Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1221 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 NAM/GFS evaluation and preliminary model preferences


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

Preliminary Preference: 00Z ECMWF/00Z CMC blend
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 00Z
UKMET) tracking the low closer to the northeast U.S. coast, while
the GFS is a little farther offshore seems a bit too fast relative
to the consensus. Ensemble spread continues to reduce with each
consecutive cycle, and the 00Z ECENS/NAEFS/06Z GEFS means were
reasonably well clustered. The closest deterministic solutions to
the ensemble consensus were the 00Z ECMWF/CMC


...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...

Preliminary Preference: 00Z ECMWF/12Z 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 faster than the ensemble means by that time, with
the 12Z NAM and 00Z ECMWF much closer. Will recommend a blend of
these two solutions at this time.


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

Preliminary 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...

Preliminary 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 00Z UKMET) were less
amplified than the 00Z ECMWF/CMC. 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