Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1217 PM EDT Sat Oct 19 2019

Valid Oct 19/1200 UTC thru Oct 23/0000 UTC

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

12Z Model Evaluation with Preferences and Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Northern stream shortwaves crossing the the West
ejecting/deepening into the Plains and eventually into the Great
Lakes...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-CMC blend thru 22.00z
          12z GFS and 00z UKMET/ECMWF (06z GEFS/00z ECENS mean)
after
Confidence: Slightly above average thru 22.00z; average after

The lead height-falls that started the pattern change, continues
to weaken and split with the northern stream shortwave/surface low
well into Canada with a sharp but thinning frontal zone
progressing across the Mississippi River Valley today while the
southern stream vort center and continues to fade but also kick
the extratropical circulation of Nestor eastward. The overall
pattern for this wave continues to be solid with no disagreement
to favor a general model blend for it.

The next more potent wave has entered the Pacific Northwest as the
left exit to the broad but strong 150+kt 250mb jet.  This wave
will continue amplify into the Wyoming Rockies, where along with
vortical stretching coming out of terrain finds favorable upper
level diffluence to rapidly develop a surface wave later today
into Sunday morning.  There has been a general trend toward a
northern shift, which has been held best by the GFS/GEFS, NAM and
UKMET; however, the 00z ECMWF has trended north as well and while
still a bit slower than the GFS/NAM and less so the 00z UKMET,
there is growing consensus and therefore confidence in this shift.
 The GFS remains faster and north than the GEFS mean but had
trended a bit weaker overall too. The ECMWF remains slightly
slower and south of the ECENS mean with both the GEFS/ECENS
showing strong agreement at least initially through the Dakotas
into the northern MS Valley. Much like the last few cycles the
operational ECMWF shows greater departure from its mean than the
GFS and its mean.  The 12z NAM, showing a stronger secondary vort
center rotating out of the CO Rockies, suggests a stronger triple
point low moving north through into the Upper Midwest by Monday,
this looks like typical Day 3 over amplification and so would
favor lower weighting of the NAM by Day 3 in the blend.  The CMC
is very slow throughout the process and is a clear outlier at this
point, so a Non-CMC blend is favored throughout the forecast
period and will favor the mass fields centered near a GEFS/ECENS
mean, which can be afforded by this non-CMC blend until 22.00z,
when the NAM is to be weighted out of the preference as well. 
Confidence is slightly above average through 22.00z and then
average thereafter.


Third fast moving shortwave entering Northern US Rockies/MT High
Plains late Tuesday
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Preference: 12z GFS/NAM and 00z CMC blend
Confidence: Average to slightly below average

The 3rd more significant shortwave, will over-top the broad
longwave ridge peaking around Vancouver Island and slip into the
Northern US Rockies and MT High Plains.  The 00z ECMWF is very
slow even compared the CMC which has the downstream issues with
the prior system.   The CMC matches well with the amplitude/timing
of the 12z GFS and NAM as well as the 00z UKMET.  However, the
UKMET is much strong particularly in the leading height falls
supporting a deeper surface reflection.  As such will favor a 12z
GFS/NAM and 00z CMC blend though given the speed of the shortwave
in the flow as well as complications with the exiting shortwave,
this clipper system confidence in the blend is average to slightly
below average.


Post-tropical Storm Nestor
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: See latest NHC advisory
Best Proxy: 00z UKMET

Nestor has lost the majority of near center convection, and with
the 15z advisory, NHC has declared Nestor to be extra-tropical. 
This is held consistent with nearly all of the global guidance as
well.  The 12z NAM continues to be the largest outlier favoring a
northwestward shift of the track of the cyclone through the
Carolinas into the NW Atlantic.  The 12z GFS and 00z CMC are along
track, until lifting north under influence of approaching northern
stream strong cyclone in the Plains/Great Lakes, as well as a
weaker surface/low level ridge across New England compared to the
UKMET/ECMWF.   The official NHC track follows the ECMWF/UKMET
closest, though toward the end of the forecast period over the
open waters, the ECMWF is faster than the official forecast,
making the UKMET the best proxy for the 15z official forecast.


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

Gallina