Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Fri Feb 08 2019

Valid Feb 08/0000 UTC thru Feb 11/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

08z update: With the rest of the 00z guidance now available, there
remains good agreement for the eastern US for the entire forecast
period. Southerly return flow ahead of the next shortwave trough
moving through the central US will draw up Gulf moisture. There
are some spatial differences in where the axis of heaviest QPF
will fall, ranging from the mid-MS River Valley to the lower OH
Valley. A model blend favored toward the latest ECMWF/GFS seems
like a good approach at this time.

For the Pacific Northwest, there is better agreement with the
stronger, secondary closed low expected to drop down Saturday
morning. A general model blend would work here. For the end of the
forecast period, the 00z UKMET was the biggest outlier of the
operational runs and should be discarded beyond 72 hours.
Otherwise, a blend of the GFS/ECMWF and perhaps some of the CMC
would be sufficient as the quick moving shortwave drops into
Washington State.


...Eastern U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

Good model agreement in the near term with the closed low and
surface cold front track/speed across the Great Lakes and
Northeast. Most of the energy with that system will pull north of
the CONUS by Saturday morning. With subtropical ridging anchoring
across southern Florida, relatively benign weather is in store for
the eastern US and with the above average model agreement for the
mass fields, a general model blend will be preferred.


...Central/Western U.S...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 00z ECMWF/GFS/NAM
Confidence: Average to slightly below average by 72 hours

An active pattern is expected to develop across the western US
through the forecast period with several impulses moving onshore.
Average to slightly above average model agreement in the beginning
drops to below normal by 72-84 hours particularly for the Pacific
Northwest.

Current closed mid/upper level low near 40N/130W will drop toward
the central California coast in the next 24 hours and then open up
as it gets absorbed in the developing troughing over the western
US. That feature then spreads quickly through the Intermountain
West and central US late in the weekend. The 00Z NAM remained more
progressive and amplified compared to the other operational models
and there is rather good agreement with the ECMWF/GFS/CMC. The
UKMET is also an outlier as it is fast like the NAM.

Back to the Pacific Northwest, a much stronger closed low is
expected to drop to the western Washington coast Saturday morning
then gradually sag southward through the remainder of the weekend.
This system will lead to high impact, low elevation snows for
portions of Oregon and Washington. Outside of the UKMET which is
too fast with the feature, the rest of the operational runs lie
well within the ensemble spread such that a general model blend is
sufficient.

Forecast confidence drops considerably past 18z Sunday through
Monday with respect to another piece of mid/upper level energy
ridging the ridge over the Pacific. While almost of the models do
indicate some type of shortwave dropping through B.C. into
Washington, there are considerable temporal, spatial, and strength
differences. The UKMET/CMC are most amplified, closing off the
feature either right on the coast or offshore. The GFS is weaker,
more open and also on the slower side. The NAM lies somewhere in
the middle, showing some characteristics of a stronger wave
(closing off) but not nearly as strong as the UKMET/CMC. The ECMWF
however is further west (offshore) and also is slower. The
operational GFS and ECMWF do show the most similarities to their
respective ensemble means, so for this cycle the WPC preference is
for a blend of the 12z ECMWF, 00z GFS and 00z NAM and discarding
the stronger/more amplified CMC/UKMET for now.


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

Taylor