Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
233 PM EDT Mon Sep 23 2019

Valid Sep 23/1200 UTC thru Sep 27/0000 UTC

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

12Z Model Evaluation with Preferences and Forecast Confidence
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...CONUS...
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Preference: General model blend
 Exception: Weight toward 12z GFS/ECMWF/CMC in Southwest on Day 3.
Confidence: Above average

19z update: With little initial spread, the the 12z ECMWF/CMC and
UKMET showed little differences in the mass fields from their 00z
runs.  Only slightly stronger/deeper reflections on Day 3 through
the Upper Ohio Valley into the Northeast/Mid-Atlantic (given
increased moisture/QPF along the front) were noted with the 12z
UKMET/CMC.  This was opposed to a slight drying in the ECMWF. 
Still this appears minor at Day 3 to keep with initial preference.

Similarly, in the Southwest, the UKMET lifts out a bit faster than
even the 00z run, but still well within the realm of moderate
ensemble spread to have high confidence in a general model blend
here as well, just weighted a bit lower than the 12z ECMWF/CMC/GFS


---Prior Discussion---
The short range pattern will be dominated by a very strong 150+kt
250mb jet currently crossing the Gulf of AK, that crosses the
Canadian Rockies and digs out a broad closed low that supports a
fast moving surface wave along the US/Canadian border with a front
that drops south through the Plains Tuesday into the Great Lakes
by Wed and into the Northeast/Mid-Atlantic by Thursday.  The mass
fields are quite agreeable with only the 12z NAM/GFS continuing a
bias of being a bit too dry relative to the ECMWF/UKMET and CMC. 
For the mass fields, a general model blend will work well and with
minor spread even internally, the confidence is high for this
portion of the weather.  However, the uncertainty in moisture
return begs some reduction in overall confidence to slightly below
average.

Ahead of this strong wave, a closed low continues to track across
the Great Lakes into the northeast with little model disagreement,
with only moderate spread on how this trof collects the remains of
Tropical Storm Jerry, which is well off coast to be an affect to
the CONUS.  As such a general model blend can be employed at above
average confidence.

GOES-W WV denotes a shortwave starting to break from the northern
stream into a closed low across the Southern Sierra Mountains. 
This wave will continue to deepen and drop into the Lower Colorado
River Basin.  Guidance is very agreeable with this evolution as
well, but eventually, an anticyclonic loop will occur and the 12z
NAM and 00z UKMET start to lift back northeast a bit faster than
the remaining guidance is expecting at the end of the forecast
period.  While, a bit fast, it is not out of the realm of
possibility and with convective influence over terrain in central
AZ into NM, this evolution/timing may be correct.  However, will
favor (weight heavier) a blend closer to the 00z ECMWF/CMC and 12z
GFS on Day 3 in a general model blend.  Confidence is above
average in this blend.


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

Gallina