Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1253 AM EDT Fri Jun 08 2018

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

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

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

...Broader model analysis for the entire CONUS...

General Preference: 12Z ECMWF; 00Z GEFS Mean; 12Z ECMWF ENS Mean
Overall Confidence: Slightly Below Average

Other than the more significant, synoptic-scale trough that will
be pushing into the Northwest, the height pattern over the
remainder of the CONUS is very benign. With the exception of the
Northwest and areas within several hundred miles of the US-Canada
border, the 500mb heights across the rest of the country are
generally within 50 meters. This means that convective-scale
features will have plenty of room to be the dominant forcing for
QPF placement, residual boundaries, and thus temperature, wind and
cloud patterns as well. The result is that convective clusters are
introducing more uncertainty than normal in the vicinity of a
stalled front from the Plains and Midwest into the Mid Atlantic.

Therefore, overall mass field preferences are trended toward the
GEFS and ECMWF ensemble means. The 12Z ECMWF is reasonably close
to these means in most portions of the country, as well as with
the amplitude and position of synoptic-scale ridges and troughs,
and thus is included in the overall preference. The 00Z NAM and
00Z GFS are stronger with convectively-induced vorticity maxima in
the northern portions of the CONUS, and this further affects the
mass fields. It seems unlikely that these vorticity maxima will be
able to maintain such strength for multiple days, as shown for a
few vort maxes by the GFS and NAM. Additionally, although some
stronger MCVs may be able to propagate for 12+ hours in some
cases, there will be natural uncertainties with placement, and
thus trending the forecast in this direction can lead to larger
errors. A blend of the ECMWF, GEFS, and ECMWF Ensemble Mean should
provide a reasonable compromise between the myriad possibilities.


...Focus Area: Midwest into the Mid Atlantic...

As can be the case in patterns dominated by convective processes,
the expectation is that models will struggle with QPF placement
(with further forecast impacts beyond that). With multiple
convective clusters occurring in successive days in the vicinity
of the same front, and the general tendency of MCS to have some
component of their propagation toward a higher thetae air mass,
the models may tend to be biased too far north with their rainfall
particularly as the forecast progresses into Days 2 and 3.
Additionally, by Sunday and Sunday Night, most GEFS+ECMWF ensemble
clusters have the greatest concentration of mid-upper level
vorticity over the KY-WV region (similar to the deterministic
ECMWF), rather than in the southern Great Lakes (like the 00Z
GFS). Therefore, WPC QPF will generally be trended toward the
southern end of model spread in this region.


...Focus Area: Northwest and Northern Rockies...

The 00Z NAM and 12Z CMC show a stronger upper level low wrapping
up over the Northern Rockies by late Sunday from a shortwave that
will round the base of the larger trough from California to the
Northeast. This depiction of the trough seems too strong relative
to most of the GEFS+ECMWF ensemble clusters, and it also leads to
more amplification at the base of the trough in the Intermountain
West. The preference for most of this region is to lean closer to
the 12Z ECMWF, 12Z UKMET, and 00Z GFS which are reasonably close
to each other and the ensemble means.


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

Lamers