Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Sun May 13 2018

Valid May 13/0000 UTC thru May 16/1200 UTC

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

00Z model preferences with confidence intervals
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GFS/NAM initialization errors do not seem to degrade their short
range forecast.


Upper low approaching CA Tuesday night
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non-NAM blend; confidence above average

The 00z NAM is a slow outlier with this system; its usual bias.  A
compromise of the 00z GFS, 00z ECMWF, 00z Canadian, and 00z UKMET
is preferred with above average confidence.


Great Basin Upper low which drifts north
Low streaking north of US/Canadian border Tue/Wed
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The guidance shows reasonable agreement with these systems.  A
compromise of the 00z ECMWF, 00z Canadian, 00z UKMET, 00z GFS, and
00z NAM is preferred with above average confidence.


Possibly convective/stacked cyclone in the Gulf of Mexico
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: GFS/NAM blend; confidence average

The 00z Canadian is somewhat northwest than the remainder of the
guidance with this system by Wednesday morning, but has trended
towards the currently consensus.  The guidance has some
convective/gridscale feedback within the atypically moist (for
May) and unstable environment.  Although the 00z ECMWF has
partially backed off its 12z solution, it takes a fed back
circulation across the FL panhandle into AL at 850 hPa which
distorts its surface pressure pattern, washing out the deep layer
cyclone in the Gulf, remaining out of sorts with the 00z GEFS/12z
ECMWF ensemble mean solutions.  The 00z UKMET was weak and east of
the ensemble mean guidance.  A compromise of the 00z GFS/00z NAM
was preferred here which fit the ensemble mean guidance best and
made the most meteorological sense.  Confidence is average in this
choice.


Base of the eastern Canada upper low/trough
Front in the northern Mid-Atlantic/New England states Tue/Wed
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: ECMWF/Canadian/UKMET blend
Confidence: Slightly above average

Aloft, the guidance agrees on rather flat/quasi-zonal flow across
the Great Lakes/Northern Mid-Atlantic states/New England states. 
At the surface, the 00z NAM in two days (before it folds in better
with the other guidance), and then the 00z GFS in three days, end
up farther north with the front near the 40th parallel.  With a
surface high of 1020+ hPa moving from southern Quebec into New
England, a more southerly frontal position towards D.C. makes the
most sense (an old NMC rule of thumb).  This is in the direction
of the 00z UKMET/00z Canadian/00z ECMWF.  A compromise of pieces
of guidance is preferred with slightly above average confidence.


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

Roth