Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
252 PM EDT Tue Jul 30 2019

Valid Jul 30/1200 UTC thru Aug 03/0000 UTC

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

12Z Model Evaluation and Final Preferences/Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overview of the CONUS features...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Average

...19Z Update...

With most of the model guidance coming into fairly good agreement
with the overall syntopic pattern and mass fields, felt a general
model blend would suffice across the entire CONUS.  Thus merged
the regional discussions into one main discussion.  Keep in mind,
there are subtle feature differences that may be reflected in the
QPF. However, these differences are minimal with more localized
variability that is hard to discern from a CONUSwide model
evaluation and preference evaluation.  Many of the key features
discussed below, troughing in the east, ridging in the south and
west and an approaching trough in the Pacific Northwest are all
depicted with general agreement among the model guidance and their
ensembles. More mesoscale features shown with the mid-level
vorticity are all illustrated by the models, but in terms of
placement and intensity it differs between the models.  Though,
again the differences are within the ensemble spread. Therefore,
felt a general model blend is preferred with no strong signal or
indication to go strongly toward a certain set of model guidance. 


...Previous Discussion...

Mid/upper level troughing expected across the eastern CONUS with
ridging building across the Plains.  Models are in fairly good
agreement in terms of mass fields with the timing and placement of
the surface front. The northern stream component of the trough is
certainly helping to push the surface front eastward. Meanwhile
the southern stream, while weak, is due to a closed upper low. The
mid-level impulses rounding the trough in the east, moving atop
the surface front, will likely result in QPF differences.  This is
most notable with the 12Z GFS/12Z UKMET/12Z NAM as vorticity is
stronger among these models, especially compared to the 12Z ECMWF.
However, these differences are fairly small and the ensemble
clustering seems reasonable.

Also, mid-level energy rounding the aforementioned ridging across
the Plains will promote an MCS feature that is depicted by all
model guidance.  The 12Z CMC seems to be a bit farther east as
compared to the rest of the model guidance.  However, the
placement and timing difference are minimal.  And it does appear
the 12Z ECMWF may be holding onto mid-level energy/divergence
aloft a bit longer than the other model guidance across portions
of the Plains on Day 1 which does seem to result in higher QPF
across NE.  However, again, these differences when looking at the
mass fields are not large enough to favor one model over another
as models have shown run to run continuity. 

Models have converged closer with the evolution of the closed low
approaching the Pacific Northwest, located just off of the British
Columbia coast, as it reaches the West Coast. The closed low is
expected to move inland into central British Columbia Wednesday
night while a shortwave trough axis, extending southwest of the
closed low, nears the coasts of Washington and Oregon early Friday
morning. A general blend is closest to the relatively agreeable
ensemble means and is thus preferred at this time.


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

Pagano