Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Tue Jun 18 2019

Valid Jun 18/0000 UTC thru Jun 21/1200 UTC

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

00Z Final Model Evaluation...with Confidence and Preferences
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...Eastern and Central CONUS...
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Preference: Non-NAM or UKMET Blend
Confidence: Slightly Above Average

07Z Update: The aforementioned concerns about the NAM remain when
compared to the 00Z Non-NCEP suite, and in fact the 00Z ECMWF is
now at the weak edge of the guidance envelope with shortwaves
moving through the flow. However, the spatial and temporal extent
of these features is well within the preferred clustering even on
the weaker ECMWF. Additionally, the new UKMET becomes out of phase
with shortwave ridging/troughing across the Ohio Valley/New
England Wed/Thu with broad cyclonic, or even zonal, flow occurring
in the Ohio Valley where the rest of the suite has a deepening
shortwave.

Previous Discussion:
Broad cyclonic flow will persist across the eastern 2/3 of the
CONUS through Wednesday before pattern amplification occurs in
response to troughing out west. Through day 2, the global suite is
in good agreement of the overall synoptic pattern, with
discrepancies only occurring with respect to shortwaves ejecting
through the flow. The CMC remains a bit fast with its translation
of these features, but not so much as previous runs, and within
the ensemble cluster at this time. Through day 2 a general model
blend should suffice.

However, by Thursday, the NAM rapidly deepens a shortwave lifting
through the Ohio Valley into a closed/negatively tilted trough.
This is not agreed upon by any other available guidance, and
continues the recent NAM trends of amplifying these shortwaves too
quickly and too strongly. For now, feel a non-NAM blend is the
best course beyond day 2 as other variations in small scale
features all fall within a reasonable spatial and temporal
envelope.


...Western CONUS...
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Preference: Non-UKMET
Confidence: Average

07Z Update: While the ECMWF evolution of the NW closed low is
considerably different due to the behavior of shortwaves rotating
around its base, these small scale features make minimal
difference on the overall synoptic regime across the CONUS. There
will likely be timing differences of QPF due to shortwave energy,
but the overall pattern from the ECMWF matches the global
consensus. This leaves just the UKMET out of the preferred blend
as it becomes several DM warmer with the 500 heights than its
counterparts in the global suite.

Previous Discussion:
Biggest challenge involves a closed low which will dig into the
PacNW Wed-Thu before stalling and shedding pieces of shortwave
energy around its base reinforcing a longwave trough in the West.
Overall model spread is minimal in thickness patterns and temporal
variation, although the exact evolution of the closed low varies
from model to model. A general model blend should be sufficient
for now, although timing and intensity differences of shortwaves
will affect heights and the QPF pattern across the West, so a
heavy weight of the ensemble means should limit this spread later
in the forecast period.


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

Weiss