Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1134 PM EST Sat Jan 26 2019

Valid Jan 27/0000 UTC thru Jan 30/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
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CONUS Overview:
~~~~~~~~~~~~~~~~
Similar to the past several model cycles, model agreement on the
synoptic pattern remains high. There is limited model spread with
the large-scale height pattern, and there is a high degree of
confidence in the position and scope of the broad, amplified
trough over the central and eastern US.


...Gulf/Florida Sun/Mon...
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Preference: 00z NAM/12z ECMWF and 18z GEFS blend
Confidence: Slightly below average

Moderate uncertainty still remains with the timing and depth of
the surface wave developing out of the Florida Straits north of
the Bahamas.  While the mid-level flow continues to show some
small timing differences, the main evolution difference may be
related to the magnitude of latent heat release of convection near
Florida to further deepen the system.  The 12z ECMWF continues to
be slowest of the deterministic guidance but has shifted faster
and now resides on the northeastern side of the ECENS member
cluster.  The 00z NAM likewise, is very close to the ECMWF and
slow, both suggesting a bit more/stronger convective upscale
growth likely from latent heat release.  The 00z GFS is on the
other side of the scale, with least amount of deep/persistent
convection and like its known bias is faster ejecting the wave
northeastward away from FL, even outpacing the vast majority of
GEFS members, making it suspect.  The 12z UKMET is closer to the
GFS and faster than the GEFS mean, but is also much flatter than
the remaining solutions and minus last evening's 00z run, has
never really latched onto the trend that the other guidance
suggested.  This leaves the 12z CMC which is more central in
timing to the cluster but is also a westward outlier, and looks a
bit off in mass field aloft.  Overall, ensemble trends/continuity
seem to compromise with a 18z GEFS mean/00z NAM and 12z ECMWF
blend, but confidence remains slightly below average given the
amount of uncertainty remaining given proximity to valid time.  


...Clipper into Dakotas through Great Lakes & subsequent cold
surge/deep closed low...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-GFS blend
Confidence: Slightly above average

Model consensus continues to grow with the depth/placement of the
clipper system deepening across the Upper Midwest into Central
Great Lakes by early Tuesday.  The only real discrepancies with
the deterministic agreement appear with the 00z GFS and 18z
FV3-GFS... both suggest a slightly slower progression and
increased occlusion of the surface low tilting back to the NW. 
This is likely under influence of the fastest solution drawing the
extreme cold air out of central Canada; reducing the spacing with
the upstream wave/deep closed low.  While the NAM/UKMET are
similarly fast, the spacing is reduced enough to not manifest the
slower/northwestward relative track like the GFS.   Here a general
model blend may be suffice though likely to hedge away from the
GFS/FV3.    As the cold air descends in latitude, the ECMWF/CMC
continue to be very slow to drop south; as a result the closed low
becomes well separated from the UKMET/NAM.  Ensembles/trends and
strength/height packing across central Canada, think the slightly
faster solutions are a bit more realistic with the cold air/upper
low. 

Further south, the 00z NAM shows a weak inflection aloft across AR
into MS producing increased QPF which is not favored by WPC, still
it is favorably timed with the frontal zone with other
guidance...unlike the faster GFS.   All considered will favor a
non-GFS/FV3 blend for the wave/QPF.  


...Wave breaking down Pacific ridge Wed...
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Preference: 12z ECENS/18z GEFS blend.
Confidence: Below average

The persistent and very strong ridge axis that has dominated the
West Coast is expected to be affected by some Pacific energy
toward the end of Tuesday into Wed.  There is a tremendous amount
of model spread and uncertainty with respect to the timing,
strength and compact nature of the wave to affect this change. 
The 12z ECMWF is the most compact, deep and uncharacteristically
fast solution crushing the ridge and nearing the Pacific coast by
12z on Wed, while there is some continuity with prior runs with
the compact nature, the depth and timing were even further out of
context to support it.  Both the 00z NAM/GFS suggest weak
shortwave trof but the ridge remains in place and strong, though
the GEFS members and FV3-GFS are opposed to the solution favoring
something similar to the ECMWF (compact), but slower.  The UKMET
is very similar to the FV3 GFS too with a compact wave just slower
than it.  The 12z CMC is more like the NAM/GFS supporting the
ridge.  Ensemble suite/trends are just as muddled so will show no
preference for a deterministic solution and support a GEFS/ECENS
mean blend for this region at well below average confidence.   


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

Gallina