Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
109 PM EDT Wed May 30 2018

Valid May 30/1200 UTC thru Jun 03/0000 UTC

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

12Z model evaluation including preferences and forecast confidence
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...System moving across upper MS Valley tonight to the upper Great
Lakes Thu.
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Preference: GFS/NAM/ECMWF blend
Confidence: Slightly above average

Upper trough crossing the northern Plain today moves east across
the upper MS Valley tonight into the upper Great Lakes and then
into Ontario Thu, when it merges with post tropical Alberto (see
section below).

There are slight timing and phasing differences but better
clustering than there was yesterday.
Agreement is good on the frontal wave gradually strengthening as
it moves northeast across Ontario.
As a result of the improved clustering a consensus based approach
can be taken to resolve remaining differences in low
pressure/frontal timing/intensity.


...post tropical Alberto...
~~~~~~~~~~~~~~~~~~
Preference: Non-UKMET model blend
Confidence: Above average

The 00z UKMET remains a bit deeper and slower than the
GFS/NAM/ECMWF/09z SREF Mean in tracking the post tropical Alberto
circulation across MI into Ontario.  The ECMWF/GFS/NAM cluster
well so a blend among these solutions would resolve small detail
differences. The circulation is forecast to merge with a frontal
wave up in Ontario.

The trailing cold front crosses the Great Lakes and Ohio Valley,
with the section below discussing the future evolution.

...Shortwave crossing the Great Lakes/Ohio Valley Thu to the lower
Lakes Fri/central Appalachians Fri and to Mid-Atlantic into Sat...
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Preference: 00z Canadian global/09z SREF Mean/UKMET blend
Confidence: Slightly Below average

A broad 700 mb northern stream trough crosses out of the MS River
Valley on Thurs and across the upper Great Lakes and Ohio Valley 
Thu night and lower Lakes and central Appalachians Fri. The models
have generally good agreement with the 00z UKMET more assertive in
developing strong low pressure along the front centered in the
Ohio Valley 18z Fri.

The models are signaling that east of the Appalachians a closed
low forms at 700 mb and possibly a wave on the front becomes a
closed low. The NAM and GFS are further north with the development
while the ECMWF/ECMWF ensemble mean mark the southern cluster of
solutions, with the middle ground consisting of the 00z UKMET/00z
Canadian global/09z SREF Mean.

Confidence on Sat remains slightly below average given the overall
spread/ensemble uncertainties.


...Mesoscale Convective System across KS/MO/OK Wed into Thurs...
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Preference: 12z GFS/06z GEFS Mean/00z ECMWF blend
Confidence: Average

A lee trough in the high plains from eastern CO and NM that
crosses ks/ok/tx tonight into MO Thu
is responsible for convective development tonight into Thu. The
CMC has a much flatter wave than the NAM/GFS respective ensemble
means, so looks like an outlier solution. The NAM seems to retain
a stronger wave into the mid-MS valley which is likely part of a
later time frame negative NAM bias.  The 00z UKMET is a bit
further south tonight. A blend of the 12z GFS and 00z ECMWF/06z
GEFS Mean blend will be favored.


...Amplified trough moving into the West Thursday, ejecting into
the Plains with surface waves in the Northern High Plains/Dakotas
& E CO/KS late Fri into Canada Sat...
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Preference: 12z NAM/06z GEFS Mean/09z SREF Mean blend
Confidence: Average

A 500 mb trough moves onshore this afternoon in the Pacific
northwest and inland Thu into the northern Rockies , followed by
the northern Plains Fri night and Saturday. Surface low pressure
develops in ID in response to the wave and moves into MT. A second
low develops near the MT/WY border and then moves across the
Dakotas Fri night, with a consolidated low center moving north
into Canada Saturday.

The 12z GFS shows a more amplified and slower moving trough aloft
and thus the surface low pressure is a few hours slower. The 06Z
GEFS Mean matches closely with the 09z SREF Mean/00z UKMET/12z NAM.
The 00z Canadian and ECMWF were a few hours faster moving low
pressure north in Canada.
  
Given better clustering among the SREF/GEFS/ECMWF ensemble means
along with the NAM, a blend of this group is recommended over
either the faster ECMWF or slower GFS. 

Further south, the models are in good agreement in developing
another area of low pressure further south
in the central Plains Fri night and moving this wave east towards
the MS Valley Sat.  Slight timing/phasing differences aloft lead
to differences in the sea level adjusted pressure field.  The
UKMET is more progressive with the wave and is least favored.  A
blend of the 12z NAM/GFS/00z ECMWF/Canadian global would work
given clustering of the frontal timing with these solutions.

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

Petersen