Prognostic Meteorological Discussion
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000
FXUS10 KWNH 171835
PMDHMD

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
135 PM EST Sat Feb 17 2018

Valid Feb 17/1200 UTC through Feb 21/0000 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

12Z model preferences with confidence intervals
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS initialization errors do not seem to degrade their short
range forecasts.


Shortwave moving offshore the Northwest in three days
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Model blend; confidence slightly above average

Dispersion is narrowing with low pressure placement and depth
associated with a southward moving shortwave moving down the
western side of the upper level trough.  Over the last several
days, the guidance has been slowly dampening this feature, though
some of the 12z guidance became a little stronger.  The 00z global
ensemble guidance has no defined surface low to track in this
region, normally implying that a weaker solution would be best.
The noticeable strengthening seen in the UKMET/Canadian guidance
lowers consideration of the 00z global ensemble guidance to some
degree.  Blending the 12z GFS, 12z NAM, 12z ECMWF, 12z UKMET, and
12z Canadian accounts for the uncertainty and is preferred with
slightly above average confidence.


Upper trough digging into the West
Pressure pattern in the Plains/Midwest/Great Lakes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Model blend; confidence slightly above average

The 12z UKMET came in looking closer to the other available
guidance, close enough to be considered plausible.  A blend of the
12z Canadian, 12z NAM, 12z GFS, 12z UKMET, and 12z ECMWF is
preferred with slightly above average confidence.


Low moving from the Southeast offshore New England
and its associated shortwave aloft
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Model blend; confidence slightly above average

While the 12z NAM is stronger aloft and a little more
northwesterly with the surface low tonight, this type of solution
has randomly seen over the last several days on various pieces of
guidance, lies within the ensemble clustering, and cannot be fully
ruled out.  Because of this, a compromise of the 12z GFS, 12z NAM,
12z UKMET, 12z Canadian, and 12z ECMWF is preferred with this
system with slightly above average confidence.


Model trends 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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