Prognostic Meteorological Discussion
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000
FXUS10 KWNH 210426
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1225 AM EDT TUE APR 21 2015

VALID APR 21/0000 UTC THRU APR 24/1200 UTC

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

00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
INITIALIZATION ERRORS WITH THE NAM/GFS DO NOT SEEM TO DEGRADE
THEIR SHORT RANGE FORECASTS.


TROUGHING IN THE SOUTHWEST WEDNESDAY INTO FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: CANADIAN/ECMWF COMPROMISE
CONFIDENCE: AVERAGE

THE 00Z NAM/00Z GFS/12Z UKMET ARE QUICKER TO PROGRESS THIS SYSTEM
EASTWARD THAN THE OTHER GUIDANCE.  IT APPEARS THE AMPLITUDE OF A
SHORTWAVE APPROACHING CA IS PARTIALLY TO BLAME HERE, WITH WHICH
THE GFS IS STRONGEST.  THE 21Z SREF AND 12Z ECMWF ENSEMBLE MEANS
SUPPORT A SLOWER PROGRESSION, WHICH TENDS TO WORK OUT WITH
SOUTHWESTERN SYSTEMS.  A COMPROMISE OF THE 12Z ECMWF/12Z CANADIAN
IS PREFERRED WITH AVERAGE CONFIDENCE.


DEEP CYCLONE APPROACHING THE NORTHWEST LATE THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/ECMWF COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z UKMET/12Z CANADIAN ARE STRONGER AND FARTHER SOUTH WITH
THIS SYSTEM (WHICH FITS A KNOWN CANADIAN BIAS).  IT APPEARS
SHORTWAVE RIDGING UPSTREAM IS NOT STRENGTHENING, WHICH SHOULD LEAD
TO A MORE EASTWARD TRAJECTORY.  THE 21Z SREF/18Z GEFS/12Z ECMWF
ENSEMBLE MEAN SOLUTIONS SUPPORT A 00Z GFS/12Z ECMWF COMPROMISE,
WHICH IS PREFERRED WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE.


CLOSED LOW MOVING ACROSS WAS INTO SOUTHWEST CANADA THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: CANADIAN/ECMWF COMPROMISE
CONFIDENCE: AVERAGE

AN AMPLIFIED RIDGE IN THE NORTHERN STREAM SHOULD ALLOW THIS SYSTEM
TO SLIDE EASTWARD UNDER ITS BASE, SIMILAR TO THE BEHAVIOR OF THE
NON-GFS GUIDANCE.  PROGRESSION ISSUES REMAIN, WITH THE 00Z NAM THE
SLOWEST AND THE UKMET THE QUICKEST -- THEIR USUAL BIASES.  PREFER
A COMPROMISE OF THE 12Z CANADIAN/12Z ECMWF WITH AVERAGE CONFIDENCE.


DEEP CYCLONE MOVING ACROSS NEW ENGLAND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/CANADIAN/ECMWF/NAM COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z UKMET IS QUICKER TO PROGRESS THE SYSTEM EASTWARD WHEN
COMPARED TO THE OTHER GUIDANCE -- ITS USUAL BIAS.  A COMPROMISE OF
THE 00Z GFS/00Z NAM/12Z CANADIAN/12Z ECMWF SHOULD EFFECTIVELY DEAL
WITH REMAINING DETAIL ISSUES WITH SLIGHTLY ABOVE AVERAGE
CONFIDENCE.


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

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

ROTH
$$





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