Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1223 PM EDT Thu Mar 21 2019
Valid Mar 21/1200 UTC thru Mar 25/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z Model Evaluation Including Preferences and Confidence
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...Trough and Coastal Low in the East...
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Preference: 12z NAM and 00z ECMWF/CMC (weight to EC/NAM).
Confidence: Slightly above average
The first phasing of shortwaves into a more concentric closed low
over the Mid-Atlantic has occurred with surface deepening on going
currently. Upstream jet/nose of jet shortwave is taking shape
over East Central Canada dropping southward. The 00z UKMET was
already off-balance compared to observations (stronger lead wave)
to have confidence for its inclusion in an otherwise tightening
guidance suite. The 12z GFS showed some typical negative bias,
especially at 7H with the last few runs trending a bit too fast
particularly with upstream amplification that should slow,
increase binary interaction across New England. After the
wobble/redevelopment along coastal ME/Gulf of ME...the GFS remains
fast to exit northeast as well. Some inclusion would be alright,
but will favor a 12z NAM and 00z ECMWF/CMC blend. Confidence
given the higher packing is slightly above average.
...Remainder of the CONUS...
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Preference: Non-UKMET blend
Confidence: Average to slightly above average
The weakly formed closed low over UT/AZ will continue to advance
into the mean ridge over the Plains. By early Sat, there has
become much strong guidance alignment for the base of the
elongating trof to stretch vertically crossing the Sangre de
Cristo Range of the Rockies into E CO/OK Panhandle. The 00z UKMET
is a bit fast and north with the ejection away from the ensemble
run to run trends. As the wave crosses the Plains, a non-UKMET
blend will suffice, but toward 84hrs the 12z GFS is first/fast to
weaken. However, it has favorably trended to a similar
track/placement to the 12z NAM and 00z ECMWF/CMC to keep it
included at lower weighting.
Upstream, a pair of lead shortwave troughs from the larger scale
cyclone over the southern Gulf of AK, advance to the West Coast in
the short-term. The lead wave approaches and shears northeastward
toward the WA coast by late Fri into early Sat, weakening quickly.
Guidance is fairly good in timing/strength, to have good
confidence in a general blend for this wave. Quick on its heels,
a more neutral oriented shortwave crosses the OR/N CA coast late
Sat. Here, only the 00z UKMET is showing greater amplification
and more concentric nature. The 12z NAM/GFS are like usual,
partnered with slightly increased depth relative to the 00z
CMC/ECMWF, but all in all, even as they translate into the
Intermountain West well. The 12z GFS weakens quickly, and the 12z
NAM/CMC are north of the ECMWF. At this point, a non-UKMET blend
would suffice but confidence is average for this wave alone.
Overall, non-UKMET is slightly above average as preferred blend.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina