Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
101 PM EDT Fri Mar 30 2018

Valid Mar 30/1200 UTC thru Apr 03/0000 UTC

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

12Z Model Evaluation...Including Model Preferences and Confidence
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...Surface low lifting northeast through New England today and
associated trailing cold front down the East Coast...
...Secondary shortwave pushing from the Mid Mississippi Valley to
the Mid Atlantic behind primary cold front...
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Preference: General model blend
Confidence: Above average

The models handle the mass field details of these systems
similarly and so a general model blend will be preferred.


...Shortwave digging into the Northwest today with a surface low
dropping down over Montana...
...Surface low evolution across the Upper Midwest/Great Lakes
through Saturday...
...Trailing cold front sweeping across the Northeast by Sunday...
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Preference: General model blend
Confidence: Above average

The models have come into considerably better agreement over the
last 12 hours compared to model cycles 24 to 48 hours ago with
this system. Earlier runs of the NAM and ECMWF which were north of
the more consistent GFS have come into agreement on a farther
south solution and are close or perhaps just a shade north of the
GFS with today's 12Z cycle. The only model that may still be out
of tolerance at this point is the 00Z CMC which appears to be a
little too weak, but overall a consensus approach will be
preferred and thus a general model blend to resolve the smaller
scale detail differences that remain.


...Low-amplitude shortwave reaching the Oregon coast on Saturday...
...Shearing downwind toward the High Plains by Sunday and Mid
Atlantic by Sunday Night...
...Surface wave activity from the Lower Mississippi/Tennessee
Valleys to the Mid-Atlantic...
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Preference: Blend of the 12Z NAM, 12Z GFS and 00Z ECMWF
Confidence: Average...becoming below average

The models generally agree that a low-amplitude shortwave will be
pushing through portions of the West this weekend before gradually
shearing downstream across the central High Plains on Sunday and
then all the way to the Mid-Atlantic region by early Monday. The
models are in good agreement with this feature on the large scale
going through early Sunday, but then there are more meaningful
differences noted by Sunday night and Monday as the remnant vort
energy translates downstream toward the Mid-Atlantic region.
Generally the 12Z NAM, 12Z GFS and 00Z ECMWF tend to hang onto a
bit more definable vort energy and thus a bit more defined surface
wave development along a front that will extend from the lower
Mississippi valley northeast across the Tennessee Valley and to
the southern Mid-Atlantic region Sunday into Monday. The NAM and
GFS are a little bit more progressive than the ECMWF with this
wave of low pressure. The 00Z UKMET and 00Z CMC are both weaker
and ill-defined with it. There is support in particular from the
euro ensemble members for a better defined surface wave, but the
support is ill-defined from the GEFS and Canadian ensemble
members. For now, a blend of the NAM, GFS and ECMWF will be
preferred, but with limited confidence by Monday and especially
with the smaller scale details.


...Large scale trough digging into the Northwest by late weekend...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z GFS and 00Z ECMWF
Confidence: Slightly above average

Additional height falls will be digging toward the Northwest U.S.
by late in the weekend, as a strong shortwave trough over the
northern Gulf of Alaska amplifies southeastward across British
Columbia. The models have come into better agreement on the idea
of a rather strong trough dropping into the Northwest by Sunday
night but there remains some differences with the depth and
progression. The 00Z UKMET is a bit deeper than the model
consensus and gradually the 12Z NAM supports a somewhat more
progressive trough. Generally the better model clustering and
ensemble support resides with the 12Z GFS and 00Z ECMWF, and a
blend of these solutions will be preferred.


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

Orrison