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Model Diagnostics Discussion
(Caution: Version displayed is not the latest version. - Issued 0434Z Dec 09, 2018)
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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
1134 PM EST Sat Dec 08 2018

Valid Dec 09/0000 UTC thru Dec 12/1200 UTC

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

12Z Model Evaluation...with Preferences and Confidence

...Central Gulf and Southeast storm...
Preference: General model blend
Confidence: Slightly above average

With the bulk of the storm now in the 24-36 hour time frame, model
solutions have largely converged on a similar track and speed with
the surface low developing in the northern Gulf of Mexico then
jumping off the southeast US coast as it lifts northeast past Cape
Hatteras. The speed has picked up a bit and this allows for a
slight jog to the north with the precipitation shield seen in
almost of the available guidance.
Overall with respect to the QPF, the NAM and ECMWF are most
similar with the deformation band axis lingering across
south-central into southeastern VA the longest while the GFS and
UKMET are lightest as it pulls away from the coast earlier.
Thermally, all of the guidance has trended a bit warmer with the
warm nose aloft. While there are mesoscale banding differences, in
the general on the large scale with the synoptic and mass fields,
the models are in good agreement and a general model blend is

...North, Great Lakes and Northeast Mon/Tues...
Preference: 00z GFS, 00z NAM, 12z CMC
Confidence: Slightly above average

A trough will swing through the northern Great Lakes region
through this forecast period. In general, model similarity is
good, except for the 12z ECMWF which is much stronger/deeper with
the trough as it pivots into the Northeast US Tuesday evening. It
is also much sharper with a secondary trough in its wake. The
GFS/NAM/CMC all show similar solutions and the UKMET seems to be
an outlier.

...West into Rockies...
Preference: 00z NAM/GFS and 12z ECMWF/ECENS mean blend
Confidence: Slightly below average

Neutrally titled trough axis will begin to move onshore the
Pacific Northwest over the next 24-48 hours where model agreement
and similarity is high. Beyond that, upstream and downstream
influences/model differences dominate a departure from best
agreement and the trough shears/elongates. As the trough slows
across southern California, some of the models forecast a cut-off
low developing (12z ECMWF, 00z NAM) while the other guidance keeps
this as open wave as it skirts through the Southwest US. The NAM
pinches off this energy and drops it into Mexico, while the GFS
holds it north into western Texas. The ECMWF has the feature
completely cut off, stalling south of California. Finally, the CMC
and UKMET are in the middle of the model spread, but vary on
strength quite a bit. The trend seems to be to keep the feature
open. A secondary trough pushes into the Pacific Northwest Tuesday
night into Wednesday. Here, the CMC seems uncharacteristically
deep/strong compared to the GFS/NAM/UKMET/ECMWF solutions. As
such, for this cycle, will prefer a blend of the 00z GFS, 00z NAM
with some weight toward the ECMWF/ECENS blend.

Model trends at
500 mb forecasts at