Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
239 PM EDT Mon Jul 29 2019

Valid Jul 29/1200 UTC thru Aug 02/0000 UTC

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

12Z Model Evaluation and final preferences
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...Central and Eastern U.S...
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Preference: General model blend
Confidence: Above average

Mid/upper-level ridging is expected to remain centered over New
Mexico through the short range with troughing east of the
Mississippi River. Models show continue to show good agreement on
upper troughing expected to move from the Great Lakes tonight/Tue
to the Northeast by Wed. Meanwhile, an elongated trough axis is
expected to persist from the Ohio Valley to the Gulf Coast. At
this time, a general model blend should resolve any minor
differences between solutions.


...West Coast...
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Preference: General model blend through Wed, GFS/ECMWF/ECENS/GEFS
blend on Thu
Confidence: Slightly below average

An upper-level low is forecast to dive southward from the Gulf of
Alaska along the coast of British Columbia through midweek. Models
show good consensus on this feature through Wed before solutions
begin to diverge a bit by Wed night/Thu. The primary differences
among the guidance are whether the low turns east and quickly
moves inland or whether this occurs more slowly and lingers near
the coast. The GFS continues to represent the slow side of this
spread, with the UKMET on the fast side. The 12Z runs of the ECMWF
and CMC appear to have slowed the feature down somewhat from their
previous runs. Ensembles do not make things any clearer by that
time, with ECENS members disbursed between the two scenarios, and
GEFS/CMCE members perhaps a bit more weighted toward the slower
GFS solution. Additionally, deterministic solutions have not been
consistent, with the last several runs of the ECMWF and GFS
showing a variety of outcomes representing the two ends of the
range as well as in between. By Thu, models show another short
wave potentially reinforcing the broader upper trough off the
Pacific Northwest, with a wave of low pressure likely along the
surface front offshore. Given potential interactions between these
two features and the uncertainty of the northern feature, some
increased weighting toward the ECENS/GEFS ensemble means seems
reasonable by Thu. Given that the 12Z ECMWF and CMC have backed
somewhat away from their faster solutions shown previously, those
solutions may now be usable as part of a blend. Will recommend a
general model blend through Wed, and a GFS/ECMWF/ECENS/GEFS blend
on Thu.


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

Ryan