Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1122 PM EST Tue Jan 14 2020
Valid Jan 15/0000 UTC thru Jan 18/1200 UTC
...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...
00Z Model Evaluation with Preferences and Forecast Confidence
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...Shortwave currently crossing Northern Rockies...
...Crossing the Upper Midwest/Northeast through Wed/Thurs...
...Deepening surface low through Gulf of Maine/Canadian Maritime
by late Thurs into Fri...
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Preference: Non-UKMET blend
Confidence: Slightly above average
Initially this system is well behaved in the guidance as the
shortwave emerges from the Northern Rockies later today supporting
a fast surface wave from KS through the Great Lakes by 16.00z
Thurs. Thereafter, stronger shortwave energy stretched from the
eastern portion of the old Arctic closed low in NW Canada through
last weekend is advected eastward sharpening the western side of
the trof and supporting favorable cyclogenesis across the
Northeast into the Gulf of Maine. Timing and magnitude
differences in this interaction appear to lead to the displacement
in the surface cyclone as well as moisture transport/warm conveyor
belt. The 12z UKMET continues to be most outside the growing
consensus being a bit faster initially and winding up the cyclone
south and east of the best clustering in the
ensemble/deterministic suite. The CMC, is not terribly out of
phase with the track/placement but is on the deeper side of the
ensemble suite, but still quite useful to account for the
shrinking probabilities. The 00z NAM trended even tighter to the
GEFS/ECENS means as well as the 12z ECMWF. The 00z GFS likewise
is very solid, with little notable change from the prior runs. As
such a non-UKMET blend can be supported at slightly above to above
average confidence.
...Deep upper trough crossing into the West by Thurs...
...Ejecting out across the Plains/Midwest late Fri/early Sat...
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Preference: 12Z ECMWF/ECENS and 18z GEFS blend
(General model blend before 17.00z)
Confidence: Above average through 48hrs becoming average through
72hr and slightly below average by 84hrs.
The remaining core of the Arctic closed low, will shear the bulk
of energy westward to form the northern portion of the developing
deep/strong closed low off of Vancouver by early Thursday. The
remaining energy is coming from a compact shortwave/surface
cyclone that continues to deepen over the SE portion of the Gulf
of AK into the Northeast Pacific Basin per GOES-W WV suite. This
rapid cyclogenesis has come into much stronger overall agreement
in the deterministic and ensemble suite to have above average
confidence in its evolution through 48hrs (17.00z). The
uncertainty remains in the precise strength/timing of the upper
level meridional jet the forms/amplifies the trof through much of
California by 48hrs as well. The magnitude/precise latitude of
peak depth remains quite uncertain which has large downstream
evolutionary impacts for the surface cyclone and Gulf Moisture
return across the Central and Southern Plains by 18.00z. Also,
the importance of interaction/amplification of shortwave energy
emerging ahead of the trof out of the subtropical stream will play
a key role and significantly reduce confidence in the systems'
evolution and meteorological impacts across the Plains and into
the upper Midwest.
Both the 12z CMC/UKMET are very strong and much further south at
the nose of the meridional jet crossing the Four Corners, but also
show faster injection of the shortwave out of the subtropics.
This makes the southern surface cyclone quite dominant and a bit
too fast/south overall. On the opposite side, the 00z NAM and
lesser so 00z GFS both favor a strong leading shortwave/vort
center but further north and in interaction with the subtropical
wave shows greater binary interaction and quicker snapping of the
base of the trof through the Central Plains in a neutral to weakly
negative tilt orientation. This make the 00z GFS much faster too,
while the NAM much stronger/compact; both in line with typical
negative bias. The interesting point, is the old GFS-based GEFS
mean shows low to moderate spread but favors a slower more middle
ground solution with the 12z ECENS and 12z ECWMF solution. This
(12z ECMWF/ECENS and 18z GEFS mean blend) will continue to be
preference after 48hrs (general model blend at above average
confidence prior to 48hrs). Confidence is average to slightly
below average by 84hrs.
...Compact shortwave/Deep surface cyclone nearing West Coast early
Sat...
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Preference: 12z ECMWF/ECENS and 18z GEFS w/some low 00z NAM
weighting
Confidence: Slightly below average
As the closed low over Vancouver island rapidly fills, a very
strong moderately broad but compact shortwave approaches across
the Northern Pacific to take its place Friday into Sat. While
there is very good agreement in the size and strength of the
system, there are large timing issues and therefore evolutionary
problems with the interaction with energy from the old system.
Here the UKMET/CMC are faster and more mature than the slowest
ECMWF and lesser so NAM with the GFS more in the middle. The
UKMET/CMC as well as the ECMWF all suggest a broader trailing trof
and associated cold front approaching the entire West Coast, while
the GFS rounds off a bit more focusing further north into the
Pacific Northwest. The GEFS and ECENS means support something
closer to the 12z ECWMF and even the 00z NAM (if just a bit south
and east of the NAM). So will favor a 12z ECMWF/ECENS mean with
18z GEFS with some smaller weighting to the 00z NAM to account for
some north-south variation/interaction with the older filling
system and remove the CMC/UKMET from preference/consideration.
Confidence is slightly below average due to the importance of
timing to the evolution/spread difference.
Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml
Gallina