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FXUS10 KWNH 280718
Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
318 AM EDT Mon May 28 2018

Valid May 28/0000 UTC thru May 31/1200 UTC

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

00Z model evaluation including final preferences and confidence

...Subtropical Storm Alberto...
Preference: See NHC Forecast
Nearest Guidance: GFS/UKMET/ECMWF blend

Much tighter clustering exists for Alberto including lifting north
through AL, eventually the 00z NAM accelerates toward deeper
height falls across the upper Midwest.  The 12z ECMWF/ECENS mean
are a shade east of the forecast track but the best proxy.  The
00z GFS shifted a bit west and now appears to match the NHC
forecast best through 72hrs; interestingly, this continues to make
it the eastern-most within the GEFS solutions. The UKMET, while
ideally on track is a few hours slower than the GFS and official
forecast. The CMC is generally weaker and favors a westward track
through the TN and Mid-MS River valley influenced by the western

07z Update: The UKMET and ECMWF shifted slightly to cluster very
tightly to the GFS (at least through 72z) to the official NHC

...Approaching northern stream shortwave and frontal zone across
northern Great Lakes into New England Mon to Tues...
...Developing surface low southeast of Long Island by early Mon...
Preference: General model blend
Confidence: Above average

The CMC continues to delay surface cyclogenesis off shore on Mon
and aloft is reduced spacing between the northern stream digging
trof and frontal zone clipping New England on late Mon/early Tues.
 As such would favor a non-CMC blend at above average confidence.

07z update: The CMC shifted faster and while it remains slightly
slower to develop it is much closer that a general model blend
will suffice at above average confidence.

...Western U.S. closed low lifting into the northern Plains by
Wed...associated lee cyclones/trof with eventual consolidation
across MT/ND by Wed...
...Shortwave ejecting east across the central Plains into the
lower Missouri Valley with surface wave in...
Preference: 00z GFS/12z ECMWF blend
Confidence: Above average shifting to average by 30/12z.

The guidance continues to show excellent agreement with the upper
low as it begins to emerge from the Rockies on Tuesday into Wed.
Convective upscale feedback seems to doom the 00z NAM a bit as the
wave rotates around the parent circulation then accelerate east
into the Central Plains and low MO river Valley too quick and much
stronger than the remaining guidance.  The 00z CMC is in a typical
slowest position, and emerges at peak heating late Tuesday into
Wed, leading to upscale growth as well leading it to be a bit more
compact and show less connection to a much weaker Alberto
circulation lifting north.  These combining streams are more
aligned in the UKMET/ECMWF and 00z GFS, though the UKMET may be a
bit too weak with the remaining energy into the Northern Red River
valley by late Wed into Thursday.  While the overall differences
may be small enough to support a general model blend, a 00z GFS
and 12z ECMWF/UKMET blend is preferred at this time at above
average confidence early but shifting to average toward
Wed/Thursday when there is more uncertainty with combining

07z update: The 00z ECMWF showed very little variation and closely
matches initial preference.  The UKMET has trended a bit deeper
but still is sufficiently weaker and north with the shortwave
lifting out of the Dakotas into Canada.  The CMC is much stronger
than the 12z run, but is much further north than the initial
preference, with less support including the 00z GEFS model...will
suggest the 00z GFS/ECMWF blend remains preferred at average
confidence (after 30/12z...above average before).

...Longwave trof amplifying south into Pacific Northwest by Wed,
reinforced near OR/CA border Thurs...
Preference: Non-NAM blend
Confidence: Slightly above average

Cycle to cycle ensemble spaghetti analysis shows an agreed upon
trend toward earlier height falls across northern Vancouver Island
 late Monday into Tuesday which broadens the trof and leads to
earlier yet sharper wavelength generally going negative tilt into
the Pacific Northwest by Wed.  The 00z NAM is even faster with the
lead height falls compared to remaining guidance/ensembles
supporting a deeper broader trof along the West Coast by Thursday
but also retains the compact inner core of the upper low over N
Vancouver Island...which would fall into typical late period NAM
negative bias.  The 00z GFS and 12z ECMWF show similar evolution
and match the overall trends noted in the ensemble suite,
including the interaction with the subtropical feed at the base of
the digging trof which has been a point of disagreement at times.
The 12z UKMET looks similar and has good timing but as is typical
may be a bit more amplified toward a closed low/concentric
circulation at the base of the trof on Thursday.  The 12z CMC is
too slow in the northern stream and much too strong across
BC/Alberta by Thursday as well to include it.  As such will favor
a 00z GFS and 12z ECMWF blend at average confidence.

07z update: Through the length of the entire trof...there was
small changes with the 00z ECMWF run, with greatest difference
with the subtropical wave at the base being a bit further south
and deeper than the other guidance but still very close in
shape/timing of the initial preference.   The 00z CMC and UKMET
both trended toward this GFS/ECMWF common solution particularly
across the Pacific Northwest to Central CA coast.  There are small
differences with the location/strength of the subtropical
shortwave phasing with the base of the trof.  Both are much weaker
than the ECMWF/GFS but close enough to be included in the
preference and adding some confidence as well.  As such a non-NAM
blend is preferred at slightly above average.

Model trends at
500 mb forecasts at


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