Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Thu Apr 11 2019

Valid Apr 11/1200 UTC thru Apr 15/0000 UTC

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

12Z Preliminary Model Evaluation Preferences and Confidence
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...Deep Plains Cyclone through Friday...
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Preference: General Model Blend (least weight on 12z/11 CMC)
Confidence: Above average

19Z Update:
The overall model spread remains minimal, but by Saturday
afternoon as the low pulls into Ontario the CMC/UKMET begin to
outpace the consensus and open a bit faster becoming weaker more
quickly. This has minimal impact on the CONUS however, so the
preferred blend remains unchanged, and will carry just a minimal
weight on the CMC for its continuity as a fast/weak model.

Previous Discussion:
Overall the model suite remains well clustered with the slowly
departing significant low. The NAM remains, as it has been
throughout, on the north edge of a thin guidance envelope through
Friday, but can still be used sparingly. The 00z/11 CMC starts to
outpace the rest of the guidance Friday night and should be used
with caution into day 2.


...Amplifying Southwest through Friday, with eventual cyclogenesis
in Texas on Saturday...
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Preference: Ensemble means consensus
Confidence: Average

19Z Update:
ECMWF continued its trend as the quickest to develop a strong
northern stream jet and weaker southern stream jet as the upper
trough tilts negatively, and while the 12Z UKMET has trended
stronger with its diffluent lift as well, it is closer towards the
ensemble mean consensus. The CMC is on the slow side to develop
this northern stream jet, but eventually approaches the middle of
the envelope with time. These differences will play significantly
into the snow potential in the Southern Plains and the progression
of the cold front through the MS VLY, so an ensemble mean approach
still seems prudent.

Previous Discussion:
The trend among the recent guidance has been for slightly stronger
energy shearing into the Southwest upper low, and a stronger
closed low over TX Saturday. The previous trends noted overnight
persist when compared to the 12Z NAM/GFS in that the UKMET/CMC are
too slow with the propagation of the upper trough, the CMC lagging
the other guidance the most, but the UKMET closing the trough too
rapidly. While these are not included in the current blend, the
means of all ensembles can be included as they lag the operational
runs just a bit. The NAM has a similar position to the consensus,
but is much stronger with secondary energy rounding the closing
trough over the Four Corners Saturday. This leaves the GFS/ECMWF
as the best available operational guidance. That being the case,
the 00z/11 ECMWF is stronger with its developing northern stream
jet atop the closing circulation, pushing the dominant diffluent
region further north and supporting heavier snow across OK/TX. The
slightly slower progression of this (keeping the southern jet
dominant longer) is supported by the 12Z GFS/NAM, but differences
are minor in the mass fields. Additionally, late on Saturday into
Sunday, the GFS starts to outpace the consensus with its cold
front across the South and becomes an outlier. For this reason a
blend of the means is supported with potentially significant
weather impacts across the South.


...Low amplitude longwave trough with embedded shortwaves and
surface cold front into the Pacific Northwest Saturday...
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Preference: General model blend
Confidence: Slightly above average

19Z Update:
12Z non-NCEP suite has followed suit with a subtly stronger
shortwave diving into British Columbia, and the envelope of the
evolution remains minimal. A general model blend is suggested.

Previous Discussion:
Overall model spread is minimal at this time, although the 12Z
GFS/NAM have edged stronger with the leading shortwave into
British Columbia Saturday. This continues the trend from the
overnight suite however, and any differences are minor. The GFS
into Sunday becomes a bit faster with the ejection of the trough
into the West in response to subtly flatter ridging across the
Pacific, but still lies within a reasonable envelope late on day 3.


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

Weiss