Prognostic Meteorological Discussion
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000
FXUS10 KWNH 291703
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
103 PM EDT SUN MAR 29 2015

VALID MAR 29/1200 UTC THRU APR 02/0000 UTC

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

12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


SHORTWAVE TRACKING FROM THE UPPER MS VALLEY SUN TO NEW ENGLAND MON
COLD FRONT REACHING THE EAST COAST MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z ECMWF/12Z GFS
CONFIDENCE: AVERAGE

THERE IS REASONABLY GOOD AGREEMENT WITH THIS SYSTEM THROUGH MONDAY
EVENING ALTHOUGH THE NAM BEGINS TO STRAY FROM THE CONSENSUS WITH A
MUCH WEAKER SURFACE LOW OVER SRN QUEBEC. THE MAJORITY OF THE
MODELS HAVE TRENDED QUICKER WITH THE UPPER TROUGH INTO TUESDAY
MORNING...EXCEPT THE NAM WHICH HAS SLOWED SIGNIFICANTLY SINCE
YESTERDAY AND IS THE SLOWEST OF THE DETERMINISTIC MODELS.
CURRENTLY...THE ENSEMBLE MEANS ARE AHEAD OF THE NAM BUT SLIGHTLY
BEHIND THE 12Z GFS AND 00Z ECMWF. HOWEVER...THE 12Z GFS AND 00Z
ECMWF REPRESENT A GOOD MIDDLE GROUND WITH RESPECT TO THE
ENSEMBLE/DETERMINISTIC SPREAD.


SHORTWAVE CROSSING THE UPPER MS VALLEY/GREAT LAKES MON INTO TUE
SURFACE LOW CROSSING THE MID ATLANTIC STATES TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 2/3 WEIGHT 12Z GFS...1/3 WEIGHT 00Z ECMWF
CONFIDENCE: AVERAGE

THE 12Z NAM IS THE FARTHEST NORTH WITH ITS MID-LEVEL SHORTWAVE OF
THE DETERMINISTIC MODELS AND OUTSIDE OF THE ENSEMBLE LOW SPREAD
WITH ITS SURFACE LOW BY TUE EVENING IN THE NRN MID-ATLANTIC
REGION. THE SURFACE LOW FROM THE 12Z GFS FITS IN VERY NICELY IN
THE MIDDLE OF THE ENSEMBLE LOW SPREAD BUT THE 00Z ECMWF IS ON THE
FAR SOUTHWEST EDGE OF THE ECMWF MEMBERS.

THE 00Z ECMWF COULD BE A BIT WEAK AND SLOW WITH THE MID-LEVEL
SHORTWAVE BUT THE 12Z GFS HAS TRENDED STRONGER THAN THE AVERAGE
DETERMINISTIC PIECE OF GUIDANCE. THE 00Z CMC/UKMET IS A
STRONG/FLAT OUTLIER RESPECTIVELY. GIVEN FAVORABLE LOW PLACEMENT
FROM THE 12Z GFS...THOUGH PERHAPS A BIT TOO STRONG...IT IS
RECOMMENDED TO BLEND THE 12Z GFS WITH 00Z ECMWF...BUT WITH A
LITTLE MORE WEIGHT ON THE GFS GIVEN THE ECMWF IS NOT IN A
FAVORABLE LOW LEVEL POSITION.


MID LEVEL TROUGH NEAR BAJA CA MON...CROSSING THE SOUTHERN PLAINS
TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~
PREFERENCE: 12Z GFS...00Z ECMWF...00Z CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z GFS IS A LITTLE WEAKER THAN THE AGREEABLE 00Z ECMWF/CMC
BUT ALL THREE SHOW A SIMILAR TIMING WITH THIS SHORTWAVE. THE 00Z
UKMET IS BY FAR THE SLOWEST AND IS NOT CONTAINED WITHIN THE
ENSEMBLE SPREAD. THE 12Z NAM IS NOT PREFERRED AS IT TAKES THE CORE
OF THE MID-LEVEL ENERGY...WHEN IT REACHES THE PLAINS TUE
MORNING...NORTH OF THE REMAINING CONSENSUS.


LONG WAVE TROUGH OFF THE PACIFIC NORTHWEST COAST MON
SHORTWAVE/COLD FRONT APPROACHING THE NORTHERN PLAINS TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE MODELS SHOW GOOD AGREEMENT THROUGH DAY 2...00Z/01...AT WHICH
POINT SOME MINOR DIFFERENCES IN STRENGTH/TIMING APPEAR. THE
QUASI-AMPLIFIED NATURE OF THE NRN STREAM WOULD IMPLY THE 00Z CMC
IS TOO FAST AS IT ALSO LIES ON THE FASTER SIDE OF THE
DETERMINISTIC GUIDANCE. BY WED EVENING...THE GEFS/GFS ARE A BIT
FASTER THAN THE ECMWF/EC ENSEMBLES REGARDING THE 540 DM HEIGHT
LINE...WITH A BLEND OF THE TWO APPEARING TO BE THE MOST LIKELY
SCENARIO AT THIS TIME. THE GFS/ECMWF BLEND IS ALSO MOST AGREEABLE
TO THE ENSEMBLE LOW CLUSTERING SEEN FROM THEIR MOST RECENT RUN.


SHORT WAVE APPROACHING THE PACIFIC NORTHWEST EARLY WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z UKMET
CONFIDENCE: SLIGHTLY BELOW AVERAGE

CONFLICTING TRENDS MAKE FOR A DIFFICULT FORECAST WITH THIS FEATURE
BUT IT APPEARS THE 12Z NAM/GFS ARE TOO SLOW GIVEN REASONABLY GOOD
ENSEMBLE SPAGHETTI HEIGHT SUPPORT FOR A FASTER SOLUTION...NEAR THE
00Z ECMWF/00Z ECMWF MEAN. THE 00Z UKMET AGREES WITH THE 00Z ECMWF
BUT THE 00Z CMC IS ON THE WEAKER SIDE OF THE GUIDANCE DESPITE
APPARENT GOOD TIMING.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

OTTO

$$




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