Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
247 AM EDT Sat Apr 28 2018

Valid Apr 28/0000 UTC thru May 01/1200 UTC

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

00Z model evaluation...with final preferences
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...Evolving eastern CONUS trough/closed low, with phasing and
consolidation of several shortwaves over the Great Lakes and
Northeast through Sunday...
...Surface low near the New England/Canadian border today/Sunday...
...Offshore surface low near Nova Scotia Sunday morning...
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Preference: General model blend
Confidence: Slightly above average

Convergence in model cycles has occurred since yesterday such that
now, the models show similarly with only minor strength/placement
differences remaining with features impacting the sensible weather
across the Northeast. Given rather tight ensemble clustering, a
general model blend is recommended to smooth out smaller scale
differences. No significant changes were noted with the new 00Z
ECMWF/UKMET/CMC compared to their 12Z Cycles.


...Closed low over the Pacific Northwest today, opening into a
trough over the Intermountain West by Monday...
...Lee cyclogenesis over the Plains by Monday with attendant cold
front...
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Preference: Blend of the 00Z GFS and 00Z ECMWF
Confidence: Slightly below average

The 00Z NAM/GFS are slightly quicker with the leading edge of the
mid-level trough axis nearing the northern Plains Sunday evening
compared to the 00Z ECMWF/UKMET/CMC but the complexity of the
individual vorticity maxima within the trough opening up proves
challenging. Ensemble scatter low plots emphasize a "southern"
surface low over North Dakota Monday morning, which agrees with
the 12Z ECMWF/UKMET/CMC, but the 00Z GFS/NAM have trended the
focus to a "northern" surface low over southern Saskatchewan. All
of the deterministic models show both surface lows, it is just the
difference in which one is more dominant. The 00Z ECMWF/CMC
trended in the direction of the 00Z GFS with a less strong
"southern" surface low, making the 00Z UKMET look to be a bit of
an outlier, but detail differences remain.

The final preference will continue a blended approach, utilizing
the 00Z GFS and the new 00Z ECMWF.


...Shortwave digging from the Aleutians tonight to off the
California coast by Monday...
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Preference: Blend of the 00Z GFS, 00Z ECMWF, 00Z CMC
Confidence: Average

The differences noted in the guidance relate mostly to timing,
with the 00Z NAM on the faster end of the spectrum and the 12Z
ECMWF slowest. The 00Z ECMWF adjusted slightly quicker toward the
00Z GFS and the 00Z CMC did not make big changes relative to its
previous run. Given the 00Z GFS is slightly faster than the middle
ground, a blend of the 00Z GFS, 00 ECMWF and 00Z CMC appears to
give a timing/strength nearest to the ensemble means. The 00Z
UKMET remains a bit stronger in the mid-levels and only weakly
supported in the ensemble guidance, so it is not preferred given
no other deterministic guidance fits its evolution.

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

Otto