Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Mon Feb 25 2019

Valid Feb 25/0000 UTC thru Feb 28/1200 UTC

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

00Z Model Evaluation...with Preferences and Confidence
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...Deep trough/closed low over Southeast Canada/Northeast...
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Preference: General model blend
Confidence: Above average

The models remain in very good agreement with the gradual exit of
a deep trough/closed low and corresponding surface low impacting
the Great Lakes and Northeast through 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: Blend of the 00Z GFS/GEFS mean
Confidence: Average

The guidance overall shows rather good agreement with the
evolution of a slow-moving, positively tilted upper trough and
closed low dropping down over the Pacific Northwest through
Monday. The guidance shows the closed low then shifting somewhat
further offshore through Tuesday and Wednesday while become a part
of a larger scale rex block over the northeast Pacific. In the
near-term, a compact vort center and associated surface low will
undercut the large scale through Monday morning and cross through
far southern and eastern OR. The guidance is in good agreement
with the details of this. However, as this energy quickly advances
inland, there will be another system approaching the West Coast
with a focus on northern CA by early Wednesday. This system will
be the remnants of an upstream closed low that will weaken and
undercut the aforementioned closed low offshore of the Pacific
Northwest by then. A surface wave associated with this next system
will move into northwest CA and then southern OR by late
Wednesday. The 00Z ECMWF/CMC solutions are a little faster with
the track of this system and bring the surface low into far
northwest CA a tad north of the 00Z GFS/NAM solutions. The NAM is
overall farthest south. The 00Z UKMET is close to the ECMWF/CMC
solutions but is a bit slower. The NAM being farther south is
related to its closed low offshore the Pacific Northwest being a
bit farther south which is helping to suppress the frontal and
surface wave position more. Overall, there is a bit better support
for a slightly more suppressed wave track that is in line with the
GFS, and since the ECMWF/CMC solutions did at least trend a little
farther south, the preference will remain with the GFS and the
GEFS mean.


...Shearing shortwave energy over the Midwest/OH Valley...
...Weak surface wave crossing the OH Valley/Mid-Atlantic...
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Preference: Blend of the 00Z NAM/GEFS mean
Confidence: Average

By late Tuesday and through Wednesday, there will be shortwave
energy shearing across the Midwest and through the OH Valley and
this will result likely in a weak wave of low pressure moving
through the OH Valley and Mid-Atlantic region Wednesday before
moving offshore Thursday. The 00Z GFS overall is the fastest
solution with this energy, with the remaining guidance a little
slower. The 00Z NAM is by a small degree the sharpest solution
with the energy, and like the GFS, it tends to track its surface
low a bit north of the non-NCEP models. The non-NCEP guidance
though have trended a bit farther north, but overall remain slower
than the GFS and to some extent the NAM. In general there is a tad
more support for the faster and northward camp, but the 00Z GEFS
mean suggests the 00Z GFS is too progressive, and also likely
pulling a warm front too quickly north through the Mid-Atlantic
region on Wednesday. Will prefer a solution that blends the NAM
and GEFS mean at this time.


...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 a coastal boundary north. There is a
tremendous amount of spread in pin-pointing the axis of heavier
QPF, but the 00Z NAM remains a clear outlier with notably heavier
rainfall across the Southeast which is tied into a bit stronger
shortwave energy shearing across the Gulf Coast states. A non-NAM
blend will be preferred given relative good clustering out of the
global models concerning their mass fields and even QPF to an
extent.


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

Orrison