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Model Diagnostics Discussion
(Latest Discussion - Issued 1945Z Apr 18, 2019)
Version Selection
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Abbreviations and acronyms used in this product
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu Apr 18 2019

Valid Apr 18/1200 UTC thru Apr 22/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence

...Longwave trough closing off over TN Valley Friday Then Moving
Into Mid-Atlantic By Sun...
Preference: Blend of the 12z GFS/UKMET/ECMWF
Confidence: Average

19z update: The 12z ECMWF continues to be on the slower/southern
side of the model spread as the shortwave trough closes off and
moves into the Mid-Atlantic. While the spread may not be as large
as it was during the previous model cycle, it still exists. The
12z UKMET actually looks like a blend between the GFS/ECMWF
solutions, so some inclusion of that model could yield a favorable
result for the mass fields.

---previous discussion---
Longwave trough currently over the southern Plains today will move
eastward and eventually close off over the Tennessee Valley Friday
then move into the central Appalachians and Mid-Atlantic Saturday
and Sunday. In general, model agreement is fairly good at the
mid/upper levels with some minor differences noted at 500 mb. The
00z ECMWF is a bit slower by 12z Saturday compared to the faster
NCEP suite (GFS/NAM) and by 12z Sunday, is also suppressed further
to the south compared to the GFS/NAM which takes the trough axis
more negative tilted. At the surface, model differences begin by
12z Friday where the ECMWF has the surface low over western KY
while the GFS is over northern KY while the NAM/UKMET/CMC lie
across central KY. The GFS continues to take on the NW side of the
model spread Friday compared to the rest of the guidance though by
Saturday, most of the guidance ends (except the UKMET) ends up
fairly similar in the low position. The GFS and its ensemble mean
are fairly clustered together while the ECMWF and its mean are
also very similar. A blend of the two would probably yield a
favorable result and is the preference at this time.

...Short wave crossing the Pacific Northwest and Northern Rockies
Fri and Sat...
Preference: General model blend through 12z Saturday, then non-CMC
Confidence: Slightly above average

19z update: No significant changes noted with the rest of the 12z
guidance now available. The 12z CMC did trend more toward the rest
of the guidance, so the preference can be a general model blend.

---previous discussion---
There is fairly good model agreement and run to run consistency
with the shortwave trough pushing into the Pacific Northwest
Friday and Saturday. Between the 00z and new 12z data coming in,
there is very good agreement through Saturday 12z such that a
general model blend is preferred. Beyond that time frame, more
model differences creep up. The CMC is a flatter, open, and more
progressive wave compared to the rest of the guidance by Sunday.
Meanwhile, the rest of the guidance attempts to close off in the
mid/upper levels and there is fairly good agreement with that idea
through Sunday 12z. Given this agreement and the outlier solution
in the CMC, will suggest a non-CMC blend for the forecast period.

...Long wave trough crossing the Baja Peninsula Fri/Sat into
Southern/Central Plains Sun...
Preference: General model blend
Confidence: Above average

19z update: No significant changes noted in the rest of the 12z
guidance. General model blend is still preferred.

---previous discussion---
There is tight clustering between the operational guidance with
the compact shortwave trough crossing through the Baja Peninsula
Friday and Saturday that then moves through the southern Rockies
and into the southern/central Plains Sunday. With the much above
average model agreement and confidence, a general model blend is

Model trends at
500 mb forecasts at