Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1247 PM EDT Tue Apr 02 2019

Valid Apr 02/1200 UTC thru Apr 06/0000 UTC

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

12Z Model Evaluation with Preferences and Confidence
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...Shortwave trough/closed low crossing the Southeast...
...Deep surface low lifting up off the East Coast...
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Preference: Non-GFS blend
Confidence: Slightly above average

Models show very low spread through early Wed with respect to this
compact and energetic system moving up the Eastern Seaboard, with
only minor timing/intensity spread developing after 12Z Wed as the
low pressure system quickly moves east of New England and into the
Canadian Maritimes. No clear outliers were present in terms of
mass fields. In terms of QPF, the 12Z GFS continues to show the
lack of a strongly forced precipitation band near/off the New
England coast late tonight/Wed - something which shows up almost
universally on other guidance (including the FV3-GFS). Thus,
despite its acceptable mass fields, the GFS was excluded from the
preference of an otherwise general model blend.


...Surface low approaching the Pacific Northwest...
...Shortwave reaching the Four Corners by Wed...
...Cyclogenesis over the Southern Plains by Thurs...
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Preference: GFS/00Z ECMWF blend
Confidence: Average

Models handle this feature similarly through late Wed/early Thu,
with some differences in amplitude developing by Thu morning as
the shortwave emerges into the Central Plains. The GFS and NAM are
among the more amplified solutions by that time, with the 00Z
non-NCEP solutions less amplified by that time. By late Thu the
NAM also becomes quicker than consensus with the easterly
progression of the system into the Mid-Mississippi and Ohio
Valleys. A blend of the GFS and 00Z ECMWF should represent a
consensus solution at this time, showing a moderate amplitude wave
across the central U.S. by early Thu moving into the Ohio Valley
by Fri.


...Upper trough over the Northern Plains/Midwest Tues...
...Surface cold front crossing the Midwest...
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Preference: General model blend
Confidence: Above average

Models handle this system similarly, and a general model blend is
preferred.


...Shortwave troughs approaching the West Coast Thu-Fri...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: GFS/00Z ECMWF blend
Confidence: Slightly below average

Models show agreement that a shortwave should reach the West Coast
by late Thu, with another following in rapid succession on Fri.
Solutions differ a bit on the separation between these features
and on the structure (closed upper low or negatively tilted but
more progressive trough). What seems clearer is that as the
leading wave encounters broad anticyclonic upper-level flow across
the Great Basin/Rockies, energy should separate out with a
southern stream component crossing reaching the Four Corners
region by Fri. At this time a blend of the GFS and 00Z ECMWF
should represent a solution close to consensus and to the ensemble
means.


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

Ryan