Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
125 AM EDT Fri May 04 2018

Valid May 04/0000 UTC thru May 07/1200 UTC

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

00Z Model Evaluation...with Preliminary Preferences and Confidence
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...Upper level trough ejecting through the Great Lakes today, with
an accompanying surface low and cold front sweeping through the
Great Lakes and Northeast...
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Preference: Non-CMC blend
Confidence: Above average

Models are generally in good agreement with this system, showing
similarity with their mass fields. The 12Z CMC does show less
amplitude to the ejecting wave, however, and has a faster
progression to the surface low as a result. The preference is for
a non-CMC blend.


...Southern stream trough pushing east through the southern Plains
today and into the Southeast this weekend...
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Preference: Non-CMC blend
Confidence: Average

The 12Z CMC showed higher heights through much of the trough
relative to the other models at initial hours of the forecast.
This eventually leads to a slightly flatter wave with a faster
progression. Otherwise, models are generally in good agreement and
a blend of the remaining models is preferred. The 00Z NAM does
appear to have a slightly stronger trough than the other models
but the difference is not substantial enough for it to be excluded
from the preference.


...Upper level trough digging into the Great Lakes on Sunday...
...Associated cold front pushing through the Midwest...
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Preference: General model blend; slight weight toward the 00Z GFS
Confidence: Average

There is a split among the models regarding trough amplitude with
this digging wave. Generally the NCEP models (NAM, GFS, GEFS Mean)
show a more amplified trough with the others (ECMWF, UKMET, CMC)
showing a less amplified trough. With a digging wave, a
pre-existing trough over the eastern US, and nothing really to
inhibit a strengthening wave as it digs southeast, the preference
would tend to be for the more amplified solution offered by the
GFS and NAM. However, GEFS+ECMWF ensemble cluster analysis shows
nearly an even split, with no clear preference for either
scenario. The preference, therefore, will be for a broader model
blend with a slight lean to the GFS.


...Low amplitude shortwave approaching British Columbia Friday...
...Secondary trough approaching the West Coast by late Saturday...
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Preference: Blend of 00Z GFS; 00Z NAM; 12Z ECMWF
Confidence: Average

The NAM, GFS, and ECMWF are fairly similar with their mass fields
for this system. The 12Z UKMET shows more amplitude to the
secondary trough over the Pacific as it approaches the West Coast
as compared to the other models, and the 12Z CMC has a
significantly different height pattern over the Western US by late
in the weekend. The preference, therefore, is a blend of the GFS,
NAM and ECMWF.


...Upper level low developing near the Bahamas...
...Inverted surface trough extending into Florida this weekend...
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Preference: Non-CMC blend
Confidence: Above average

Models show similarity with this system, although the CMC shows a
weaker low and stronger ridge to the northwest compared to other
models.


Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Lamers