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Model Diagnostics Discussion
 
(Latest Discussion - Issued 0645Z Apr 05, 2020)
 
Version Selection
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Sun Apr 05 2020

Valid Apr 05/0000 UTC thru Apr 08/1200 UTC

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

00Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Overall Pattern Across the CONUS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
 Exception: Non-NAM from Northern High Plains to Great Lakes
Mon-Wed
Confidence: Slightly above average

19z update: The 00z UKMET was a tad faster and north relative to
the closed low and its prior run but still well within an
acceptable envelope, but also builds some confidence toward the
faster NAM/GFS solution...still believe a general model blend will
work for the closed low.

The northern stream shortwave and associated surface low/frontal
zone through the Ohio Valley/Great Lakes on Day 3, saw little
sizable change with exception of the ECMWF trending even slightly
faster.  This reduces confidence in this solution as it may be too
weak and fast.  Still, so will reduce some of the ECMWF influence
in a preferred blend here, but still a Non-NAM blend is best.


---Prior Discussion---
Expanding/deepening closed low along the West Coast dominates the
large scale CONUS mass fields, with a strong/well defined
subtropical jet streaming across Northern Old Mexico into/along
the Gulf Coast states.  A shear axis/pair of shortwaves are well
north of the US/Canadian border at this point; though it will
continue to extend eastward under the strong Arctic anticyclone,
eventually the wave consolidates and clips northern New England
Monday, broadening and maintaining NW flow influence through the
remainder of the period.  While the 12z CMC is initially slower it
is not terribly so and the overall evolution through the Northeast
can be supported by a general model blend.

Back to the west, the closed low has also started to consolidate
in model spread/evolution; and while there remains some internal
shortwave/vorticity center differences, the evolution is only
slightly different.  The GFS had been much more phased to the
northern stream, both making it generally weaker but also
progressing it faster, but the 00z run has tempered this a bit. It
remains a faster solution in the overall suite, but more in the
realm of acceptable bias, especially combined with typical
acceptable biases being slower in the ECMWF/CMC and too strong
(tad fast) with the 00z NAM.  As such a general model blend is
supported but still a tad lower weight to the GFS. 

The sharp northern stream trof across BC/Alberta will be pressed
eastward by the stronger upstream Pacific jet, with some small
timing differences.  Mainly the 00z NAM is a bit stronger and
slower with its eastward progression and southeastward
height-falls across the northern Plains.  The resultant cold
front/surface lows match initially but eventually track well south
and slow in the surface low cluster suite to remove it from any
preference at this time.  The 00z GFS, as alluded to before, is
more disconnected with the southern stream closed low and become
more progressive like the ECMWF, even surpassing the 12z
UKMET/CMC.  Still, with the ECMWF being fastest, that is a
uncharacteristic position within the suite, so will hedge a bit
toward a non-NAM blend overall. 

So to encapsulate the CONUS preference, a general model blend is
supported with the exception of the 00z NAM across the northern
tier to the Great Lakes from Mon to Wed. with perhaps a tad less
weighting to the GFS by the end of day 3 in S CA.  Confidence is
slightly above average in this blend for the mass fields; however,
the QPF across the Mid-MS valley to Gulf Coast is not.  The return
moisture under influence of the height-falls/surface cyclone
across the Plains into the MS Valley is not well agreed upon both
in magnitude and timing, so convective activation is a bit less
certain, and so below average with QPF placement.


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

Gallina