Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1242 PM EDT Mon Apr 15 2019

Valid Apr 15/1200 UTC thru Apr 19/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: Non-NAM blend
Confidence: Slightly above average

Models are generally in good agreement over the next few days,
with a highly amplified pattern evolving over the CONUS. A trough
will be centered on the Plains by Thursday morning, with amplified
ridges on the West and East Coasts. ECMWF normalized ensemble
spread is below the 30-day average everywhere over the CONUS
except in the core of the trough on Day 3 (Thursday). The
similarity of mass fields suggests a general model blend would be
reasonable over the next few days.

The exception to this would be with the 12Z NAM. The NAM shows a
stronger trough (a typical bias) digging into the Southwest, which
leads to a slower progression of the base of the trough relative
to most of the ensemble distribution. The downstream ridge over
the East is also less amplified as a result. These differences do
have a substantial effect on the forecast, so the NAM is excluded
from the model preference.

General structure of QPF maxima is very similar on the remaining
deterministic models, even out to Thursday. However, by Day 3
there are some notable differences in the relative magnitudes. The
00Z ECMWF and UKMET show more substantial QPF in the Midwest than
the 00Z CMC and 12Z GFS, which emphasize the QPF max in the Lower
Mississippi Valley more. A blended approach should help address
the uncertainty surrounding these differences, although a slight
preference is given toward the CMC and GFS. The southern QPF max
will have greater access to Gulf moisture and stronger instability.


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

Lamers