Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1244 AM EDT Sun Apr 07 2019

Valid Apr 07/0000 UTC thru Apr 10/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
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...Northern Tier of CONUS...
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Preference: 00z GFS/NAM and ECMWF (weight to GFS, then EC)
Confidence: Average

Quasi-zonal flow, with multiple shortwaves associated with
different airmass/frontal zones makes the mass fields quite
muddled across the Great Lakes into New England.  Yet, the
guidance is fairly agreeable in the general evolution with the
undercutting jet streak shunting the initial wave out toward SE
Canada/Canadian Maritimes by late Mon/Tuesday.  The old occluded
low/shacked northern stream shortwave will then return across the
Great Lakes on Tuesday and through New England early Wed. 
Overall, the CMC seems a bit more stretched out West to East with
the slowest/lingering surface wave and associated shortwave
upstream by the end of the forecast period.  The 12z UKMET also
shows a greater amplification by Day 3, having drawn shortwave
energy back from the east across Quebec leading to southern and
stronger closed low, building this deeper trof.  Ensembles support
the remaining guidance, weighted a bit more to the GFS over the
ECMWF and lower to the 00z NAM.  As such will support that blend
but with so much small scale variability the confidence is only
average.


...Southern stream system affecting Gulf Coast...
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Preference: 00z GFS/FV3-GFS and 12z UKMET/CMC blend
Confidence: Slightly below average

The 00z ECMWF/ECENS mean are the clear outliers in initial
assessment of in the ensemble spread even compared to prior cycles
of the ensemble.  However, the 00z GFS has shown a trend to be
slightly faster having a much less amplified (ie closed low)
across the South.  The 00z NAM remains the strongest and
therefore, slowest to break down and stretch NE-SW in the Western
Atlantic into the Eastern Gulf.  Much of this variation appears to
be related to the magnitude of upscale latent heat feed-back (not
grid-scale feedback) from the MCS complex expected to emerge from
N Mexico tonight.  The greater convection and closer to the
centroid of the shortwave, leads to more concentrated closed low. 
The 00z FV3-GFS depicts this process well compared to the
operational GFS, showing strong convection near the upper low
feeding a more closed upper wave and slower to weaken surface
wave.  Given the complex has not developed, this leads to a
sizable uncertainty to this feedback.  The 00z ECWMF while
typically reliable, shows an atypical result and so it less
favorable, while the GFS trending this way, falls in line with a
typical bias but is near/closer to the UKMET.  As such will favor
a GFS/GFS-FV3/UKMET/CMC blend compromise at slightly below average
confidence.


...Upper-level trof entering Northwest into Intermountain West
Tues/Wed...
...Central High Plains Surface low Wed...
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Preference: General model blend
            Non-NAM after 10/00z
Confidence: Slightly above to above average

Strong baroclinic zone and zonal flow supports a strong
atmospheric river into the OR/CA vicinity with very good model
agreement but towards late Monday, greater amplification to the
flow starts upstream of the Coast building toward landfall by
early Tuesday.  Model agreement continues to be fairly impressive
though the Intermountain west, though the ECMWF/ECENS mean start
to shift a bit faster, likely due to the downstream faster
evacuation across the south.  This leads QPF axis/intersection
with return moisture from the Gulf to develop a bit further south
as it emerges into the Plains overnight Tues into Wed, compared to
most of the other guidance.  As such will reduce some weighting of
the ECMWF late in the period.  Likewise, by the end of Day 3, the
12z CMC is a bit more north and weaker with the developing closed
low.  To reduce its importance, will weight a bit lower too.   The
00z NAM does not show much weakening across the Northern Plains of
the trof showing no pinching off into a closed low, this allows
for the NAM's QPF axis to shift north into MN, while other
guidance would suggest otherwise.  As such will eliminate the NAM
in the preference after 10/00z Wed.   So all in all a general
model blend can be employed with only elimination of the NAM, very
late and lowering of weighting to the CMC then the ECMWF slightly.
  Confidence is slightly above to above average in this blend
given the small model variation.    


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

Gallina