Prognostic Meteorological Discussion
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FXUS10 KWNH 171845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
142 PM 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 MODEL EVALUATION AND PREFERENCES
==============================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==============================================

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

PREFERENCE: 12Z GFS/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 12Z CMC REMAINS FLAT ACROSS THE
SOUTHWEST...WHILE THE 12Z UKMET...AFTER BEING MORE AMPLIFIED
EARLY...JUMPS INTO THE CONSENSUS POSITION BY DAY 3. THE 12Z ECMWF
WAS CLOSE TO ITS 00Z POSITIONS...AND REMAINS PART OF THE PREFERRED
BLEND.


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

PREFERENCE: BLEND OF 12Z GFS/ECMWF/CMC
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/ECMWF OFFER THE MORE AMPLIFIED SOLUTION...WHILE
MAINTAINING SOME OF THE MOMENTUM OF THE MID LEVEL FLOW. THE 12Z
CMC BECAME MORE AMPLIFIED WITH ITS SOLUTION ACROSS THE LOWER OH
VALLEY...WHILE THE 12Z UKMET BECOMES FASTER THAN THE CONSENSUS
DURING DAY 3.

GIVEN THE THE 12Z GFS/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/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 12Z 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/ECMWF BLEND.


...NORTHEAST...

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

DESPITE THE FACT THAT THERE IS...IN GENERAL...GOOD MODEL
CLUSTERING WITH RESPECT TO THE POSITION OF MID LEVEL SYSTEM CLOSED
OFF OVER NORTHERN NEW ENGLAND ON DAY 1...THE 12Z NAM CONTINUES TO
BE THE WESTERNMOST SOLUTION WITH RESPECT TO THE PLACEMENT OF THE
SURFACE LOW. CONVERSELY...THE 12Z GFS/CMC SURFACE LOW POSITIONS
ARE ON THE EASTERN EDGE OF THE ENVELOPE ON DAY 1....WHILE THE 12Z
ECMWF/UKMET ARE CLOSE THROUGH DAY 1. DUE TO THE CLUSTERING...THE
12Z ECMWF/UKMET IS PREFERRED FOR THE TRACK OF THE SURFACE LOW ON
DAY 1.

AS THE CLOSED LOW STARTS WOBBLING NORTHEAST DURING DAYS
2/3...DIFFERENCES IN THE TRACK OF THE SURFACE LOW EMERGE.
HOWEVER...THE DIFFERENCES HAVE BECOME LESS SIGNIFICANT...AS THE
12Z ECMWF HAS JOINED THE CONSENSUS WITH THE POSITION OF THE
SURFACE LOW ON DAYS 2 AND 3. THERE ARE SOME POSITIONAL DIFFERENCES
ON DAY 2...AS THE 12Z ECMWF CATCHES UP TO THE CONSENSUS...BYT THE
SENSIBLE WEATHER DIFFERENCES SHOULD BE FAIRLY LIMITED.


...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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