Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
229 PM EDT Sun Apr 08 2018

Valid Apr 08/1200 UTC thru Apr 12/0000 UTC

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

12Z model evaluation...with preferences and confidence
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Upper trough crossing the Northeast through early Monday...
...Strong surface low lifting up across the Canadian maritimes...
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models bring an upper trough across the Northeast through
tonight and early Monday which will amplify into a closed low
feature over the Canadian maritimes. These height falls will phase
with the energy lifting up off the East Coast and will result in a
strong surface low impacting the Canadian maritimes on Monday.
Given the good mass field agreement seen, a general model blend
will be preferred.


...Strong closed low and trough impacting the Northwest today...
...Shortwaves crossing the Plains Sunday/Monday...
...Advancing across the Mississippi and Ohio Valleys Tuesday...
...Surface low activity from the Plains to the Southeast U.S...
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z GFS, 12Z UKMET and 12Z ECMWF
Confidence: Average

The models are in very good agreement with the details of the
closed low/upper trough arriving in across the Northwest today. A
lead shortwave though ahead of these height falls will eject east
across the Plains later today and help drive a wave of low
pressure down across the immediate northern High Plains and across
South Dakota before then crossing the upper Midwest by Monday. The
guidance is well clustered with this surface wave, but the 12Z NAM
is a little stronger than the global models with the shortwave
itself. Meanwhile, a secondary shortwave making up the remnants of
the former closed low will eject east and drop down across the
Plains Monday and then toward the Ohio and Tennessee Valleys by
Tuesday. The NAM again is a little deeper than the model consensus
aloft and this allows the NAM to temporarily have a stronger
surface low developing off the Southeast coast by late Monday
compared to the other models. The NAM is also focusing the low
pressure a bit north of the global models. By Tuesday, all of the
models show low pressure developing off the East Coast. The 12Z
CMC is overall the strongest solution with the NAM becoming one of
the weakest. The 12Z GFS, 12Z UKMET and 12Z ECMWF are clustered in
between. Will favor a GFS, UKMET and ECMWF blend at this time.


...Upper trough and cold front approaching West Coast by
Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z NAM and 12Z ECMWF
Confidence: Average

The models are in good agreement bringing an upper trough toward
the West Coast on Tuesday along with a cold front that will be
arriving across coastal areas of Washington, Oregon and northern
California. The 12Z GFS is the most progressive solution with the
12Z CMC still overall the slowest. The 12Z NAM, 12Z UKMET and 12Z
ECMWF are clustered in between, but the UKMET has a stronger
surface low lifting up along the front. The CMC also has a
similarly strong surface low. Given the good clustering and
approximation of the model consensus, the preference will be
toward a NAM and ECMWF blend.


...Upper trough arriving across the West Coast late Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z NAM, 12Z GFS and 12Z ECMWF
Confidence: Average

The guidance allows another upper trough to arrive across the West
Coast by late Wednesday which will allow another cold front to
cross the region. The 12Z NAM, 12Z GFS and 12Z ECMWF are all a
little more progressive than the 12Z UKMET and 12Z CMC. Will lean
toward the slightly more progressive consensus at this time.


...Shortwave crossing the Southeast Tuesday night/Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z GFS and 12Z ECMWF
Confidence: Average

The models bring a shortwave across the Southeast by late Tuesday
and through early Wednesday. The 12Z UKMET is still a bit stronger
than the model consensus, with the 12Z CMC a bit weaker. The
better model clustering resides more with the 12Z GFS and 12Z
ECMWF, with the 12Z NAM a little stronger than the GFS/ECMWF camp.
Will prefer a GFS and ECMWF blend at this time.


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

Orrison