Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1211 AM EDT Tue May 08 2018

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

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

===== 00Z Model Evaluation with Preferences and Confidence =====

...Eastern U.S. trough, consolidating and lifting from the
Southeast into the Mid Atlantic...
...Weak surface low off the East Coast...

Preference: General model blend
Confidence: Above average

Models show fairly good agreement in their mass fields for this
system, with most of the precipitation likely to be focused
offshore. The preference is for a general model blend, which
should account for small remaining uncertainties from minor
differences.


...Northern stream shortwaves consolidating over the Upper Midwest
by Wednesday, and pushing into the Northeast on Thursday...
...Surface low moving through the Great Lakes with cold front
sweeping across the northern tier of states...

Preference: Blend of 00Z GFS; 12Z ECMWF; 12Z UKMET
Confidence: Average

Some model differences persist with this system, likely related to
the complexities involved with several shortwaves phasing and
consolidating into a more compact wave over the next couple days.
The 00Z GFS is relatively similar to the 12Z ECMWF and 12Z UKMET,
and their mass fields are also fairly close to the GEFS and ECMWF
ensemble means. Therefore, the preference is to lean toward these
models. The 00Z NAM shows a less amplified wave as it arrives in
the Great Lakes, with less support from the global models. The 12Z
CMC has a more robust downstream shortwave ridge, which seems to
lead to a slower progression than the other models.


...Upper level trough approaching the Pacific Northwest Tuesday
and Tuesday Night...
...General evolution to zonal flow over the western U.S. with
several embedded shortwaves by late in the week...

Preference: Blend of 12Z ECMWF; 12Z CMC; 12Z UKMET
Confidence: Slightly below average

More substantial model differences exist in the western U.S. with
a variety of mass fields. The 00Z GFS and 00Z NAM continue to show
stronger shortwaves and vorticity maxima embedded in the flow
across the region, carving out the base of the trough a bit more.
Therefore, the GFS, NAM, and GEFS members are south of most of the
other available global models and ECMWF ensemble members. As the
GFS and NAM strengthen some of these vort maxes without a very
likely mechanism for doing so, the preference is to continue to
lean away from these models.


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

Lamers