Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1145 AM EST Wed Feb 27 2019
Valid Feb 27/1200 UTC thru Mar 03/0000 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
12Z NAM/GFS Evaluation...with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...Closed low/trough across the Pacific Northwest/Northern
Rockies...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend through 01/12z
12Z GFS/00Z ECWMF ensemble mean blend after 01/12z
Confidence: Average
The 12Z NAM/GFS are close to the consensus with the evolution of
the closed low off the OR coast as it transitions into a strong
short wave after 01/12z. After that time, the 12Z NAM become
faster and flatter with the short wave as it crosses the Northern
Rockies. By contrast, the 12Z GFS remained fairly consistent with
the timing of the short wave, especially after 02/00z over the
Northern Rockies. The 00Z ECMWF/UKMET remain slower than the
consensus after 01/12z, though there are members of the 00Z ECMWF
ensemble output that are faster than the consensus.
Given the amount of spread with this system, the 12Z GFS/00Z ECMWF
ensemble mean comprise the preferred blend, as they have exhibited
the best consistency, especially after 01/12z. However, given the
spread, confidence is average at best.
...Short wave energy crossing the Midwest/OH Valley...
...Weak surface wave crossing the OH Valley/Mid Atlantic...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-12Z NAM blend
Confidence: Slightly above average
The 12Z NAM is close to the consensus with the short wave shearing
out of the fast mid level flow south of the strong closed low over
central Canada through about 01/12Z. After that time, however, the
12Z NAM stands alone as it deepens and slows the short wave as it
crosses Upper MS Valley and Upper Great Lakes. When compared to
the tightly clustered consensus, it stands out as an outlier, and
was not included in the preferred blend.
...Deep closed low/trough over southern Canada...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12Z GFS/00Z ECMWF blend
Confidence: Average
The 12Z NAM is close to the consensus as it brings a dumb belling
strong closed mid level system across Manitoba and Saskatchewan
through 02/00Z. After that time, the 12Z NAM becomes slower than
the consensus (as well as slower than its 06Z solution), The 12Z
GFS remains closer to the consensus as it crosses Ontario by
03/00Z. This position is supported by the 00Z ECMWF/00Z ECMWF
ensemble mean, so the blend of operational 12Z GFS/00Z ECMWF is
the preferred, as the 00Z CMC/UKMET bookend the consensus position
late in the period.
...Gulf Coast/Southeast/Mid Atlantic short waves...
...Surface waves over the Southeast/Mid Atlantic Thu into Sat...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend...first shortwave/surface low
00Z UKMET/ECMWF blend...second shortwave/surface low
Confidence: Average...first shortwave/surface low
Below average...second shortwave/surface low
There are subtle differences in the timing of short wave energy in
the fast mid level flow across the Southern US (which would be
expected in such as fast flow), with the 12Z NAM/GFS close to the
consensus with the short wave energy that spins up a surface low
off the Southeast coast through 02/00Z. However, at the surface,
the 12Z NAM becomes much further north with the first surface wave
on the frontal boundary extending off the Southeast and Mid
Atlantic coasts (as it has been for at least three model
solutions). Because of this, the 12Z NAM was not included in the
blend with the first surface low.
Both the 12Z NAM/GFS remain faster and flatter with the second
short wave in the fast mid level flow, resulting in a weaker and
more progressive second surface low that passes well southeast of
southeast New England by 03/00Z. In contrast, The non-NCEP
guidance is a bit deeper with the short wave, producing a slightly
stronger surface low that passes closer to the southeast New
England coast.
While the 00Z CMC looks too close to the New England coast (though
it does have the support of the majority of its ensemble members
placing it there), there is better ensemble support for something
closer to a 00Z UKMET/ECMWF blend. Since there is so much spread
here, forecast confidence remains below average.
...Southern stream trough/surface low approaching CA Sat...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend through 02/00z
00Z UKMET/CMC/ECMWF blend after 02/00z
Confidence: Slightly above average
The 12Z NAM/GFS are close to the model consensus as a closed mid
level low near 34N 133W at 02/00Z. After the time, both solutions
become slower and deeper (even slower than the 00Z/06Z versions of
these models). The non-NCEP camp is faster and flatter with the
short wave weakening as it reaches the CA coast by 03/00Z. At this
point, given the strong mid level flow upstream of the short wave,
a faster and flatter solutions appears more likely, so a non-NCEP
solutions is favored later in the period.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Hayes