Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
347 PM EDT Sun Apr 07 2019

Valid Apr 07/1200 UTC thru Apr 11/0000 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: Compromise between 12Z GFS and 12Z ECMWF
Confidence: Average

---19Z UPDATE---
No major change to preliminary preference or reasoning. Most
deterministic models moved closer to the GFS with their timing of
the southern stream trough. Meanwhile, non-GFS models remained
consistently south of the GFS with the deep Plains cyclone by the
end of the period.

---PREVIOUS DISCUSSION---
Deterministic models are showing reasonable similarity with
synoptic features over the next few days, although some detail
differences remain. Therefore, confidence is fairly high in the
existence of several larger QPF maxima across the CONUS, with
lower confidence in the specific timing and placement. In general,
WPC QPF follows a compromise between the 12Z GFS and the 00Z ECMWF
in several areas.

Along the Gulf Coast, a southern stream trough will push east over
the Southeast through Tuesday. Much of the model spread in this
region is due to timing differences. Greater weight was given to
the GFS; with a low closing off at times aloft and a distinct
separation from the northern stream, the preference was to lean on
the slower end of the model spread (represented by the GFS) but
still be a little closer to a median timing (some weight given to
the faster ECMWF).

Part of the reason the ECMWF is a faster with the southern stream
trough is that it shows greater amplification to the trough over
the Great Lakes and Northeast. The greater influence of the
northern stream likely leads to a faster progression. Given the
preference for the slower GFS, the forecast also leans more in the
direction of the GFS in the Great Lakes and Northeast, although
model QPFs are in fairly good agreement through 09.00Z so a
general model blend would still be fairly representative for the
main round of precipitation in the Northeast.

Over the West, models are in very good agreement through 09.12Z
until the trough begins to dig through the Intermountain region.
The one notable difference through that point is with the 00Z CMC
which is considerably less amplified than the other models. A
non-CMC blend seems reasonable until that point. Afterward, the
GFS brings its vorticity maximum further north with a faster
progression, and more quickly closes off a low aloft. This leads
to a northward displacement of the Plains surface cyclone by
Wednesday afternoon relative to the other models (excludes the
CMC). Even the 06Z GEFS Mean is considerably further south. In
this case, WPC QPF still struck a compromise between the latitude
of the QPF max between the GFS and ECMWF, but greater weight was
given to the ECMWF, especially given support from the very
consistent 00Z UKMET.


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

Lamers