Prognostic Meteorological Discussion
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FXUS10 KWNH 210635
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
135 AM EST TUE NOV 21 2017

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

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

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


SYSTEM MOVING BY THE NORTHWEST ALONG THE US/CAN BORDER THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND; CONFIDENCE ABOVE AVERAGE

THE 00Z NAM BECOMES A SLOW/DEEP OUTLIER WITH THIS SYSTEM, ITS
USUAL BIAS ON DAY 3.  THE FLOW IN WHICH THE SYSTEM IS EMBEDDED --
SUPERGEOSTROPHIC OVER THE TOP OF A RIDGE -- FAVORS A PROGRESSIVE
SYSTEM.  A COMPROMISE OF THE 00Z GFS, 12Z ECMWF, 12Z UKMET, AND
12Z CANADIAN IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE.


TROUGHING ACROSS THE GREAT LAKES/NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE TWO SYSTEMS EMBEDDED WITHIN THIS TROUGH SHOW GOOD AGREEMENT
OVER THE NEXT FEW DAYS.  A COMPROMISE OF THE 00Z GFS, 00Z NAM, 12Z
ECMWF, 12Z UKMET, AND 12Z CANADIAN IS FAVORED WITH ABOVE AVERAGE
CONFIDENCE.


TROUGH AMPLIFYING AS IT EDGES THROUGH THE GULF OF MEXICO
SURFACE LOWS IN THE EASTERN GULF OF MEXICO/NEAR FLORIDA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND; CONFIDENCE SLIGHTLY ABOVE AVE

STARTING TUESDAY EVENING, THE NAM STARTS DIVERGING FROM THE OTHER
GUIDANCE IN BECOMING DEEPER/SLOWER ALOFT WITH THIS SYSTEM -- ITS
USUAL DAY 3 BIAS.  CONSIDERING THE BROAD AND FLATTENING RIDGING
UPSTREAM, A BROADER/SLIGHTLY MORE PROGRESSIVE SOLUTION SIMILAR TO
A COMPROMISE OF THE 00Z GFS, 12Z CANADIAN, 12Z UKMET, AND 12Z
ECMWF MAKES SENSE MASS FIELD-WISE.  FOR QPF CONSIDERATIONS, SEE
OUR QUANTITATIVE PRECIPITATION DISCUSSION (QPFPFD).


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Roth
$$





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