW
POSITION LOOKS TO FAR NORTHEAST....WITH THE 12Z GFS/00Z UKMET
BLEND OFFERING THE BEST SOLUTION BY DAY 3.

SO...FOR THE DAY 1/2 TIME FAME...THE 00Z ECMWF/UKMET OFFERS THE
BEST SURFACE LOW TRACK. FOR DAY 3...THE 12Z GFS/00Z UKMET OFFER
THE MORE PLAUSIBLE SURFACE TRACK...AS THE 12Z NAM LOOKS TOO FAR
WEST AND THE 00Z ECMWF TOO FAR NORTHEAST.


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

HAYES

$$





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