Prognostic Meteorological Discussion
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000
FXUS10 KWNH 181639
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 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 NAM/GFS EVALUATION AND PRELIMINARY 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 / 00Z UKMET

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. LOOKING INTO THE
DETAILS...THE 00Z ECMWF AND CANADIAN WERE SOMEWHAT SLOW AT THE
SURFACE. THE ECMWF WAS ALSO WEAKER AND FARTHER WEST THAN CONSENSUS
WITH A SURFACE LOW / FRONTAL WAVE LIFTING NORTHWARD ACROSS
MICHIGAN ON MONDAY. THE 12Z NAM AND GFS SHOWED IDENTICAL
TRENDS...WITH THIS FEATURE BECOMING BETTER DEFINED AND EVEN A
LITTLE FASTER TO PROGRESS NORTH AND EAST. THE NAM MAY GET TO 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. WHEN TAKING THESE DETAILS INTO ACCOUNT...WE PREFER THE
00Z UKMET AS BEING REPRESENTATIVE OF THE PREVIOUS CONSENSUS...AND
THE 12Z GFS FOR CAPTURING THE TRENDS.


...ENERGY DROPPING SOUTHWARD OFFSHORE CALIFORNIA...

PREFERENCE: BLEND OF 12Z NAM/GFS WITH 00Z ECMWF

A BROAD AND RELATIVELY WEAK UPPER LEVEL TROUGH WILL TAKE SHAPE AS
ENERGY NEARLY CUTOFF FROM THE MAIN BELT OF WESTERLIES SINKS
OFFSHORE OF CALIFORNIA. MODEL FORECASTS ARE VERY SIMILAR TO ONE
ANOTHER. THE 00Z CANADIAN WAS THE CLOSEST THING TO AN OUTLIER...AS
IT SHIFTED THE BULK OF MID LEVEL TROUGHING FARTHER EAST TOWARD
SOUTHERN CA AND BAJA WITH TIME. THE 00Z UKMET DEPICTED A SLIGHTLY
DIFFERENT ORIENTATION TO THE 500-700 MB TROUGH BY TUESDAY IN
COMPARISON TO THE MORE AGREEABLE CLUSTER OF THE NAM/GFS/ECMWF.


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

PREFERENCE: BLEND OF THE OPERATIONAL MODELS...EXCLUDING THE 00Z
ECMWF

OVER THE CENTRAL PACIFIC THE 00Z ECMWF WAS THE SLOWEST AND MOST
CLOSED SOLUTION NORTHWEST OF HAWAII BY DAY 3. DOWNSTREAM THE ECMWF
WAS THEREFORE SLOWER TO BUILD RIDGING ALONG 145 DEGREES WEST
LONGITUDE...YIELDING A FLATTER SHORTWAVE TROUGH COMING INTO
BRITISH COLUMBIA AND NEARING WESTERN WASHINGTON TUESDAY. THE OTHER
MODELS ARE IN BETTER AGREEMENT AS TO THE DEPTH OF THE SHORTWAVE
ACCOMPANYING A SURFACE BOUNDARY HERE. ALTHOUGH THE 12Z GFS TRENDED
STRONGER...IT STILL FEATURES THE SAME TIMING...AND COULD BE
BLENDED WITH THE NAM/UKMET/CANADIAN TO FORM A CONSENSUS WHICH FITS
THE ENSEMBLE MEANS.

...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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