Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
244 PM EDT Sat Jun 02 2018

Valid Jun 02/1200 UTC thru Jun 06/0000 UTC

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

12Z model evaluation and preferences


...Slow moving upper trough over the Mid-Atlantic region today...
...Coastal low off of the northern Mid-Atlantic coast through
Monday morning...

Preference: ECMWF
Confidence: Average

The track of the eventual surface low off the Mid-Atlantic coast
continues to be the most significant point of contention among the
guidance. As the low initially develops across southeastern VA
later today or tonight, model spread is quite low. Spread begins
to increase bit by Sun night as the low begins to track
northeastward along the coast, with 12Z NAM (along with the UKMET)
tracking the low closest to the northeast U.S. coast, while the
GFS is a little farther offshore and the ECMWF on the eastern side
of the deterministic spread. The ECMWF remains to the west of its
ensemble mean, while the 12Z GEFS mean is right in line with the
ECMWF (east of the GFS). Thus, the 12Z ECMWF seems like a good
consensus solution at this time.


...Negatively titled upper trough crossing the upper MS Valley
Saturday night and Great Lakes on Sunday...
...Surface low crossing the Great Lakes on Sun...
...Upper low across the Northeast by Tue...

Preference: ECMWF/NAM blend
Confidence: Average

Model consensus is relatively good with respect to this system
through Sun morning and the 12Z NAM/GFS are well clustered with
consensus. After that, the GFS appears to become slightly too fast
with the upper wave while the NAM timing fits more closely with
the ensemble means and other deterministic solutions. Despite
slight differences aloft, models/ensembles are very tightly
clustered with the track of the surface low expected to develop
across the Great Lakes Sun afternoon and then track north into
Ontario. Most solutions show an upper low closing off Mon over
Ontario/Quebec, which should reach the northeastern U.S. by Tue.
The GFS remains a little faster than the ensemble means by that
time, with the NAM and ECMWF closer. Will recommend a blend of
these two solutions at this time.


...Mid-level vorticity maximum entering the Southwest U.S. on
Saturday...

Preference: General model blend
Confidence: Slightly above average

The models handle this system similarly, with minor detail
differences best resolved with a general model blend.


...Upper trough reaching the West Coast on Monday...

Preference: Non-NAM blend
Confidence: Average

Models differences surrounding this feature are primarily with
respect to the amplitude of the trough, as models are very closely
aligned in terms of timing. The NAM appears to become weaker than
the consensus with the trough as it reaches the coast on Mon. As
the wave moves moves inland, across the northern Intermountain
Region by Tue, the NAM/GFS (along with the UKMET/CMC) were less
amplified than the ECMWF. At this time, ensemble members show both
as possibilities, so a blend/compromise is likely the best
approach. Will recommend a Non-NAM blend given that the NAM was
likely too weak even as the trough reaches the coast.


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

Ryan