Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
124 PM EDT Sun May 20 2018

Valid May 20/1200 UTC thru May 24/0000 UTC

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

12Z NAM/GFS/UKMET evaluation...with preliminary preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...Shortwave troughs exiting the East today/tonight with cold
front across the Northeast...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
Preference: General model blend
Confidence: Above average

The models show similarly with this system.


...Weakening shortwave trough over the central Plains today and
crossing the Midwest through Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non 12Z NAM blend
Confidence: Average

Decent model agreement begins to break down after 00Z/22 with the
12Z NAM appearing stronger with the mid-level shortwave and
surface low near the Great Lakes Tuesday morning. The 12Z NAM also
ends up toward the faster side of the model spread with the latest
ensemble guidance not showing much support for a low as it tracks
east through the Ohio valley. Outside of the 12z NAM, the models
show enough agreement for a blend.


...Closed low digging into the Southwest Monday and Tuesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Above average

The models continue to show similarly with this system, displaying
only minor depth spread noted toward the end of the period. Will
prefer a general model blend.


...Mid level trough over the eastern Gulf of Mexico...
...Lifting up across the Southeast on Monday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: General model blend
Confidence: Slightly above average

Only minor differences exist with this system such that a general
model blend can be used for this system.


...Shortwave energy/vorts lifting across the Plains Tuesday and
Wednesday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Blend of the 12Z GFS, 00Z UKMET and 00Z ECMWF
Confidence: Average

A complex evolution with weak height falls into the central and
northern Plains makes for a challenging forecast. The 12Z NAM
stands out with a more aggressive shortwave lifting into the
northern Plains early Wednesday and a farther north warm front
extending roughly northwest to southeast across the north-central
U.S.  The 12z GFS is also north with the 00Z ECMWF/UKMET south.
The ensemble means support their parent models which leaves room
for changes for future cycles. For now, given the GFS is within
the ensemble spread and does not stand out enough to discount it
from a blend, it will be included as part of the preference with
the 00Z ECMWF/UKMET from continuity. The CMC looks too deep with
the shortwave energy by 00Z/24 over Montana/Wyoming and will be
excluded from the preference.


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

Otto