Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
110 PM EDT Thu Apr 05 2018

Valid Apr 05/1200 UTC thru Apr 09/0000 UTC

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

12Z NAM/GFS evaluation with preliminary preferences
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS initialization errors do not seem to degrade their short
range forecasts.


...Amplifying shortwave trough into the West on Saturday with
accompanying surface cyclone...
...Surface lows emerging into the Plains Saturday night/Sunday
morning...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: Non 00Z CMC blend through 06Z/08
            12Z NAM/00Z ECMWF blend 06Z/08 - 00Z/09
Confidence: Slightly above average

The 00Z CMC was significant different with the 500 mb reflection
(farther south) compared to the remaining deterministic guidance
and continued to appear the least likely model across the West.
Timing differences among the non-CMC guidance had reduced since
yesterday, but the 12Z NAM remained slightly quicker to bring the
upper trough/related cold front across the West Coast.

Beyond Sunday morning, timing differences appeared with the
shortwave which crosses the Intermountain West, to the south of
the weakening closed low across the Pacific Northwest. The 12Z GFS
and GEFS had been trending faster through the latest 00Z/05 cycle
across the Midwest, but the GFS/GEFS leaned toward the front edge
of the ensemble spread. The better agreement with the ensemble
means was toward the 00Z ECMWF and 12Z NAM...hence the preference.


...Southern stream shortwave crossing through the Plains Friday
night with East Coast troughing becoming better established on
Saturday...
...Surface lows tracking across the Southeast and offshore the
East Coast Saturday/Sunday...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: 12Z NAM, 12Z GFS, 00Z ECMWF blend
Confidence: Average

While trends had been to drop the surface low farther south along
the East Coast Saturday morning compared to Wednesday's model
runs, ensemble spread remained somewhat large for a 48-72 hour
forecast despite fairly good agreement today. The 12Z NAM, 12Z GFS
and 00Z ECMWF were pretty much in agreement with the surface
low(s) evolution across the Mid-Atlantic into the western Atlantic
Ocean, but the 12Z GFS was slightly more suppressed with the
surface low located roughly 200 miles east of the VA/NC border
valid 00Z/08. The 00Z UKMET was noted to be slightly slower with
the upper trough evolution with a surface low on the western side
of the ensemble spread valid 00Z/08, while the 00Z CMC was
slightly faster aloft resulting in a surface low tracking through
the western Atlantic more quickly than the consensus. A blend of
the 12Z NAM, 12Z GFS and 00Z ECMWF should resolve remaining detail
differences among the preferred guidance.


...Disturbance moving through Michigan early Friday morning late
Thursday/Friday and across the Northeast by late Saturday
morning...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: non 00Z UKMET blend
Confidence: Above average

Outside of the faster/deeper progression at 500 mb noted in the
00Z UKMET, no significant differences were noted with this system.
The result in the 00Z UKMET is for the surface cold front to
progress more quickly through the Mid-Atlantic region Saturday
morning.


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

Otto