Prognostic Meteorological Discussion
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FXUS10 KWNH 180505
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
105 AM EDT THU SEP 18 2014

VALID SEP 18/0000 UTC THRU SEP 21/1200 UTC

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

00Z MODEL EVALUATION...INCLUDING THE 00Z NAM/GFS.


...TROPICAL DEPRESSION ODILE...

PREFERENCE: 12Z ECMWF

AS ODILE WEAKENS AS IT MOVES EAST NORTHEAST...THE LOW LEVEL CENTER
WEAKENS SO THAT IT BECOMES INDISTINGUISHABLE AFTER DAY 1. THE MID
LEVEL CENTER IS MORE EASILY TRACKED...AND THE 00Z NAM IS IN WITHIN
THE MODEL SPREAD DURING DAYS 1 AND 2 ACROSS THE SOUTHWEST STATES.
AFTER THAT...THE 00Z NAM MID LEVEL POSITIONS SLOWS...AS DOES THE
00Z GFS. THE 12Z ECMWF SEEMS TO POSSESS THE BEST CONTINUITY WITH
THE MID LEVEL SYSTEM...SO IT IS PREFERRED.


...DEEP UPPER TROUGH/CLOSED LOW AFFECTING THE WESTERN STATES
THROUGH SAT...

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

BOTH THE 00Z NAM AND 00Z GFS ARE WITHIN THE MODEL SOLUTION
ENVELOPE WITH RESPECT TO POSITION OF THE UPPER TROUGH/CLOSED
LOW...AS THE LARGE SCALE RIDGE OVER THE WEST SHIFTS EAST. THIS
ALLOWS THE MID LEVEL SYSTEM TO APPROACH THE SOUTHWEST STATES. THE
00Z GFS AND 12Z ECMWF SHOW THE BEST CONTINUITY WITH RESPECT TO
MASS FIELDS...SO THIS COMBINATION IS PREFERRED.


...MID LEVEL TROUGH OVER THE NORTHEAST...

PREFERENCE: NON-00Z NAM COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE 00Z NAM SLOWS WITH RESPECT TO THE MODEL CONSENSUS WITH TIME
(ESPECIALLY DURING DAY 3) ACROSS THE NORTHEAST. OTHERWISE...THERE
IS VERY GOOD MASS FIELD AGREEMENT AMONG THE REMAINDER OF THE MODEL
SUITE MEMBERS...WITH INCLUDES THE 00Z GFS. THUS...A NON-00Z NAM
BLEND IS PREFERRED.


...UPPER TROUGH DIGGING INTO THE NORTHERN PLAINS ON FRI...

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

THE 00Z NAM IS SLOWER THAN THE MODEL CONSENSUS WITH THIS
FEATURE...ESPECIALLY DURING DAYS 2 AND 3. THE 00Z GFS IS DEEPER BY
THE END OF DAY 3 THAN THE MODEL CONSENSUS...BUT CLOSE SPATIALLY TO
THE 12Z ECMWF. IT APPEARS AS THOUGH THE 12Z UKMET/CMC ARE PROBABLY
TOO FAST IN THE SHEARED FLOW...SO A BLEND OF THE 00Z GFS/12Z ECMWF
IS PREFERRED.


...SURFACE LOW DEVELOPING OFF THE SOUTHEAST UNITED STATES COAST
SAT...

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

SURFACE LOW PRESSURE DEVELOPING ON THE END OF AN OLD FRONTAL
BOUNDARY NORTH OF THE BAHAMAS ON DAY 2 TRACKS NORTH DURING THE
REMAINDER OF DAY 2 INTO DAY 3. THE 12Z CMC IS THE FASTEST WITH THE
SYSTEM... WHICH LOOKS TOO FAST GIVEN THE MID LEVEL FLOW. THE 12Z
UKMET IS SLOWER THAN THE CONSENSUS...WHICH LOOKS MORE CORRECT THAN
THE 12Z CMC GIVEN THE MID LEVEL FLOW.

THE 00Z NAM/GFS/12Z ECMWF ARE CLUSTERED WELL WITH THIS
SYSTEM...AND THIS COMBINATION IS PREFERRED.


...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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