Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Wed Jun 19 2019

Valid Jun 19/0000 UTC thru Jun 22/1200 UTC

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

00Z Preliminary Model Evaluation...with Confidence and Preferences
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...Eastern and Central CONUS...
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Preference: Non-NAM/CMC blend
Confidence: Slightly Above Average

07Z Update: The CMC is usable through Thursday, but on Friday it
swings a deep shortwave up from Mexico and across Texas. While the
remaining suite indicates a subtle impulse may lift around the
ridge at this time, the CMC is much too deep and even brings the
shortwave too far south into the ridge as opposed to around its
periphery. This seems unlikely, especially as the ridge will be
strengthening downstream of a trough in the west at this time.
Otherwise, the previous blend remains unchanged.

Previous Discussion:
Broad cyclonic flow will persist across the eastern 2/3 of the
CONUS before ridging blossoms from the Gulf Coast during Friday.
The most significant differences arise with the evolution of a
shortwave digging into a longwave trough moving from the Ohio
Valley into the northeast. The NAM is noticeably stronger with
this feature and digs 500mb heights much further south than the
remaining guidance. This has been a common thread among the NAM
with recent runs in that it strengthens shortwaves moving across
the country too deeply, and should be used with caution across the
east. Otherwise, minor latitudinal and longitudinal differences
exist in the evolution of this trough moving through on day 2, and
the ridging bulging from the Gulf on day 3, but the guidance
appears to be within the ensemble envelope so can be included in
the blend.


...Western CONUS...
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Preference: ECENS/GEFS means
Confidence: Below average

07Z Update: Through day 2, the guidance shows reasonable agreement
in the evolution of an upper low digging into the Northwest CONUS.
Small scale features show differences in timing and intensity, but
the synoptic pattern depicts a relatively modest spread.
Thereafter, however, into Friday the guidance spreads considerably
due to uncertainty and disagreement into how a strong shortwave
rotating around the mean trough will evolve, and its impact on the
parent upper feature. As the primary low begins to lift slowly
northeast into Central Canada, a potent shortwave will lag into
the Great Basin, maintaining a deep positive tilt to the longwave
trough. The intensity of this second shortwave and whether it will
close off, and how deeply it will dig into the Southwest, as well
as at what speed, varies considerably at this time range. Sticking
close to the means is a reasonable solution at day 3, with minimal
spread among the ECENS/GEFS/NAEFS and even the CMC mean.

Previous Discussion:
Through the forecast period an anomalously deep upper trough will
dig into the Northwest and close off near Montana. Around this
closed low, repeated pieces of shortwave energy will eject into
the west around the base of the trough creating QPF and
reinforcing the longwave trough. The GFS/ECMWF are in reasonably
good agreement with the evolution of this feature, and due to
significant discrepancies arising as early as day 2, are the
preferred blend for the west at this time. The UKMET continues to
be several DM too warm with its heights in the west, while the CMC
and NAM are too progressive with features moving down from Canada.

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

Weiss