Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1223 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 including the NAM/GFS and preliminary
preferences
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...Central and Eastern U.S...
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Preliminary 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...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preliminary Preference: General model blend through Wed, blend of
ECENS/GEFS means 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, as the 12Z NAM along with the 00Z ECMWF/UKMET/CMC
showed, or whether this occurs more slowly and lingers near the
coast for longer as shown by the 12Z GFS. Ensembles do not make
things any clearer by that time, with ECENS member 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.
Additionally, models show another short wave potentially
reinforcing the broader upper trough off the Pacific Northwest by
Thu, 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, with a general model blend sufficient prior to that time.


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

Ryan