Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1110 PM EST Sat Mar 02 2019
Valid Mar 03/0000 UTC thru Mar 06/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation Including Preference and Forecast Confidence
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...Phasing short waves and resulting surface low tracking from the
Mid Atlantic to Newfoundland...
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Preference: General model blend through 04/06z
Non-12z ECMWF blend thereafter
Confidence: Slightly above average
Flattening shortwave crossing out of the Central Rockies will
support surface development in the Mid-South that will shift
across the Carolinas and deepen near the 40N70W benchmark.
Guidance has come into solid agreement with the phasing/timing of
this feature, with one exception. The 12z ECMWF continues to be
stronger and cyclonically track left of the consensus track toward
SE MA early Monday, which also affects the QPF axis. It remains
slightly out of place, but with the CMC a bit slow and the UKMET a
bit east...its incorporation seems perfectly fine across the south
and southeast, but not so much across the Northeast. The 00z
NAM/GFS both continue to be fairly consistent and agreeable to
this blend. As such confidence is increasing to slightly above
average in a Non-ECMWF blend after 04/06z.
...Closed mid-level low near WA coast Monday...
...Trough approaching CA Coast Tuesday....
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Preference: General model blend
Except the 12z ECMWF in the Pacific Northwest
Confidence: Average
At the tail end of the elongated trof across the Northern Plains
into the Northwest, flow weakens and supports a consolidation of
vorticity energy over the Pacific Northwest and by early Tuesday
there is fairly solid consensus of a concentric closed low.
Upstream near the AK panhandle, a secondary tail end trof is
closing into a compact system as well. Model spread significantly
increases on the magnitude/timing of a binary interaction (or lack
thereof) of these two features. The 00z NAM does not interact
these features with only a slight northward drift of the NW
system. The 00z GFS, relative to prior GFS runs, still favors the
northern stream shortwave in the binary interaction, but has
trended toward greater distance/angle of rotation. The 12z
UKMET/CMC both show a more even strength and tight rotation to
each, even greater than the GFS. The 12z ECMWF is a clear
outlier, showing a faster/southward acceleration of the northern
stream shortwave but rotating at a well distant angle of rotation
standing out relative to the ensemble suite, including a bulk of
the ECMWF members. Low levels are generally dry and low impact on
sensible weather fields is fairly minimal overall, however, there
is some effect to an approaching central Pacific shortwave
feature...and only minimally by Wed.
The 12z ECMWF digging the trof out of the Pacific Northwest
increases the steering flow gradient allowing for the southern
stream wave to shift faster within the overall suite of guidance,
even compared to the UKMET/NAM. The GFS having trended a bit
faster with the binary interaction has increased the southern
stream wave nearly matching the other guidance. A such a general
model blend can be supported (mass and QPF) for the southern
stream trough approaching CA at slightly above average confidence,
but the 12z ECMWF cannot be included in the mass field blend as it
clearly is an outlier...and would suggest incorporating the ECENS
mean as an alternate for the Pacific Northwest. Confidence is
average given multiple streams, binary interactions that are
highly contingent on timing/precise strength of each feature).
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina