Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1231 PM EDT Mon Sep 16 2019

Valid Sep 16/1200 UTC thru Sep 20/0000 UTC

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

12Z NAM/GFS Evaluation with Preferences and Forecast Confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Full latitude Western trough over the west and reinforcing
closed low late Tue...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General Model Blend
Confidence: Above average

The 12z NAM and 12z GFS are close to the consensus with the
strength and timing as it weakens and takes on a negative tilt
across the northern Rockies and northern Plains after 12z Tue.
These model are also close to the consensus taking the closed mid
level over the Gulf of Alaska and dropping it to a position near
Vancouver Island by 00z Wed.


...Short wave over CO crossing the Central Plains before moving
over the Northern Plains Tue
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend through 60 hours; non-NAM after
that
Confidence: Slightly above average

The 12z NAM and 12z GFS are close to the consensus taking the
short wave over CO this afternoon and tracking it into the
northern Plains and Upper MS Valley by 18/12z. After that time,
the 12z NAM retains a closed low feature longer than the rest of
the guidance, causing it to become slower than the consensus over
Ontario.


...Gulf of Mexico Tropical Wave...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General Model Blend through 19/00z: 12z NAM/00z UKMET
thereafter
Confidence: Average through 19/00z, Below Average after that time

The 12z NAM is close to the consensus through 19/00z, as there is
better agreement with the track of the mid level system and
surface low associated with the tropical wave over the western
Gulf of Mexico this afternoon. After that time, there is still
reasonable agreement with the mid level system over southeast TX.
However, there is considerably more spread with respect to the
track of the surface low. The 12z NAM is close to the 00z UKMET
(which has been fairly consistent with its track of the surface
low over the past three model runs) through 20/00z.

The 12z GFS/00z ECMWF are much further west with the surface low,
winding up closer to the Rio Grande River in the form of an
elongated surface trough. Many of the 00z ECMWF/CMC ensemble
members are close across the Upper TX Coast through 19/00z, which
lends some credence to the 12z NAM/00z UKMET placement. After that
time, the 00z ECMWF/CMC members spread out across eastern TX.

Based on this, the 12z NAM/00z UKMET are preferred with the track
of the surface low, though confidence is below average, especially
after 19/00z.


...Hurricane Humberto...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Official NHC Forecast
Best Proxy: ECMWF/GFS
Confidence: Below Average

The 12z NAM continues to be faster than the latest NHC forecast
(as does the 00z CMC). The 12z GFS is close to the track and the
00z ECMWF through 19/00z, ahead of a long wave trough crossing the
Mid Atlantic and Northeast. After that time, there is increasing
spread concerning quickly the mid level system closes off, and how
this affects any slowing of the surface system. This results in
gradually decreasing confidence in the timing after 19/00z.


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

Hayes