The Weather Prediction Center

Model Diagnostic Discussion

[Abbreviations and acronyms used in this product]
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Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Sun Apr 21 2019

Valid Apr 21/1200 UTC thru Apr 25/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence

...Overall Pattern Across the CONUS...
Preference: 12z GFS/NAM, 12z ECMWF blend
Confidence: Above average

19z update: No significant changes to the model preference with
the rest of the 12z guidance now available.

---previous discussion---
The synoptic pattern will transition through the forecast period
to a faster zonal flow across the northern US while a shortwave
trough moving into the Southwest US closes off across the southern
Plains. In general terms, most of the guidance offers similar
solutions with just some minor model differences note especially
by Day 3 (Wednesday). For the eastern US closed low, that system
will be slowly moving off to the northeast through Day 1 with the
rest of the precipitation exiting out of New England. Next, a pair
of shortwaves (one from the Rockies and one from southern Canada)
begin to phase over the Upper Midwest on Tuesday. As this system
then tracks east, model differences creep up. The UKMET is a
flatter, more open wave and also much faster compared to the rest
of the guidance. The GFS/NAM are in good agreement, closing off
north of Lake Ontario. It's relatively close in position and
strength to the 00z ECMWF. Meanwhile, the CMC lags significantly
than the rest of the guidance. For this feature, a blend of the
ECMWF/GFS/NAM is preferred.

Across the southern Plains, model mass fields are in better
agreement and with very few differences noted at the surface and
aloft, a general model blend can be used. QPF and convective
issues do come into play though but even there, there is above
average consistency and signal for the highest QPF placement.

Model trends at
500 mb forecasts at


Last Updated: 331 PM EDT Sun Apr 21 2019