Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1139 AM EST Sun Feb 24 2019

Valid Feb 24/1200 UTC thru Feb 28/0000 UTC

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

12Z Model Evaluation...with Preferences and Confidence
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...Phasing trough/closed low over Midwest/Great Lakes...
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Preference: General model blend
Confidence: Above average

The models remain in very good agreement with the strong closed
low moving across the Great Lakes. The system will be phasing with
an intrusion of northern stream shortwave energy as it does so,
and allowing for rapid surface pressure falls over the Great Lakes
region and resulting in a large scale high-wind event that will
impact large areas of the Great Lakes, OH Valley, northern
Mid-Atlantic and Northeast Sunday into Monday. A general model
blend will be preferred at this time concerning the mass fields
with this system.


...Deep closed low/trough over the Pacific Northwest...
...Undercutting shortwave arriving over northern CA Wed...
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Preference: Non-NAM blend
Confidence: Average

Last 4 cycles of the ensemble spaghetti analysis continue to
depict a slower shortwave entering the Pacific Northwest trof
early Tuesday increasing WSW elongation in the ECMWF.  This allows
for the tapping of an undercutting shortwave to accelerate and
increased southward troughing of the increasingly concentric
Pacific Northwest closed low.  The 00z CMC trended this way as
well but did not amplify/phase as much as the ECMWF with the
undercutting shortwave...this seems more sensible.  While the GFS
continues to be faster initially, reducing the westward
elongation, there is some trending to start the binary interaction
with undercutting shortwave a bit earlier but also allow for the
closed low to swing through by 00z Thursday.  The 00z UKMET, while
a bit stronger than the GFS (which is a positive) shows similar
timing/axis with the QPF/AR plume with the GFS and even the
CMC/ECMWF.  Overall, these trends would support a non-NAM solution
preference, with reduced weighting to the ECMWF (especially in the
speed of the undercutting trof and sfc reflection), relative to
the CMC/UKMET and GFS.  Given the pattern based on timing
differences of the jet rotating into the SE of the Omega Block,
the spread is actually not bad but remains modest enough to have
average confidence in this preference.


...Shortwave Energy bleeding out of the Pacific Northwest late
Tues/early Wed...
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Preference: General model blend
Confidence: Average

By late Tues, fairly flat shortwave energy will emerge from the
Pacific NW trof and translate across the Northern US Rockies into
the Northern Plains Wed.  The 12z GFS is a bit relative to the
other guidance, but otherwise there is solid agreement.  However,
the uncertainty as the wave shifts east is related to the
magnitude of mid-level amplification over the SW Hudson Bay and
how fast that draws cold air/northerly jet across Central Canada. 
The 00z ECMWF/ECENS members have been very weak/flat with this
amplification, and stood out in the ensemble suite for the last
few cycles.  They did shift with the 00z cycle slightly toward the
other guidance, but the larger consensus actually shifted in
agreement greater toward the ECMWF solution.   The 00z CMC is the
most amplified/deepest with the Canadian cyclone, which in turn,
deepens the wave in the Great Lakes Wed.  The 12z NAM/GFS both
deepen but also shift northwest supporting a faster southward
surge of the cold air/jet.  Would hedge more middle ground,
thinking the ECMWF is too weak/flat overall and the CMC is a bit
too amplified; and so believe a general model blend of all
solutions will provide the best in position/timing as well as
magnitude/depth.  This compromise can also be employed well in the
QPF fields as well.  Given spread, uncertainty and multiple stream
interaction confidence is average in this blend preference.


...Remainder of the CONUS...
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Preference: Non-NAM blend
Confidence: Above average

Broad zonal flow will dominate the southern two-thirds of the
CONUS after late Monday. Subtle waves moving out of the Pacific
and crossing the southern Plains into the Mid-South will help to
draw Gulf moisture and coastal boundary north (broadly speaking). 
There is a tremendous amount of spread in pin-pointing QPF maxima
to have any real confidence; however, the 12z NAM is a clear
outlier with significant convective output across the Southeast
and given its issues elsewhere, is it fully rejected, with QPF
preference shifting toward the maximum QPF probabilities in the
ensemble suites.  Mass field-wise, a non-NAM blend is preference
at fairly high confidence.


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

Gallina