Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1252 AM EDT Tue May 01 2018

Valid May 01/0000 UTC thru May 04/1200 UTC

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

00Z NAM/GFS evaluation including preliminary preferences
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...Closed low/surface low departing from the Northeast today...
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Preference: General model blend
Confidence: Above average

The models show similarly with this system.


...Weakening low amplitude shortwave(s) moving into south-central
Canada today/tonight...
...Elongated surface trof with main surface low near the upper MS
valley this morning and tracking through Ontario/Quebec through
tonight...
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Preference: General model blend through 12Z/03
            non 12Z CMC blend 12Z/03-12Z/04
Confidence: Slightly above average

Only the 12Z CMC stands out significantly with this system in that
its surface low near New England Thursday lies toward the north
and slow side of the latest deterministic guidance as well as
ensemble data. Otherwise, the models show only minor differences
with this system.


...Western trof/closed low ejecting into the central Plains on
Thursday with deepening surface low in the central High Plains and
lingering mid-level troughing across AZ/NM/NW Mexico...
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Preference: Non 12Z CMC blend through 12Z/03
            00Z GFS/12Z ECMWF blend 12Z/03-00Z/04
Confidence: Slightly above average, becoming slightly below average

The 12Z CMC again stands out with it surface low starting Thursday
morning, lying on the northern end of the latest ensemble guidance
and well north of the remaining deterministic consensus.

As the accompanying shortwave over the central Plains nears the
Great Lakes Friday morning, it begins to meet with a separate
shortwave amplifying southward from Manitoba and Ontario. The 12Z
ECMWF/UKMET/CMC are more amplified with the northern shortwave,
while the 00Z NAM/GFS are flatter. Model trends are inconclusive,
but the 12Z ECMWF mean appears to be a reasonable middle ground
between the deeper and flatter solutions. This translates to a 12Z
ECMWF/00Z GFS blend concerning a surface low over lower Michigan
and the corresponding cold front extending southwestward into the
southern Plains.


...Mid-level shortwave approaching British Columbia Friday
morning...
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Preference: non 12Z ECMWF blend
Confidence: Slightly below average

Ensemble trends sped up with the progression of a shortwave off of
the British Columbia coast Friday morning, with the 12Z ECMWF
toward the faster side of the latest ensemble guidance. There is
fair agreement among the non-12Z ECMWF models, so that will be the
preference at this time. Given the uncertainty of the source
region over the open Pacific, confidence is slightly reduced.


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

Otto