Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1250 PM EDT Thu Jun 27 2019

Valid Jun 27/1200 UTC thru Jul 01/0000 UTC

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

12Z Model Evaluation...with Confidence and Preferences
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...Deep upper low over the Northwest...
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Preference: Blend of the 12Z GFS and 00Z ECMWF
Confidence: Slightly above average

The models take an upper low over the Northwest U.S. gradually off
to the northeast over the next couple of days with the bulk of the
height falls shifting into southwest Canada by late Friday. By
this weekend, a portion of the energy will be left behind over the
Pacific Northwest and will be reinforced by additional offshore
shortwave energy arriving. Overall model spread is rather modest
as there is decent agreement with the timing and depth of the
energy. Although, the better model clustering at this point
resides with the 12Z GFS and 00Z ECMWF which is well supported by
the 06Z GEFS mean and 00Z ECENS mean. Thus a GFS/ECMWF blend will
be preferred.


...Lead shortwave/MCV over the upper Midwest...
...Amplifying trough over the Northeast...
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Preference: Non-NAM blend...lead MCV impulse
            General model blend...large scale trough
Confidence: Above average

A well-defined shortwave which is essentially taking the form of a
MCV will be crossing the upper Midwest today and then sliding
southeast toward the Great Lakes tonight and Friday as it crosses
over top the deeper layer mean ridge over the central Plains and
Midwest. This energy will dig into the Northeast by Saturday as a
much stronger northern stream trough dives southeast from Quebec.
Not really seeing much larger scale spread with the model mass
fields with the larger scale trough that arrives this weekend, but
the 12Z NAM does appear to be too strong with the lead MCV energy
as compared to the remaining global model guidance. Will prefer a
non-NAM blend with the MCV impulse and then a general model blend
as it relates to the larger scale trough amplification over the
Northeast.


...MCV over the mid-MS Valley...
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Preference: Non-NAM blend
Confidence: Slightly above average

The models all agree in taking the small scale MCV over the mid-MS
Valley down to the southwest over the next few days as a deeper
layer ridge builds over top of it across adjacent areas of the
Midwest and back over the central Plains. There is only modest
timing spread with this feature as it drifts southwestward down
toward areas of the lower MS Valley and eventually the southern
Plains, but the 12Z NAM does tend to be a bit stronger than any
other model. Therefore, will lean toward a non-NAM blend with this
feature.


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

Orrison