Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
143 PM EST Thu Jan 31 2019

Valid Jan 31/1200 UTC thru Feb 04/0000 UTC

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

12Z Model Evaluation...with Final Preferences and Confidence
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...Overall Pattern across the CONUS...
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Preference: 12Z GFS, 12Z ECMWF, 12Z UKMET blend
Confidence: Average

---18Z UPDATE---
No change to the preliminary preference. Models have started to
converge for the forecasts of the low approaching the West Coast
on Saturday, and the developing low in the Plains on Sunday.

---PREVIOUS DISCUSSION---
The synoptic pattern across the CONUS will be shifting markedly
over the next few days, with the broad, strong upper level low
departing the Great Lakes and Northeast, and a trough beginning to
amplify into the West. As is typical with significant pattern
changes, models show some differences on the evolution.

The first area of noteworthy variation is with the closed low
approaching the West Coast today. This will devolve into an open
wave and then deamplify across the Southern US as significant
height rises spread into the central and eastern US in the wake of
the departing trough. The 00Z CMC and 12Z NAM are most amplified
and fastest, which is not preferred. The expectation would be for
more deamplification given the large scale trend toward rising
heights.

Along the West Coast another low will quickly deepen on Friday and
Friday Night. The 00Z ECMWF, UKMET and ECMWF Ensemble Mean show
the surface low further north, reaching around 40N. However, the
12Z GFS, NAM and 00Z GEFS Mean and CMC are further south. At this
time, there is no strong preference for the exact location and a
compromise in positioning of precipitation maxima was generally
followed. The 00Z UKMET is the deterministic model forecast
closest to a median solution.

As the wave kicks out into the Plains, lee cyclogenesis should
lead to a surface low somewhere in the Central Plains by Sunday.
The GFS, UKMET and ECMWF are relatively closely clustered, with
the NAM further north and the CMC further south. The preference is
to lean toward the tightly clustered forecasts as they are also
close to the GEFS Mean and ECMWF Ensemble Mean.

Other differences exist elsewhere, but a compromise between the
ECMWF, GFS and UKMET provides a reasonable forecast at this time
that is fairly well supported by ensemble clusters.


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

Lamers