Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
228 AM EDT Wed May 15 2019

Valid May 15/0000 UTC thru May 18/1200 UTC

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

00z Model Evaluation with Preferences and Forecast Confidence
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...Overall Pattern across the Continental U.S....
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Preference: 00z GFS/CMC/ECMWF blend along the North/Northeast
            Non-CMC in Northeast Thursday
            General model blend elsewhere
Confidence: Slightly above average in the north; above average
elsewhere

07z update: Little changes noted with the closed low off the west
coast, perhaps the ECMWF is a bit weaker overall and therefore
slightly faster transitioning out of the Rockies into the Central
Plains into Sat. Still a general blend is good here.  Likewise,
the 00z CMC remains a bit weaker across New England on
Thursday...so will keep initial non-CMC blend there as well.

The main difference across the north, saw a sizable shift in the
ECMWF toward the initial preference/growing consensus, while it is
in a typically slower position/timing compared to the GFS/NAM, it
looks much better to include with some increased confidence.  With
the gain of the ECMWF, we lose the UKMET which shows evolution of
a weak pivot over SW Hudson Bay, this allows for a much faster
transition of the wave across Ontario into Quebec into a flat, but
strong trof well in advance of the growing consensus.  As such
will favor a Non-UKMET blend for the northern tier into New
England, still removing the NAM after 60hrs.  Confidence remains
slightly above average for this portion of the CONUS, but above
average elsewhere.

---Prior Discussion---
A synoptic ridge will dominate the early period placing most
weather systems on the margins of the CONUS.  The closed low over
the northeast continues to be well agreed upon and now the
upstream, smaller scale shortwave that amplifies through New
England on Thursday is starting to match.  Only the 12z CMC is out
of phase, much too weak and northeast with the feature. Likewise,
the broad Eastern Pacific trof will advance and northern stream
energy (strong UL jet) will carve out a closed low late today into
early Thursday off the CA coast.  The 12z UKMET is a tad slower to
the overall strong timing/placement through Thursday.  However,
after this time, as the large closed low moves into the Great
Basin, the vortex breaks down into smaller shortwave features that
show some smaller scale timing/strength differences. Yet, even the
UKMET shows a very similar/agreeable solution with the mass fields
and QPF axis to suggest a general model blend is a slightly above
average confident selection for preference through Day 3.

The large model spread continues to be related with the shearing
of the elongated Arctic closed low across NW Territories/Nunavut
at this time.  The overall pattern supports a pivot to set up on
the SW corner of Hudson Bay with the inner core of the wave
dropping south through northern Saskatchewan/Manitoba, directing
the weather producing shortwave emerging from the southern
Canadian Rockies across S Canada Wed and Thurs.  This shortwave is
accompanied by a fast moving surface wave and inverted trof/cold
front across the Northern Plains (back to NE CO).   Guidance is
very agreeable with the timing of the surface wave through the
Great Lakes into the Northeast by Friday with the frontal zone
draped back across the Lower Lakes from Erie PA to Chicago toward
the deepening surface wave in CO associated with the closed low in
the West.  The bulk of the guidance, suggests the pivot in Hudson
will be the anchor with the remaining portion of the vortex
shearing through S Canada.  However, the ECMWF is very stubborn is
keeping the core of the vortex very compact as it rolls south then
eastward, leading to increased spread in SE Canada and the
northeast into Sat.  This is even against a bulk of the ECENS
members, so the ECMWF is not favored in this portion of the CONUS.
  The 00z NAM by the end of the forecast on Sat, shows typical end
of run over-amplification issues across the Northeast and is not
longer within the preference after 60hrs.   So overall a 00z GFS
and 12 UKMET/CMC blend is preferred along the Northern
Plains/Great Lakes and Northeast with this system.


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

Gallina