Prognostic Meteorological Discussion
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000
FXUS10 KWNH 290646
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 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 MODEL EVALUATION ALONG WITH FINAL 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

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 00Z ECMWF/00Z GFS
CONFIDENCE: SLIGHTLY BELOW AVERAGE

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

HOWEVER...BOTH THE 00Z NAM AND GFS (AS WELL AS THE 00Z UKMET) SPED
UP ON DAY 2 AND DAY 3. THE 00Z CMC IS NOW CLOSER TO THE CONSENSUS
POSITION...BUT STILL TOO SLOW WITH THIS SYSTEM. THE 00Z ECMWF
JOINED THE PACK WITH A FASTER SOLUTION...AS DOES THE 00Z UKMET
(WHICH BECOMES THE EASTERNMOST OUTLIER DURING DAY 3). BASED ON THE
ABOVE...THE FASTER SOLUTION IS NOW PREFERRED...WITH A BLEND OF THE
00Z ECMWF/GFS REPRESENTING THE BEST CLUSTERING.


SHORTWAVE CROSSING THE UPPER MS VALLEY/GREAT LAKES MON INTO TUE
SURFACE LOW CROSSING THE MID ATLANTIC STATES TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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 (ITS SURFACE LOW IS
ALSO THE FURTHEST NORTH BY THE END OF DAY 3). 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 00Z UKMET
CONTINUES TO BE FLAT...WHILE THE 00Z CMC TIMING LOOKS GOOD...BUT
BECOMES MUCH DEEPER WITH THE SHORT WAVE DURING DAY 3 OFF THE EAST
COAST.

THE 00Z ECMWF CONTINUES TO BE THE SOUTHERNMOST SOLUTION WITH THIS
SHORT WAVE...ESPECIALLY DURING DAY 2 WITH ITS PRECIPITATION SWATH.
THE 12Z ECMWF WAS A BETTER FIT (THOUGH STILL FURTHER SOUTH THAT
THE 00Z GFS). AT THIS POINT...THE 00Z ECMWF IS TOO FAR SOUTH TO
KEEP IN THE PREFERENCE BLEND...AND THE 12Z ECMWF SOLUTION IS
RETAINED. 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 00Z UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

THE 00Z NAM/GFS/00Z CMC/00Z ECMWF 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 00Z
UKMET CONTINUES TO LAG 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 00Z UKMET HAS SLOWED CONSIDERABLY (COMPARED TO ITS 12Z
SOLUTION)...AND IS NOW ON THE SLOWER SIDE OF THE GUIDANCE
SUITE...ESPECIALLY WITH THE SURFACE FRONT APPROACHING THE NORTHERN
PLAINS. BECAUSE OF THE LARGE CHANGE IN THE 00Z UKMET SOLUTION...IT
IS NO LONGER PART OF THE PREFERRED BLEND. THE 00Z ECMWF IS ALSO A
BIT SLOWER WITH ITS SOLUTION AT THE SURFACE AND IN THE MID
LEVELS...BUT REMAINS CLOSE ENOUGH TO THE CONSENSUS TO RETAIN IN
THE BLEND.


SHORT WAVE APPROACHING THE PACIFIC NORTHWEST LATE TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z GFS
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 00Z UKMET SPED
UP ITS TIMING WITH THE SHORT WAVE...AS HAS THE 00Z CMC. THE 00Z
ECMWF ALSO SPED UP ITS SOLUTION...AND FOR NOW THE FASTER SOLUTION
IS PREFERRED GIVEN THE FAST LOW AMPLITUDE FLOW.

FOR NOW...A BLEND OF THE 00Z ECMWF/GFS IS PREFERRED.
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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