Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
235 AM EST Wed Jan 09 2019

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

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

00Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern Across the CONUS...
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Preference: 00z GFS/NAM/CMC, 12z ECMWF blend
Confidence: Slightly above average

08z update: The more significant model differences lie across the
the western/central US later in the forecast period as the upper
level flow becomes more amplified. One shortwave trough will move
through will spawn a surface low across TX Friday, where models
differ spatially. The 00Z  UKMET is a northern outlier compared to
the rest of the guidance. Meanwhile, another system will approach
the west coast Friday. Model differences are larger with its
surface low placement, ranging from the CMC outlier (south) to the
ECMWF (north). The GFS appears odd with its depiction of the
surface feature, well displaced to the northwest and not
consistent with the GEFS mean solution. Quickly following that
system, another will approach the west coast. At this time, model
agreement is slightly better.

Overall, will continue with the GFS/NAM/ECMWF/CMC blend
(non-UKMET) for the CONUS, noting the differences seen with the
GFS off the west coast later in the forecast periods.

---previous discussion---
Through the forecast period, the upper level pattern is expected
to an anomalously deep trough over the Northeast US while a couple
of troughs push across the western US into the central US by the
end of the period. Model guidance for the Northeast US system is
in very good agreement with the surface low position and strength
by Wednesday afternoon off the coast of Maine.

The flow pattern becomes more amplified over the western/central
US for the latter half of the period as an initial shortwave
trough moves across the southwest US. Here, model guidance is not
terribly out of phase but the NAM is a bit stronger/further north
with the trough axis especially by 12.12z. The GFS is on the
faster side of the spread but within the ensemble spread. A
surface low develops in response to this wave ejecting out into
the southern Plains, with the UKMET having the low position the
furthest north /TX panhandle/ compared to the CMC/GFS/NAM which
are similarly placed in west-central TX. The ECMWF is weakest with
the signal but spatially similar to the GFS.

Finally, a stronger trough will move across the western US Friday
night into Saturday. Models are in good agreement showing the the
longwave trough will become split with the southern stream energy
outrunning into the blocked ridge flow over the Rockies while the
northern stream energy gets absorbed into B.C. and then followed
by another storm system. There are considerable spatial and
temporal differences. The CMC/UKMET is stronger compared to the
GFS/ECMWF/NAM solutions, and also are the fastest to split the
flow.

With this in mind, the WPC preference for this cycle will be a
blend of the 00z GFS/NAM/CMC and 12z ECMWF.


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

Taylor