Prognostic Meteorological Discussion
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000
FXUS10 KWNH 181846
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EDT SAT APR 18 2015

VALID APR 18/1200 UTC THRU APR 22/0000 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.
==============================================

...CENTRAL AND EASTERN U.S...

PREFERENCE: BLEND OF 12Z GFS/ECMWF/CANADIAN
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

MERGING OF THE CLOSED LOW IN THE ROCKIES WITH A DIGGING NORTHERN
STREAM SHORTWAVE WILL PRODUCE A CONSOLIDATED BROAD SCALE TROUGH
CENTERED OVER THE GREAT LAKES BY TUESDAY. THESE ARE ALL LARGE
SCALE FEATURES EMBEDDED WITHIN THE NORTH AMERICAN UPPER AIR
NETWORK...SO THE MODELS SHOW GOOD AGREEMENT. THE MOST NOTEWORTHY
TREND OF THE 12Z CYCLE WAS TOWARD GREATER DEFINITION AND FASTER
PROGRESSION OF A SURFACE LOW / FRONTAL WAVE LIFTING NORTHWARD
ACROSS MICHIGAN ON MONDAY. THE NAM/GFS BEGAN THIS TREND AND WERE
MATCHED BY THE CANADIAN AND ECMWF. ALTHOUGH AT 00Z THE UKMET HAD
BEEN AT THE MIDDLE OF THE PREVIOUS CONSENSUS...ITS 12Z RUN DID NOT
CONFORM TO THE TREND...SO IT NOW APPEARS SLOW. THE NAM MAY BE TOO
FAST BY THE END OF DAY 2 IN THE GREAT LAKES AND NEW
ENGLAND...ALTHOUGH IT PROGRESSES THE FRONT MORE SLOWLY IN THE MID
ATLANTIC. FOR THE OVERALL 1 TO 3 DAY FORECAST WE PREFER THE
TIGHTLY CLUSTERED 12Z GFS/ECMWF/CANADIAN.


...ENERGY DROPPING SOUTHWARD OFFSHORE CALIFORNIA...

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

A BROAD AND RELATIVELY WEAK UPPER LEVEL TROUGH WILL TAKE SHAPE AS
ENERGY THAT WAS NEARLY CUTOFF FROM THE MAIN BELT OF WESTERLIES
SINKS OFFSHORE OF CALIFORNIA. MODEL FORECASTS ARE VERY SIMILAR TO
ONE ANOTHER. THE CANADIAN WAS THE CLOSEST THING TO AN OUTLIER...AS
IT ALLOWS MORE TROUGHING DOWNSTREAM INTO THE SOUTHWEST U.S. BY DAY
3. THE SHORTWAVE RIDGE OVER NEW MEXICO AT THAT TIME IS WEAKEST IN
THE CANADIAN SOLUTION. THE 12Z UKMET WAS JUST SLIGHTLY DEEPER THAN
CONSENSUS WITHIN THE BASE OF THE TROUGH OFFSHORE. ALTHOUGH THE
UKMET COULD BE INCLUDED AS PART OF A BLENDED CONSENSUS...WE PREFER
THE MORE AGREEABLE CLUSTER OF THE NAM/GFS/ECMWF.


...FRONT APPROACHING THE PACIFIC NORTHWEST TUESDAY...

PREFERENCE: BLEND OF THE OPERATIONAL MODELS...WITH 06Z GFS BETTER
PREFERRED THAN 12Z GFS
CONFIDENCE: AVERAGE

WITH IMPROVEMENT TO THE ECMWF SOLUTION / SEE PREVIOUS DISCUSSION /
THE MODELS ARE IN GOOD AGREEMENT AS TO THE TIMING AND DEPTH OF A
SHORTWAVE TROUGH THAT WILL ACCOMPANY A SURFACE BOUNDARY
APPROACHING BRITISH COLUMBIA AND WESTERN WASHINGTON ON TUESDAY.
THE 12Z GFS TRENDED SOMEWHAT SHARPER AND DEEPER WITHOUT SEEING
MUCH SUPPORT EXCEPT FROM GFS ENSEMBLE MEMBERS. THE 06Z GFS BETTER
FITS THE MULTI MODEL AND MULTI ENSEMBLE CONSENSUS...ALTHOUGH THE
12Z RUN IS NOT SO DIFFERENT AS TO BE LABELED AN OUTLIER.

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

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

BURKE
$$





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