Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1244 PM EDT Wed Apr 10 2019

Valid Apr 10/1200 UTC thru Apr 14/0000 UTC

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

12z Preliminary Model Evaluation with Preferences and Confidence
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...Deep Plains Cyclone through Friday...
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Preference: General Model Blend (limited NAM)
Confidence: Above average

12Z NAM remains on the north side of the well-clustered model
suite with respect to the mid-level circulation moving through the
Plains. Despite that, the trend in the GFS has been for a subtly
slower and further NW closed low, continuing that seen in the
global suite over the past few runs. The run-to-run consistency
among the various guidance remains quite high, with the most
glaring differences showing up Friday with the NAM and 00z/10 CMC
ejecting the closed circulation likely too quickly into the Great
Lakes, faster than the ensemble means. This is reflected in the
QPF fields with the cold front and surging moisture through the
MS/OH Valleys Friday outpacing the remaining global suite. For
this reason a general model blend is reasonable although with less
weight on the NAM through day 2, and a strong preference towards
the GFS/ECMWF/UKMET on day 3.


...Pair of Northern Pacific Shortwaves amplifying into the
Southwest longwave trough...
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Preference: General model(w/low NAM weight) or Non-NAM blend
Confidence: Slightly above average

Interaction of multiple features will amplify a trough across the
west with strong vorticity rotating around the base into Friday.
Persistence of the inherited blend preference remains reasonable
with the speed and amplitude of the longwave trough development,
as the NAM remains a strong outlier both with the digging energy
into the Pacific NW, as well as the southern energy rotating
through the Southwest on Friday. This speeds the trough axis too
quickly into the Four Corners as a neutral tilt, while the
remaining global suite remains positively tilted with an overall
weakening trend noted in the GFS. Some discrepancy continues with
the intensity of the energy digging around this trough, and how
much phasing will occur between the distinct shortwaves, but the
error margins appear near normal thresholds by day 3 outside of
the NAM so minimal changes to the preferred blend are needed.


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

Weiss