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FXUS10 KWNH 201852
Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Wed Jun 20 2018

Valid Jun 20/1200 UTC thru Jun 24/0000 UTC

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

12Z model evaluation...including preferences and confidence

...19z update...

No significant departures were noted for the 12z ECMWF/UKMET/CMC
and GEFS from initial preferences and 00z runs, as such initial
thoughts/preferences remains the same as below...

...Redeveloping upper low in Central Plains today moving into the
Ohio Valley/Great Lakes by Sat...
Preference: General model blend
Confidence: Above average

The 12z NAM and GFS are a tad deeper particularly across the Ohio
Valley sliding into the confluence zone across the Great
Lakes/Northeast by later Sat into Sun, which lead them to be a
shade slower too, but not dramatically so.  As such will favor a
general model blend at above average confidence.

...Series of upper troughs crossing the Northwest through Friday...
Preference: Non-NAM blend
Confidence: Slightly above average

The 12z NAM continues to amplify the shortwave entering SW OR/N CA
into E WA a bit more, slowing it as it slides through MT/WY by Fri
and remaining sharp/slow with the trof through the remainder of
the forecast period.  The 12z GFS/06Z GEFS are a bit slower due to
slightly more amplified solution as well compared to the
fastest/flattest UKMET and ECMWF/CMC/ECENS means. This becomes
most apparent 00z Sun in the central plains but just may a bit too
far south compared to the ECMWF/CMC/UKMET.

The next shortwave entering the Pacific NW on late Fri into Sat,
has some similar issues due to the downstream evolution... the NAM
having a more amplified downstream trof is slow to amplify this
system, while the GFS/ECMWF CMC and UKMET all are a bit deeper and
south.  The CMC is a bit slower toward the end of the period but
only minor so.  As such a Non-NAM blend is suggested at slightly
above average for both systems (lower weighting to the GFS in the
initial system due to south shift).

...Large scale troughing over the Northeast this period...
Preference: General model blend
Confidence: Above average

The models are in good agreement with this system.

...Mid level low center/surface trough over Texas...
Preference: General model blend
Confidence: Slightly above average

While the NAM and UKMET continue to be a bit more compact with the
main MCV across S TX than the GFS/ECMWF or CMC, the
shape/orientation of the trof as a whole, shearing into the
northern stream across the mid-MS/TN and eastern OH Valleys seems
to be in much better agreement supporting a general model blend.
Confidence is Slightly above average.

Model trends at
500 mb forecasts at


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