Prognostic Meteorological Discussion
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FXUS10 KWNH 290439
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1238 AM EDT SUN MAR 29 2015

VALID MAR 29/0000 UTC THRU APR 01/1200 UTC

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

00Z 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.


LONGWAVE TROUGH DEPARTING THE EAST COAST ON SUN
DEEPENING SURFACE LOW TRACKING UP EAST OF NOVA SCOTIA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

WHILE THE 12Z CMC WAS A BIT SLOWER AND DEEPER WITH THE MID LEVEL
SYSTEM OFF NOVA SCOTIA... THERE IS NOT MUCH MODEL SPREAD WITH THIS
SYSTEM...AT THE SURFACE OR ALOFT. SINCE REMAINING IMPACTS TO THE
UNITED STATES ARE MINIMAL...A GENERAL MODEL COMPROMISE IS
PREFERRED.


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

ON DAY 1...THERE IS LITTLE SPREAD AMONG MODEL CONCERNING THE TRACK
AND STRENGTH OF THE SHORT WAVE. THEREFORE...BOTH THE 00Z NAM AND
GFS COULD BE ADDED TO THE PREFERENCE FOR THAT DAY.

HOWEVER...BOTH THE 00Z NAM AND GFS SPEED UP ON DAY 2...AND
CONTINUE THE FASTER FLOW ON DAY 3. BECAUSE OF THIS...THE 00Z GFS
IS NO LONGER PREFERRED ON DAY 2 AND 3 ACROSS NEW ENGLAND. THE 12Z
CMC IS STILL TOO SLOW WITH THIS SYSTEM ON DAY 2...AND CONTINUES
THE TREND ON DAY 3.
SINCE THE 12Z ECMWF/UKMET CONTINUE TO SHOW THE BEST CONTINUITY
WITH THIS SYSTEM...THIS BLEND IS PREFERRED.


SHORTWAVE CROSSING THE UPPER MS VALLEY/GREAT LAKES MON INTO TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 00Z NAM BECOMES FASTER AND DEEPER WITH THIS SYSTEM...BEGINNING
ON DAY 1 AND CONTINUES THE TREND THROUGH TUE. THE 00Z GFS HAS COME
BACK TO THE PACK WITH RESPECT TO SPEED...THOUGH IT CONTINUES TO BE
ON THE NORTHERN EDGE OF THE CONSENSUS ENVELOPE. THE 12Z ECMWF
CONTINUES TO BE ON THE SOUTHERN EDGE OF THE ENVELOPE. THE 12Z
UKMET CONTINUES TO BE FLAT...WHILE THE 12Z CMC TIMING LOOKS
GOOD...BUT HAS BECOME STRONGER WITH TIME.

THE 00Z GFS/12Z ECMWF BLEND IS PREFERRED...SIMPLY BECAUSE IT
PROBABLY ENDS UP CLOSEST TO THE EVENTUAL TRACK OF THE SHORT WAVE
AND ITS ATTENDANT SURFACE LOW. HOWEVER...DUE TO THE DIFFERENCES
MENTIONED ABOVE...FORECAST CONFIDENCE HAS BEEN DROPPED TO SLIGHTLY
BELOW AVERAGE.


MID LEVEL TROUGH NEAR BAJA CA MON...CROSSING THE SOUTHERN PLAINS
TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~
PREFERENCE: NON 12Z UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS WITH THE POSITION AND
STRENGTH OF THE MID LEVEL TROUGH TRACKING ACROSS BAJA CA
MON...WHICH THEN CROSSES THE SOUTHERN PLAINS TUE. THE 12Z UKMET
LAGS BEHIND THE CONSENSUS THROUGHOUT THE PERIOD...AND BECAUSE OF
THIS CANNOT BE INCLUDED IN THE PREFERENCE.


LONG WAVE TROUGH OFF THE PACIFIC NORTHWEST COAST MON
SHORTWAVE/COLD FRONT APPROACHING THE NORTHERN PLAINS TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z NAM BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 00Z NAM CONTINUES TO BE THE SLOW OUTLIER WITH THE SHORT WAVE
THAT CROSSES THE PACIFIC NORTHWEST MON NIGHT INTO TUE...AND SLOWS
A BIT MORE AS THE COLD FRONT WITH THE SHORT WAVE APPROACHES THE
NORTHERN PLAINS. THE 00Z GFS APPEARS TO BE IN THE MIDDLE OF THE
SPREAD WITH RESPECT TO THE SHORT WAVE TIMING AND PLACEMENT OF THE
SURFACE FRONT TUE. THE 12Z UKMET APPEARS TO BE ON THE FAST SIDE OF
THE ENVELOPE...BUT CLOSE ENOUGH TO KEEP IN THE PREFERENCE WITH
THIS SYSTEM.


SHORT WAVE APPROACHING THE PACIFIC NORTHWEST LATE TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET
CONFIDENCE: BELOW AVERAGE

THE 00Z NAM IS SLOW WITH THIS FEATURE AS IT APPROACHES THE PACIFIC
NORTHWEST COAST LATE TUE NIGHT...WHILE THE 00Z GFS IS ON THE
FASTER SIDE OF THE GUIDANCE SOLUTION ENVELOPE. THE 12Z UKMET
SUPPORTS THE TIMING OF THE 12Z ECMWF/ECMWF ENSEMBLE MEAN WITH THIS
FEATURE. HOWEVER... THERE IS STILL ENOUGH SPREAD IN THE GUIDANCE
FOR CONFIDENCE TO BE BELOW AVERAGE.



...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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